adjust flow

Mega blast

.dockerignore

@@ -0,0 +1,3 @@
+.git
+node_modules
+.DS_Store

.editorconfig

@@ -0,0 +1,15 @@
+root = true
+
+[*]
+indent_style = space
+indent_size = 4
+end_of_line = lf
+charset = utf-8
+trim_trailing_whitespace = true
+insert_final_newline = true
+
+[Makefile]
+indent_style = tab
+
+[*.go]
+indent_style = tab

.gitignore

@@ -0,0 +1,47 @@
+# OS
+.DS_Store
+Thumbs.db
+
+# Editors
+*.swp
+*.swo
+*~
+*.bak
+.idea/
+.vscode/
+*.sublime-*
+
+# Node
+node_modules/
+
+# Environment / secrets
+.env
+.env.*
+*.pem
+*.key
+
+# Go build artifacts
+backend/bin/
+backend/api
+backend/poller
+*.exe
+*.exe~
+*.dll
+*.so
+*.dylib
+*.test
+*.out
+vendor/
+tmp/
+
+# Frontend build output
+frontend/dist/
+frontend/build/
+frontend/.vite/
+
+# Prompts directory (local tooling, not part of the project)
+Prompts/
+
+# Logs
+*.log
+.claude

.prettierignore

@@ -0,0 +1,7 @@
+node_modules/
+frontend/dist/
+frontend/build/
+backend/bin/
+*.lock
+Prompts/
+.claude/

.prettierrc

@@ -0,0 +1,4 @@
+{
+    "tabWidth": 4,
+    "proseWrap": "always"
+}

Dockerfile

@@ -0,0 +1,22 @@
+# syntax=docker/dockerfile:1
+
+# golang:1.24-alpine, 2025-02-28
+FROM golang:1.24-alpine@sha256:8bee1901f1e530bfb4a7850aa7a479d17ae3a18beb6e09064ed54cfd245b7191
+
+# Install system dependencies: Node.js, npm, make, git
+RUN apk add --no-cache nodejs npm make git
+
+# Install golangci-lint at a pinned commit hash
+# golangci-lint v2.10.1 (2025-02-17), commit 5d1e709b7be35cb2025444e19de266b056b7b7ee
+RUN GOBIN=/usr/local/bin go install \
+    github.com/golangci/golangci-lint/cmd/golangci-lint@5d1e709b7be35cb2025444e19de266b056b7b7ee
+
+WORKDIR /app
+
+COPY . .
+
+# Install frontend dependencies
+RUN cd frontend && npm ci
+
+# Run all checks — build fails if the branch is not green
+RUN make check

LICENSE

@@ -0,0 +1,20 @@
+MIT License
+
+Copyright (c) 2026 Steven Jannette
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

Makefile

@@ -0,0 +1,90 @@
+.PHONY: test lint fmt fmt-check check docker hooks build run dev clean \
+        test-go test-js lint-go lint-js fmt-go fmt-js fmt-check-go fmt-check-js \
+        build-go build-js
+
+GODIR    := backend
+JSDIR    := frontend
+PRETTIER := $(JSDIR)/node_modules/.bin/prettier
+
+# ── required targets ────────────────────────────────────────────
+
+all: check
+
+check: test lint fmt-check
+
+test: test-go test-js
+
+lint: lint-go lint-js
+
+fmt: fmt-go fmt-js
+
+fmt-check: fmt-check-go fmt-check-js
+
+# ── go ──────────────────────────────────────────────────────────
+
+test-go:
+	cd $(GODIR) && go test -timeout 30s ./...
+
+lint-go:
+	cd $(GODIR) && golangci-lint run ./...
+
+fmt-go:
+	cd $(GODIR) && gofmt -w .
+
+fmt-check-go:
+	@diff=$$(cd $(GODIR) && gofmt -l .); \
+	if [ -n "$$diff" ]; then \
+		echo "Go files need formatting:"; \
+		echo "$$diff"; \
+		exit 1; \
+	fi
+
+# ── js / frontend ───────────────────────────────────────────────
+
+test-js:
+	cd $(JSDIR) && npm test
+
+lint-js:
+	$(PRETTIER) --check '**/*.{js,jsx,ts,tsx,css,md,json}'
+
+fmt-js:
+	$(PRETTIER) --write '**/*.{js,jsx,ts,tsx,css,md,json}'
+
+fmt-check-js:
+	$(PRETTIER) --check '**/*.{js,jsx,ts,tsx,css,md,json}'
+
+# ── build ───────────────────────────────────────────────────────
+
+build: build-go build-js
+
+build-go:
+	cd $(GODIR) && go build -o bin/api ./cmd/api
+	cd $(GODIR) && go build -o bin/poller ./cmd/poller
+
+build-js:
+	cd $(JSDIR) && npm run build
+
+# ── dev / run ───────────────────────────────────────────────────
+
+run:
+	cd $(GODIR) && go run ./cmd/api
+
+dev:
+	cd $(GODIR) && go run ./cmd/api
+
+# ── docker ──────────────────────────────────────────────────────
+
+docker:
+	docker build -t koin-ping .
+
+# ── hooks ───────────────────────────────────────────────────────
+
+hooks:
+	printf '#!/bin/sh\nmake check\n' > .git/hooks/pre-commit
+	chmod +x .git/hooks/pre-commit
+
+# ── clean ───────────────────────────────────────────────────────
+
+clean:
+	rm -rf $(GODIR)/bin/
+	rm -rf $(JSDIR)/dist/

README.md

@@ -1,95 +1,156 @@
 # Koin Ping
-
 A lightweight on-chain monitoring and alerting system designed to give users situational awareness over blockchain addresses they care about.
 
-## Overview
+# Overview
 
-Koin Ping is designed to reliably observe on-chain activity and notify users when predefined conditions are met. It does not execute transactions, manage wallets, or speculate on prices.
-
-## Project Structure
-
-```
-koin_ping/
-├── backend/                  # Node.js + Express + PostgreSQL backend
-│   ├── api/                 # API endpoints and server configuration
-│   ├── poller/              # Blockchain polling logic
-│   ├── alerts/              # Alert evaluation and management
-│   ├── notifications/       # Notification delivery system
-│   ├── domain/              # Domain models and business logic
-│   ├── infra/               # Infrastructure (database, external services)
-│   └── shared/              # Shared utilities and helpers
-│
-└── frontend/                 # React + Vite frontend
-    ├── public/              # Static assets
-    └── src/
-        ├── api/             # Frontend API calls to backend
-        ├── components/      # Reusable UI components
-        ├── pages/           # Top-level pages (views)
-        └── utils/           # Utility functions
-
-```
-
-## Tech Stack
-
-### Backend
-- **Runtime:** Node.js
-- **Framework:** Express
-- **Database:** PostgreSQL
-- **Key Dependencies:** 
-  - `pg` - PostgreSQL client
-  - `dotenv` - Environment variable management
-  - `cors` - CORS middleware
-  - `nodemon` - Development auto-reload
-
-### Frontend
-- **Framework:** React 19
-- **Build Tool:** Vite
-- **Language:** JavaScript/TypeScript (mixed)
-- **Type Checking:** TypeScript
+Koin Ping observes on-chain activity and notifies users when predefined conditions are met. It does not execute transactions, manage wallets, or speculate on prices.
 
 ## Getting Started
 
 ### Prerequisites
-- Node.js (v18 or higher recommended)
-- PostgreSQL database
-- npm or yarn
 
-### Backend Setup
+- Go 1.24+
+- Node.js 18+ and npm (or yarn — preferred per repo policy)
+- PostgreSQL 15+
+- `golangci-lint` v2 (for `make lint`)
 
-1. Navigate to the backend directory:
-   ```bash
-   cd backend
+### Setup
+
+```bash
+# Clone and enter the repo
+git clone <repo-url>
+cd koin_ping_0.2.0
+
+# Install pre-commit hook
+make hooks
+
+# Install frontend dependencies
+cd frontend && npm install && cd ..
+
+# Copy and fill in environment variables
+cp backend/.env.example backend/.env
+# edit backend/.env with your DATABASE_URL, FIREBASE_PROJECT_ID, ETH_RPC_URL
+
+# Run checks (requires golangci-lint)
+make check
+
+# Start the API server
+make run
+
+# Start the poller (separate terminal)
+cd backend && go run ./cmd/poller
+
+# Start the frontend dev server (separate terminal)
+cd frontend && npm run dev
+```
+
+The API listens on `http://localhost:3001` and the frontend on
+`http://localhost:3000` by default for development.
+
+## Rationale
+
+Crypto users may actively monitor addresses with webhooks integrating popular 
+messaging platforms: Discord, Slack, Telegram.
+This lightweight, reliable framework makes instant awareness of on-chain 
+activity trivial, without polling block explorers manually. Koin Ping watches 
+addresses, evaluates configurable alert rules (incoming transactions, outgoing 
+transactions, "large" transfers, balance thresholds), and sends notifications.
+
+## Design
+
+The system is split into two independently deployable processes and one
+frontend:
+
+```
+koin_ping_0.2.0/
+├── backend/                # Go monorepo root
+│   ├── cmd/api/               # HTTP REST API server
+│   ├── cmd/poller/            # Blockchain polling daemon
+│   └── internal/
+│       ├── config/            # Environment-based config loading
+│       ├── database/          # pgx connection pool
+│       ├── domain/            # Shared domain types
+│       ├── firebase/          # Firebase auth client
+│       ├── handlers/          # HTTP handler wiring
+│       ├── middleware/         # Auth middleware
+│       ├── models/            # SQL persistence layer
+│       ├── notifications/     # Discord webhook delivery
+│       ├── protocols/ethereum/ # Ethereum JSON-RPC client
+│       ├── services/          # Observer and evaluator business logic
+│       └── wei/               # ETH/Wei conversion utilities
+└── frontend/                  # React + Vite SPA
+    └── src/
+        ├── api/               # Fetch wrappers for the REST API
+        ├── components/        # Reusable UI components
+        ├── contexts/          # React contexts (auth, etc.)
+        ├── firebase/          # Firebase SDK initialization
+        └── pages/             # Top-level route pages
+```
+
+**API server** (`cmd/api`): standard-library `net/http` with Firebase JWT
+authentication middleware. Exposes CRUD endpoints for addresses, alert rules,
+alert events, and notification configuration.
+
+**Poller** (`cmd/poller`): long-running daemon that polls Ethereum via JSON-RPC,
+compares observed transactions against persisted alert rules, fires alert events
+to the database, and dispatches Discord notifications.
+
+**Frontend** (`frontend/`): React 19 SPA built with Vite. Authenticates with
+Firebase, communicates with the API via fetch, and renders the address/alert
+management UI.
+
+## Setting Up Your Alert Platforms
+
+Koin Ping can send real-time alerts to **Telegram**, **Discord**, **Slack**, and **Email**. Each channel is configured per-user through the **Notification Settings** panel on the Alerts page.
+
+Below are step-by-step guides for setting up each platform.
+
+---
+
+### Telegram
+
+To receive alerts via Telegram, you need to create a bot and get your chat ID.
+
+#### 1. Create a Telegram Bot
+
+1. Open Telegram and search for **@BotFather** (look for the blue verified checkmark).
+2. Open the conversation with BotFather and send: `/newbot`
+3. BotFather will ask for a **display name** — enter something like `Koin Ping Alerts`.
+4. BotFather will ask for a **username** — it must end in `bot`, e.g. `MyKoinPingBot`.
+5. BotFather will reply with your **Bot Token** — a string that looks like `123456789:ABCdefGHIjklMNOpqrSTUvwxYZ`. Copy it.
+
+#### 2. Get Your Chat ID
+
+1. In Telegram, search for the bot username you just created and open the chat.
+2. Tap **Start** or send any message (e.g. `hello`).
+3. Open the following URL in your browser, replacing `YOUR_BOT_TOKEN` with the token from step 1:
+
+   ```
+   https://api.telegram.org/botYOUR_BOT_TOKEN/getUpdates
    ```
 
-2. Install dependencies (already done):
-   ```bash
-   npm install
-   ```
+4. In the JSON response, find the `"chat"` object — the `"id"` field is your **Chat ID** (a numeric value).
 
-3. Create a `.env` file (see backend/README.md for required variables)
+   > **Tip:** If the `'result"` array is empty, make sure you sent a message to your bot first, then refresh the page.
 
-4. Start the development server:
-   ```bash
-   npm run dev
-   ```
+#### 3. Save in Koin Ping
 
-The backend will run on `http://localhost:3001`
+1. Go to the **Alerts** page in Koin Ping.
+2. In the **Notification Settings** panel, find the **Telegram** section.
+3. Paste your **Bot Token** and **Chat ID** into the corresponding fields.
+4. Click **Save Settings**.
+5. Click **Test All Channels** to verify — you should receive a test message from your bot in Telegram.
 
-### Frontend Setup
+---
 
-1. Navigate to the frontend directory:
-   ```bash
-   cd frontend
-   ```
+*Guides for Discord, Slack, and Email coming soon.*
 
-2. Install dependencies (already done):
-   ```bash
-   npm install
-   ```
+## License
+
+MIT. See [LICENSE](LICENSE).
+
+## Author
+
+Steven Jannette
 
-3. Start the development server:
-   ```bash
-   npm run dev
-   ```
 
-The frontend will run on `http://localhost:3000`

backend-go/.env.example

@@ -1,16 +0,0 @@
-# Server
-PORT=3001
-API_BASE_PATH=/v1
-NODE_ENV=development
-
-# Database
-DATABASE_URL=postgresql://user:password@localhost:5432/koin_ping
-
-# Ethereum JSON-RPC
-ETH_RPC_URL=https://mainnet.infura.io/v3/YOUR-PROJECT-ID
-
-# Polling interval (ms, minimum 1000)
-POLL_INTERVAL_MS=60000
-
-# Firebase
-FIREBASE_PROJECT_ID=koin-ping

backend-go/README.md

@@ -1,4 +0,0 @@
-Run Backend:
-
-cd /Users/kjannette/workspace/koin_ping/backend-go
-go run ./cmd/api

backend-go/cmd/api/main.go

@@ -1,105 +0,0 @@
-package main
-
-import (
-	"fmt"
-	"log"
-	"net/http"
-	"os"
-
-	"github.com/joho/godotenv"
-	"github.com/kjannette/koin-ping/backend-go/internal/config"
-	"github.com/kjannette/koin-ping/backend-go/internal/database"
-	"github.com/kjannette/koin-ping/backend-go/internal/firebase"
-	"github.com/kjannette/koin-ping/backend-go/internal/handlers"
-	"github.com/kjannette/koin-ping/backend-go/internal/middleware"
-	"github.com/kjannette/koin-ping/backend-go/internal/models"
-	"github.com/kjannette/koin-ping/backend-go/internal/protocols/ethereum"
-)
-
-func main() {
-	_ = godotenv.Load()
-
-	cfg, err := config.Load()
-	if err != nil {
-		log.Fatalf("Failed to load config: %v", err)
-	}
-
-	pool, err := database.Connect(cfg.DSN())
-	if err != nil {
-		log.Fatalf("Failed to connect to database: %v", err)
-	}
-	defer database.Close()
-
-	if err := firebase.Init(cfg.FirebaseProjectID); err != nil {
-		log.Fatalf("Failed to initialize Firebase: %v", err)
-	}
-
-	var eth ethereum.EthereumObserver
-	if cfg.EthRPCURL != "" {
-		eth, err = ethereum.NewJsonRpcEthereum(cfg.EthRPCURL)
-		if err != nil {
-			log.Printf("Warning: Failed to create Ethereum observer: %v", err)
-		}
-	}
-
-	addressModel := models.NewAddressModel(pool)
-	alertRuleModel := models.NewAlertRuleModel(pool)
-	alertEventModel := models.NewAlertEventModel(pool)
-	notifConfigModel := models.NewNotificationConfigModel(pool)
-	checkpointModel := models.NewCheckpointModel(pool)
-
-	addressHandler := handlers.NewAddressHandler(addressModel)
-	alertRuleHandler := handlers.NewAlertRuleHandler(alertRuleModel, addressModel)
-	alertEventHandler := handlers.NewAlertEventHandler(alertEventModel)
-	notifConfigHandler := handlers.NewNotificationConfigHandler(notifConfigModel)
-	statusHandler := handlers.NewStatusHandler(eth, checkpointModel)
-
-	mux := http.NewServeMux()
-	b := cfg.APIBasePath
-
-	mux.HandleFunc("GET "+b+"/health", handlers.HealthCheck)
-	mux.HandleFunc("GET "+b+"/status", statusHandler.SystemStatus)
-
-	mux.Handle("POST "+b+"/addresses", middleware.Authenticate(http.HandlerFunc(addressHandler.Create)))
-	mux.Handle("GET "+b+"/addresses", middleware.Authenticate(http.HandlerFunc(addressHandler.List)))
-	mux.Handle("DELETE "+b+"/addresses/{addressId}", middleware.Authenticate(http.HandlerFunc(addressHandler.Remove)))
-
-	mux.Handle("POST "+b+"/addresses/{addressId}/alerts", middleware.Authenticate(http.HandlerFunc(alertRuleHandler.Create)))
-	mux.Handle("GET "+b+"/addresses/{addressId}/alerts", middleware.Authenticate(http.HandlerFunc(alertRuleHandler.ListByAddress)))
-	mux.Handle("PATCH "+b+"/alerts/{alertId}", middleware.Authenticate(http.HandlerFunc(alertRuleHandler.UpdateStatus)))
-	mux.Handle("DELETE "+b+"/alerts/{alertId}", middleware.Authenticate(http.HandlerFunc(alertRuleHandler.Remove)))
-
-	mux.Handle("GET "+b+"/alert-events", middleware.Authenticate(http.HandlerFunc(alertEventHandler.List)))
-
-	mux.Handle("GET "+b+"/notification-config", middleware.Authenticate(http.HandlerFunc(notifConfigHandler.GetConfig)))
-	mux.Handle("PUT "+b+"/notification-config", middleware.Authenticate(http.HandlerFunc(notifConfigHandler.UpdateConfig)))
-	mux.Handle("DELETE "+b+"/notification-config", middleware.Authenticate(http.HandlerFunc(notifConfigHandler.DeleteConfig)))
-	mux.Handle("POST "+b+"/notification-config/test", middleware.Authenticate(http.HandlerFunc(notifConfigHandler.TestWebhook)))
-
-	handler := corsMiddleware(mux)
-
-	addr := fmt.Sprintf(":%d", cfg.Port)
-	log.Printf("Server running on port %d", cfg.Port)
-	log.Printf("API base path: %s", cfg.APIBasePath)
-	log.Printf("Environment: %s", cfg.NodeEnv)
-
-	if err := http.ListenAndServe(addr, handler); err != nil {
-		log.Fatalf("Server failed: %v", err)
-		os.Exit(1)
-	}
-}
-
-func corsMiddleware(next http.Handler) http.Handler {
-	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		w.Header().Set("Access-Control-Allow-Origin", "*")
-		w.Header().Set("Access-Control-Allow-Methods", "GET, POST, PUT, PATCH, DELETE, OPTIONS")
-		w.Header().Set("Access-Control-Allow-Headers", "Content-Type, Authorization")
-
-		if r.Method == http.MethodOptions {
-			w.WriteHeader(http.StatusNoContent)
-			return
-		}
-
-		next.ServeHTTP(w, r)
-	})
-}

backend-go/internal/config/config.go

@@ -1,93 +0,0 @@
-package config
-
-import (
-	"fmt"
-	"os"
-	"strconv"
-	"strings"
-)
-
-type Config struct {
-	Port              int
-	APIBasePath       string
-	DatabaseURL       string
-	DBHost            string
-	DBPort            int
-	DBUser            string
-	DBPassword        string
-	DBName            string
-	FirebaseProjectID string
-	EthRPCURL         string
-	PollIntervalMS    int
-	NodeEnv           string
-
-	SMTPHost     string
-	SMTPPort     int
-	SMTPUser     string
-	SMTPPassword string
-	SMTPFrom     string
-}
-
-func Load() (*Config, error) {
-	cfg := &Config{
-		Port:           getEnvInt("PORT", 3001),
-		APIBasePath:    getEnv("API_BASE_PATH", "/v1"),
-		DatabaseURL:    os.Getenv("DATABASE_URL"),
-		DBHost:         getEnv("DB_HOST", "localhost"),
-		DBPort:         getEnvInt("DB_PORT", 5432),
-		DBUser:         os.Getenv("DB_USER"),
-		DBPassword:     os.Getenv("DB_PASSWORD"),
-		DBName:         os.Getenv("DB_NAME"),
-		FirebaseProjectID: os.Getenv("FIREBASE_PROJECT_ID"),
-		EthRPCURL:      os.Getenv("ETH_RPC_URL"),
-		PollIntervalMS: getEnvInt("POLL_INTERVAL_MS", 60000),
-		NodeEnv:        getEnv("NODE_ENV", "development"),
-
-		SMTPHost:     os.Getenv("SMTP_HOST"),
-		SMTPPort:     getEnvInt("SMTP_PORT", 587),
-		SMTPUser:     os.Getenv("SMTP_USER"),
-		SMTPPassword: os.Getenv("SMTP_PASSWORD"),
-		SMTPFrom:     os.Getenv("SMTP_FROM"),
-	}
-
-	if cfg.PollIntervalMS < 1000 {
-		return nil, fmt.Errorf("POLL_INTERVAL_MS must be >= 1000, got %d", cfg.PollIntervalMS)
-	}
-
-	return cfg, nil
-}
-
-func (c *Config) DSN() string {
-	if c.DatabaseURL != "" {
-		// pgx defaults to sslmode=prefer, which fails against local Postgres.
-		// Append sslmode=disable if not already specified.
-		if !strings.Contains(c.DatabaseURL, "sslmode=") {
-			sep := "?"
-			if strings.Contains(c.DatabaseURL, "?") {
-				sep = "&"
-			}
-			return c.DatabaseURL + sep + "sslmode=disable"
-		}
-		return c.DatabaseURL
-	}
-	return fmt.Sprintf(
-		"host=%s port=%d user=%s password=%s dbname=%s sslmode=disable",
-		c.DBHost, c.DBPort, c.DBUser, c.DBPassword, c.DBName,
-	)
-}
-
-func getEnv(key, fallback string) string {
-	if v := os.Getenv(key); v != "" {
-		return v
-	}
-	return fallback
-}
-
-func getEnvInt(key string, fallback int) int {
-	if v := os.Getenv(key); v != "" {
-		if n, err := strconv.Atoi(v); err == nil {
-			return n
-		}
-	}
-	return fallback
-}

backend-go/internal/config/config_test.go

@@ -1,115 +0,0 @@
-package config
-
-import (
-	"os"
-	"strings"
-	"testing"
-)
-
-func TestLoad_Defaults(t *testing.T) {
-	for _, key := range []string{"PORT", "API_BASE_PATH", "POLL_INTERVAL_MS", "NODE_ENV", "SMTP_PORT"} {
-		os.Unsetenv(key)
-	}
-
-	cfg, err := Load()
-	if err != nil {
-		t.Fatalf("unexpected error: %v", err)
-	}
-
-	if cfg.Port != 3001 {
-		t.Errorf("Port = %d, want 3001", cfg.Port)
-	}
-	if cfg.APIBasePath != "/v1" {
-		t.Errorf("APIBasePath = %q, want /v1", cfg.APIBasePath)
-	}
-	if cfg.PollIntervalMS != 60000 {
-		t.Errorf("PollIntervalMS = %d, want 60000", cfg.PollIntervalMS)
-	}
-	if cfg.NodeEnv != "development" {
-		t.Errorf("NodeEnv = %q, want development", cfg.NodeEnv)
-	}
-	if cfg.SMTPPort != 587 {
-		t.Errorf("SMTPPort = %d, want 587", cfg.SMTPPort)
-	}
-}
-
-func TestLoad_InvalidPollInterval(t *testing.T) {
-	os.Setenv("POLL_INTERVAL_MS", "500")
-	defer os.Unsetenv("POLL_INTERVAL_MS")
-
-	_, err := Load()
-	if err == nil {
-		t.Fatal("expected error for poll interval < 1000")
-	}
-}
-
-func TestDSN_DatabaseURL(t *testing.T) {
-	cfg := &Config{DatabaseURL: "postgres://user:pass@localhost/db"}
-	dsn := cfg.DSN()
-	if !strings.Contains(dsn, "sslmode=disable") {
-		t.Error("DSN should append sslmode=disable")
-	}
-	if !strings.HasPrefix(dsn, "postgres://user:pass@localhost/db") {
-		t.Error("DSN should preserve original URL")
-	}
-}
-
-func TestDSN_DatabaseURL_WithSSLMode(t *testing.T) {
-	cfg := &Config{DatabaseURL: "postgres://user:pass@localhost/db?sslmode=require"}
-	dsn := cfg.DSN()
-	if strings.Count(dsn, "sslmode=") != 1 {
-		t.Error("DSN should not duplicate sslmode")
-	}
-}
-
-func TestDSN_Components(t *testing.T) {
-	cfg := &Config{
-		DBHost:     "myhost",
-		DBPort:     5433,
-		DBUser:     "myuser",
-		DBPassword: "mypass",
-		DBName:     "mydb",
-	}
-	dsn := cfg.DSN()
-	if !strings.Contains(dsn, "host=myhost") {
-		t.Error("DSN should contain host")
-	}
-	if !strings.Contains(dsn, "port=5433") {
-		t.Error("DSN should contain port")
-	}
-	if !strings.Contains(dsn, "user=myuser") {
-		t.Error("DSN should contain user")
-	}
-	if !strings.Contains(dsn, "dbname=mydb") {
-		t.Error("DSN should contain dbname")
-	}
-}
-
-func TestGetEnv(t *testing.T) {
-	os.Setenv("TEST_KEY_KOINPING", "value")
-	defer os.Unsetenv("TEST_KEY_KOINPING")
-
-	if got := getEnv("TEST_KEY_KOINPING", "fallback"); got != "value" {
-		t.Errorf("got %q, want %q", got, "value")
-	}
-	if got := getEnv("NONEXISTENT_KEY_KOINPING", "fallback"); got != "fallback" {
-		t.Errorf("got %q, want %q", got, "fallback")
-	}
-}
-
-func TestGetEnvInt(t *testing.T) {
-	os.Setenv("TEST_INT_KOINPING", "42")
-	defer os.Unsetenv("TEST_INT_KOINPING")
-
-	if got := getEnvInt("TEST_INT_KOINPING", 0); got != 42 {
-		t.Errorf("got %d, want 42", got)
-	}
-	if got := getEnvInt("NONEXISTENT_INT_KOINPING", 99); got != 99 {
-		t.Errorf("got %d, want 99", got)
-	}
-
-	os.Setenv("TEST_INT_KOINPING", "notanumber")
-	if got := getEnvInt("TEST_INT_KOINPING", 99); got != 99 {
-		t.Errorf("got %d, want 99 for invalid int", got)
-	}
-}

backend-go/internal/domain/types.go

@@ -1,114 +0,0 @@
-package domain
-
-import "time"
-
-type Address struct {
-	ID        int       `json:"id"`
-	UserID    string    `json:"user_id"`
-	Address   string    `json:"address"`
-	Label     *string   `json:"label"`
-	CreatedAt time.Time `json:"created_at"`
-}
-
-type AlertType string
-
-const (
-	AlertIncomingTx    AlertType = "incoming_tx"
-	AlertOutgoingTx    AlertType = "outgoing_tx"
-	AlertLargeTransfer AlertType = "large_transfer"
-	AlertBalanceBelow  AlertType = "balance_below"
-)
-
-var ValidAlertTypes = []AlertType{
-	AlertIncomingTx,
-	AlertOutgoingTx,
-	AlertLargeTransfer,
-	AlertBalanceBelow,
-}
-
-var ThresholdRequiredTypes = []AlertType{
-	AlertLargeTransfer,
-	AlertBalanceBelow,
-}
-
-func IsValidAlertType(t string) bool {
-	for _, v := range ValidAlertTypes {
-		if string(v) == t {
-			return true
-		}
-	}
-	return false
-}
-
-func IsThresholdRequired(t AlertType) bool {
-	for _, v := range ThresholdRequiredTypes {
-		if v == t {
-			return true
-		}
-	}
-	return false
-}
-
-type AlertRule struct {
-	ID        int       `json:"id"`
-	AddressID int       `json:"address_id"`
-	Type      AlertType `json:"type"`
-	Threshold *float64  `json:"threshold"`
-	Enabled   bool      `json:"enabled"`
-	CreatedAt time.Time `json:"created_at"`
-}
-
-type AlertEvent struct {
-	ID          int       `json:"id"`
-	AlertRuleID int       `json:"alert_rule_id"`
-	Message     string    `json:"message"`
-	AddressLabel *string  `json:"address_label"`
-	TxHash      *string   `json:"tx_hash"`
-	Timestamp   time.Time `json:"timestamp"`
-}
-
-type AddressCheckpoint struct {
-	AddressID        int       `json:"address_id"`
-	LastCheckedBlock int       `json:"last_checked_block"`
-	LastCheckedAt    time.Time `json:"last_checked_at"`
-}
-
-type CheckpointDetail struct {
-	AddressID        int       `json:"address_id"`
-	Address          string    `json:"address"`
-	Label            *string   `json:"label"`
-	LastCheckedBlock int       `json:"last_checked_block"`
-	LastCheckedAt    time.Time `json:"last_checked_at"`
-}
-
-type NotificationConfig struct {
-	UserID              string     `json:"user_id"`
-	DiscordWebhookURL   *string    `json:"discord_webhook_url"`
-	SlackWebhookURL     *string    `json:"slack_webhook_url"`
-	Email               *string    `json:"email"`
-	NotificationEnabled bool       `json:"notification_enabled"`
-	CreatedAt           *time.Time `json:"created_at,omitempty"`
-	UpdatedAt           *time.Time `json:"updated_at,omitempty"`
-}
-
-type NormalizedTx struct {
-	Hash           string `json:"hash"`
-	From           string `json:"from"`
-	To             *string `json:"to"`
-	Value          string `json:"value"` // Wei as string for precision
-	BlockNumber    int    `json:"block_number"`
-	BlockTimestamp int64  `json:"block_timestamp"`
-}
-
-type Direction string
-
-const (
-	DirectionIncoming Direction = "incoming"
-	DirectionOutgoing Direction = "outgoing"
-)
-
-type ObservedTx struct {
-	NormalizedTx
-	AddressID int       `json:"address_id"`
-	Direction Direction `json:"direction"`
-}

backend-go/internal/domain/types_test.go

@@ -1,35 +0,0 @@
-package domain
-
-import "testing"
-
-func TestIsValidAlertType(t *testing.T) {
-	valid := []string{"incoming_tx", "outgoing_tx", "large_transfer", "balance_below"}
-	for _, v := range valid {
-		if !IsValidAlertType(v) {
-			t.Errorf("IsValidAlertType(%q) = false, want true", v)
-		}
-	}
-
-	invalid := []string{"", "invalid", "INCOMING_TX", "send", "receive"}
-	for _, v := range invalid {
-		if IsValidAlertType(v) {
-			t.Errorf("IsValidAlertType(%q) = true, want false", v)
-		}
-	}
-}
-
-func TestIsThresholdRequired(t *testing.T) {
-	required := []AlertType{AlertLargeTransfer, AlertBalanceBelow}
-	for _, at := range required {
-		if !IsThresholdRequired(at) {
-			t.Errorf("IsThresholdRequired(%q) = false, want true", at)
-		}
-	}
-
-	notRequired := []AlertType{AlertIncomingTx, AlertOutgoingTx}
-	for _, at := range notRequired {
-		if IsThresholdRequired(at) {
-			t.Errorf("IsThresholdRequired(%q) = true, want false", at)
-		}
-	}
-}

backend-go/internal/handlers/status.go

@@ -1,79 +0,0 @@
-package handlers
-
-import (
-	"context"
-	"log"
-	"net/http"
-	"time"
-
-	"github.com/kjannette/koin-ping/backend-go/internal/models"
-	"github.com/kjannette/koin-ping/backend-go/internal/protocols/ethereum"
-)
-
-func HealthCheck(w http.ResponseWriter, r *http.Request) {
-	writeJSON(w, http.StatusOK, map[string]interface{}{
-		"status":    "ok",
-		"timestamp": time.Now().UTC().Format(time.RFC3339),
-		"service":   "koin-ping-backend",
-	})
-}
-
-type StatusHandler struct {
-	eth         ethereum.EthereumObserver
-	checkpoints *models.CheckpointModel
-}
-
-func NewStatusHandler(eth ethereum.EthereumObserver, checkpoints *models.CheckpointModel) *StatusHandler {
-	return &StatusHandler{eth: eth, checkpoints: checkpoints}
-}
-
-func (h *StatusHandler) SystemStatus(w http.ResponseWriter, r *http.Request) {
-	ctx, cancel := context.WithTimeout(r.Context(), 10*time.Second)
-	defer cancel()
-
-	status := "healthy"
-
-	if h.eth == nil {
-		writeJSON(w, http.StatusOK, map[string]interface{}{
-			"latestBlock":      0,
-			"lag":              0,
-			"trackedAddresses": 0,
-			"status":           "no_rpc",
-			"timestamp":        time.Now().UTC().Format(time.RFC3339),
-		})
-		return
-	}
-
-	latestBlock, err := h.eth.GetLatestBlockNumber(ctx)
-	if err != nil {
-		log.Printf("Failed to get latest block: %v", err)
-		status = "degraded"
-		latestBlock = 0
-	}
-
-	lag := 0
-	checkpoints, err := h.checkpoints.ListAll(ctx)
-	if err != nil {
-		log.Printf("Failed to list checkpoints: %v", err)
-	} else if len(checkpoints) > 0 && latestBlock > 0 {
-		minChecked := checkpoints[0].LastCheckedBlock
-		for _, cp := range checkpoints[1:] {
-			if cp.LastCheckedBlock < minChecked {
-				minChecked = cp.LastCheckedBlock
-			}
-		}
-		lag = latestBlock - minChecked
-	}
-
-	if lag > 50 {
-		status = "syncing"
-	}
-
-	writeJSON(w, http.StatusOK, map[string]interface{}{
-		"latestBlock":      latestBlock,
-		"lag":              lag,
-		"trackedAddresses": len(checkpoints),
-		"status":           status,
-		"timestamp":        time.Now().UTC().Format(time.RFC3339),
-	})
-}

backend-go/internal/middleware/auth.go

@@ -1,98 +0,0 @@
-package middleware
-
-import (
-	"context"
-	"encoding/json"
-	"log"
-	"net/http"
-	"strings"
-
-	fbauth "github.com/kjannette/koin-ping/backend-go/internal/firebase"
-)
-
-type contextKey string
-
-const (
-	UserIDKey    contextKey = "user_id"
-	UserEmailKey contextKey = "user_email"
-)
-
-type errorResponse struct {
-	Error   string `json:"error"`
-	Message string `json:"message"`
-}
-
-func writeJSON(w http.ResponseWriter, status int, v interface{}) {
-	w.Header().Set("Content-Type", "application/json")
-	w.WriteHeader(status)
-	json.NewEncoder(w).Encode(v)
-}
-
-func Authenticate(next http.Handler) http.Handler {
-	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		authHeader := r.Header.Get("Authorization")
-		if authHeader == "" || !strings.HasPrefix(authHeader, "Bearer ") {
-			log.Println("No Authorization header or invalid format")
-			writeJSON(w, http.StatusUnauthorized, errorResponse{
-				Error:   "UNAUTHORIZED",
-				Message: "No authentication token provided",
-			})
-			return
-		}
-
-		token := strings.TrimPrefix(authHeader, "Bearer ")
-		if token == "" {
-			log.Println("Empty token")
-			writeJSON(w, http.StatusUnauthorized, errorResponse{
-				Error:   "UNAUTHORIZED",
-				Message: "Invalid token format",
-			})
-			return
-		}
-
-		log.Println("Verifying Firebase token...")
-		decoded, err := fbauth.Auth().VerifyIDToken(r.Context(), token)
-		if err != nil {
-			log.Printf("Token verification failed: %v", err)
-
-			errMsg := err.Error()
-			if strings.Contains(errMsg, "expired") {
-				writeJSON(w, http.StatusUnauthorized, errorResponse{
-					Error:   "TOKEN_EXPIRED",
-					Message: "Authentication token has expired",
-				})
-				return
-			}
-
-			writeJSON(w, http.StatusUnauthorized, errorResponse{
-				Error:   "UNAUTHORIZED",
-				Message: "Failed to verify authentication token",
-			})
-			return
-		}
-
-		userID := decoded.UID
-		email, _ := decoded.Claims["email"].(string)
-
-		log.Printf("Token verified! User ID: %s, Email: %s", userID, email)
-
-		ctx := context.WithValue(r.Context(), UserIDKey, userID)
-		ctx = context.WithValue(ctx, UserEmailKey, email)
-
-		next.ServeHTTP(w, r.WithContext(ctx))
-	})
-}
-
-func GetUserID(ctx context.Context) string {
-	if v, ok := ctx.Value(UserIDKey).(string); ok {
-		return v
-	}
-	return ""
-}
-
-func GetUserEmail(ctx context.Context) string {
-	if v, ok := ctx.Value(UserEmailKey).(string); ok {
-		return v
-	}
-	return ""
-}

backend-go/internal/models/alert_rule.go

@@ -1,113 +0,0 @@
-package models
-
-import (
-	"context"
-
-	"github.com/jackc/pgx/v5/pgxpool"
-	"github.com/kjannette/koin-ping/backend-go/internal/domain"
-)
-
-type AlertRuleModel struct {
-	pool *pgxpool.Pool
-}
-
-func NewAlertRuleModel(pool *pgxpool.Pool) *AlertRuleModel {
-	return &AlertRuleModel{pool: pool}
-}
-
-func (m *AlertRuleModel) Create(ctx context.Context, addressID int, alertType domain.AlertType, threshold *float64) (*domain.AlertRule, error) {
-	var r domain.AlertRule
-	err := m.pool.QueryRow(ctx,
-		`INSERT INTO alert_rules (address_id, type, threshold, enabled)
-		 VALUES ($1, $2, $3, TRUE)
-		 RETURNING id, address_id, type, threshold, enabled, created_at`,
-		addressID, string(alertType), threshold,
-	).Scan(&r.ID, &r.AddressID, &r.Type, &r.Threshold, &r.Enabled, &r.CreatedAt)
-	if err != nil {
-		return nil, err
-	}
-	return &r, nil
-}
-
-func (m *AlertRuleModel) ListByAddress(ctx context.Context, addressID int) ([]domain.AlertRule, error) {
-	rows, err := m.pool.Query(ctx,
-		`SELECT id, address_id, type, threshold, enabled, created_at
-		 FROM alert_rules
-		 WHERE address_id = $1
-		 ORDER BY created_at DESC`,
-		addressID,
-	)
-	if err != nil {
-		return nil, err
-	}
-	defer rows.Close()
-
-	var rules []domain.AlertRule
-	for rows.Next() {
-		var r domain.AlertRule
-		if err := rows.Scan(&r.ID, &r.AddressID, &r.Type, &r.Threshold, &r.Enabled, &r.CreatedAt); err != nil {
-			return nil, err
-		}
-		rules = append(rules, r)
-	}
-	return rules, rows.Err()
-}
-
-func (m *AlertRuleModel) FindByID(ctx context.Context, id int, userID *string) (*domain.AlertRule, error) {
-	var r domain.AlertRule
-	var err error
-
-	if userID != nil {
-		err = m.pool.QueryRow(ctx,
-			`SELECT ar.id, ar.address_id, ar.type, ar.threshold, ar.enabled, ar.created_at
-			 FROM alert_rules ar
-			 JOIN addresses a ON a.id = ar.address_id
-			 WHERE ar.id = $1 AND a.user_id = $2`,
-			id, *userID,
-		).Scan(&r.ID, &r.AddressID, &r.Type, &r.Threshold, &r.Enabled, &r.CreatedAt)
-	} else {
-		err = m.pool.QueryRow(ctx,
-			`SELECT id, address_id, type, threshold, enabled, created_at
-			 FROM alert_rules
-			 WHERE id = $1`,
-			id,
-		).Scan(&r.ID, &r.AddressID, &r.Type, &r.Threshold, &r.Enabled, &r.CreatedAt)
-	}
-
-	if err != nil {
-		if err.Error() == "no rows in result set" {
-			return nil, nil
-		}
-		return nil, err
-	}
-	return &r, nil
-}
-
-func (m *AlertRuleModel) UpdateEnabled(ctx context.Context, id int, enabled bool) (*domain.AlertRule, error) {
-	var r domain.AlertRule
-	err := m.pool.QueryRow(ctx,
-		`UPDATE alert_rules
-		 SET enabled = $2
-		 WHERE id = $1
-		 RETURNING id, address_id, type, threshold, enabled, created_at`,
-		id, enabled,
-	).Scan(&r.ID, &r.AddressID, &r.Type, &r.Threshold, &r.Enabled, &r.CreatedAt)
-	if err != nil {
-		if err.Error() == "no rows in result set" {
-			return nil, nil
-		}
-		return nil, err
-	}
-	return &r, nil
-}
-
-func (m *AlertRuleModel) Remove(ctx context.Context, id int) (bool, error) {
-	tag, err := m.pool.Exec(ctx,
-		`DELETE FROM alert_rules WHERE id = $1`,
-		id,
-	)
-	if err != nil {
-		return false, err
-	}
-	return tag.RowsAffected() > 0, nil
-}

backend-go/internal/models/notification_config.go

@@ -1,94 +0,0 @@
-package models
-
-import (
-	"context"
-
-	"github.com/jackc/pgx/v5/pgxpool"
-	"github.com/kjannette/koin-ping/backend-go/internal/domain"
-)
-
-type NotificationConfigModel struct {
-	pool *pgxpool.Pool
-}
-
-func NewNotificationConfigModel(pool *pgxpool.Pool) *NotificationConfigModel {
-	return &NotificationConfigModel{pool: pool}
-}
-
-func (m *NotificationConfigModel) GetConfig(ctx context.Context, userID string) (*domain.NotificationConfig, error) {
-	var c domain.NotificationConfig
-	err := m.pool.QueryRow(ctx,
-		`SELECT user_id, discord_webhook_url, slack_webhook_url,
-		        email, notification_enabled, created_at, updated_at
-		 FROM user_notification_configs
-		 WHERE user_id = $1`,
-		userID,
-	).Scan(&c.UserID, &c.DiscordWebhookURL, &c.SlackWebhookURL,
-		&c.Email, &c.NotificationEnabled, &c.CreatedAt, &c.UpdatedAt)
-	if err != nil {
-		if err.Error() == "no rows in result set" {
-			return nil, nil
-		}
-		return nil, err
-	}
-	return &c, nil
-}
-
-func (m *NotificationConfigModel) UpsertConfig(ctx context.Context, userID string, cfg domain.NotificationConfig) (*domain.NotificationConfig, error) {
-	var c domain.NotificationConfig
-	err := m.pool.QueryRow(ctx,
-		`INSERT INTO user_notification_configs
-		   (user_id, discord_webhook_url, slack_webhook_url, email, notification_enabled, updated_at)
-		 VALUES ($1, $2, $3, $4, $5, NOW())
-		 ON CONFLICT (user_id)
-		 DO UPDATE SET
-		   discord_webhook_url = COALESCE($2, user_notification_configs.discord_webhook_url),
-		   slack_webhook_url = COALESCE($3, user_notification_configs.slack_webhook_url),
-		   email = COALESCE($4, user_notification_configs.email),
-		   notification_enabled = $5,
-		   updated_at = NOW()
-		 RETURNING user_id, discord_webhook_url, slack_webhook_url,
-		           email, notification_enabled, created_at, updated_at`,
-		userID, cfg.DiscordWebhookURL, cfg.SlackWebhookURL,
-		cfg.Email, cfg.NotificationEnabled,
-	).Scan(&c.UserID, &c.DiscordWebhookURL, &c.SlackWebhookURL,
-		&c.Email, &c.NotificationEnabled, &c.CreatedAt, &c.UpdatedAt)
-	if err != nil {
-		return nil, err
-	}
-	return &c, nil
-}
-
-func (m *NotificationConfigModel) Remove(ctx context.Context, userID string) (bool, error) {
-	tag, err := m.pool.Exec(ctx,
-		`DELETE FROM user_notification_configs WHERE user_id = $1`,
-		userID,
-	)
-	if err != nil {
-		return false, err
-	}
-	return tag.RowsAffected() > 0, nil
-}
-
-func (m *NotificationConfigModel) ListEnabled(ctx context.Context) ([]domain.NotificationConfig, error) {
-	rows, err := m.pool.Query(ctx,
-		`SELECT user_id, discord_webhook_url, slack_webhook_url, email
-		 FROM user_notification_configs
-		 WHERE notification_enabled = TRUE`,
-	)
-	if err != nil {
-		return nil, err
-	}
-	defer rows.Close()
-
-	var configs []domain.NotificationConfig
-	for rows.Next() {
-		var c domain.NotificationConfig
-		if err := rows.Scan(&c.UserID, &c.DiscordWebhookURL, &c.SlackWebhookURL, &c.Email); err != nil {
-			return nil, err
-		}
-		c.NotificationEnabled = true
-		configs = append(configs, c)
-	}
-	return configs, rows.Err()
-}

backend-go/internal/notifications/discord_test.go

@@ -1,99 +0,0 @@
-package notifications
-
-import (
-	"encoding/json"
-	"io"
-	"net/http"
-	"net/http/httptest"
-	"testing"
-)
-
-func TestSendDiscordNotification(t *testing.T) {
-	var receivedPayload discordPayload
-
-	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		if r.Method != http.MethodPost {
-			t.Errorf("expected POST, got %s", r.Method)
-		}
-
-		body, _ := io.ReadAll(r.Body)
-		json.Unmarshal(body, &receivedPayload)
-
-		w.WriteHeader(http.StatusNoContent)
-	}))
-	defer server.Close()
-
-	meta := AlertMetadata{
-		TxHash:       "0xabc123",
-		AddressLabel: "Treasury",
-		AlertType:    "incoming_tx",
-		Address:      "0x1234567890abcdef1234567890abcdef12345678",
-	}
-
-	sent, err := SendDiscordNotification(server.URL, "Incoming transaction: 5.5 ETH received", meta)
-	if err != nil {
-		t.Fatalf("unexpected error: %v", err)
-	}
-	if !sent {
-		t.Fatal("expected sent to be true")
-	}
-
-	if len(receivedPayload.Embeds) != 1 {
-		t.Fatalf("expected 1 embed, got %d", len(receivedPayload.Embeds))
-	}
-	embed := receivedPayload.Embeds[0]
-	if embed.Title != "Koin Ping Alert" {
-		t.Errorf("title = %q, want %q", embed.Title, "Koin Ping Alert")
-	}
-	if embed.Color != 0x00ff00 {
-		t.Errorf("color = %x, want %x (green for incoming_tx)", embed.Color, 0x00ff00)
-	}
-	if len(embed.Fields) != 3 {
-		t.Errorf("expected 3 fields (address, blockchain address, tx), got %d", len(embed.Fields))
-	}
-}
-
-func TestSendDiscordNotification_ServerError(t *testing.T) {
-	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		w.WriteHeader(http.StatusBadRequest)
-	}))
-	defer server.Close()
-
-	sent, err := SendDiscordNotification(server.URL, "test", AlertMetadata{})
-	if err == nil {
-		t.Fatal("expected error for bad response")
-	}
-	if sent {
-		t.Fatal("expected sent to be false")
-	}
-}
-
-func TestTestDiscordWebhook(t *testing.T) {
-	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		w.WriteHeader(http.StatusNoContent)
-	}))
-	defer server.Close()
-
-	ok, err := TestDiscordWebhook(server.URL)
-	if err != nil {
-		t.Fatalf("unexpected error: %v", err)
-	}
-	if !ok {
-		t.Fatal("expected ok to be true")
-	}
-}
-
-func TestColorForAlertType(t *testing.T) {
-	tests := map[string]int{
-		"incoming_tx":    0x00ff00,
-		"outgoing_tx":    0xff9900,
-		"large_transfer": 0xff0000,
-		"balance_below":  0xff0000,
-		"unknown":        0x0099ff,
-	}
-	for alertType, want := range tests {
-		if got := colorForAlertType(alertType); got != want {
-			t.Errorf("colorForAlertType(%q) = %x, want %x", alertType, got, want)
-		}
-	}
-}

backend-go/internal/notifications/email.go

@@ -1,111 +0,0 @@
-package notifications
-
-import (
-	"fmt"
-	"log"
-	"net/smtp"
-	"strings"
-)
-
-type SMTPConfig struct {
-	Host     string
-	Port     int
-	Username string
-	Password string
-	From     string
-}
-
-func (c *SMTPConfig) IsConfigured() bool {
-	return c.Host != "" && c.From != ""
-}
-
-func (c *SMTPConfig) addr() string {
-	return fmt.Sprintf("%s:%d", c.Host, c.Port)
-}
-
-func SendEmailNotification(cfg SMTPConfig, toEmail, message string, meta AlertMetadata) (bool, error) {
-	if !cfg.IsConfigured() {
-		return false, fmt.Errorf("SMTP is not configured")
-	}
-
-	subject := fmt.Sprintf("Koin Ping Alert: %s", humanAlertType(meta.AlertType))
-
-	body := buildEmailBody(message, meta)
-
-	msg := strings.Join([]string{
-		fmt.Sprintf("From: %s", cfg.From),
-		fmt.Sprintf("To: %s", toEmail),
-		fmt.Sprintf("Subject: %s", subject),
-		"MIME-Version: 1.0",
-		"Content-Type: text/html; charset=UTF-8",
-		"",
-		body,
-	}, "\r\n")
-
-	var auth smtp.Auth
-	if cfg.Username != "" {
-		auth = smtp.PlainAuth("", cfg.Username, cfg.Password, cfg.Host)
-	}
-
-	err := smtp.SendMail(cfg.addr(), auth, cfg.From, []string{toEmail}, []byte(msg))
-	if err != nil {
-		log.Printf("Failed to send email notification to %s: %v", toEmail, err)
-		return false, err
-	}
-
-	return true, nil
-}
-
-func TestEmailNotification(cfg SMTPConfig, toEmail string) (bool, error) {
-	meta := AlertMetadata{AlertType: "test"}
-	return SendEmailNotification(cfg, toEmail,
-		"This is a test notification from Koin Ping. Your email is configured correctly!", meta)
-}
-
-func buildEmailBody(message string, meta AlertMetadata) string {
-	txSection := ""
-	if meta.TxHash != "" {
-		txSection = fmt.Sprintf(
-			`<tr><td style="padding:8px 0;color:#666">Transaction</td>`+
-				`<td style="padding:8px 0"><a href="https://etherscan.io/tx/%s" style="color:#4f46e5">View on Etherscan</a></td></tr>`,
-			meta.TxHash,
-		)
-	}
-
-	return fmt.Sprintf(`<!DOCTYPE html>
-<html>
-<body style="margin:0;padding:0;font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Roboto,sans-serif;background:#f5f5f5">
-  <div style="max-width:560px;margin:24px auto;background:#fff;border-radius:8px;overflow:hidden;box-shadow:0 1px 3px rgba(0,0,0,.1)">
-    <div style="background:#4f46e5;padding:20px 24px">
-      <h1 style="margin:0;color:#fff;font-size:18px">Koin Ping Alert</h1>
-    </div>
-    <div style="padding:24px">
-      <p style="margin:0 0 16px;font-size:15px;color:#333">%s</p>
-      <table style="width:100%%;border-collapse:collapse;font-size:14px">
-        <tr><td style="padding:8px 0;color:#666">Address</td><td style="padding:8px 0">%s</td></tr>
-        <tr><td style="padding:8px 0;color:#666">Blockchain Address</td><td style="padding:8px 0;font-family:monospace;font-size:12px">%s</td></tr>
-        %s
-      </table>
-    </div>
-    <div style="padding:16px 24px;background:#fafafa;font-size:12px;color:#999;text-align:center">
-      Sent by Koin Ping
-    </div>
-  </div>
-</body>
-</html>`, message, meta.AddressLabel, meta.Address, txSection)
-}
-
-func humanAlertType(alertType string) string {
-	switch alertType {
-	case "incoming_tx":
-		return "Incoming Transaction"
-	case "outgoing_tx":
-		return "Outgoing Transaction"
-	case "large_transfer":
-		return "Large Transfer"
-	case "balance_below":
-		return "Balance Below Threshold"
-	default:
-		return "Alert"
-	}
-}

backend-go/internal/notifications/email_test.go

@@ -1,102 +0,0 @@
-package notifications
-
-import (
-	"strings"
-	"testing"
-)
-
-func TestSMTPConfig_IsConfigured(t *testing.T) {
-	tests := []struct {
-		name string
-		cfg  SMTPConfig
-		want bool
-	}{
-		{"fully configured", SMTPConfig{Host: "smtp.example.com", Port: 587, From: "noreply@example.com"}, true},
-		{"missing host", SMTPConfig{Port: 587, From: "noreply@example.com"}, false},
-		{"missing from", SMTPConfig{Host: "smtp.example.com", Port: 587}, false},
-		{"empty", SMTPConfig{}, false},
-	}
-
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			if got := tt.cfg.IsConfigured(); got != tt.want {
-				t.Errorf("IsConfigured() = %v, want %v", got, tt.want)
-			}
-		})
-	}
-}
-
-func TestSMTPConfig_Addr(t *testing.T) {
-	cfg := SMTPConfig{Host: "smtp.example.com", Port: 587}
-	if got := cfg.addr(); got != "smtp.example.com:587" {
-		t.Errorf("addr() = %q, want %q", got, "smtp.example.com:587")
-	}
-}
-
-func TestBuildEmailBody(t *testing.T) {
-	meta := AlertMetadata{
-		TxHash:       "0xabc123",
-		AddressLabel: "Treasury",
-		AlertType:    "incoming_tx",
-		Address:      "0x1234567890abcdef1234567890abcdef12345678",
-	}
-
-	body := buildEmailBody("Incoming transaction: 5.5 ETH received", meta)
-
-	if !strings.Contains(body, "Koin Ping Alert") {
-		t.Error("body should contain title")
-	}
-	if !strings.Contains(body, "Incoming transaction: 5.5 ETH received") {
-		t.Error("body should contain message")
-	}
-	if !strings.Contains(body, "Treasury") {
-		t.Error("body should contain address label")
-	}
-	if !strings.Contains(body, "0x1234567890abcdef") {
-		t.Error("body should contain blockchain address")
-	}
-	if !strings.Contains(body, "etherscan.io/tx/0xabc123") {
-		t.Error("body should contain etherscan link")
-	}
-}
-
-func TestBuildEmailBody_NoTxHash(t *testing.T) {
-	meta := AlertMetadata{
-		AddressLabel: "Cold Storage",
-		AlertType:    "balance_below",
-		Address:      "0xabcdef",
-	}
-
-	body := buildEmailBody("Balance dropped below threshold", meta)
-
-	if strings.Contains(body, "etherscan.io") {
-		t.Error("body should not contain etherscan link when no tx hash")
-	}
-}
-
-func TestHumanAlertType(t *testing.T) {
-	tests := map[string]string{
-		"incoming_tx":    "Incoming Transaction",
-		"outgoing_tx":    "Outgoing Transaction",
-		"large_transfer": "Large Transfer",
-		"balance_below":  "Balance Below Threshold",
-		"unknown":        "Alert",
-		"test":           "Alert",
-	}
-	for alertType, want := range tests {
-		if got := humanAlertType(alertType); got != want {
-			t.Errorf("humanAlertType(%q) = %q, want %q", alertType, got, want)
-		}
-	}
-}
-
-func TestSendEmailNotification_NotConfigured(t *testing.T) {
-	cfg := SMTPConfig{}
-	sent, err := SendEmailNotification(cfg, "user@example.com", "test", AlertMetadata{})
-	if err == nil {
-		t.Fatal("expected error for unconfigured SMTP")
-	}
-	if sent {
-		t.Fatal("expected sent to be false")
-	}
-}

backend-go/internal/notifications/slack.go

@@ -1,128 +0,0 @@
-package notifications
-
-import (
-	"bytes"
-	"encoding/json"
-	"fmt"
-	"log"
-	"net/http"
-	"time"
-)
-
-type slackBlock struct {
-	Type     string      `json:"type"`
-	Text     *slackText  `json:"text,omitempty"`
-	Fields   []slackText `json:"fields,omitempty"`
-	Elements []slackText `json:"elements,omitempty"`
-}
-
-type slackText struct {
-	Type string `json:"type"`
-	Text string `json:"text"`
-}
-
-type slackPayload struct {
-	Blocks []slackBlock `json:"blocks"`
-}
-
-func SendSlackNotification(webhookURL, message string, meta AlertMetadata) (bool, error) {
-	etherscanLink := ""
-	if meta.TxHash != "" {
-		etherscanLink = fmt.Sprintf("<%s|View on Etherscan>", "https://etherscan.io/tx/"+meta.TxHash)
-	}
-
-	blocks := []slackBlock{
-		{
-			Type: "header",
-			Text: &slackText{Type: "plain_text", Text: emojiForAlertType(meta.AlertType) + " Koin Ping Alert"},
-		},
-		{
-			Type: "section",
-			Text: &slackText{Type: "mrkdwn", Text: message},
-		},
-		{
-			Type: "section",
-			Fields: []slackText{
-				{Type: "mrkdwn", Text: fmt.Sprintf("*Address:*\n%s", meta.AddressLabel)},
-				{Type: "mrkdwn", Text: fmt.Sprintf("*Blockchain Address:*\n`%s`", meta.Address)},
-			},
-		},
-	}
-
-	if etherscanLink != "" {
-		blocks = append(blocks, slackBlock{
-			Type: "section",
-			Text: &slackText{Type: "mrkdwn", Text: fmt.Sprintf("*Transaction:* %s", etherscanLink)},
-		})
-	}
-
-	blocks = append(blocks, slackBlock{
-		Type: "context",
-		Elements: []slackText{
-			{Type: "mrkdwn", Text: fmt.Sprintf("Koin Ping | %s", time.Now().UTC().Format(time.RFC3339))},
-		},
-	})
-
-	payload := slackPayload{Blocks: blocks}
-	body, err := json.Marshal(payload)
-	if err != nil {
-		return false, fmt.Errorf("marshal slack payload: %w", err)
-	}
-
-	resp, err := http.Post(webhookURL, "application/json", bytes.NewReader(body))
-	if err != nil {
-		log.Printf("Failed to send Slack notification: %v", err)
-		return false, err
-	}
-	defer resp.Body.Close()
-
-	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
-		log.Printf("Slack webhook failed: HTTP %d", resp.StatusCode)
-		return false, fmt.Errorf("slack webhook failed: HTTP %d", resp.StatusCode)
-	}
-
-	return true, nil
-}
-
-func TestSlackWebhook(webhookURL string) (bool, error) {
-	payload := slackPayload{
-		Blocks: []slackBlock{
-			{
-				Type: "section",
-				Text: &slackText{
-					Type: "mrkdwn",
-					Text: "Koin Ping test notification — Your Slack webhook is configured correctly!",
-				},
-			},
-		},
-	}
-
-	body, err := json.Marshal(payload)
-	if err != nil {
-		return false, err
-	}
-
-	resp, err := http.Post(webhookURL, "application/json", bytes.NewReader(body))
-	if err != nil {
-		log.Printf("Slack webhook test failed: %v", err)
-		return false, err
-	}
-	defer resp.Body.Close()
-
-	return resp.StatusCode >= 200 && resp.StatusCode < 300, nil
-}
-
-func emojiForAlertType(alertType string) string {
-	switch alertType {
-	case "incoming_tx":
-		return "📥"
-	case "outgoing_tx":
-		return "📤"
-	case "large_transfer":
-		return "🚨"
-	case "balance_below":
-		return "⚠️"
-	default:
-		return "🔔"
-	}
-}

backend-go/internal/notifications/slack_test.go

@@ -1,128 +0,0 @@
-package notifications
-
-import (
-	"encoding/json"
-	"io"
-	"net/http"
-	"net/http/httptest"
-	"testing"
-)
-
-func TestSendSlackNotification(t *testing.T) {
-	var receivedPayload slackPayload
-
-	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		if r.Method != http.MethodPost {
-			t.Errorf("expected POST, got %s", r.Method)
-		}
-		if r.Header.Get("Content-Type") != "application/json" {
-			t.Errorf("expected application/json content type")
-		}
-
-		body, _ := io.ReadAll(r.Body)
-		json.Unmarshal(body, &receivedPayload)
-
-		w.WriteHeader(http.StatusOK)
-	}))
-	defer server.Close()
-
-	meta := AlertMetadata{
-		TxHash:       "0xabc123",
-		AddressLabel: "Treasury",
-		AlertType:    "incoming_tx",
-		Address:      "0x1234567890abcdef1234567890abcdef12345678",
-	}
-
-	sent, err := SendSlackNotification(server.URL, "Incoming transaction: 5.5 ETH received", meta)
-	if err != nil {
-		t.Fatalf("unexpected error: %v", err)
-	}
-	if !sent {
-		t.Fatal("expected sent to be true")
-	}
-
-	if len(receivedPayload.Blocks) < 3 {
-		t.Fatalf("expected at least 3 blocks, got %d", len(receivedPayload.Blocks))
-	}
-	if receivedPayload.Blocks[0].Type != "header" {
-		t.Errorf("first block should be header, got %s", receivedPayload.Blocks[0].Type)
-	}
-}
-
-func TestSendSlackNotification_ServerError(t *testing.T) {
-	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		w.WriteHeader(http.StatusInternalServerError)
-	}))
-	defer server.Close()
-
-	sent, err := SendSlackNotification(server.URL, "test", AlertMetadata{})
-	if err == nil {
-		t.Fatal("expected error for server error response")
-	}
-	if sent {
-		t.Fatal("expected sent to be false")
-	}
-}
-
-func TestSendSlackNotification_NoTxHash(t *testing.T) {
-	var receivedPayload slackPayload
-
-	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		body, _ := io.ReadAll(r.Body)
-		json.Unmarshal(body, &receivedPayload)
-		w.WriteHeader(http.StatusOK)
-	}))
-	defer server.Close()
-
-	meta := AlertMetadata{
-		AddressLabel: "Treasury",
-		AlertType:    "balance_below",
-		Address:      "0x1234567890abcdef1234567890abcdef12345678",
-	}
-
-	sent, err := SendSlackNotification(server.URL, "Balance dropped below threshold", meta)
-	if err != nil {
-		t.Fatalf("unexpected error: %v", err)
-	}
-	if !sent {
-		t.Fatal("expected sent to be true")
-	}
-
-	for _, block := range receivedPayload.Blocks {
-		if block.Text != nil && block.Type == "section" {
-			if block.Text.Text == "*Transaction:*" {
-				t.Error("should not include transaction block when TxHash is empty")
-			}
-		}
-	}
-}
-
-func TestTestSlackWebhook(t *testing.T) {
-	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		w.WriteHeader(http.StatusOK)
-	}))
-	defer server.Close()
-
-	ok, err := TestSlackWebhook(server.URL)
-	if err != nil {
-		t.Fatalf("unexpected error: %v", err)
-	}
-	if !ok {
-		t.Fatal("expected ok to be true")
-	}
-}
-
-func TestEmojiForAlertType(t *testing.T) {
-	tests := map[string]string{
-		"incoming_tx":    "📥",
-		"outgoing_tx":    "📤",
-		"large_transfer": "🚨",
-		"balance_below":  "⚠️",
-		"unknown":        "🔔",
-	}
-	for alertType, want := range tests {
-		if got := emojiForAlertType(alertType); got != want {
-			t.Errorf("emojiForAlertType(%q) = %q, want %q", alertType, got, want)
-		}
-	}
-}

backend-go/internal/protocols/ethereum/jsonrpc.go

@@ -1,211 +0,0 @@
-package ethereum
-
-import (
-	"bytes"
-	"context"
-	"encoding/json"
-	"fmt"
-	"math/big"
-	"net/http"
-	"strings"
-	"time"
-
-	"github.com/kjannette/koin-ping/backend-go/internal/domain"
-)
-
-const rpcTimeoutMS = 30000
-
-type JsonRpcEthereum struct {
-	rpcURL string
-	client *http.Client
-}
-
-func NewJsonRpcEthereum(rpcURL string) (*JsonRpcEthereum, error) {
-	if rpcURL == "" {
-		return nil, fmt.Errorf("JsonRpcEthereum requires a valid RPC URL")
-	}
-	return &JsonRpcEthereum{
-		rpcURL: rpcURL,
-		client: &http.Client{
-			Timeout: time.Duration(rpcTimeoutMS) * time.Millisecond,
-		},
-	}, nil
-}
-
-type rpcRequest struct {
-	JSONRPC string        `json:"jsonrpc"`
-	ID      int64         `json:"id"`
-	Method  string        `json:"method"`
-	Params  []interface{} `json:"params"`
-}
-
-type rpcResponse struct {
-	JSONRPC string          `json:"jsonrpc"`
-	ID      int64           `json:"id"`
-	Result  json.RawMessage `json:"result"`
-	Error   *rpcError       `json:"error"`
-}
-
-type rpcError struct {
-	Code    int    `json:"code"`
-	Message string `json:"message"`
-}
-
-func (j *JsonRpcEthereum) callRPC(ctx context.Context, method string, params ...interface{}) (json.RawMessage, error) {
-	if params == nil {
-		params = []interface{}{}
-	}
-
-	body, err := json.Marshal(rpcRequest{
-		JSONRPC: "2.0",
-		ID:      time.Now().UnixMilli(),
-		Method:  method,
-		Params:  params,
-	})
-	if err != nil {
-		return nil, fmt.Errorf("marshal RPC request: %w", err)
-	}
-
-	req, err := http.NewRequestWithContext(ctx, http.MethodPost, j.rpcURL, bytes.NewReader(body))
-	if err != nil {
-		return nil, fmt.Errorf("create RPC request: %w", err)
-	}
-	req.Header.Set("Content-Type", "application/json")
-
-	resp, err := j.client.Do(req)
-	if err != nil {
-		return nil, fmt.Errorf("RPC call failed [%s]: %w", method, err)
-	}
-	defer resp.Body.Close()
-
-	if resp.StatusCode != http.StatusOK {
-		return nil, fmt.Errorf("HTTP %d: %s for %s", resp.StatusCode, resp.Status, method)
-	}
-
-	var rpcResp rpcResponse
-	if err := json.NewDecoder(resp.Body).Decode(&rpcResp); err != nil {
-		return nil, fmt.Errorf("decode RPC response: %w", err)
-	}
-
-	if rpcResp.Error != nil {
-		return nil, fmt.Errorf("RPC Error [%s]: %s (code: %d)", method, rpcResp.Error.Message, rpcResp.Error.Code)
-	}
-
-	return rpcResp.Result, nil
-}
-
-func (j *JsonRpcEthereum) GetLatestBlockNumber(ctx context.Context) (int, error) {
-	result, err := j.callRPC(ctx, "eth_blockNumber")
-	if err != nil {
-		return 0, err
-	}
-
-	var hexBlock string
-	if err := json.Unmarshal(result, &hexBlock); err != nil {
-		return 0, fmt.Errorf("unmarshal block number: %w", err)
-	}
-
-	return hexToInt(hexBlock)
-}
-
-type rpcBlock struct {
-	Timestamp    string  `json:"timestamp"`
-	Transactions []rpcTx `json:"transactions"`
-}
-
-type rpcTx struct {
-	Hash        string  `json:"hash"`
-	From        string  `json:"from"`
-	To          *string `json:"to"`
-	Value       string  `json:"value"`
-	BlockNumber string  `json:"blockNumber"`
-}
-
-func (j *JsonRpcEthereum) GetBlockTransactions(ctx context.Context, blockNumber int) ([]domain.NormalizedTx, error) {
-	hexBlock := fmt.Sprintf("0x%x", blockNumber)
-
-	result, err := j.callRPC(ctx, "eth_getBlockByNumber", hexBlock, true)
-	if err != nil {
-		return nil, err
-	}
-
-	if string(result) == "null" {
-		return nil, nil
-	}
-
-	var block rpcBlock
-	if err := json.Unmarshal(result, &block); err != nil {
-		return nil, fmt.Errorf("unmarshal block: %w", err)
-	}
-
-	blockTimestamp, err := hexToInt64(block.Timestamp)
-	if err != nil {
-		return nil, fmt.Errorf("parse block timestamp: %w", err)
-	}
-
-	txs := make([]domain.NormalizedTx, 0, len(block.Transactions))
-	for _, tx := range block.Transactions {
-		bn, _ := hexToInt(tx.BlockNumber)
-
-		var toLower *string
-		if tx.To != nil {
-			s := strings.ToLower(*tx.To)
-			toLower = &s
-		}
-
-		txs = append(txs, domain.NormalizedTx{
-			Hash:           tx.Hash,
-			From:           strings.ToLower(tx.From),
-			To:             toLower,
-			Value:          hexToDecimalString(tx.Value),
-			BlockNumber:    bn,
-			BlockTimestamp: blockTimestamp,
-		})
-	}
-
-	return txs, nil
-}
-
-func (j *JsonRpcEthereum) GetBalance(ctx context.Context, address string) (string, error) {
-	result, err := j.callRPC(ctx, "eth_getBalance", address, "latest")
-	if err != nil {
-		return "", err
-	}
-
-	var hexBalance string
-	if err := json.Unmarshal(result, &hexBalance); err != nil {
-		return "", fmt.Errorf("unmarshal balance: %w", err)
-	}
-
-	return hexToDecimalString(hexBalance), nil
-}
-
-func hexToInt(hex string) (int, error) {
-	hex = strings.TrimPrefix(hex, "0x")
-	n, ok := new(big.Int).SetString(hex, 16)
-	if !ok {
-		return 0, fmt.Errorf("invalid hex: %s", hex)
-	}
-	return int(n.Int64()), nil
-}
-
-func hexToInt64(hex string) (int64, error) {
-	hex = strings.TrimPrefix(hex, "0x")
-	n, ok := new(big.Int).SetString(hex, 16)
-	if !ok {
-		return 0, fmt.Errorf("invalid hex: %s", hex)
-	}
-	return n.Int64(), nil
-}
-
-func hexToDecimalString(hex string) string {
-	if hex == "" || hex == "0x" || hex == "0x0" {
-		return "0"
-	}
-	clean := strings.TrimPrefix(hex, "0x")
-	n, ok := new(big.Int).SetString(clean, 16)
-	if !ok {
-		return "0"
-	}
-	return n.String()
-}

backend-go/internal/protocols/ethereum/jsonrpc_test.go

@@ -1,96 +0,0 @@
-package ethereum
-
-import (
-	"math/big"
-	"testing"
-)
-
-func TestHexToInt(t *testing.T) {
-	tests := []struct {
-		hex  string
-		want int
-	}{
-		{"0x0", 0},
-		{"0x1", 1},
-		{"0xa", 10},
-		{"0xff", 255},
-		{"0x100", 256},
-		{"0x1234", 4660},
-	}
-
-	for _, tt := range tests {
-		got, err := hexToInt(tt.hex)
-		if err != nil {
-			t.Fatalf("hexToInt(%q) error: %v", tt.hex, err)
-		}
-		if got != tt.want {
-			t.Errorf("hexToInt(%q) = %d, want %d", tt.hex, got, tt.want)
-		}
-	}
-}
-
-func TestHexToInt_Invalid(t *testing.T) {
-	_, err := hexToInt("xyz")
-	if err == nil {
-		t.Fatal("expected error for invalid hex")
-	}
-}
-
-func TestHexToInt64(t *testing.T) {
-	got, err := hexToInt64("0x5f5e100")
-	if err != nil {
-		t.Fatalf("unexpected error: %v", err)
-	}
-	if got != 100000000 {
-		t.Errorf("got %d, want 100000000", got)
-	}
-}
-
-func TestHexToDecimalString(t *testing.T) {
-	tests := []struct {
-		hex  string
-		want string
-	}{
-		{"0x0", "0"},
-		{"0x", "0"},
-		{"", "0"},
-		{"0x1", "1"},
-		{"0xde0b6b3a7640000", "1000000000000000000"},
-	}
-
-	for _, tt := range tests {
-		got := hexToDecimalString(tt.hex)
-		if got != tt.want {
-			t.Errorf("hexToDecimalString(%q) = %q, want %q", tt.hex, got, tt.want)
-		}
-	}
-}
-
-func TestHexToDecimalString_LargeValues(t *testing.T) {
-	expected := new(big.Int).Mul(
-		big.NewInt(100),
-		new(big.Int).Exp(big.NewInt(10), big.NewInt(18), nil),
-	)
-	hex := "0x" + expected.Text(16)
-	got := hexToDecimalString(hex)
-	if got != expected.String() {
-		t.Errorf("got %q, want %q", got, expected.String())
-	}
-}
-
-func TestNewJsonRpcEthereum_EmptyURL(t *testing.T) {
-	_, err := NewJsonRpcEthereum("")
-	if err == nil {
-		t.Fatal("expected error for empty URL")
-	}
-}
-
-func TestNewJsonRpcEthereum_ValidURL(t *testing.T) {
-	eth, err := NewJsonRpcEthereum("https://example.com/rpc")
-	if err != nil {
-		t.Fatalf("unexpected error: %v", err)
-	}
-	if eth == nil {
-		t.Fatal("expected non-nil client")
-	}
-}

backend-go/internal/services/evaluator.go

@@ -1,251 +0,0 @@
-package services
-
-import (
-	"context"
-	"fmt"
-	"log"
-
-	"github.com/kjannette/koin-ping/backend-go/internal/domain"
-	"github.com/kjannette/koin-ping/backend-go/internal/models"
-	"github.com/kjannette/koin-ping/backend-go/internal/notifications"
-	"github.com/kjannette/koin-ping/backend-go/internal/protocols/ethereum"
-	"github.com/kjannette/koin-ping/backend-go/internal/wei"
-)
-
-type EvaluatorService struct {
-	eth          ethereum.EthereumObserver
-	alertRules   *models.AlertRuleModel
-	alertEvents  *models.AlertEventModel
-	addresses    *models.AddressModel
-	notifConfigs *models.NotificationConfigModel
-	smtpConfig   notifications.SMTPConfig
-}
-
-func NewEvaluatorService(
-	eth ethereum.EthereumObserver,
-	alertRules *models.AlertRuleModel,
-	alertEvents *models.AlertEventModel,
-	addresses *models.AddressModel,
-	notifConfigs *models.NotificationConfigModel,
-	smtpCfg notifications.SMTPConfig,
-) *EvaluatorService {
-	return &EvaluatorService{
-		eth:          eth,
-		alertRules:   alertRules,
-		alertEvents:  alertEvents,
-		addresses:    addresses,
-		notifConfigs: notifConfigs,
-		smtpConfig:   smtpCfg,
-	}
-}
-
-func (s *EvaluatorService) Evaluate(ctx context.Context, observations []domain.ObservedTx) (int, error) {
-	alertsFired := 0
-
-	for _, obs := range observations {
-		fired, err := s.evaluateObservation(ctx, obs)
-		if err != nil {
-			log.Printf("Error evaluating observation for address ID %d: %v", obs.AddressID, err)
-			continue
-		}
-		alertsFired += fired
-	}
-
-	return alertsFired, nil
-}
-
-func (s *EvaluatorService) evaluateObservation(ctx context.Context, obs domain.ObservedTx) (int, error) {
-	rules, err := s.alertRules.ListByAddress(ctx, obs.AddressID)
-	if err != nil {
-		return 0, err
-	}
-
-	alertsFired := 0
-	for _, rule := range rules {
-		if !rule.Enabled {
-			continue
-		}
-
-		matches, err := s.ruleMatches(ctx, rule, obs)
-		if err != nil {
-			log.Printf("Error matching rule %d: %v", rule.ID, err)
-			continue
-		}
-
-		if matches {
-			if err := s.fireAlert(ctx, rule, obs); err != nil {
-				log.Printf("Error firing alert for rule %d: %v", rule.ID, err)
-				continue
-			}
-			alertsFired++
-		}
-	}
-
-	return alertsFired, nil
-}
-
-func (s *EvaluatorService) ruleMatches(ctx context.Context, rule domain.AlertRule, obs domain.ObservedTx) (bool, error) {
-	switch rule.Type {
-	case domain.AlertIncomingTx:
-		return obs.Direction == domain.DirectionIncoming, nil
-	case domain.AlertOutgoingTx:
-		return obs.Direction == domain.DirectionOutgoing, nil
-	case domain.AlertLargeTransfer:
-		return s.matchesLargeTransfer(rule, obs)
-	case domain.AlertBalanceBelow:
-		return s.matchesBalanceBelow(ctx, rule, obs)
-	default:
-		log.Printf("Unknown rule type: %s", rule.Type)
-		return false, nil
-	}
-}
-
-func (s *EvaluatorService) matchesLargeTransfer(rule domain.AlertRule, obs domain.ObservedTx) (bool, error) {
-	if rule.Threshold == nil {
-		return false, nil
-	}
-
-	thresholdWei, err := wei.FromEth(*rule.Threshold)
-	if err != nil {
-		return false, err
-	}
-
-	return wei.GreaterThanOrEqual(obs.Value, thresholdWei)
-}
-
-// matchesBalanceBelow only triggers after outgoing transactions, since incoming
-// transactions increase balance and can't cause it to drop below threshold.
-func (s *EvaluatorService) matchesBalanceBelow(ctx context.Context, rule domain.AlertRule, obs domain.ObservedTx) (bool, error) {
-	if rule.Threshold == nil {
-		return false, nil
-	}
-
-	if obs.Direction != domain.DirectionOutgoing {
-		return false, nil
-	}
-
-	addr, err := s.addresses.FindByID(ctx, obs.AddressID, nil)
-	if err != nil {
-		return false, err
-	}
-	if addr == nil {
-		log.Printf("Address ID %d not found", obs.AddressID)
-		return false, nil
-	}
-
-	balanceWei, err := s.eth.GetBalance(ctx, addr.Address)
-	if err != nil {
-		return false, err
-	}
-
-	thresholdWei, err := wei.FromEth(*rule.Threshold)
-	if err != nil {
-		return false, err
-	}
-
-	return wei.LessThan(balanceWei, thresholdWei)
-}
-
-func (s *EvaluatorService) fireAlert(ctx context.Context, rule domain.AlertRule, obs domain.ObservedTx) error {
-	addr, err := s.addresses.FindByID(ctx, obs.AddressID, nil)
-	if err != nil {
-		return err
-	}
-
-	addressLabel := "Unknown"
-	if addr != nil {
-		if addr.Label != nil {
-			addressLabel = *addr.Label
-		} else {
-			addressLabel = addr.Address
-		}
-	}
-
-	message := s.buildMessage(rule, obs)
-	txHash := &obs.Hash
-
-	_, err = s.alertEvents.Create(ctx, rule.ID, message, &addressLabel, txHash)
-	if err != nil {
-		return err
-	}
-
-	log.Printf("[ALERT FIRED] Rule %d (%s) - %s - TX: %s", rule.ID, rule.Type, message, obs.Hash)
-
-	if addr != nil {
-		go s.sendNotifications(ctx, addr.UserID, message, obs, addressLabel, rule, addr.Address)
-	}
-
-	return nil
-}
-
-func (s *EvaluatorService) sendNotifications(ctx context.Context, userID, message string, obs domain.ObservedTx, addressLabel string, rule domain.AlertRule, address string) {
-	notifConfig, err := s.notifConfigs.GetConfig(ctx, userID)
-	if err != nil {
-		log.Printf("Failed to get notification config: %v", err)
-		return
-	}
-
-	if notifConfig == nil || !notifConfig.NotificationEnabled {
-		return
-	}
-
-	meta := notifications.AlertMetadata{
-		TxHash:       obs.Hash,
-		AddressLabel: addressLabel,
-		AlertType:    string(rule.Type),
-		Address:      address,
-	}
-
-	if notifConfig.DiscordWebhookURL != nil && *notifConfig.DiscordWebhookURL != "" {
-		sent, err := notifications.SendDiscordNotification(*notifConfig.DiscordWebhookURL, message, meta)
-		if err != nil || !sent {
-			log.Printf("Discord notification failed for user %s: %v", userID, err)
-		} else {
-			log.Printf("Discord notification sent to user %s", userID)
-		}
-	}
-
-	if notifConfig.SlackWebhookURL != nil && *notifConfig.SlackWebhookURL != "" {
-		sent, err := notifications.SendSlackNotification(*notifConfig.SlackWebhookURL, message, meta)
-		if err != nil || !sent {
-			log.Printf("Slack notification failed for user %s: %v", userID, err)
-		} else {
-			log.Printf("Slack notification sent to user %s", userID)
-		}
-	}
-
-	if notifConfig.Email != nil && *notifConfig.Email != "" && s.smtpConfig.IsConfigured() {
-		sent, err := notifications.SendEmailNotification(s.smtpConfig, *notifConfig.Email, message, meta)
-		if err != nil || !sent {
-			log.Printf("Email notification failed for user %s: %v", userID, err)
-		} else {
-			log.Printf("Email notification sent to user %s (%s)", userID, *notifConfig.Email)
-		}
-	}
-}
-
-func (s *EvaluatorService) buildMessage(rule domain.AlertRule, obs domain.ObservedTx) string {
-	switch rule.Type {
-	case domain.AlertIncomingTx:
-		ethStr, _ := wei.FormatAsEth(obs.Value, 4)
-		return fmt.Sprintf("Incoming transaction: %s received", ethStr)
-	case domain.AlertOutgoingTx:
-		ethStr, _ := wei.FormatAsEth(obs.Value, 4)
-		return fmt.Sprintf("Outgoing transaction: %s sent", ethStr)
-	case domain.AlertLargeTransfer:
-		ethStr, _ := wei.FormatAsEth(obs.Value, 4)
-		threshold := float64(0)
-		if rule.Threshold != nil {
-			threshold = *rule.Threshold
-		}
-		return fmt.Sprintf("Large transfer detected: %s (threshold: %g ETH)", ethStr, threshold)
-	case domain.AlertBalanceBelow:
-		threshold := float64(0)
-		if rule.Threshold != nil {
-			threshold = *rule.Threshold
-		}
-		return fmt.Sprintf("Balance dropped below threshold of %g ETH", threshold)
-	default:
-		return "Alert triggered"
-	}
-}

backend-go/internal/services/observer_test.go

@@ -1,113 +0,0 @@
-package services
-
-import (
-	"testing"
-
-	"github.com/kjannette/koin-ping/backend-go/internal/domain"
-)
-
-func TestFilterRelevantTransactions(t *testing.T) {
-	to1 := "0xaaaa"
-	to2 := "0xbbbb"
-	to3 := "0xcccc"
-
-	txs := []domain.NormalizedTx{
-		{Hash: "0x1", From: "0xaaaa", To: &to2, Value: "1000"},
-		{Hash: "0x2", From: "0xbbbb", To: &to1, Value: "2000"},
-		{Hash: "0x3", From: "0xcccc", To: &to3, Value: "3000"},
-		{Hash: "0x4", From: "0xdddd", To: nil, Value: "0"},
-	}
-
-	t.Run("finds outgoing", func(t *testing.T) {
-		result := filterRelevantTransactions(txs, "0xAAAA")
-		if len(result) != 2 {
-			t.Fatalf("expected 2 relevant txs (1 from, 1 to), got %d", len(result))
-		}
-	})
-
-	t.Run("finds incoming", func(t *testing.T) {
-		result := filterRelevantTransactions(txs, "0xBBBB")
-		if len(result) != 2 {
-			t.Fatalf("expected 2 relevant txs, got %d", len(result))
-		}
-	})
-
-	t.Run("no match", func(t *testing.T) {
-		result := filterRelevantTransactions(txs, "0x9999")
-		if len(result) != 0 {
-			t.Fatalf("expected 0 relevant txs, got %d", len(result))
-		}
-	})
-
-	t.Run("case insensitive", func(t *testing.T) {
-		result := filterRelevantTransactions(txs, "0xAAAA")
-		if len(result) == 0 {
-			t.Fatal("should match case-insensitively")
-		}
-	})
-}
-
-func TestCreateObservedTx(t *testing.T) {
-	to := "0xaaaa"
-	tx := domain.NormalizedTx{
-		Hash:  "0xhash",
-		From:  "0xbbbb",
-		To:    &to,
-		Value: "1000",
-	}
-
-	t.Run("incoming direction", func(t *testing.T) {
-		addr := domain.Address{ID: 1, Address: "0xaaaa"}
-		obs := createObservedTx(tx, addr)
-		if obs.Direction != domain.DirectionIncoming {
-			t.Errorf("expected incoming, got %s", obs.Direction)
-		}
-		if obs.AddressID != 1 {
-			t.Errorf("expected address ID 1, got %d", obs.AddressID)
-		}
-	})
-
-	t.Run("outgoing direction", func(t *testing.T) {
-		addr := domain.Address{ID: 2, Address: "0xbbbb"}
-		obs := createObservedTx(tx, addr)
-		if obs.Direction != domain.DirectionOutgoing {
-			t.Errorf("expected outgoing, got %s", obs.Direction)
-		}
-	})
-}
-
-func TestGetStartBlock(t *testing.T) {
-	s := &ObserverService{}
-
-	t.Run("no checkpoint uses latest", func(t *testing.T) {
-		got := s.getStartBlock(0, false, 1000)
-		if got != 1000 {
-			t.Errorf("expected 1000, got %d", got)
-		}
-	})
-
-	t.Run("with checkpoint uses next block", func(t *testing.T) {
-		got := s.getStartBlock(999, true, 1000)
-		if got != 1000 {
-			t.Errorf("expected 1000, got %d", got)
-		}
-	})
-}
-
-func TestGetEndBlock(t *testing.T) {
-	s := &ObserverService{}
-
-	t.Run("caps at latest", func(t *testing.T) {
-		got := s.getEndBlock(990, 1000)
-		if got != 1000 {
-			t.Errorf("expected 1000, got %d", got)
-		}
-	})
-
-	t.Run("caps at maxBlocksPerRun", func(t *testing.T) {
-		got := s.getEndBlock(0, 200)
-		if got != maxBlocksPerRun-1 {
-			t.Errorf("expected %d, got %d", maxBlocksPerRun-1, got)
-		}
-	})
-}

backend-go/internal/wei/converter_test.go

@@ -1,179 +0,0 @@
-package wei
-
-import (
-	"math"
-	"testing"
-)
-
-func TestToEth(t *testing.T) {
-	tests := []struct {
-		name    string
-		wei     string
-		want    float64
-		wantErr bool
-	}{
-		{"zero string", "0", 0, false},
-		{"empty string", "", 0, false},
-		{"1 ETH", "1000000000000000000", 1.0, false},
-		{"0.5 ETH", "500000000000000000", 0.5, false},
-		{"10 ETH", "10000000000000000000", 10.0, false},
-		{"small amount", "1000000000000000", 0.001, false},
-		{"1 Wei", "1", 1e-18, false},
-		{"invalid", "notanumber", 0, true},
-	}
-
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			got, err := ToEth(tt.wei)
-			if tt.wantErr {
-				if err == nil {
-					t.Fatal("expected error")
-				}
-				return
-			}
-			if err != nil {
-				t.Fatalf("unexpected error: %v", err)
-			}
-			if math.Abs(got-tt.want) > 1e-10 {
-				t.Fatalf("ToEth(%q) = %v, want %v", tt.wei, got, tt.want)
-			}
-		})
-	}
-}
-
-func TestFromEth(t *testing.T) {
-	tests := []struct {
-		name    string
-		eth     float64
-		want    string
-		wantErr bool
-	}{
-		{"zero", 0, "0", false},
-		{"1 ETH", 1.0, "1000000000000000000", false},
-		{"0.5 ETH", 0.5, "500000000000000000", false},
-		{"10 ETH", 10.0, "10000000000000000000", false},
-		{"0.001 ETH", 0.001, "1000000000000000", false},
-	}
-
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			got, err := FromEth(tt.eth)
-			if tt.wantErr {
-				if err == nil {
-					t.Fatal("expected error")
-				}
-				return
-			}
-			if err != nil {
-				t.Fatalf("unexpected error: %v", err)
-			}
-			if got != tt.want {
-				t.Fatalf("FromEth(%v) = %q, want %q", tt.eth, got, tt.want)
-			}
-		})
-	}
-}
-
-func TestRoundTrip(t *testing.T) {
-	values := []float64{0.001, 0.1, 1.0, 5.5, 10.0, 100.0}
-	for _, eth := range values {
-		weiStr, err := FromEth(eth)
-		if err != nil {
-			t.Fatalf("FromEth(%v) error: %v", eth, err)
-		}
-		back, err := ToEth(weiStr)
-		if err != nil {
-			t.Fatalf("ToEth(%q) error: %v", weiStr, err)
-		}
-		if math.Abs(back-eth) > 1e-10 {
-			t.Fatalf("round-trip %v → %q → %v (diff: %v)", eth, weiStr, back, back-eth)
-		}
-	}
-}
-
-func TestCompare(t *testing.T) {
-	tests := []struct {
-		name string
-		a, b string
-		want int
-	}{
-		{"equal", "1000", "1000", 0},
-		{"a > b", "2000", "1000", 1},
-		{"a < b", "1000", "2000", -1},
-		{"zero equal", "0", "0", 0},
-	}
-
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			got, err := Compare(tt.a, tt.b)
-			if err != nil {
-				t.Fatalf("unexpected error: %v", err)
-			}
-			if got != tt.want {
-				t.Fatalf("Compare(%q, %q) = %d, want %d", tt.a, tt.b, got, tt.want)
-			}
-		})
-	}
-}
-
-func TestGreaterThanOrEqual(t *testing.T) {
-	ok, err := GreaterThanOrEqual("2000", "1000")
-	if err != nil {
-		t.Fatal(err)
-	}
-	if !ok {
-		t.Fatal("expected true")
-	}
-
-	ok, err = GreaterThanOrEqual("1000", "1000")
-	if err != nil {
-		t.Fatal(err)
-	}
-	if !ok {
-		t.Fatal("expected true for equal")
-	}
-
-	ok, err = GreaterThanOrEqual("500", "1000")
-	if err != nil {
-		t.Fatal(err)
-	}
-	if ok {
-		t.Fatal("expected false")
-	}
-}
-
-func TestLessThan(t *testing.T) {
-	ok, err := LessThan("500", "1000")
-	if err != nil {
-		t.Fatal(err)
-	}
-	if !ok {
-		t.Fatal("expected true")
-	}
-
-	ok, err = LessThan("1000", "1000")
-	if err != nil {
-		t.Fatal(err)
-	}
-	if ok {
-		t.Fatal("expected false for equal")
-	}
-}
-
-func TestFormatAsEth(t *testing.T) {
-	got, err := FormatAsEth("1000000000000000000", 4)
-	if err != nil {
-		t.Fatal(err)
-	}
-	if got != "1.0000 ETH" {
-		t.Fatalf("got %q, want %q", got, "1.0000 ETH")
-	}
-
-	got, err = FormatAsEth("500000000000000000", 2)
-	if err != nil {
-		t.Fatal(err)
-	}
-	if got != "0.50 ETH" {
-		t.Fatalf("got %q, want %q", got, "0.50 ETH")
-	}
-}

backend/.golangci.yml

@@ -0,0 +1,32 @@
+version: "2"
+
+run:
+  timeout: 5m
+  modules-download-mode: readonly
+
+linters:
+  default: all
+  disable:
+    # Genuinely incompatible with project patterns
+    - exhaustruct      # Requires all struct fields
+    - depguard         # Dependency allow/block lists
+    - godot            # Requires comments to end with periods
+    - wsl              # Deprecated, replaced by wsl_v5
+    - wrapcheck        # Too verbose for internal packages
+    - varnamelen       # Short names like db, id are idiomatic Go
+
+linters-settings:
+  lll:
+    line-length: 88
+  funlen:
+    lines: 80
+    statements: 50
+  cyclop:
+    max-complexity: 15
+  dupl:
+    threshold: 100
+
+issues:
+  exclude-use-default: false
+  max-issues-per-linter: 0
+  max-same-issues: 0

backend/ENV_TEMPLATE.md

@@ -37,16 +37,20 @@ cp ENV_TEMPLATE.md .env
 
 ## Firebase Setup
 
-For Firebase Admin SDK to work, you need to set up Application Default Credentials:
+For Firebase Admin SDK to work, you need to set up Application Default
+Credentials:
 
 **Option 1: Use Firebase Project ID (easiest for development)**
+
 - Just set `FIREBASE_PROJECT_ID` in .env
 - Firebase Admin will use Application Default Credentials
 
 **Option 2: Use Service Account Key (production)**
+
 1. Go to Firebase Console > Project Settings > Service Accounts
 2. Click "Generate new private key"
 3. Download the JSON file
 4. Either:
-   - Set `GOOGLE_APPLICATION_CREDENTIALS=/path/to/serviceAccountKey.json` in .env
-   - Or keep it in backend/ and add to .gitignore
+    - Set `GOOGLE_APPLICATION_CREDENTIALS=/path/to/serviceAccountKey.json` in
+      .env
+    - Or keep it in backend/ and add to .gitignore

backend/Makefile

@@ -37,7 +37,7 @@ tidy:
 
 # Database setup
 db-setup:
-	psql -d koin_ping_dev -f infra/schema.sql
+	psql -d koin_ping -f infra/schema.sql
 
 vet:
 	go vet ./...

backend/README.md

@@ -0,0 +1,32 @@
+Backend startup quickstarat:
+----------------------------->  BEST
+## 1. brew services start postgresql@15
+
+          OR 
+
+      /opt/homebrew/opt/postgresql@15/bin/pg_ctl -D /opt/homebrew/var/postgresql@15 start
+
+## 2.   ALLIN ONE: 
+        Make dev-all — Runs both the API and poller concurrently.
+----------------------------->  BEST
+
+          - OR - 
+          
+           
+## 3.  Option 1: Single command (both API + poller)
+       cd /Users/kjannette/workspace/koin_ping_0.2.0/backendmake dev-all
+
+## 4.   Option 2: Two separate terminals
+        Terminal 1 (API server):
+        cd /Users/kjannette/workspace/koin_ping_0.2.0/backend go run ./cmd/api
+        
+        make run — Builds and runs the API server.
+        make dev — Runs the API server with auto-reload via air (falls back to go run if air isn't installed).
+
+## 5.   Terminal 2 (Poller):
+        cd /Users/kjannette/workspace/koin_ping_0.2.0/backend 
+        go run ./cmd/poller
+
+        make poller — Builds and runs the poller.
+        make poller-dev — Runs the poller with auto-reload.
+

backend/cmd/api/main.go

@@ -0,0 +1,176 @@
+// Package main is the entry point for the API server.
+package main
+
+import (
+	"fmt"
+	"log"
+	"net/http"
+	"time"
+
+	"github.com/joho/godotenv"
+	"github.com/kjannette/koin-ping/backend/internal/config"
+	"github.com/kjannette/koin-ping/backend/internal/database"
+	"github.com/kjannette/koin-ping/backend/internal/firebase"
+	"github.com/kjannette/koin-ping/backend/internal/handlers"
+	"github.com/kjannette/koin-ping/backend/internal/middleware"
+	"github.com/kjannette/koin-ping/backend/internal/models"
+	"github.com/kjannette/koin-ping/backend/internal/services"
+)
+
+const (
+	// max duration to read a request.
+	serverReadTimeoutSeconds = 5
+	// maxiduration to write a response.
+	serverWriteTimeoutSeconds = 10
+)
+
+//nolint:funlen
+func main() {
+	_ = godotenv.Load() // .env is optional; env vars can also be set externally
+
+	cfg, err := config.Load()
+	if err != nil {
+		log.Fatalf("Failed to load config: %v", err)
+	}
+
+	pool, err := database.Connect(cfg.DSN())
+	if err != nil {
+		log.Fatalf("Failed to connect to database: %v", err)
+	}
+
+	if err := firebase.Init(cfg.FirebaseProjectID); err != nil {
+		log.Fatalf("Failed to initialize Firebase: %v", err)
+	}
+
+	defer database.Close()
+
+	userModel := models.NewUserModel(pool)
+	addressModel := models.NewAddressModel(pool)
+	alertRuleModel := models.NewAlertRuleModel(pool)
+	alertEventModel := models.NewAlertEventModel(pool)
+	checkpointModel := models.NewCheckpointModel(pool)
+	notifConfigModel := models.NewNotificationConfigModel(pool)
+
+	emailDigestSvc := services.NewEmailDigestService(
+		cfg.ResendAPIKey, cfg.EmailFrom, alertEventModel, notifConfigModel,
+	)
+
+	addressHandler := handlers.NewAddressHandler(addressModel, userModel)
+	alertRuleHandler := handlers.NewAlertRuleHandler(alertRuleModel, addressModel, userModel)
+	alertEventHandler := handlers.NewAlertEventHandler(alertEventModel)
+	notifConfigHandler := handlers.NewNotificationConfigHandler(notifConfigModel, userModel, cfg)
+	emailDigestHandler := handlers.NewEmailDigestHandler(emailDigestSvc, notifConfigModel)
+	statusHandler := handlers.NewStatusHandler(checkpointModel)
+	stripeHandler := handlers.NewStripeHandler(userModel, cfg)
+	accountHandler := handlers.NewAccountHandler(userModel, addressModel, cfg)
+
+	authenticate := middleware.Authenticate(userModel)
+	requireSub := middleware.RequireSubscription(userModel)
+
+	// authAndSub chains authentication + subscription check for protected routes.
+	authAndSub := func(h http.Handler) http.Handler {
+		return authenticate(requireSub(h))
+	}
+
+	mux := http.NewServeMux()
+	b := cfg.APIBasePath // e.g. "/v1"
+
+	// Public routes
+	mux.HandleFunc("GET "+b+"/health", handlers.HealthCheck)
+	mux.HandleFunc("GET "+b+"/status", statusHandler.GetStatus)
+
+	// Stripe webhook (public — called by Stripe, not authenticated)
+	mux.HandleFunc("POST "+b+"/stripe/webhook", stripeHandler.HandleWebhook)
+
+	// Onboarding checkout (public — account doesn't exist yet)
+	mux.HandleFunc("POST "+b+"/stripe/create-onboarding-checkout", stripeHandler.CreateOnboardingCheckout)
+
+	// Stripe routes (auth required, NO subscription required)
+	mux.Handle("POST "+b+"/stripe/create-checkout-session",
+		authenticate(http.HandlerFunc(stripeHandler.CreateCheckoutSession)))
+	mux.Handle("GET "+b+"/stripe/subscription-status",
+		authenticate(http.HandlerFunc(stripeHandler.GetSubscriptionStatus)))
+	mux.Handle("POST "+b+"/stripe/verify-checkout",
+		authenticate(http.HandlerFunc(stripeHandler.VerifyCheckoutSession)))
+	mux.Handle("POST "+b+"/stripe/create-portal-session",
+		authenticate(http.HandlerFunc(stripeHandler.CreatePortalSession)))
+	mux.Handle("POST "+b+"/stripe/activate-free",
+		authenticate(http.HandlerFunc(stripeHandler.ActivateFreeTier)))
+
+	// Account route (auth required, NO subscription required)
+	mux.Handle("GET "+b+"/user/account",
+		authenticate(http.HandlerFunc(accountHandler.GetAccount)))
+
+	// Authenticated + subscribed routes — addresses
+	mux.Handle("POST "+b+"/addresses",
+		authAndSub(http.HandlerFunc(addressHandler.Create)))
+	mux.Handle("GET "+b+"/addresses",
+		authAndSub(http.HandlerFunc(addressHandler.List)))
+	mux.Handle("DELETE "+b+"/addresses/{addressId}",
+		authAndSub(http.HandlerFunc(addressHandler.Remove)))
+	mux.Handle("PATCH "+b+"/addresses/{addressId}",
+		authAndSub(http.HandlerFunc(addressHandler.UpdateLabel)))
+
+	// Authenticated + subscribed routes — alert rules
+	mux.Handle("POST "+b+"/addresses/{addressId}/alerts",
+		authAndSub(http.HandlerFunc(alertRuleHandler.Create)))
+	mux.Handle("GET "+b+"/addresses/{addressId}/alerts",
+		authAndSub(http.HandlerFunc(alertRuleHandler.ListByAddress)))
+	mux.Handle("PATCH "+b+"/alerts/{alertId}",
+		authAndSub(http.HandlerFunc(alertRuleHandler.UpdateStatus)))
+	mux.Handle("DELETE "+b+"/alerts/{alertId}",
+		authAndSub(http.HandlerFunc(alertRuleHandler.Remove)))
+
+	// Authenticated + subscribed routes — alert events
+	mux.Handle("GET "+b+"/alert-events",
+		authAndSub(http.HandlerFunc(alertEventHandler.List)))
+
+	// Authenticated + subscribed routes — notification config
+	mux.Handle("GET "+b+"/notification-config",
+		authAndSub(http.HandlerFunc(notifConfigHandler.GetConfig)))
+	mux.Handle("PUT "+b+"/notification-config",
+		authAndSub(http.HandlerFunc(notifConfigHandler.UpdateConfig)))
+	mux.Handle("DELETE "+b+"/notification-config",
+		authAndSub(http.HandlerFunc(notifConfigHandler.DeleteConfig)))
+	mux.Handle("POST "+b+"/notification-config/test",
+		authAndSub(http.HandlerFunc(notifConfigHandler.TestChannels)))
+
+	// Authenticated + subscribed routes — email digest
+	mux.Handle("POST "+b+"/email/setup",
+		authAndSub(http.HandlerFunc(emailDigestHandler.SetupEmail)))
+	mux.Handle("POST "+b+"/email/digest",
+		authAndSub(http.HandlerFunc(emailDigestHandler.SendDigest)))
+
+	handler := corsMiddleware(mux)
+
+	addr := fmt.Sprintf(":%d", cfg.Port)
+	log.Printf("Server running on port %d", cfg.Port)
+	log.Printf("API base path: %s", cfg.APIBasePath)
+	log.Printf("Environment: %s", cfg.NodeEnv)
+
+	server := &http.Server{
+		Addr:         addr,
+		Handler:      handler,
+		ReadTimeout:  serverReadTimeoutSeconds * time.Second,
+		WriteTimeout: serverWriteTimeoutSeconds * time.Second,
+	}
+	if err := server.ListenAndServe(); err != nil {
+		log.Fatalf("Server failed: %v", err)
+	}
+}
+
+func corsMiddleware(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Access-Control-Allow-Origin", "*")
+		w.Header().Set("Access-Control-Allow-Methods", "GET, POST, PUT, PATCH, DELETE, OPTIONS")
+		w.Header().Set("Access-Control-Allow-Headers", "Content-Type, Authorization")
+
+		if r.Method == http.MethodOptions {
+			w.WriteHeader(http.StatusNoContent)
+
+			return
+		}
+
+		next.ServeHTTP(w, r)
+	})
+}

backend/cmd/poller/main.go

@@ -1,3 +1,4 @@
+// Package main is the entry point for the blockchain observer poller.
 package main
 
 import (
@@ -11,14 +12,21 @@ import (
 	"time"
 
 	"github.com/joho/godotenv"
-	"github.com/kjannette/koin-ping/backend-go/internal/config"
-	"github.com/kjannette/koin-ping/backend-go/internal/database"
-	"github.com/kjannette/koin-ping/backend-go/internal/models"
-	"github.com/kjannette/koin-ping/backend-go/internal/notifications"
-	"github.com/kjannette/koin-ping/backend-go/internal/protocols/ethereum"
-	"github.com/kjannette/koin-ping/backend-go/internal/services"
+	"github.com/kjannette/koin-ping/backend/internal/config"
+	"github.com/kjannette/koin-ping/backend/internal/database"
+	"github.com/kjannette/koin-ping/backend/internal/models"
+	"github.com/kjannette/koin-ping/backend/internal/protocols/ethereum"
+	"github.com/kjannette/koin-ping/backend/internal/services"
 )
 
+const (
+	// separatorWidth is the number of characters in log separator lines.
+	separatorWidth = 60
+	// msPerSecond converts milliseconds to seconds.
+	msPerSecond = 1000
+)
+
+//nolint:funlen
 func main() {
 	_ = godotenv.Load()
 
@@ -35,29 +43,26 @@ func main() {
 	if err != nil {
 		log.Fatalf("Failed to connect to database: %v", err)
 	}
-	defer database.Close()
 
 	eth, err := ethereum.NewJsonRpcEthereum(cfg.EthRPCURL)
 	if err != nil {
 		log.Fatalf("Failed to create Ethereum observer: %v", err)
 	}
 
+	defer database.Close()
+
+	userModel := models.NewUserModel(pool)
 	addressModel := models.NewAddressModel(pool)
 	alertRuleModel := models.NewAlertRuleModel(pool)
 	alertEventModel := models.NewAlertEventModel(pool)
 	checkpointModel := models.NewCheckpointModel(pool)
 	notifConfigModel := models.NewNotificationConfigModel(pool)
 
-	smtpCfg := notifications.SMTPConfig{
-		Host:     cfg.SMTPHost,
-		Port:     cfg.SMTPPort,
-		Username: cfg.SMTPUser,
-		Password: cfg.SMTPPassword,
-		From:     cfg.SMTPFrom,
-	}
-
 	observer := services.NewObserverService(eth, addressModel, checkpointModel)
-	evaluator := services.NewEvaluatorService(eth, alertRuleModel, alertEventModel, addressModel, notifConfigModel, smtpCfg)
+	evaluator := services.NewEvaluatorService(
+		eth, alertRuleModel, alertEventModel, addressModel, userModel, notifConfigModel,
+	)
+	digestSvc := services.NewEmailDigestService(cfg.ResendAPIKey, cfg.EmailFrom, alertEventModel, notifConfigModel)
 
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
@@ -67,53 +72,74 @@ func main() {
 	go func() {
 		<-sigCh
 		log.Println()
-		log.Println(strings.Repeat("=", 60))
+		log.Println(strings.Repeat("=", separatorWidth))
 		log.Println("Shutting down poller gracefully...")
-		log.Println(strings.Repeat("=", 60))
+		log.Println(strings.Repeat("=", separatorWidth))
 		cancel()
 	}()
 
 	interval := time.Duration(cfg.PollIntervalMS) * time.Millisecond
+	digestInterval := time.Duration(cfg.DigestIntervalHours) * time.Hour
 
-	log.Println(strings.Repeat("=", 60))
+	log.Println(strings.Repeat("=", separatorWidth))
 	log.Println("Koin Ping Observer Poller Starting")
-	log.Println(strings.Repeat("=", 60))
+	log.Println(strings.Repeat("=", separatorWidth))
 	log.Printf("RPC URL: %s", cfg.EthRPCURL)
-	log.Printf("Poll Interval: %dms (%ds)", cfg.PollIntervalMS, cfg.PollIntervalMS/1000)
-	log.Println(strings.Repeat("=", 60))
+	log.Printf("Poll Interval: %dms (%ds)", cfg.PollIntervalMS, cfg.PollIntervalMS/msPerSecond)
+	log.Printf("Digest Interval: %dh", cfg.DigestIntervalHours)
+	log.Println(strings.Repeat("=", separatorWidth))
 
 	runCycle(ctx, observer, evaluator)
 
 	ticker := time.NewTicker(interval)
 	defer ticker.Stop()
 
+	digestTicker := time.NewTicker(digestInterval)
+	defer digestTicker.Stop()
+
 	for {
 		select {
 		case <-ctx.Done():
 			log.Println("Poller stopped")
+
 			return
 		case <-ticker.C:
 			runCycle(ctx, observer, evaluator)
+		case <-digestTicker.C:
+			sent, digestErr := digestSvc.SendDigestsForAllUsers(ctx)
+			if digestErr != nil {
+				log.Printf("Email digest failed: %v", digestErr)
+			} else {
+				log.Printf("Sent %d email digests", sent)
+			}
 		}
 	}
 }
 
-func runCycle(ctx context.Context, observer *services.ObserverService, evaluator *services.EvaluatorService) {
+func runCycle(
+	ctx context.Context,
+	observer *services.ObserverService,
+	evaluator *services.EvaluatorService,
+) {
 	startTime := time.Now()
 	log.Printf("[%s] Starting observation cycle...", time.Now().UTC().Format(time.RFC3339))
 
 	observations, err := observer.RunOnce(ctx)
 	if err != nil {
 		log.Printf("[%s] Observation cycle failed: %v", time.Now().UTC().Format(time.RFC3339), err)
+
 		return
 	}
 
 	alertsFired, err := evaluator.Evaluate(ctx, observations)
 	if err != nil {
 		log.Printf("[%s] Evaluation failed: %v", time.Now().UTC().Format(time.RFC3339), err)
+
 		return
 	}
 
+	evaluator.WaitForNotifications()
+
 	duration := time.Since(startTime)
 	log.Printf("[%s] Cycle complete: %d observations, %d alerts fired in %s",
 		time.Now().UTC().Format(time.RFC3339),

backend/go.mod

@@ -1,4 +1,4 @@
-module github.com/kjannette/koin-ping/backend-go
+module github.com/kjannette/koin-ping/backend
 
 go 1.25.0
 
@@ -42,7 +42,9 @@ require (
 	github.com/jackc/puddle/v2 v2.2.2 // indirect
 	github.com/joho/godotenv v1.5.1 // indirect
 	github.com/planetscale/vtprotobuf v0.6.1-0.20240319094008-0393e58bdf10 // indirect
+	github.com/resend/resend-go/v3 v3.1.1 // indirect
 	github.com/spiffe/go-spiffe/v2 v2.6.0 // indirect
+	github.com/stripe/stripe-go/v82 v82.5.1 // indirect
 	go.opentelemetry.io/auto/sdk v1.2.1 // indirect
 	go.opentelemetry.io/contrib/detectors/gcp v1.39.0 // indirect
 	go.opentelemetry.io/contrib/instrumentation/google.golang.org/grpc/otelgrpc v0.61.0 // indirect

backend/go.sum

@@ -92,6 +92,8 @@ github.com/planetscale/vtprotobuf v0.6.1-0.20240319094008-0393e58bdf10/go.mod h1
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2 h1:Jamvg5psRIccs7FGNTlIRMkT8wgtp5eCXdBlqhYGL6U=
 github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/resend/resend-go/v3 v3.1.1 h1:Uwpf/tZU+O/r/3nMWE6zUAMIG9dX/vTBS3wlQzYJKSw=
+github.com/resend/resend-go/v3 v3.1.1/go.mod h1:iI7VA0NoGjWvsNii5iNC5Dy0llsI3HncXPejhniYzwE=
 github.com/spiffe/go-spiffe/v2 v2.6.0 h1:l+DolpxNWYgruGQVV0xsfeya3CsC7m8iBzDnMpsbLuo=
 github.com/spiffe/go-spiffe/v2 v2.6.0/go.mod h1:gm2SeUoMZEtpnzPNs2Csc0D/gX33k1xIx7lEzqblHEs=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
@@ -99,6 +101,8 @@ github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UV
 github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
 github.com/stretchr/testify v1.11.1 h1:7s2iGBzp5EwR7/aIZr8ao5+dra3wiQyKjjFuvgVKu7U=
 github.com/stretchr/testify v1.11.1/go.mod h1:wZwfW3scLgRK+23gO65QZefKpKQRnfz6sD981Nm4B6U=
+github.com/stripe/stripe-go/v82 v82.5.1 h1:05q6ZDKoe8PLMpQV072obF74HCgP4XJeJYoNuRSX2+8=
+github.com/stripe/stripe-go/v82 v82.5.1/go.mod h1:majCQX6AfObAvJiHraPi/5udwHi4ojRvJnnxckvHrX8=
 github.com/yuin/goldmark v1.4.13/go.mod h1:6yULJ656Px+3vBD8DxQVa3kxgyrAnzto9xy5taEt/CY=
 go.opentelemetry.io/auto/sdk v1.2.1 h1:jXsnJ4Lmnqd11kwkBV2LgLoFMZKizbCi5fNZ/ipaZ64=
 go.opentelemetry.io/auto/sdk v1.2.1/go.mod h1:KRTj+aOaElaLi+wW1kO/DZRXwkF4C5xPbEe3ZiIhN7Y=

backend/infra/migrations/003_add_slack_webhook.sql

@@ -1,4 +1,2 @@
 ALTER TABLE user_notification_configs
-  DROP COLUMN IF EXISTS telegram_chat_id,
-  DROP COLUMN IF EXISTS telegram_bot_token,
   ADD COLUMN IF NOT EXISTS slack_webhook_url TEXT;

backend/infra/migrations/004_alert_event_dedup.sql

@@ -0,0 +1,3 @@
+CREATE UNIQUE INDEX IF NOT EXISTS idx_alert_events_dedup
+    ON alert_events (alert_rule_id, tx_hash)
+    WHERE tx_hash IS NOT NULL;

backend/infra/migrations/005_create_users_table.sql

@@ -0,0 +1,13 @@
+-- Migration 005: Create users table with UUID primary key
+-- This establishes a local user record for each Firebase-authenticated user.
+
+CREATE TABLE IF NOT EXISTS users (
+  id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+  firebase_uid VARCHAR(128) NOT NULL UNIQUE,
+  email VARCHAR(255) NOT NULL,
+  display_name VARCHAR(255),
+  created_at TIMESTAMP DEFAULT NOW(),
+  updated_at TIMESTAMP DEFAULT NOW()
+);
+
+CREATE INDEX IF NOT EXISTS idx_users_firebase_uid ON users(firebase_uid);

backend/infra/migrations/006_migrate_user_ids_to_uuid.sql

@@ -0,0 +1,73 @@
+-- Migration 006: Migrate user_id columns from Firebase UID strings to user UUIDs
+--
+-- Prerequisites: migration 005 (users table) must be applied first.
+-- This migration backfills the users table from existing data, then swaps the
+-- VARCHAR user_id columns for UUID foreign keys referencing users(id).
+
+BEGIN;
+
+-- 1. Backfill users table from existing Firebase UIDs in addresses
+INSERT INTO users (firebase_uid, email)
+  SELECT DISTINCT user_id, ''
+  FROM addresses
+  WHERE user_id IS NOT NULL
+ON CONFLICT (firebase_uid) DO NOTHING;
+
+-- 2. Backfill from notification configs (catches users with configs but no addresses)
+INSERT INTO users (firebase_uid, email)
+  SELECT DISTINCT user_id, ''
+  FROM user_notification_configs
+  WHERE user_id IS NOT NULL
+ON CONFLICT (firebase_uid) DO NOTHING;
+
+-- ============================================================
+-- 3. Migrate addresses.user_id from VARCHAR to UUID
+-- ============================================================
+
+ALTER TABLE addresses ADD COLUMN user_uuid UUID;
+
+UPDATE addresses a
+SET user_uuid = u.id
+FROM users u
+WHERE u.firebase_uid = a.user_id;
+
+-- Drop old constraints and column
+ALTER TABLE addresses DROP CONSTRAINT IF EXISTS addresses_user_id_address_key;
+DROP INDEX IF EXISTS idx_addresses_user_id;
+ALTER TABLE addresses DROP COLUMN user_id;
+
+-- Rename and constrain
+ALTER TABLE addresses RENAME COLUMN user_uuid TO user_id;
+ALTER TABLE addresses ALTER COLUMN user_id SET NOT NULL;
+ALTER TABLE addresses ADD CONSTRAINT fk_addresses_user
+  FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE;
+ALTER TABLE addresses ADD CONSTRAINT addresses_user_id_address_key
+  UNIQUE (user_id, address);
+CREATE INDEX idx_addresses_user_id ON addresses(user_id);
+
+-- ============================================================
+-- 4. Migrate user_notification_configs.user_id from VARCHAR to UUID
+-- ============================================================
+
+-- Drop the PK first (it's on user_id)
+ALTER TABLE user_notification_configs DROP CONSTRAINT IF EXISTS user_notification_configs_pkey;
+DROP INDEX IF EXISTS idx_notification_configs_enabled;
+
+ALTER TABLE user_notification_configs ADD COLUMN user_uuid UUID;
+
+UPDATE user_notification_configs nc
+SET user_uuid = u.id
+FROM users u
+WHERE u.firebase_uid = nc.user_id;
+
+ALTER TABLE user_notification_configs DROP COLUMN user_id;
+ALTER TABLE user_notification_configs RENAME COLUMN user_uuid TO user_id;
+ALTER TABLE user_notification_configs ALTER COLUMN user_id SET NOT NULL;
+ALTER TABLE user_notification_configs ADD CONSTRAINT user_notification_configs_pkey
+  PRIMARY KEY (user_id);
+ALTER TABLE user_notification_configs ADD CONSTRAINT fk_notification_configs_user
+  FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE;
+CREATE INDEX idx_notification_configs_enabled
+  ON user_notification_configs(notification_enabled);
+
+COMMIT;

backend/infra/migrations/007_add_stripe_to_users.sql

@@ -0,0 +1,8 @@
+-- Migration 007: Add Stripe subscription fields to users table
+
+ALTER TABLE users ADD COLUMN IF NOT EXISTS stripe_customer_id VARCHAR(255);
+ALTER TABLE users ADD COLUMN IF NOT EXISTS stripe_subscription_id VARCHAR(255);
+ALTER TABLE users ADD COLUMN IF NOT EXISTS subscription_status VARCHAR(50) DEFAULT 'none';
+ALTER TABLE users ADD COLUMN IF NOT EXISTS subscription_created_at TIMESTAMP;
+
+CREATE INDEX IF NOT EXISTS idx_users_stripe_customer_id ON users(stripe_customer_id);

backend/infra/migrations/008_add_min_max_to_alert_rules.sql

@@ -0,0 +1,6 @@
+ALTER TABLE alert_rules ADD COLUMN minimum DECIMAL(20, 6);
+ALTER TABLE alert_rules ADD COLUMN maximum DECIMAL(20, 6);
+
+ALTER TABLE alert_rules ADD CONSTRAINT non_negative_minimum CHECK (minimum IS NULL OR minimum >= 0);
+ALTER TABLE alert_rules ADD CONSTRAINT non_negative_maximum CHECK (maximum IS NULL OR maximum >= 0);
+ALTER TABLE alert_rules ADD CONSTRAINT min_lte_max CHECK (minimum IS NULL OR maximum IS NULL OR minimum <= maximum);

backend/infra/migrations/009_add_subscription_tier.sql

@@ -0,0 +1,8 @@
+ALTER TABLE users ADD COLUMN IF NOT EXISTS subscription_tier VARCHAR(20) DEFAULT 'free';
+
+-- Existing active/trialing subscribers were on the single paid plan,
+-- which is now the "premium" tier. Backfill them so they aren't downgraded.
+UPDATE users
+SET subscription_tier = 'premium'
+WHERE subscription_status IN ('active', 'trialing')
+  AND stripe_subscription_id IS NOT NULL;

backend/infra/schema.sql

@@ -4,15 +4,29 @@ DROP TABLE IF EXISTS alert_rules CASCADE;
 DROP TABLE IF EXISTS address_checkpoints CASCADE;
 DROP TABLE IF EXISTS user_notification_configs CASCADE;
 DROP TABLE IF EXISTS addresses CASCADE;
+DROP TABLE IF EXISTS users CASCADE;
+
+CREATE TABLE users (
+  id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+  firebase_uid VARCHAR(128) NOT NULL UNIQUE,
+  email VARCHAR(255) NOT NULL,
+  display_name VARCHAR(255),
+  stripe_customer_id VARCHAR(255),
+  stripe_subscription_id VARCHAR(255),
+  subscription_status VARCHAR(50) DEFAULT 'none',
+  subscription_tier VARCHAR(20) DEFAULT 'free',
+  subscription_created_at TIMESTAMP,
+  created_at TIMESTAMP DEFAULT NOW(),
+  updated_at TIMESTAMP DEFAULT NOW()
+);
 
 CREATE TABLE addresses (
   id SERIAL PRIMARY KEY,
-  user_id VARCHAR(128) NOT NULL,       -- Firebase user ID (multi-user support)
+  user_id UUID NOT NULL REFERENCES users(id) ON DELETE CASCADE,
   address VARCHAR(42) NOT NULL,        -- Ethereum address format (0x + 40 hex chars)
   label VARCHAR(255),                  -- Optional human-readable label
   created_at TIMESTAMP DEFAULT NOW(),
 
-  -- Unique users can track the same address independently
   UNIQUE(user_id, address)
 );
 
@@ -22,6 +36,8 @@ CREATE TABLE alert_rules (
   address_id INTEGER NOT NULL REFERENCES addresses(id) ON DELETE CASCADE,
   type VARCHAR(50) NOT NULL,           -- 'incoming_tx', 'outgoing_tx', 'large_transfer', 'balance_below'
   threshold DECIMAL(20, 6),            -- ETH amount threshold (nullable for tx types that don't need it)
+  minimum DECIMAL(20, 6),              -- Optional min amount filter for incoming/outgoing alerts
+  maximum DECIMAL(20, 6),              -- Optional max amount filter for incoming/outgoing alerts
   enabled BOOLEAN DEFAULT TRUE,
   created_at TIMESTAMP DEFAULT NOW(),
 
@@ -31,7 +47,11 @@ CREATE TABLE alert_rules (
 
   CONSTRAINT positive_threshold CHECK (
     threshold IS NULL OR threshold > 0
-  )
+  ),
+
+  CONSTRAINT non_negative_minimum CHECK (minimum IS NULL OR minimum >= 0),
+  CONSTRAINT non_negative_maximum CHECK (maximum IS NULL OR maximum >= 0),
+  CONSTRAINT min_lte_max CHECK (minimum IS NULL OR maximum IS NULL OR minimum <= maximum)
 );
 
 
@@ -51,16 +71,20 @@ CREATE TABLE address_checkpoints (
 );
 
 CREATE TABLE user_notification_configs (
-  user_id VARCHAR(128) PRIMARY KEY,
+  user_id UUID PRIMARY KEY REFERENCES users(id) ON DELETE CASCADE,
   discord_webhook_url TEXT,            -- Discord webhook URL (nullable)
-  slack_webhook_url TEXT,              -- Slack incoming webhook URL (nullable)
+  telegram_chat_id VARCHAR(128),       -- Telegram chat ID (nullable)
+  telegram_bot_token VARCHAR(255),     -- Telegram bot token (nullable)
   email VARCHAR(255),                  -- Email for notifications (nullable)
+  slack_webhook_url TEXT,              -- Slack incoming webhook URL (nullable)
   notification_enabled BOOLEAN DEFAULT TRUE,  -- Master on/off switch
   created_at TIMESTAMP DEFAULT NOW(),
   updated_at TIMESTAMP DEFAULT NOW()
 );
 
 -- Create indexes for common queries
+CREATE INDEX idx_users_firebase_uid ON users(firebase_uid);
+CREATE INDEX idx_users_stripe_customer_id ON users(stripe_customer_id);
 CREATE INDEX idx_addresses_user_id ON addresses(user_id);
 CREATE INDEX idx_alert_rules_address_id ON alert_rules(address_id);
 CREATE INDEX idx_alert_rules_enabled ON alert_rules(enabled);

backend/internal/config/config.go

@@ -0,0 +1,126 @@
+//loads environment-based configuration.
+package config
+
+import (
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+)
+
+const (
+	defaultPort = 3001
+	defaultDBPort = 5432
+	defaultPollIntervalMS = 60000
+	minPollIntervalMS = 1000
+	defaultDigestIntervalHours = 24
+)
+
+type Config struct {
+	Port              int
+	APIBasePath       string
+	DatabaseURL       string
+	DBHost            string
+	DBPort            int
+	DBUser            string
+	DBPassword        string
+	DBName            string
+	FirebaseProjectID string
+	EthRPCURL         string
+	PollIntervalMS    int
+	NodeEnv           string
+	ResendAPIKey         string
+	EmailFrom            string
+	DigestIntervalHours  int
+	StripeSecretKey        string
+	StripeWebhookSecret    string
+	StripePriceIDPremium   string
+	StripePriceIDPro       string
+	StripePublishableKey   string
+	FrontendURL            string
+}
+
+// Load reads configuration from environment variables and returns a Config.
+func Load() (*Config, error) {
+	cfg := &Config{
+		Port:              getEnvInt("PORT", defaultPort),
+		APIBasePath:       getEnv("API_BASE_PATH", "/v1"),
+		DatabaseURL:       os.Getenv("DATABASE_URL"),
+		DBHost:            getEnv("DB_HOST", "localhost"),
+		DBPort:            getEnvInt("DB_PORT", defaultDBPort),
+		DBUser:            os.Getenv("DB_USER"),
+		DBPassword:        os.Getenv("DB_PASSWORD"),
+		DBName:            os.Getenv("DB_NAME"),
+		FirebaseProjectID: os.Getenv("FIREBASE_PROJECT_ID"),
+		EthRPCURL:         os.Getenv("ETH_RPC_URL"),
+		PollIntervalMS:    getEnvInt("POLL_INTERVAL_MS", defaultPollIntervalMS),
+		NodeEnv:           getEnv("NODE_ENV", "development"),
+		ResendAPIKey:        os.Getenv("RESEND_API_KEY"),
+		EmailFrom:           getEnv("EMAIL_FROM", "Koin Ping <alerts@koinping.com>"),
+		DigestIntervalHours:  getEnvInt("DIGEST_INTERVAL_HOURS", defaultDigestIntervalHours),
+		StripeSecretKey:        os.Getenv("STRIPE_SECRET_KEY"),
+		StripeWebhookSecret:    os.Getenv("STRIPE_WEBHOOK_SECRET"),
+		StripePriceIDPremium:   os.Getenv("STRIPE_PRICE_ID_PREMIUM"),
+		StripePriceIDPro:       os.Getenv("STRIPE_PRICE_ID_PRO"),
+		StripePublishableKey:   os.Getenv("STRIPE_PUBLISHABLE_KEY"),
+		FrontendURL:          getEnv("FRONTEND_URL", "http://localhost:3000"),
+	}
+
+	if cfg.PollIntervalMS < minPollIntervalMS {
+		return nil, fmt.Errorf("POLL_INTERVAL_MS must be >= 1000, got %d", cfg.PollIntervalMS) //nolint:err113
+	}
+
+	return cfg, nil
+}
+
+func (c *Config) DSN() string {
+	if c.DatabaseURL != "" {
+		// Append sslmode=disable if not already specified.
+		if !strings.Contains(c.DatabaseURL, "sslmode=") {
+			sep := "?"
+			if strings.Contains(c.DatabaseURL, "?") {
+				sep = "&"
+			}
+
+			return c.DatabaseURL + sep + "sslmode=disable"
+		}
+
+		return c.DatabaseURL
+	}
+
+	return fmt.Sprintf(
+		"host=%s port=%d user=%s password=%s dbname=%s sslmode=disable",
+		c.DBHost, c.DBPort, c.DBUser, c.DBPassword, c.DBName,
+	)
+}
+
+// TierForPriceID maps a Stripe price ID back to the corresponding
+// subscription tier. Returns empty string if the price is unrecognised.
+func (c *Config) TierForPriceID(priceID string) string {
+	switch priceID {
+	case c.StripePriceIDPremium:
+		return "premium"
+	case c.StripePriceIDPro:
+		return "pro"
+	default:
+		return ""
+	}
+}
+
+func getEnv(key, fallback string) string {
+	if v := os.Getenv(key); v != "" {
+		return v
+	}
+
+	return fallback
+}
+
+func getEnvInt(key string, fallback int) int {
+	if v := os.Getenv(key); v != "" {
+		if n, err := strconv.Atoi(v); err == nil {
+			return n
+		}
+	}
+
+	return fallback
+}

backend/internal/config/config_test.go

@@ -0,0 +1,28 @@
+package config
+
+import "testing"
+
+func TestTierForPriceID(t *testing.T) {
+	t.Parallel()
+
+	cfg := &Config{
+		StripePriceIDPremium: "price_premium_123",
+		StripePriceIDPro:     "price_pro_456",
+	}
+
+	tests := []struct {
+		priceID string
+		want    string
+	}{
+		{"price_premium_123", "premium"},
+		{"price_pro_456", "pro"},
+		{"price_unknown", ""},
+		{"", ""},
+	}
+
+	for _, tt := range tests {
+		if got := cfg.TierForPriceID(tt.priceID); got != tt.want {
+			t.Errorf("TierForPriceID(%q) = %q, want %q", tt.priceID, got, tt.want)
+		}
+	}
+}

backend/internal/database/postgres.go

@@ -9,20 +9,34 @@ import (
 	"github.com/jackc/pgx/v5/pgxpool"
 )
 
-var pool *pgxpool.Pool
+const (
 
+	maxConnIdleSeconds = 30
+
+	maxConnLifetimeMinutes = 5
+
+	connectTimeoutSeconds = 10
+
+	maxConns = 20
+
+	minConns = 2
+)
+
+var pool *pgxpool.Pool //nolint:gochecknoglobals
+
+// establishPostgreSQL connection pool using the given DSN.
 func Connect(dsn string) (*pgxpool.Pool, error) {
 	cfg, err := pgxpool.ParseConfig(dsn)
 	if err != nil {
 		return nil, fmt.Errorf("parse database config: %w", err)
 	}
 
-	cfg.MaxConns = 20
-	cfg.MinConns = 2
-	cfg.MaxConnIdleTime = 30 * time.Second
-	cfg.MaxConnLifetime = 5 * time.Minute
+	cfg.MaxConns = maxConns
+	cfg.MinConns = minConns
+	cfg.MaxConnIdleTime = maxConnIdleSeconds * time.Second
+	cfg.MaxConnLifetime = maxConnLifetimeMinutes * time.Minute
 
-	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+	ctx, cancel := context.WithTimeout(context.Background(), connectTimeoutSeconds*time.Second)
 	defer cancel()
 
 	p, err := pgxpool.NewWithConfig(ctx, cfg)
@@ -32,11 +46,13 @@ func Connect(dsn string) (*pgxpool.Pool, error) {
 
 	if err := p.Ping(ctx); err != nil {
 		p.Close()
+
 		return nil, fmt.Errorf("ping database: %w", err)
 	}
 
 	log.Println("Connected to PostgreSQL database")
 	pool = p
+
 	return p, nil
 }
 

backend/internal/domain/types.go

@@ -0,0 +1,211 @@
+package domain
+
+import "time"
+
+type SubscriptionTier string
+
+const (
+	TierFree    SubscriptionTier = "free"
+	TierPremium SubscriptionTier = "premium"
+	TierPro     SubscriptionTier = "pro"
+)
+
+func IsValidTier(t string) bool {
+	switch SubscriptionTier(t) {
+	case TierFree, TierPremium, TierPro:
+		return true
+	}
+	return false
+}
+
+const unlimitedLimit = -1
+
+type TierLimits struct {
+	MaxAddresses    int      `json:"max_addresses"`
+	MaxAlertTypes   int      `json:"max_alert_types"`
+	AllowedChannels []string `json:"allowed_channels"`
+}
+
+func GetTierLimits(tier SubscriptionTier) TierLimits {
+	switch tier {
+	case TierPremium:
+		return TierLimits{
+			MaxAddresses:    3,
+			MaxAlertTypes:   2,
+			AllowedChannels: []string{"email", "discord", "telegram"},
+		}
+	case TierPro:
+		return TierLimits{
+			MaxAddresses:    unlimitedLimit,
+			MaxAlertTypes:   unlimitedLimit,
+			AllowedChannels: []string{"email", "discord", "telegram", "slack"},
+		}
+	default:
+		return TierLimits{
+			MaxAddresses:    1,
+			MaxAlertTypes:   1,
+			AllowedChannels: []string{"email"},
+		}
+	}
+}
+
+func (l TierLimits) IsUnlimitedAddresses() bool  { return l.MaxAddresses == unlimitedLimit }
+func (l TierLimits) IsUnlimitedAlertTypes() bool  { return l.MaxAlertTypes == unlimitedLimit }
+
+func (l TierLimits) ChannelAllowed(channel string) bool {
+	for _, c := range l.AllowedChannels {
+		if c == channel {
+			return true
+		}
+	}
+	return false
+}
+
+type User struct {
+	ID                    string           `json:"id"`
+	FirebaseUID           string           `json:"-"`
+	Email                 string           `json:"email"`
+	DisplayName           *string          `json:"display_name"`           //nolint:tagliatelle
+	StripeCustomerID      *string          `json:"-"`
+	StripeSubscriptionID  *string          `json:"-"`
+	SubscriptionStatus    string           `json:"subscription_status"`    //nolint:tagliatelle
+	SubscriptionTier      SubscriptionTier `json:"subscription_tier"`      //nolint:tagliatelle
+	SubscriptionCreatedAt *time.Time       `json:"subscription_created_at,omitempty"` //nolint:tagliatelle
+	CreatedAt             time.Time        `json:"created_at"`             //nolint:tagliatelle
+	UpdatedAt             time.Time        `json:"updated_at"`             //nolint:tagliatelle
+}
+
+type Address struct {
+	ID        int       `json:"id"`
+	UserID    string    `json:"user_id"`    //nolint:tagliatelle
+	Address   string    `json:"address"`
+	Label     *string   `json:"label"`
+	CreatedAt time.Time `json:"created_at"` //nolint:tagliatelle
+}
+
+type AlertType string
+
+func (a AlertType) String() string { return string(a) }
+
+const (
+	AlertIncomingTx    AlertType = "incoming_tx"
+	AlertOutgoingTx    AlertType = "outgoing_tx"
+	AlertLargeTransfer AlertType = "large_transfer"
+	AlertBalanceBelow  AlertType = "balance_below"
+)
+
+var ValidAlertTypes = []AlertType{ //nolint:gochecknoglobals
+	AlertIncomingTx,
+	AlertOutgoingTx,
+	AlertLargeTransfer,
+	AlertBalanceBelow,
+}
+
+// ThresholdRequiredTypes lists alert types that require a threshold value.
+var ThresholdRequiredTypes = []AlertType{ //nolint:gochecknoglobals
+	AlertLargeTransfer,
+	AlertBalanceBelow,
+}
+
+// returns true if the given string matches a known AlertType.
+func IsValidAlertType(t string) bool {
+	for _, v := range ValidAlertTypes {
+		if string(v) == t {
+			return true
+		}
+	}
+
+	return false
+}
+
+func IsThresholdRequired(t AlertType) bool {
+	for _, v := range ThresholdRequiredTypes {
+		if v == t {
+			return true
+		}
+	}
+
+	return false
+}
+
+type AlertRule struct {
+	ID        int       `json:"id"`
+	AddressID int       `json:"address_id"` //nolint:tagliatelle
+	Type      AlertType `json:"type"`
+	Threshold *float64  `json:"threshold"`
+	Minimum   *float64  `json:"minimum"`
+	Maximum   *float64  `json:"maximum"`
+	Enabled   bool      `json:"enabled"`
+	CreatedAt time.Time `json:"created_at"` //nolint:tagliatelle
+}
+
+type AlertEvent struct {
+	ID           int       `json:"id"`
+	AlertRuleID  int       `json:"alert_rule_id"`   //nolint:tagliatelle
+	Message      string    `json:"message"`
+	AddressLabel *string   `json:"address_label"`   //nolint:tagliatelle
+	TxHash       *string   `json:"tx_hash"`         //nolint:tagliatelle
+	Timestamp    time.Time `json:"timestamp"`
+}
+
+type AddressCheckpoint struct {
+	AddressID        int       `json:"address_id"`         //nolint:tagliatelle
+	LastCheckedBlock int       `json:"last_checked_block"` //nolint:tagliatelle
+	LastCheckedAt    time.Time `json:"last_checked_at"`    //nolint:tagliatelle
+}
+
+type CheckpointDetail struct {
+	AddressID        int       `json:"address_id"`         //nolint:tagliatelle
+	Address          string    `json:"address"`
+	Label            *string   `json:"label"`
+	LastCheckedBlock int       `json:"last_checked_block"` //nolint:tagliatelle
+	LastCheckedAt    time.Time `json:"last_checked_at"`    //nolint:tagliatelle
+}
+
+//  holds a user's notification preferences.
+type NotificationConfig struct {
+	UserID              string     `json:"user_id"`              //nolint:tagliatelle
+	DiscordWebhookURL   *string    `json:"discord_webhook_url"`  //nolint:tagliatelle
+	TelegramChatID      *string    `json:"telegram_chat_id"`     //nolint:tagliatelle
+	TelegramBotToken    *string    `json:"telegram_bot_token"`   //nolint:tagliatelle
+	Email               *string    `json:"email"`
+	SlackWebhookURL     *string    `json:"slack_webhook_url"`    //nolint:tagliatelle
+	NotificationEnabled bool       `json:"notification_enabled"` //nolint:tagliatelle
+	CreatedAt           *time.Time `json:"created_at,omitempty"` //nolint:tagliatelle
+	UpdatedAt           *time.Time `json:"updated_at,omitempty"` //nolint:tagliatelle
+}
+
+// NormalizedTx is a blockchain transaction normalized for internal use.
+type NormalizedTx struct {
+	Hash           string  `json:"hash"`
+	From           string  `json:"from"`
+	To             *string `json:"to"`
+	Value          string  `json:"value"` // Wei as string for precision
+	BlockNumber    int     `json:"block_number"`    //nolint:tagliatelle
+	BlockTimestamp int64   `json:"block_timestamp"` //nolint:tagliatelle
+
+	// ERC-20 token transfer fields (nil for native ETH transfers)
+	TokenContract *string `json:"token_contract,omitempty"` //nolint:tagliatelle
+	TokenSymbol   *string `json:"token_symbol,omitempty"`   //nolint:tagliatelle
+	TokenDecimals *int    `json:"token_decimals,omitempty"` //nolint:tagliatelle
+	TokenValue    *string `json:"token_value,omitempty"`    //nolint:tagliatelle
+}
+
+func (tx NormalizedTx) IsTokenTransfer() bool {
+	return tx.TokenContract != nil
+}
+
+type Direction string
+
+func (d Direction) String() string { return string(d) }
+
+const (
+	DirectionIncoming Direction = "incoming"
+	DirectionOutgoing Direction = "outgoing"
+)
+
+type ObservedTx struct {
+	NormalizedTx
+	AddressID int       `json:"address_id"` //nolint:tagliatelle
+	Direction Direction `json:"direction"`
+}

backend/internal/domain/types_test.go

@@ -0,0 +1,104 @@
+package domain
+
+import "testing"
+
+func TestIsValidTier(t *testing.T) {
+	t.Parallel()
+
+	valid := []string{"free", "premium", "pro"}
+	for _, tier := range valid {
+		if !IsValidTier(tier) {
+			t.Errorf("expected %q to be valid", tier)
+		}
+	}
+
+	invalid := []string{"", "basic", "enterprise", "FREE", "Pro"}
+	for _, tier := range invalid {
+		if IsValidTier(tier) {
+			t.Errorf("expected %q to be invalid", tier)
+		}
+	}
+}
+
+func TestGetTierLimits_Free(t *testing.T) {
+	t.Parallel()
+
+	limits := GetTierLimits(TierFree)
+	if limits.MaxAddresses != 1 {
+		t.Errorf("free MaxAddresses = %d, want 1", limits.MaxAddresses)
+	}
+	if limits.MaxAlertTypes != 1 {
+		t.Errorf("free MaxAlertTypes = %d, want 1", limits.MaxAlertTypes)
+	}
+	if len(limits.AllowedChannels) != 1 || limits.AllowedChannels[0] != "email" {
+		t.Errorf("free AllowedChannels = %v, want [email]", limits.AllowedChannels)
+	}
+	if limits.IsUnlimitedAddresses() {
+		t.Error("free should not have unlimited addresses")
+	}
+	if limits.IsUnlimitedAlertTypes() {
+		t.Error("free should not have unlimited alert types")
+	}
+}
+
+func TestGetTierLimits_Premium(t *testing.T) {
+	t.Parallel()
+
+	limits := GetTierLimits(TierPremium)
+	if limits.MaxAddresses != 3 {
+		t.Errorf("premium MaxAddresses = %d, want 3", limits.MaxAddresses)
+	}
+	if limits.MaxAlertTypes != 2 {
+		t.Errorf("premium MaxAlertTypes = %d, want 2", limits.MaxAlertTypes)
+	}
+	if !limits.ChannelAllowed("email") {
+		t.Error("premium should allow email")
+	}
+	if !limits.ChannelAllowed("discord") {
+		t.Error("premium should allow discord")
+	}
+	if !limits.ChannelAllowed("telegram") {
+		t.Error("premium should allow telegram")
+	}
+	if limits.ChannelAllowed("slack") {
+		t.Error("premium should NOT allow slack")
+	}
+}
+
+func TestGetTierLimits_Pro(t *testing.T) {
+	t.Parallel()
+
+	limits := GetTierLimits(TierPro)
+	if !limits.IsUnlimitedAddresses() {
+		t.Error("pro should have unlimited addresses")
+	}
+	if !limits.IsUnlimitedAlertTypes() {
+		t.Error("pro should have unlimited alert types")
+	}
+	for _, ch := range []string{"email", "discord", "telegram", "slack"} {
+		if !limits.ChannelAllowed(ch) {
+			t.Errorf("pro should allow %s", ch)
+		}
+	}
+}
+
+func TestGetTierLimits_Unknown(t *testing.T) {
+	t.Parallel()
+
+	limits := GetTierLimits(SubscriptionTier("unknown"))
+	if limits.MaxAddresses != 1 {
+		t.Errorf("unknown tier should default to free limits, got MaxAddresses=%d", limits.MaxAddresses)
+	}
+}
+
+func TestChannelAllowed_NotInList(t *testing.T) {
+	t.Parallel()
+
+	limits := GetTierLimits(TierFree)
+	if limits.ChannelAllowed("discord") {
+		t.Error("free should not allow discord")
+	}
+	if limits.ChannelAllowed("nonexistent") {
+		t.Error("nonexistent channel should not be allowed")
+	}
+}

backend/internal/firebase/admin.go

@@ -10,10 +10,10 @@ import (
 	"google.golang.org/api/option"
 )
 
-var (
-	authClient *auth.Client
-	once       sync.Once
-	initErr    error
+var ( //nolint:gochecknoglobals
+	authClient *auth.Client //nolint:gochecknoglobals
+	once       sync.Once    //nolint:gochecknoglobals
+	errInit    error        //nolint:gochecknoglobals
 )
 
 func Init(projectID string) error {
@@ -30,18 +30,20 @@ func Init(projectID string) error {
 			app, err = fb.NewApp(ctx, nil)
 		}
 		if err != nil {
-			initErr = fmt.Errorf("initialize firebase app: %w", err)
+			errInit = fmt.Errorf("initialize firebase app: %w", err)
+
 			return
 		}
 
 		authClient, err = app.Auth(ctx)
 		if err != nil {
-			initErr = fmt.Errorf("initialize firebase auth: %w", err)
+			errInit = fmt.Errorf("initialize firebase auth: %w", err)
+
 			return
 		}
 	})
 
-	return initErr
+	return errInit
 }
 
 func Auth() *auth.Client {

backend/internal/handlers/account.go

@@ -0,0 +1,88 @@
+package handlers
+
+import (
+	"log"
+	"net/http"
+	"time"
+
+	"github.com/kjannette/koin-ping/backend/internal/config"
+	"github.com/kjannette/koin-ping/backend/internal/domain"
+	"github.com/kjannette/koin-ping/backend/internal/middleware"
+	"github.com/kjannette/koin-ping/backend/internal/models"
+)
+
+type AccountHandler struct {
+	users     *models.UserModel
+	addresses *models.AddressModel
+	cfg       *config.Config
+}
+
+func NewAccountHandler(users *models.UserModel, addresses *models.AddressModel, cfg *config.Config) *AccountHandler {
+	return &AccountHandler{users: users, addresses: addresses, cfg: cfg}
+}
+
+type accountResponse struct {
+	UserID             string            `json:"user_id"`
+	Email              string            `json:"email"`
+	UserName           string            `json:"user_name"`
+	SubscriptionStatus string            `json:"subscription_status"`
+	SubscriptionTier   string            `json:"subscription_tier"`
+	SubscriptionPlan   string            `json:"subscription_plan"`
+	TierLimits         domain.TierLimits `json:"tier_limits"`
+	AddressCount       int               `json:"address_count"`
+	MemberSince        *string           `json:"member_since,omitempty"`
+	NextBillingDate    *string           `json:"next_billing_date,omitempty"`
+	CancelAtPeriodEnd  bool              `json:"cancel_at_period_end"`
+	PeriodEndDate      *string           `json:"period_end_date,omitempty"`
+}
+
+var tierPlanLabels = map[domain.SubscriptionTier]string{ //nolint:gochecknoglobals
+	domain.TierFree:    "Free Trial",
+	domain.TierPremium: "Premium / $1.99 mo",
+	domain.TierPro:     "Pro / $11.99 mo",
+}
+
+func (h *AccountHandler) GetAccount(w http.ResponseWriter, r *http.Request) {
+	userID := middleware.GetUserID(r.Context())
+	email := middleware.GetUserEmail(r.Context())
+
+	user, err := h.users.GetByID(r.Context(), userID)
+	if err != nil || user == nil {
+		log.Printf("Account: failed to get user %s: %v", userID, err)
+		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to load user")
+		return
+	}
+
+	addrCount, err := h.addresses.CountByUser(r.Context(), userID)
+	if err != nil {
+		log.Printf("Account: failed to count addresses for %s: %v", userID, err)
+		addrCount = 0
+	}
+
+	planLabel := tierPlanLabels[user.SubscriptionTier]
+	if planLabel == "" {
+		planLabel = "Free Trial"
+	}
+
+	resp := accountResponse{
+		UserID:             user.ID,
+		Email:              email,
+		UserName:           email,
+		SubscriptionStatus: user.SubscriptionStatus,
+		SubscriptionTier:   string(user.SubscriptionTier),
+		SubscriptionPlan:   planLabel,
+		TierLimits:         domain.GetTierLimits(user.SubscriptionTier),
+		AddressCount:       addrCount,
+	}
+
+	if user.SubscriptionCreatedAt != nil {
+		t := user.SubscriptionCreatedAt.Format(time.DateOnly)
+		resp.MemberSince = &t
+	}
+
+	resp.NextBillingDate = nil
+	resp.CancelAtPeriodEnd = false
+	resp.PeriodEndDate = nil
+
+	writeJSON(w, http.StatusOK, resp)
+}

backend/internal/handlers/address.go

@@ -1,25 +1,28 @@
+// Package handlers implements HTTP request handlers for the API.
 package handlers
 
 import (
 	"encoding/json"
+	"fmt"
 	"log"
 	"net/http"
 	"regexp"
 	"strings"
 
-	"github.com/kjannette/koin-ping/backend-go/internal/domain"
-	"github.com/kjannette/koin-ping/backend-go/internal/middleware"
-	"github.com/kjannette/koin-ping/backend-go/internal/models"
+	"github.com/kjannette/koin-ping/backend/internal/domain"
+	"github.com/kjannette/koin-ping/backend/internal/middleware"
+	"github.com/kjannette/koin-ping/backend/internal/models"
 )
 
 var ethAddressRe = regexp.MustCompile(`^0x[a-fA-F0-9]{40}$`)
 
 type AddressHandler struct {
 	addresses *models.AddressModel
+	users     *models.UserModel
 }
 
-func NewAddressHandler(addresses *models.AddressModel) *AddressHandler {
-	return &AddressHandler{addresses: addresses}
+func NewAddressHandler(addresses *models.AddressModel, users *models.UserModel) *AddressHandler {
+	return &AddressHandler{addresses: addresses, users: users}
 }
 
 func (h *AddressHandler) Create(w http.ResponseWriter, r *http.Request) {
@@ -32,29 +35,56 @@ func (h *AddressHandler) Create(w http.ResponseWriter, r *http.Request) {
 	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
 		log.Printf("Failed to decode address request body: %v", err)
 		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "Invalid request body")
+
 		return
 	}
 
 	if body.Address == "" {
 		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "Address is required")
+
 		return
 	}
 
 	if !ethAddressRe.MatchString(body.Address) {
 		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "Invalid Ethereum address format")
+
 		return
 	}
 
+	user, err := h.users.GetByID(r.Context(), userID)
+	if err != nil || user == nil {
+		log.Printf("Failed to get user %s for tier check: %v", userID, err)
+		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to verify account")
+		return
+	}
+
+	limits := domain.GetTierLimits(user.SubscriptionTier)
+	if !limits.IsUnlimitedAddresses() {
+		count, err := h.addresses.CountByUser(r.Context(), userID)
+		if err != nil {
+			log.Printf("Failed to count addresses for user %s: %v", userID, err)
+			writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to create address")
+			return
+		}
+		if count >= limits.MaxAddresses {
+			writeError(w, http.StatusForbidden, "TIER_LIMIT_REACHED",
+				fmt.Sprintf("Your %s plan allows %d address(es). Upgrade to track more.", user.SubscriptionTier, limits.MaxAddresses))
+			return
+		}
+	}
+
 	log.Printf("User %s creating address: %s", userID, body.Address)
 
 	addr, err := h.addresses.Create(r.Context(), userID, body.Address, body.Label)
 	if err != nil {
 		if strings.Contains(err.Error(), "23505") || strings.Contains(err.Error(), "unique") {
 			writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "You are already tracking this address")
+
 			return
 		}
 		log.Printf("Error creating address: %v", err)
 		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to create address")
+
 		return
 	}
 
@@ -62,6 +92,7 @@ func (h *AddressHandler) Create(w http.ResponseWriter, r *http.Request) {
 	writeJSON(w, http.StatusCreated, addr)
 }
 
+// List handles GET requests to list all tracked addresses for the current user.
 func (h *AddressHandler) List(w http.ResponseWriter, r *http.Request) {
 	userID := middleware.GetUserID(r.Context())
 	log.Printf("User %s listing addresses", userID)
@@ -70,6 +101,7 @@ func (h *AddressHandler) List(w http.ResponseWriter, r *http.Request) {
 	if err != nil {
 		log.Printf("Error listing addresses: %v", err)
 		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to list addresses")
+
 		return
 	}
 
@@ -81,11 +113,51 @@ func (h *AddressHandler) List(w http.ResponseWriter, r *http.Request) {
 	writeJSON(w, http.StatusOK, addresses)
 }
 
+//  handles PATCH requests to update an address label.
+func (h *AddressHandler) UpdateLabel(w http.ResponseWriter, r *http.Request) {
+	userID := middleware.GetUserID(r.Context())
+	addressID, ok := parseIntParam(r.PathValue("addressId"))
+	if !ok {
+		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "Invalid address ID")
+
+		return
+	}
+
+	var body struct {
+		Label *string `json:"label"`
+	}
+	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "Invalid request body")
+
+		return
+	}
+
+	log.Printf("User %s updating label for address ID: %d", userID, addressID)
+
+	addr, err := h.addresses.UpdateLabel(r.Context(), addressID, userID, body.Label)
+	if err != nil {
+		log.Printf("Error updating address label: %v", err)
+		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to update address")
+
+		return
+	}
+
+	if addr == nil {
+		writeError(w, http.StatusNotFound, "NOT_FOUND", "Address not found")
+
+		return
+	}
+
+	writeJSON(w, http.StatusOK, addr)
+}
+
+// Remove handles DELETE requests to remove a tracked address.
 func (h *AddressHandler) Remove(w http.ResponseWriter, r *http.Request) {
 	userID := middleware.GetUserID(r.Context())
 	addressID, ok := parseIntParam(r.PathValue("addressId"))
 	if !ok {
 		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "Invalid address ID")
+
 		return
 	}
 
@@ -95,12 +167,14 @@ func (h *AddressHandler) Remove(w http.ResponseWriter, r *http.Request) {
 	if err != nil {
 		log.Printf("Error deleting address: %v", err)
 		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to delete address")
+
 		return
 	}
 
 	if !deleted {
 		log.Printf("Address %d not found or not owned by user", addressID)
 		writeError(w, http.StatusNotFound, "NOT_FOUND", "Address not found")
+
 		return
 	}
 

backend/internal/handlers/alert_event.go

@@ -5,18 +5,22 @@ import (
 	"net/http"
 	"strconv"
 
-	"github.com/kjannette/koin-ping/backend-go/internal/middleware"
-	"github.com/kjannette/koin-ping/backend-go/internal/models"
+	"github.com/kjannette/koin-ping/backend/internal/domain"
+	"github.com/kjannette/koin-ping/backend/internal/middleware"
+	"github.com/kjannette/koin-ping/backend/internal/models"
 )
 
+// AlertEventHandler handles HTTP requests for alert event history.
 type AlertEventHandler struct {
 	alertEvents *models.AlertEventModel
 }
 
+// NewAlertEventHandler creates a new AlertEventHandler.
 func NewAlertEventHandler(alertEvents *models.AlertEventModel) *AlertEventHandler {
 	return &AlertEventHandler{alertEvents: alertEvents}
 }
 
+// List handles GET requests to list recent alert events for the current user.
 func (h *AlertEventHandler) List(w http.ResponseWriter, r *http.Request) {
 	userID := middleware.GetUserID(r.Context())
 
@@ -32,6 +36,7 @@ func (h *AlertEventHandler) List(w http.ResponseWriter, r *http.Request) {
 
 	if limit < 1 || limit > 100 {
 		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "Limit must be between 1 and 100")
+
 		return
 	}
 
@@ -39,10 +44,15 @@ func (h *AlertEventHandler) List(w http.ResponseWriter, r *http.Request) {
 	if err != nil {
 		log.Printf("Error listing alert events: %v", err)
 		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to list alert events")
+
 		return
 	}
 
 	log.Printf("Found %d alert events for user", len(events))
 
+	if events == nil {
+		events = []domain.AlertEvent{}
+	}
+
 	writeJSON(w, http.StatusOK, events)
 }

backend/internal/handlers/alert_rule.go

@@ -2,24 +2,28 @@ package handlers
 
 import (
 	"encoding/json"
+	"errors"
 	"fmt"
 	"log"
 	"net/http"
 	"strconv"
 	"strings"
 
-	"github.com/kjannette/koin-ping/backend-go/internal/domain"
-	"github.com/kjannette/koin-ping/backend-go/internal/middleware"
-	"github.com/kjannette/koin-ping/backend-go/internal/models"
+	"github.com/kjannette/koin-ping/backend/internal/domain"
+	"github.com/kjannette/koin-ping/backend/internal/middleware"
+	"github.com/kjannette/koin-ping/backend/internal/models"
 )
 
+var errThresholdFormat = errors.New("unsupported threshold format")
+
 type AlertRuleHandler struct {
 	alertRules *models.AlertRuleModel
 	addresses  *models.AddressModel
+	users      *models.UserModel
 }
 
-func NewAlertRuleHandler(alertRules *models.AlertRuleModel, addresses *models.AddressModel) *AlertRuleHandler {
-	return &AlertRuleHandler{alertRules: alertRules, addresses: addresses}
+func NewAlertRuleHandler(alertRules *models.AlertRuleModel, addresses *models.AddressModel, users *models.UserModel) *AlertRuleHandler {
+	return &AlertRuleHandler{alertRules: alertRules, addresses: addresses, users: users}
 }
 
 func (h *AlertRuleHandler) Create(w http.ResponseWriter, r *http.Request) {
@@ -27,16 +31,20 @@ func (h *AlertRuleHandler) Create(w http.ResponseWriter, r *http.Request) {
 	addressID, ok := parseIntParam(r.PathValue("addressId"))
 	if !ok {
 		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "Invalid address ID")
+
 		return
 	}
 
 	var body struct {
 		Type      string          `json:"type"`
 		Threshold json.RawMessage `json:"threshold"`
+		Minimum   json.RawMessage `json:"minimum"`
+		Maximum   json.RawMessage `json:"maximum"`
 	}
 	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
 		log.Printf("Failed to decode alert request body: %v", err)
 		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "Invalid request body")
+
 		return
 	}
 
@@ -44,6 +52,41 @@ func (h *AlertRuleHandler) Create(w http.ResponseWriter, r *http.Request) {
 	if err != nil {
 		log.Printf("Failed to parse threshold: %v", err)
 		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "threshold must be a valid number")
+
+		return
+	}
+
+	minimum, err := parseThreshold(body.Minimum)
+	if err != nil {
+		log.Printf("Failed to parse minimum: %v", err)
+		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "minimum must be a valid number")
+
+		return
+	}
+
+	maximum, err := parseThreshold(body.Maximum)
+	if err != nil {
+		log.Printf("Failed to parse maximum: %v", err)
+		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "maximum must be a valid number")
+
+		return
+	}
+
+	if minimum != nil && *minimum < 0 {
+		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "minimum must be non-negative")
+
+		return
+	}
+
+	if maximum != nil && *maximum < 0 {
+		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "maximum must be non-negative")
+
+		return
+	}
+
+	if minimum != nil && maximum != nil && *minimum > *maximum {
+		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "minimum must not exceed maximum")
+
 		return
 	}
 
@@ -51,16 +94,18 @@ func (h *AlertRuleHandler) Create(w http.ResponseWriter, r *http.Request) {
 
 	if body.Type == "" {
 		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "Alert type is required")
+
 		return
 	}
 
 	if !domain.IsValidAlertType(body.Type) {
 		types := make([]string, len(domain.ValidAlertTypes))
 		for i, t := range domain.ValidAlertTypes {
-			types[i] = string(t)
+			types[i] = t.String()
 		}
 		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR",
-			fmt.Sprintf("Invalid alert type. Must be one of: %s", strings.Join(types, ", ")))
+			"Invalid alert type. Must be one of: "+strings.Join(types, ", "))
+
 		return
 	}
 
@@ -69,6 +114,7 @@ func (h *AlertRuleHandler) Create(w http.ResponseWriter, r *http.Request) {
 		if threshold == nil || *threshold <= 0 {
 			writeError(w, http.StatusBadRequest, "VALIDATION_ERROR",
 				fmt.Sprintf("Alert type '%s' requires a positive threshold value", body.Type))
+
 			return
 		}
 	}
@@ -77,18 +123,43 @@ func (h *AlertRuleHandler) Create(w http.ResponseWriter, r *http.Request) {
 	if err != nil {
 		log.Printf("Error finding address: %v", err)
 		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to create alert rule")
+
 		return
 	}
 	if addr == nil {
 		log.Printf("Address %d not found or not owned by user", addressID)
 		writeError(w, http.StatusNotFound, "NOT_FOUND", "Address not found")
+
 		return
 	}
 
-	newAlert, err := h.alertRules.Create(r.Context(), addressID, alertType, threshold)
+	user, userErr := h.users.GetByID(r.Context(), userID)
+	if userErr != nil || user == nil {
+		log.Printf("Failed to get user %s for tier check: %v", userID, userErr)
+		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to verify account")
+		return
+	}
+
+	limits := domain.GetTierLimits(user.SubscriptionTier)
+	if !limits.IsUnlimitedAlertTypes() {
+		typeCount, countErr := h.alertRules.CountDistinctTypesByAddress(r.Context(), addressID)
+		if countErr != nil {
+			log.Printf("Failed to count alert types for address %d: %v", addressID, countErr)
+			writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to create alert rule")
+			return
+		}
+		if typeCount >= limits.MaxAlertTypes {
+			writeError(w, http.StatusForbidden, "TIER_LIMIT_REACHED",
+				fmt.Sprintf("Your %s plan allows %d alert type(s) per address. Upgrade for more.", user.SubscriptionTier, limits.MaxAlertTypes))
+			return
+		}
+	}
+
+	newAlert, err := h.alertRules.Create(r.Context(), addressID, alertType, threshold, minimum, maximum)
 	if err != nil {
 		log.Printf("Error creating alert rule: %v", err)
 		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to create alert rule")
+
 		return
 	}
 
@@ -98,12 +169,12 @@ func (h *AlertRuleHandler) Create(w http.ResponseWriter, r *http.Request) {
 
 func parseThreshold(raw json.RawMessage) (*float64, error) {
 	if len(raw) == 0 {
-		return nil, nil
+		return nil, nil //nolint:nilnil
 	}
 
 	// Check null before number -- json.Unmarshal treats null as valid for float64 (sets to 0).
 	if string(raw) == "null" {
-		return nil, nil
+		return nil, nil //nolint:nilnil
 	}
 
 	var asNumber float64
@@ -115,23 +186,26 @@ func parseThreshold(raw json.RawMessage) (*float64, error) {
 	if err := json.Unmarshal(raw, &asString); err == nil {
 		asString = strings.TrimSpace(asString)
 		if asString == "" {
-			return nil, nil
+			return nil, nil //nolint:nilnil
 		}
 		parsed, parseErr := strconv.ParseFloat(asString, 64)
 		if parseErr != nil {
 			return nil, parseErr
 		}
+
 		return &parsed, nil
 	}
 
-	return nil, fmt.Errorf("unsupported threshold format")
+	return nil, errThresholdFormat
 }
 
+// ListByAddress handles GET requests to list alert rules for an address.
 func (h *AlertRuleHandler) ListByAddress(w http.ResponseWriter, r *http.Request) {
 	userID := middleware.GetUserID(r.Context())
 	addressID, ok := parseIntParam(r.PathValue("addressId"))
 	if !ok {
 		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "Invalid address ID")
+
 		return
 	}
 
@@ -141,11 +215,13 @@ func (h *AlertRuleHandler) ListByAddress(w http.ResponseWriter, r *http.Request)
 	if err != nil {
 		log.Printf("Error finding address: %v", err)
 		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to list alerts")
+
 		return
 	}
 	if addr == nil {
 		log.Printf("Address %d not found or not owned by user", addressID)
 		writeError(w, http.StatusNotFound, "NOT_FOUND", "Address not found")
+
 		return
 	}
 
@@ -153,6 +229,7 @@ func (h *AlertRuleHandler) ListByAddress(w http.ResponseWriter, r *http.Request)
 	if err != nil {
 		log.Printf("Error listing alerts: %v", err)
 		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to list alerts")
+
 		return
 	}
 
@@ -164,27 +241,34 @@ func (h *AlertRuleHandler) ListByAddress(w http.ResponseWriter, r *http.Request)
 	writeJSON(w, http.StatusOK, alerts)
 }
 
+// UpdateStatus handles PATCH requests to enable/disable an alert rule and/or update min/max thresholds.
 func (h *AlertRuleHandler) UpdateStatus(w http.ResponseWriter, r *http.Request) {
 	userID := middleware.GetUserID(r.Context())
 	alertID, ok := parseIntParam(r.PathValue("alertId"))
 	if !ok {
 		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "Invalid alert ID")
+
 		return
 	}
 
 	var body struct {
-		Enabled *bool `json:"enabled"`
+		Enabled        *bool           `json:"enabled"`
+		Minimum        json.RawMessage `json:"minimum"`
+		Maximum        json.RawMessage `json:"maximum"`
+		UpdateMinMax   bool            `json:"update_min_max"`   //nolint:tagliatelle
 	}
 	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
 		log.Printf("Failed to decode update request body: %v", err)
 		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "Invalid request body")
+
 		return
 	}
 
 	log.Printf("User %s updating alert ID: %d", userID, alertID)
 
-	if body.Enabled == nil {
-		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "enabled must be a boolean value")
+	if body.Enabled == nil && !body.UpdateMinMax {
+		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "must provide enabled (boolean) or update_min_max with minimum/maximum values")
+
 		return
 	}
 
@@ -192,30 +276,84 @@ func (h *AlertRuleHandler) UpdateStatus(w http.ResponseWriter, r *http.Request)
 	if err != nil {
 		log.Printf("Error finding alert: %v", err)
 		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to update alert")
+
 		return
 	}
 	if alert == nil {
 		log.Printf("Alert %d not found or not owned by user", alertID)
 		writeError(w, http.StatusNotFound, "NOT_FOUND", "Alert rule not found")
+
 		return
 	}
 
-	updated, err := h.alertRules.UpdateEnabled(r.Context(), alertID, *body.Enabled)
-	if err != nil {
-		log.Printf("Error updating alert: %v", err)
-		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to update alert")
-		return
+	var updated *domain.AlertRule
+
+	if body.UpdateMinMax {
+		minimum, parseErr := parseThreshold(body.Minimum)
+		if parseErr != nil {
+			writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "minimum must be a valid number")
+
+			return
+		}
+
+		maximum, parseErr := parseThreshold(body.Maximum)
+		if parseErr != nil {
+			writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "maximum must be a valid number")
+
+			return
+		}
+
+		if minimum != nil && *minimum < 0 {
+			writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "minimum must be non-negative")
+
+			return
+		}
+
+		if maximum != nil && *maximum < 0 {
+			writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "maximum must be non-negative")
+
+			return
+		}
+
+		if minimum != nil && maximum != nil && *minimum > *maximum {
+			writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "minimum must not exceed maximum")
+
+			return
+		}
+
+		updated, err = h.alertRules.UpdateThresholds(r.Context(), alertID, minimum, maximum)
+		if err != nil {
+			log.Printf("Error updating alert thresholds: %v", err)
+			writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to update alert")
+
+			return
+		}
+
+		log.Printf("Alert %d thresholds updated: min=%v, max=%v", alertID, minimum, maximum)
+	}
+
+	if body.Enabled != nil {
+		updated, err = h.alertRules.UpdateEnabled(r.Context(), alertID, *body.Enabled)
+		if err != nil {
+			log.Printf("Error updating alert: %v", err)
+			writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to update alert")
+
+			return
+		}
+
+		log.Printf("Alert %d updated: enabled=%v", alertID, *body.Enabled)
 	}
 
-	log.Printf("Alert %d updated: enabled=%v", alertID, *body.Enabled)
 	writeJSON(w, http.StatusOK, updated)
 }
 
+// Remove handles DELETE requests to remove an alert rule.
 func (h *AlertRuleHandler) Remove(w http.ResponseWriter, r *http.Request) {
 	userID := middleware.GetUserID(r.Context())
 	alertID, ok := parseIntParam(r.PathValue("alertId"))
 	if !ok {
 		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "Invalid alert ID")
+
 		return
 	}
 
@@ -225,17 +363,20 @@ func (h *AlertRuleHandler) Remove(w http.ResponseWriter, r *http.Request) {
 	if err != nil {
 		log.Printf("Error finding alert: %v", err)
 		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to delete alert")
+
 		return
 	}
 	if alert == nil {
 		log.Printf("Alert %d not found or not owned by user", alertID)
 		writeError(w, http.StatusNotFound, "NOT_FOUND", "Alert rule not found")
+
 		return
 	}
 
 	if _, err := h.alertRules.Remove(r.Context(), alertID); err != nil {
 		log.Printf("Error deleting alert: %v", err)
 		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to delete alert")
+
 		return
 	}
 

backend/internal/handlers/alert_rule_test.go

@@ -1,3 +1,4 @@
+//nolint:testpackage // parseThreshold is unexported; internal test package required
 package handlers
 
 import (
@@ -6,8 +7,13 @@ import (
 	"testing"
 )
 
+//nolint:gocognit
 func TestParseThreshold(t *testing.T) {
+	t.Parallel()
+
 	t.Run("nil/empty raw message returns nil", func(t *testing.T) {
+		t.Parallel()
+
 		val, err := parseThreshold(nil)
 		if err != nil {
 			t.Fatalf("unexpected error: %v", err)
@@ -18,6 +24,8 @@ func TestParseThreshold(t *testing.T) {
 	})
 
 	t.Run("empty slice returns nil", func(t *testing.T) {
+		t.Parallel()
+
 		val, err := parseThreshold(json.RawMessage{})
 		if err != nil {
 			t.Fatalf("unexpected error: %v", err)
@@ -28,6 +36,8 @@ func TestParseThreshold(t *testing.T) {
 	})
 
 	t.Run("JSON null returns nil", func(t *testing.T) {
+		t.Parallel()
+
 		val, err := parseThreshold(json.RawMessage("null"))
 		if err != nil {
 			t.Fatalf("unexpected error: %v", err)
@@ -38,6 +48,8 @@ func TestParseThreshold(t *testing.T) {
 	})
 
 	t.Run("number 10 returns 10.0", func(t *testing.T) {
+		t.Parallel()
+
 		val, err := parseThreshold(json.RawMessage("10"))
 		if err != nil {
 			t.Fatalf("unexpected error: %v", err)
@@ -51,6 +63,8 @@ func TestParseThreshold(t *testing.T) {
 	})
 
 	t.Run("number 0.5 returns 0.5", func(t *testing.T) {
+		t.Parallel()
+
 		val, err := parseThreshold(json.RawMessage("0.5"))
 		if err != nil {
 			t.Fatalf("unexpected error: %v", err)
@@ -61,6 +75,8 @@ func TestParseThreshold(t *testing.T) {
 	})
 
 	t.Run("string '10' returns 10.0", func(t *testing.T) {
+		t.Parallel()
+
 		val, err := parseThreshold(json.RawMessage(`"10"`))
 		if err != nil {
 			t.Fatalf("unexpected error: %v", err)
@@ -71,6 +87,8 @@ func TestParseThreshold(t *testing.T) {
 	})
 
 	t.Run("string '0.001' returns 0.001", func(t *testing.T) {
+		t.Parallel()
+
 		val, err := parseThreshold(json.RawMessage(`"0.001"`))
 		if err != nil {
 			t.Fatalf("unexpected error: %v", err)
@@ -81,6 +99,8 @@ func TestParseThreshold(t *testing.T) {
 	})
 
 	t.Run("string with spaces '  10  ' returns 10.0", func(t *testing.T) {
+		t.Parallel()
+
 		val, err := parseThreshold(json.RawMessage(`"  10  "`))
 		if err != nil {
 			t.Fatalf("unexpected error: %v", err)
@@ -91,6 +111,8 @@ func TestParseThreshold(t *testing.T) {
 	})
 
 	t.Run("empty string returns nil", func(t *testing.T) {
+		t.Parallel()
+
 		val, err := parseThreshold(json.RawMessage(`""`))
 		if err != nil {
 			t.Fatalf("unexpected error: %v", err)
@@ -101,6 +123,8 @@ func TestParseThreshold(t *testing.T) {
 	})
 
 	t.Run("whitespace-only string returns nil", func(t *testing.T) {
+		t.Parallel()
+
 		val, err := parseThreshold(json.RawMessage(`"   "`))
 		if err != nil {
 			t.Fatalf("unexpected error: %v", err)
@@ -111,6 +135,8 @@ func TestParseThreshold(t *testing.T) {
 	})
 
 	t.Run("invalid string returns error", func(t *testing.T) {
+		t.Parallel()
+
 		_, err := parseThreshold(json.RawMessage(`"abc"`))
 		if err == nil {
 			t.Fatal("expected error for non-numeric string")
@@ -118,6 +144,8 @@ func TestParseThreshold(t *testing.T) {
 	})
 
 	t.Run("boolean returns error", func(t *testing.T) {
+		t.Parallel()
+
 		_, err := parseThreshold(json.RawMessage("true"))
 		if err == nil {
 			t.Fatal("expected error for boolean")
@@ -125,6 +153,8 @@ func TestParseThreshold(t *testing.T) {
 	})
 
 	t.Run("array returns error", func(t *testing.T) {
+		t.Parallel()
+
 		_, err := parseThreshold(json.RawMessage("[1,2]"))
 		if err == nil {
 			t.Fatal("expected error for array")
@@ -132,7 +162,10 @@ func TestParseThreshold(t *testing.T) {
 	})
 }
 
+//nolint:funlen
 func TestDecodeAlertBody(t *testing.T) {
+	t.Parallel()
+
 	// Verifies that the struct used in Create handler can decode all
 	// payload shapes the frontend might send.
 
@@ -183,12 +216,15 @@ func TestDecodeAlertBody(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
 			var body alertBody
 			err := json.Unmarshal([]byte(tt.payload), &body)
 			if tt.wantErr {
 				if err == nil {
 					t.Fatal("expected decode error")
 				}
+
 				return
 			}
 			if err != nil {
@@ -199,6 +235,8 @@ func TestDecodeAlertBody(t *testing.T) {
 }
 
 func TestOldStructFailsWithStringThreshold(t *testing.T) {
+	t.Parallel()
+
 	// Documents the original bug: *float64 cannot decode a string threshold.
 	type oldAlertBody struct {
 		Type      string   `json:"type"`

backend/internal/handlers/email_digest.go

@@ -0,0 +1,101 @@
+package handlers
+
+import (
+	"log"
+	"net/http"
+
+	"github.com/kjannette/koin-ping/backend/internal/middleware"
+	"github.com/kjannette/koin-ping/backend/internal/models"
+	"github.com/kjannette/koin-ping/backend/internal/services"
+)
+
+type EmailDigestHandler struct {
+	digestSvc *services.EmailDigestService
+	configs   *models.NotificationConfigModel
+}
+
+func NewEmailDigestHandler(
+	digestSvc *services.EmailDigestService,
+	configs *models.NotificationConfigModel,
+) *EmailDigestHandler {
+	return &EmailDigestHandler{digestSvc: digestSvc, configs: configs}
+}
+
+// SetupEmail reads the user's email from their notification config and sends
+// a confirmation message via Resend to verify the integration works.
+func (h *EmailDigestHandler) SetupEmail(w http.ResponseWriter, r *http.Request) {
+	userID := middleware.GetUserID(r.Context())
+
+	if !h.digestSvc.Configured() {
+		writeError(w, http.StatusServiceUnavailable, "EMAIL_NOT_CONFIGURED",
+			"Email service is not configured on the server")
+		return
+	}
+
+	cfg, err := h.configs.GetConfig(r.Context(), userID)
+	if err != nil {
+		log.Printf("Error getting notification config for email setup: %v", err)
+		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR",
+			"Failed to load notification config")
+		return
+	}
+
+	if cfg == nil || cfg.Email == nil || *cfg.Email == "" {
+		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR",
+			"Save an email address in notification settings first")
+		return
+	}
+
+	if err := h.digestSvc.SetupEmail(*cfg.Email); err != nil {
+		log.Printf("Email setup failed for user %s: %v", userID, err)
+		writeError(w, http.StatusBadGateway, "EMAIL_SEND_FAILED",
+			"Failed to send confirmation email — check server email config")
+		return
+	}
+
+	log.Printf("Email setup confirmation sent to user %s (%s)", userID, *cfg.Email)
+	writeJSON(w, http.StatusOK, map[string]any{
+		"success": true,
+		"email":   *cfg.Email,
+		"message": "Confirmation email sent",
+	})
+}
+
+// SendDigest compiles and sends a digest of recent alerts to the user's email.
+func (h *EmailDigestHandler) SendDigest(w http.ResponseWriter, r *http.Request) {
+	userID := middleware.GetUserID(r.Context())
+
+	if !h.digestSvc.Configured() {
+		writeError(w, http.StatusServiceUnavailable, "EMAIL_NOT_CONFIGURED",
+			"Email service is not configured on the server")
+		return
+	}
+
+	cfg, err := h.configs.GetConfig(r.Context(), userID)
+	if err != nil {
+		log.Printf("Error getting notification config for digest: %v", err)
+		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR",
+			"Failed to load notification config")
+		return
+	}
+
+	if cfg == nil || cfg.Email == nil || *cfg.Email == "" {
+		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR",
+			"No email address configured")
+		return
+	}
+
+	if err := h.digestSvc.SendDigest(r.Context(), userID, *cfg.Email); err != nil {
+		log.Printf("Digest send failed for user %s: %v", userID, err)
+		writeError(w, http.StatusBadGateway, "DIGEST_SEND_FAILED",
+			"Failed to send digest email")
+		return
+	}
+
+	log.Printf("Digest sent to user %s (%s)", userID, *cfg.Email)
+	writeJSON(w, http.StatusOK, map[string]any{
+		"success": true,
+		"email":   *cfg.Email,
+		"message": "Digest email sent",
+	})
+}

backend/internal/handlers/notification_config.go

@@ -7,20 +7,23 @@ import (
 	"regexp"
 	"strings"
 
-	"github.com/kjannette/koin-ping/backend-go/internal/domain"
-	"github.com/kjannette/koin-ping/backend-go/internal/middleware"
-	"github.com/kjannette/koin-ping/backend-go/internal/models"
-	"github.com/kjannette/koin-ping/backend-go/internal/notifications"
+	"github.com/kjannette/koin-ping/backend/internal/config"
+	"github.com/kjannette/koin-ping/backend/internal/domain"
+	"github.com/kjannette/koin-ping/backend/internal/middleware"
+	"github.com/kjannette/koin-ping/backend/internal/models"
+	"github.com/kjannette/koin-ping/backend/internal/notifications"
 )
 
 var emailRe = regexp.MustCompile(`^[^\s@]+@[^\s@]+\.[^\s@]+$`)
 
 type NotificationConfigHandler struct {
 	configs *models.NotificationConfigModel
+	users   *models.UserModel
+	cfg     *config.Config
 }
 
-func NewNotificationConfigHandler(configs *models.NotificationConfigModel) *NotificationConfigHandler {
-	return &NotificationConfigHandler{configs: configs}
+func NewNotificationConfigHandler(configs *models.NotificationConfigModel, users *models.UserModel, cfg *config.Config) *NotificationConfigHandler {
+	return &NotificationConfigHandler{configs: configs, users: users, cfg: cfg}
 }
 
 func (h *NotificationConfigHandler) GetConfig(w http.ResponseWriter, r *http.Request) {
@@ -51,8 +54,10 @@ func (h *NotificationConfigHandler) UpdateConfig(w http.ResponseWriter, r *http.
 
 	var body struct {
 		DiscordWebhookURL   *string `json:"discord_webhook_url"`
-		SlackWebhookURL     *string `json:"slack_webhook_url"`
+		TelegramChatID      *string `json:"telegram_chat_id"`
+		TelegramBotToken    *string `json:"telegram_bot_token"`
 		Email               *string `json:"email"`
+		SlackWebhookURL     *string `json:"slack_webhook_url"`
 		NotificationEnabled *bool   `json:"notification_enabled"`
 	}
 	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
@@ -63,8 +68,9 @@ func (h *NotificationConfigHandler) UpdateConfig(w http.ResponseWriter, r *http.
 
 	log.Printf("User %s updating notification config", userID)
 
-	if body.DiscordWebhookURL == nil && body.SlackWebhookURL == nil &&
-		body.Email == nil && body.NotificationEnabled == nil {
+	if body.DiscordWebhookURL == nil && body.TelegramChatID == nil &&
+		body.TelegramBotToken == nil && body.Email == nil &&
+		body.SlackWebhookURL == nil && body.NotificationEnabled == nil {
 		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR",
 			"At least one configuration field must be provided")
 		return
@@ -90,6 +96,26 @@ func (h *NotificationConfigHandler) UpdateConfig(w http.ResponseWriter, r *http.
 		return
 	}
 
+	user, userErr := h.users.GetByID(r.Context(), userID)
+	if userErr != nil || user == nil {
+		log.Printf("Failed to get user %s for tier check: %v", userID, userErr)
+		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to verify account")
+		return
+	}
+
+	limits := domain.GetTierLimits(user.SubscriptionTier)
+
+	if !limits.ChannelAllowed("discord") {
+		body.DiscordWebhookURL = nil
+	}
+	if !limits.ChannelAllowed("telegram") {
+		body.TelegramBotToken = nil
+		body.TelegramChatID = nil
+	}
+	if !limits.ChannelAllowed("slack") {
+		body.SlackWebhookURL = nil
+	}
+
 	enabled := true
 	if body.NotificationEnabled != nil {
 		enabled = *body.NotificationEnabled
@@ -97,8 +123,10 @@ func (h *NotificationConfigHandler) UpdateConfig(w http.ResponseWriter, r *http.
 
 	cfg := domain.NotificationConfig{
 		DiscordWebhookURL:   body.DiscordWebhookURL,
-		SlackWebhookURL:     body.SlackWebhookURL,
+		TelegramChatID:      body.TelegramChatID,
+		TelegramBotToken:    body.TelegramBotToken,
 		Email:               body.Email,
+		SlackWebhookURL:     body.SlackWebhookURL,
 		NotificationEnabled: enabled,
 	}
 
@@ -135,49 +163,75 @@ func (h *NotificationConfigHandler) DeleteConfig(w http.ResponseWriter, r *http.
 	w.WriteHeader(http.StatusNoContent)
 }
 
-func (h *NotificationConfigHandler) TestWebhook(w http.ResponseWriter, r *http.Request) {
-	_ = middleware.GetUserID(r.Context())
-
-	var body struct {
-		Type string `json:"type"`
-		URL  string `json:"url"`
-	}
-	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
-		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "Invalid request body")
-		return
-	}
-
-	if body.URL == "" {
-		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "URL is required")
-		return
-	}
-
-	var ok bool
-	var err error
-
-	switch body.Type {
-	case "slack":
-		if !strings.HasPrefix(body.URL, "https://hooks.slack.com/") {
-			writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "Invalid Slack webhook URL")
-			return
-		}
-		ok, err = notifications.TestSlackWebhook(body.URL)
-	case "discord":
-		if !strings.HasPrefix(body.URL, "https://discord.com/api/webhooks/") {
-			writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "Invalid Discord webhook URL")
-			return
-		}
-		ok, err = notifications.TestDiscordWebhook(body.URL)
-	default:
-		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "Type must be 'slack' or 'discord'")
-		return
-	}
+// TestChannels sends a test message to all configured notification channels.
+func (h *NotificationConfigHandler) TestChannels(w http.ResponseWriter, r *http.Request) {
+	userID := middleware.GetUserID(r.Context())
+	log.Printf("User %s testing notification channels", userID)
 
+	cfg, err := h.configs.GetConfig(r.Context(), userID)
 	if err != nil {
-		log.Printf("Webhook test failed: %v", err)
-		writeJSON(w, http.StatusOK, map[string]interface{}{"success": false, "error": err.Error()})
+		log.Printf("Error getting notification config for test: %v", err)
+		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to get notification config")
 		return
 	}
 
-	writeJSON(w, http.StatusOK, map[string]interface{}{"success": ok})
+	if cfg == nil {
+		writeError(w, http.StatusNotFound, "NOT_FOUND", "No notification configuration found")
+		return
+	}
+
+	type channelResult struct {
+		Channel string `json:"channel"`
+		Success bool   `json:"success"`
+		Error   string `json:"error,omitempty"`
+	}
+
+	var results []channelResult
+
+	if cfg.DiscordWebhookURL != nil && *cfg.DiscordWebhookURL != "" {
+		ok, testErr := notifications.TestDiscordWebhook(*cfg.DiscordWebhookURL)
+		res := channelResult{Channel: "discord", Success: ok}
+		if testErr != nil {
+			res.Error = testErr.Error()
+		}
+		results = append(results, res)
+	}
+
+	if cfg.TelegramBotToken != nil && *cfg.TelegramBotToken != "" &&
+		cfg.TelegramChatID != nil && *cfg.TelegramChatID != "" {
+		ok, testErr := notifications.TestTelegramWebhook(*cfg.TelegramBotToken, *cfg.TelegramChatID)
+		res := channelResult{Channel: "telegram", Success: ok}
+		if testErr != nil {
+			res.Error = testErr.Error()
+		}
+		results = append(results, res)
+	}
+
+	if cfg.SlackWebhookURL != nil && *cfg.SlackWebhookURL != "" {
+		ok, testErr := notifications.TestSlackWebhook(*cfg.SlackWebhookURL)
+		res := channelResult{Channel: "slack", Success: ok}
+		if testErr != nil {
+			res.Error = testErr.Error()
+		}
+		results = append(results, res)
+	}
+
+	if cfg.Email != nil && *cfg.Email != "" {
+		ok, testErr := notifications.TestEmailNotification(
+			h.cfg.ResendAPIKey, h.cfg.EmailFrom, *cfg.Email,
+		)
+		res := channelResult{Channel: "email", Success: ok}
+		if testErr != nil {
+			res.Error = testErr.Error()
+		}
+		results = append(results, res)
+	}
+
+	if len(results) == 0 {
+		writeError(w, http.StatusBadRequest, "NO_CHANNELS",
+			"No notification channels are configured")
+		return
+	}
+
+	writeJSON(w, http.StatusOK, map[string]any{"results": results})
 }

backend/internal/handlers/status.go

@@ -0,0 +1,71 @@
+package handlers
+
+import (
+	"log"
+	"net/http"
+	"time"
+
+	"github.com/kjannette/koin-ping/backend/internal/models"
+)
+
+// StatusHandler handles the system status endpoint.
+type StatusHandler struct {
+	checkpoints *models.CheckpointModel
+}
+
+// NewStatusHandler creates a new StatusHandler.
+func NewStatusHandler(checkpoints *models.CheckpointModel) *StatusHandler {
+	return &StatusHandler{checkpoints: checkpoints}
+}
+
+// GetStatus returns real-time system status derived from checkpoint data.
+func (h *StatusHandler) GetStatus(w http.ResponseWriter, r *http.Request) {
+	block, checkedAt, err := h.checkpoints.GetLatestBlock(r.Context())
+	if err != nil {
+		log.Printf("Error querying latest block: %v", err)
+		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to get system status")
+
+		return
+	}
+
+	latestBlock := 0
+	lag := 0
+	status := "starting"
+
+	if checkedAt != nil {
+		lag = int(time.Since(*checkedAt).Seconds())
+		if lag > 600 { //nolint:mnd
+			status = "idle"
+		} else {
+			status = "active"
+		}
+	}
+
+	if block != nil {
+		latestBlock = *block
+	}
+
+	writeJSON(w, http.StatusOK, map[string]interface{}{
+		"status":        status,
+		"latestBlock":   latestBlock,
+		"lag":           lag,
+		"lastCheckedAt": checkedAtStr(checkedAt),
+		"timestamp":     time.Now().UTC().Format(time.RFC3339),
+	})
+}
+
+func checkedAtStr(t *time.Time) string {
+	if t == nil {
+		return ""
+	}
+
+	return t.UTC().Format(time.RFC3339)
+}
+
+func HealthCheck(w http.ResponseWriter, r *http.Request) {
+	writeJSON(w, http.StatusOK, map[string]interface{}{
+		"status":    "ok",
+		"timestamp": time.Now().UTC().Format(time.RFC3339),
+		"service":   "koin-ping-backend",
+	})
+}

backend/internal/handlers/stripe.go

@@ -0,0 +1,429 @@
+package handlers
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"log"
+	"net/http"
+
+	"github.com/stripe/stripe-go/v82"
+	portalsession "github.com/stripe/stripe-go/v82/billingportal/session"
+	checkoutsession "github.com/stripe/stripe-go/v82/checkout/session"
+	"github.com/stripe/stripe-go/v82/webhook"
+
+	"github.com/kjannette/koin-ping/backend/internal/config"
+	"github.com/kjannette/koin-ping/backend/internal/domain"
+	"github.com/kjannette/koin-ping/backend/internal/middleware"
+	"github.com/kjannette/koin-ping/backend/internal/models"
+)
+
+const webhookMaxBodyBytes = 65536
+
+type StripeHandler struct {
+	users *models.UserModel
+	cfg   *config.Config
+}
+
+func NewStripeHandler(users *models.UserModel, cfg *config.Config) *StripeHandler {
+	stripe.Key = cfg.StripeSecretKey
+	return &StripeHandler{users: users, cfg: cfg}
+}
+
+func (h *StripeHandler) priceIDForTier(tier domain.SubscriptionTier) (string, error) {
+	switch tier {
+	case domain.TierPremium:
+		return h.cfg.StripePriceIDPremium, nil
+	case domain.TierPro:
+		return h.cfg.StripePriceIDPro, nil
+	default:
+		return "", fmt.Errorf("no Stripe price for tier %q", tier) //nolint:err113
+	}
+}
+
+// CreateCheckoutSession creates a Stripe Checkout session for the selected tier.
+func (h *StripeHandler) CreateCheckoutSession(w http.ResponseWriter, r *http.Request) {
+	userID := middleware.GetUserID(r.Context())
+
+	var body struct {
+		Tier string `json:"tier"`
+	}
+	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+		writeError(w, http.StatusBadRequest, "BAD_REQUEST", "Invalid request body")
+		return
+	}
+
+	if body.Tier == "" {
+		body.Tier = "premium"
+	}
+
+	tier := domain.SubscriptionTier(body.Tier)
+	if tier != domain.TierPremium && tier != domain.TierPro {
+		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "Tier must be 'premium' or 'pro'")
+		return
+	}
+
+	priceID, err := h.priceIDForTier(tier)
+	if err != nil {
+		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", err.Error())
+		return
+	}
+
+	user, err := h.users.GetByID(r.Context(), userID)
+	if err != nil || user == nil {
+		log.Printf("Failed to get user %s: %v", userID, err)
+		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to load user")
+		return
+	}
+
+	params := &stripe.CheckoutSessionParams{
+		Mode: stripe.String(string(stripe.CheckoutSessionModeSubscription)),
+		LineItems: []*stripe.CheckoutSessionLineItemParams{
+			{
+				Price:    stripe.String(priceID),
+				Quantity: stripe.Int64(1),
+			},
+		},
+		SuccessURL:        stripe.String(h.cfg.FrontendURL + "/subscribe?payment=success&session_id={CHECKOUT_SESSION_ID}"),
+		CancelURL:         stripe.String(h.cfg.FrontendURL + "/subscribe?payment=cancelled"),
+		ClientReferenceID: stripe.String(userID),
+		CustomerEmail:     stripe.String(user.Email),
+	}
+
+	params.AddMetadata("tier", string(tier))
+
+	if user.StripeCustomerID != nil && *user.StripeCustomerID != "" {
+		params.Customer = user.StripeCustomerID
+		params.CustomerEmail = nil
+	}
+
+	s, err := checkoutsession.New(params)
+	if err != nil {
+		log.Printf("Failed to create Stripe checkout session: %v", err)
+		writeError(w, http.StatusInternalServerError, "STRIPE_ERROR", "Failed to create checkout session")
+		return
+	}
+
+	writeJSON(w, http.StatusOK, map[string]string{"url": s.URL})
+}
+
+// GetSubscriptionStatus returns the current user's subscription state.
+func (h *StripeHandler) GetSubscriptionStatus(w http.ResponseWriter, r *http.Request) {
+	userID := middleware.GetUserID(r.Context())
+
+	user, err := h.users.GetByID(r.Context(), userID)
+	if err != nil || user == nil {
+		log.Printf("Failed to get user %s: %v", userID, err)
+		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to load user")
+		return
+	}
+
+	writeJSON(w, http.StatusOK, map[string]any{
+		"subscription_status": user.SubscriptionStatus,
+		"subscription_tier":   user.SubscriptionTier,
+		"subscription_created_at": user.SubscriptionCreatedAt,
+	})
+}
+
+// VerifyCheckoutSession retrieves a completed checkout session from Stripe,
+// confirms payment, and activates the user's subscription in the database.
+func (h *StripeHandler) VerifyCheckoutSession(w http.ResponseWriter, r *http.Request) {
+	userID := middleware.GetUserID(r.Context())
+
+	var body struct {
+		SessionID string `json:"session_id"`
+	}
+	if err := json.NewDecoder(r.Body).Decode(&body); err != nil || body.SessionID == "" {
+		writeError(w, http.StatusBadRequest, "BAD_REQUEST", "Missing session_id")
+		return
+	}
+
+	s, err := checkoutsession.Get(body.SessionID, nil)
+	if err != nil {
+		log.Printf("Failed to retrieve checkout session %s: %v", body.SessionID, err)
+		writeError(w, http.StatusBadRequest, "STRIPE_ERROR", "Invalid checkout session")
+		return
+	}
+
+	if s.ClientReferenceID != "" && s.ClientReferenceID != userID {
+		writeError(w, http.StatusForbidden, "FORBIDDEN", "Session does not belong to this user")
+		return
+	}
+
+	if s.PaymentStatus != stripe.CheckoutSessionPaymentStatusPaid {
+		writeError(w, http.StatusBadRequest, "PAYMENT_INCOMPLETE", "Payment has not been completed")
+		return
+	}
+
+	tier := domain.TierPremium
+	if t, ok := s.Metadata["tier"]; ok && domain.IsValidTier(t) {
+		tier = domain.SubscriptionTier(t)
+	}
+
+	customerID := ""
+	if s.Customer != nil {
+		customerID = s.Customer.ID
+	}
+	subscriptionID := ""
+	if s.Subscription != nil {
+		subscriptionID = s.Subscription.ID
+	}
+
+	if customerID != "" {
+		if err := h.users.UpdateStripeCustomer(r.Context(), userID, customerID); err != nil {
+			log.Printf("VerifyCheckout: failed to save customer ID: %v", err)
+		}
+	}
+	if subscriptionID != "" && customerID != "" {
+		if err := h.users.ActivateSubscription(r.Context(), customerID, subscriptionID, "active", tier); err != nil {
+			log.Printf("VerifyCheckout: failed to activate subscription: %v", err)
+		}
+	}
+
+	log.Printf("Checkout verified for user %s, customer %s, subscription %s, tier %s", userID, customerID, subscriptionID, tier)
+	writeJSON(w, http.StatusOK, map[string]string{
+		"subscription_status": "active",
+		"subscription_tier":   string(tier),
+	})
+}
+
+// ActivateFreeTier sets the user to the free tier without Stripe involvement.
+func (h *StripeHandler) ActivateFreeTier(w http.ResponseWriter, r *http.Request) {
+	userID := middleware.GetUserID(r.Context())
+
+	if err := h.users.ActivateFreeTier(r.Context(), userID); err != nil {
+		log.Printf("ActivateFreeTier: failed for user %s: %v", userID, err)
+		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to activate free tier")
+		return
+	}
+
+	log.Printf("Free tier activated for user %s", userID)
+	writeJSON(w, http.StatusOK, map[string]string{
+		"subscription_status": "active",
+		"subscription_tier":   "free",
+	})
+}
+
+// CreateOnboardingCheckout creates a Stripe Checkout session for a user who
+// has not yet created an account. This is a public endpoint (no auth required).
+// The Firebase account is created on the frontend only after payment succeeds.
+func (h *StripeHandler) CreateOnboardingCheckout(w http.ResponseWriter, r *http.Request) {
+	var body struct {
+		Email string `json:"email"`
+		Tier  string `json:"tier"`
+	}
+	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+		writeError(w, http.StatusBadRequest, "BAD_REQUEST", "Invalid request body")
+		return
+	}
+
+	if body.Email == "" {
+		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "Email is required")
+		return
+	}
+
+	if body.Tier == "" {
+		body.Tier = "premium"
+	}
+
+	tier := domain.SubscriptionTier(body.Tier)
+	if tier != domain.TierPremium && tier != domain.TierPro {
+		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "Tier must be 'premium' or 'pro'")
+		return
+	}
+
+	priceID, err := h.priceIDForTier(tier)
+	if err != nil {
+		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", err.Error())
+		return
+	}
+
+	params := &stripe.CheckoutSessionParams{
+		Mode: stripe.String(string(stripe.CheckoutSessionModeSubscription)),
+		LineItems: []*stripe.CheckoutSessionLineItemParams{
+			{
+				Price:    stripe.String(priceID),
+				Quantity: stripe.Int64(1),
+			},
+		},
+		SuccessURL:    stripe.String(h.cfg.FrontendURL + "/subscribe?payment=success&session_id={CHECKOUT_SESSION_ID}"),
+		CancelURL:     stripe.String(h.cfg.FrontendURL + "/subscribe?payment=cancelled"),
+		CustomerEmail: stripe.String(body.Email),
+	}
+	params.AddMetadata("tier", string(tier))
+	params.AddMetadata("onboarding", "true")
+
+	s, err := checkoutsession.New(params)
+	if err != nil {
+		log.Printf("Failed to create onboarding checkout session: %v", err)
+		writeError(w, http.StatusInternalServerError, "STRIPE_ERROR", "Failed to create checkout session")
+		return
+	}
+
+	writeJSON(w, http.StatusOK, map[string]string{"url": s.URL})
+}
+
+// CreatePortalSession creates a Stripe Billing Portal session so the user can
+// manage their subscription (cancel, update payment method, view invoices).
+func (h *StripeHandler) CreatePortalSession(w http.ResponseWriter, r *http.Request) {
+	userID := middleware.GetUserID(r.Context())
+
+	user, err := h.users.GetByID(r.Context(), userID)
+	if err != nil || user == nil {
+		log.Printf("Portal: failed to get user %s: %v", userID, err)
+		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to load user")
+		return
+	}
+
+	if user.StripeCustomerID == nil || *user.StripeCustomerID == "" {
+		writeError(w, http.StatusBadRequest, "NO_CUSTOMER", "No Stripe customer on file")
+		return
+	}
+
+	params := &stripe.BillingPortalSessionParams{
+		Customer:  user.StripeCustomerID,
+		ReturnURL: stripe.String(h.cfg.FrontendURL + "/account"),
+	}
+
+	s, err := portalsession.New(params)
+	if err != nil {
+		log.Printf("Portal: failed to create portal session: %v", err)
+		writeError(w, http.StatusInternalServerError, "STRIPE_ERROR", "Failed to create portal session")
+		return
+	}
+
+	writeJSON(w, http.StatusOK, map[string]string{"url": s.URL})
+}
+
+// HandleWebhook processes incoming Stripe webhook events.
+func (h *StripeHandler) HandleWebhook(w http.ResponseWriter, r *http.Request) {
+	payload, err := io.ReadAll(io.LimitReader(r.Body, webhookMaxBodyBytes))
+	if err != nil {
+		log.Printf("Error reading webhook body: %v", err)
+		w.WriteHeader(http.StatusServiceUnavailable)
+		return
+	}
+
+	sig := r.Header.Get("Stripe-Signature")
+	event, err := webhook.ConstructEvent(payload, sig, h.cfg.StripeWebhookSecret)
+	if err != nil {
+		log.Printf("Webhook signature verification failed: %v", err)
+		w.WriteHeader(http.StatusBadRequest)
+		return
+	}
+
+	switch event.Type {
+	case "checkout.session.completed":
+		h.handleCheckoutCompleted(r, event)
+	case "customer.subscription.updated":
+		h.handleSubscriptionUpdated(r, event)
+	case "customer.subscription.deleted":
+		h.handleSubscriptionDeleted(r, event)
+	default:
+		log.Printf("Unhandled Stripe event type: %s", event.Type)
+	}
+
+	w.WriteHeader(http.StatusOK)
+}
+
+func (h *StripeHandler) handleCheckoutCompleted(r *http.Request, event stripe.Event) {
+	var session stripe.CheckoutSession
+	if err := json.Unmarshal(event.Data.Raw, &session); err != nil {
+		log.Printf("Error parsing checkout session: %v", err)
+		return
+	}
+
+	userID := session.ClientReferenceID
+	if userID == "" {
+		log.Println("Checkout session missing client_reference_id")
+		return
+	}
+
+	tier := domain.TierPremium
+	if t, ok := session.Metadata["tier"]; ok && domain.IsValidTier(t) {
+		tier = domain.SubscriptionTier(t)
+	}
+
+	customerID := ""
+	if session.Customer != nil {
+		customerID = session.Customer.ID
+	}
+	subscriptionID := ""
+	if session.Subscription != nil {
+		subscriptionID = session.Subscription.ID
+	}
+
+	if customerID != "" {
+		if err := h.users.UpdateStripeCustomer(r.Context(), userID, customerID); err != nil {
+			log.Printf("Failed to save Stripe customer ID: %v", err)
+		}
+	}
+
+	if subscriptionID != "" && customerID != "" {
+		if err := h.users.ActivateSubscription(r.Context(), customerID, subscriptionID, "active", tier); err != nil {
+			log.Printf("Failed to activate subscription: %v", err)
+		}
+	}
+
+	log.Printf("Checkout completed for user %s, customer %s, subscription %s, tier %s", userID, customerID, subscriptionID, tier)
+}
+
+func (h *StripeHandler) handleSubscriptionUpdated(r *http.Request, event stripe.Event) {
+	var sub stripe.Subscription
+	if err := json.Unmarshal(event.Data.Raw, &sub); err != nil {
+		log.Printf("Error parsing subscription update: %v", err)
+		return
+	}
+
+	customerID := ""
+	if sub.Customer != nil {
+		customerID = sub.Customer.ID
+	}
+	if customerID == "" {
+		return
+	}
+
+	status := string(sub.Status)
+
+	// Detect tier from the subscription's current price so that
+	// upgrades/downgrades via the Stripe portal are reflected.
+	tier := domain.TierPremium
+	if sub.Items != nil {
+		for _, item := range sub.Items.Data {
+			if item.Price != nil {
+				if t := h.cfg.TierForPriceID(item.Price.ID); t != "" {
+					tier = domain.SubscriptionTier(t)
+					break
+				}
+			}
+		}
+	}
+
+	if err := h.users.ActivateSubscription(r.Context(), customerID, sub.ID, status, tier); err != nil {
+		log.Printf("Failed to update subscription: %v", err)
+	}
+
+	log.Printf("Subscription %s updated to %s (tier %s) for customer %s", sub.ID, status, tier, customerID)
+}
+
+func (h *StripeHandler) handleSubscriptionDeleted(r *http.Request, event stripe.Event) {
+	var sub stripe.Subscription
+	if err := json.Unmarshal(event.Data.Raw, &sub); err != nil {
+		log.Printf("Error parsing subscription deletion: %v", err)
+		return
+	}
+
+	customerID := ""
+	if sub.Customer != nil {
+		customerID = sub.Customer.ID
+	}
+	if customerID == "" {
+		return
+	}
+
+	if err := h.users.UpdateSubscriptionStatus(r.Context(), customerID, "canceled"); err != nil {
+		log.Printf("Failed to mark subscription canceled: %v", err)
+	}
+
+	log.Printf("Subscription canceled for customer %s", customerID)
+}

backend/internal/middleware/auth.go

@@ -0,0 +1,161 @@
+// Package middleware provides HTTP middleware for authentication and context injection.
+package middleware
+
+import (
+	"context"
+	"encoding/json"
+	"log"
+	"net/http"
+	"strings"
+
+	fbauth "github.com/kjannette/koin-ping/backend/internal/firebase"
+	"github.com/kjannette/koin-ping/backend/internal/models"
+)
+
+type contextKey string
+
+const (
+	UserIDKey    contextKey = "user_id"
+	UserEmailKey contextKey = "user_email"
+	UserTierKey  contextKey = "user_tier"
+)
+
+type errorResponse struct {
+	Error   string `json:"error"`
+	Message string `json:"message"`
+}
+
+func writeJSON(w http.ResponseWriter, status int, v interface{}) {
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(status)
+	json.NewEncoder(w).Encode(v) //nolint:errcheck
+}
+
+// Authenticate verifies the Firebase ID token and auto-provisions a local user
+// record. The local user UUID (not the Firebase UID) is placed into context so
+// all downstream handlers use it as the canonical user identifier.
+func Authenticate(userModel *models.UserModel) func(http.Handler) http.Handler {
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			authHeader := r.Header.Get("Authorization")
+			if authHeader == "" || !strings.HasPrefix(authHeader, "Bearer ") {
+				log.Println("No Authorization header or invalid format")
+				writeJSON(w, http.StatusUnauthorized, errorResponse{
+					Error:   "UNAUTHORIZED",
+					Message: "No authentication token provided",
+				})
+				return
+			}
+
+			token := strings.TrimPrefix(authHeader, "Bearer ")
+			if token == "" {
+				log.Println("Empty token")
+				writeJSON(w, http.StatusUnauthorized, errorResponse{
+					Error:   "UNAUTHORIZED",
+					Message: "Invalid token format",
+				})
+				return
+			}
+
+			log.Println("Verifying Firebase token...")
+			decoded, err := fbauth.Auth().VerifyIDToken(r.Context(), token)
+			if err != nil {
+				log.Printf("Token verification failed: %v", err)
+
+				errMsg := err.Error()
+				if strings.Contains(errMsg, "expired") {
+					writeJSON(w, http.StatusUnauthorized, errorResponse{
+						Error:   "TOKEN_EXPIRED",
+						Message: "Authentication token has expired",
+					})
+					return
+				}
+
+				writeJSON(w, http.StatusUnauthorized, errorResponse{
+					Error:   "UNAUTHORIZED",
+					Message: "Failed to verify authentication token",
+				})
+				return
+			}
+
+			firebaseUID := decoded.UID
+			email, _ := decoded.Claims["email"].(string)
+
+			user, err := userModel.FindOrCreateByFirebaseUID(r.Context(), firebaseUID, email)
+			if err != nil {
+				log.Printf("Failed to provision local user for Firebase UID %s: %v", firebaseUID, err)
+				writeJSON(w, http.StatusInternalServerError, errorResponse{
+					Error:   "INTERNAL_ERROR",
+					Message: "Failed to initialize user account",
+				})
+				return
+			}
+
+			log.Printf("Token verified! User UUID: %s, Email: %s", user.ID, email)
+
+			ctx := context.WithValue(r.Context(), UserIDKey, user.ID)
+			ctx = context.WithValue(ctx, UserEmailKey, email)
+			ctx = context.WithValue(ctx, UserTierKey, string(user.SubscriptionTier))
+
+			next.ServeHTTP(w, r.WithContext(ctx))
+		})
+	}
+}
+
+// RequireSubscription blocks requests from users without an active subscription.
+// Must be applied after Authenticate.
+func RequireSubscription(userModel *models.UserModel) func(http.Handler) http.Handler {
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			userID := GetUserID(r.Context())
+			if userID == "" {
+				writeJSON(w, http.StatusUnauthorized, errorResponse{
+					Error:   "UNAUTHORIZED",
+					Message: "Authentication required",
+				})
+				return
+			}
+
+			user, err := userModel.GetByID(r.Context(), userID)
+			if err != nil || user == nil {
+				log.Printf("RequireSubscription: failed to load user %s: %v", userID, err)
+				writeJSON(w, http.StatusInternalServerError, errorResponse{
+					Error:   "INTERNAL_ERROR",
+					Message: "Failed to verify subscription",
+				})
+				return
+			}
+
+			if user.SubscriptionStatus != "active" && user.SubscriptionStatus != "trialing" {
+				writeJSON(w, http.StatusForbidden, errorResponse{
+					Error:   "SUBSCRIPTION_REQUIRED",
+					Message: "An active subscription is required to use this feature",
+				})
+				return
+			}
+
+			next.ServeHTTP(w, r)
+		})
+	}
+}
+
+func GetUserID(ctx context.Context) string {
+	if v, ok := ctx.Value(UserIDKey).(string); ok {
+		return v
+	}
+	return ""
+}
+
+func GetUserEmail(ctx context.Context) string {
+	if v, ok := ctx.Value(UserEmailKey).(string); ok {
+		return v
+	}
+	return ""
+}
+
+func GetUserTier(ctx context.Context) string {
+	if v, ok := ctx.Value(UserTierKey).(string); ok {
+		return v
+	}
+	return "free"
+}

backend/internal/middleware/auth_test.go

@@ -0,0 +1,60 @@
+package middleware
+
+import (
+	"context"
+	"testing"
+)
+
+func TestGetUserID_Empty(t *testing.T) {
+	t.Parallel()
+
+	ctx := context.Background()
+	if id := GetUserID(ctx); id != "" {
+		t.Errorf("expected empty user ID, got %q", id)
+	}
+}
+
+func TestGetUserID_Set(t *testing.T) {
+	t.Parallel()
+
+	ctx := context.WithValue(context.Background(), UserIDKey, "abc-123")
+	if id := GetUserID(ctx); id != "abc-123" {
+		t.Errorf("expected abc-123, got %q", id)
+	}
+}
+
+func TestGetUserEmail_Empty(t *testing.T) {
+	t.Parallel()
+
+	ctx := context.Background()
+	if email := GetUserEmail(ctx); email != "" {
+		t.Errorf("expected empty email, got %q", email)
+	}
+}
+
+func TestGetUserEmail_Set(t *testing.T) {
+	t.Parallel()
+
+	ctx := context.WithValue(context.Background(), UserEmailKey, "test@example.com")
+	if email := GetUserEmail(ctx); email != "test@example.com" {
+		t.Errorf("expected test@example.com, got %q", email)
+	}
+}
+
+func TestGetUserTier_Default(t *testing.T) {
+	t.Parallel()
+
+	ctx := context.Background()
+	if tier := GetUserTier(ctx); tier != "free" {
+		t.Errorf("expected default tier 'free', got %q", tier)
+	}
+}
+
+func TestGetUserTier_Set(t *testing.T) {
+	t.Parallel()
+
+	ctx := context.WithValue(context.Background(), UserTierKey, "pro")
+	if tier := GetUserTier(ctx); tier != "pro" {
+		t.Errorf("expected 'pro', got %q", tier)
+	}
+}

backend/internal/models/address.go

@@ -2,9 +2,11 @@ package models
 
 import (
 	"context"
+	"errors"
 
+	"github.com/jackc/pgx/v5"
 	"github.com/jackc/pgx/v5/pgxpool"
-	"github.com/kjannette/koin-ping/backend-go/internal/domain"
+	"github.com/kjannette/koin-ping/backend/internal/domain"
 )
 
 type AddressModel struct {
@@ -53,12 +55,14 @@ func (m *AddressModel) ListByUser(ctx context.Context, userID string) ([]domain.
 	return addresses, rows.Err()
 }
 
-// ListAll returns all addresses system-wide (used by the poller).
+// ListAll returns addresses for users with an active subscription (used by the poller).
 func (m *AddressModel) ListAll(ctx context.Context) ([]domain.Address, error) {
 	rows, err := m.pool.Query(ctx,
-		`SELECT id, user_id, address, label, created_at
-		 FROM addresses
-		 ORDER BY created_at DESC`,
+		`SELECT a.id, a.user_id, a.address, a.label, a.created_at
+		 FROM addresses a
+		 JOIN users u ON u.id = a.user_id
+		 WHERE u.subscription_status IN ('active', 'trialing')
+		 ORDER BY a.created_at DESC`,
 	)
 	if err != nil {
 		return nil, err
@@ -97,7 +101,7 @@ func (m *AddressModel) FindByID(ctx context.Context, id int, userID *string) (*d
 	}
 
 	if err != nil {
-		if err.Error() == "no rows in result set" {
+		if errors.Is(err, pgx.ErrNoRows) {
 			return nil, nil
 		}
 		return nil, err
@@ -105,6 +109,33 @@ func (m *AddressModel) FindByID(ctx context.Context, id int, userID *string) (*d
 	return &a, nil
 }
 
+// UpdateLabel updates the label for an address owned by userID.
+// Returns nil, nil if no row matched (address not found or not owned by user).
+func (m *AddressModel) UpdateLabel(ctx context.Context, id int, userID string, label *string) (*domain.Address, error) {
+	var a domain.Address
+	err := m.pool.QueryRow(ctx,
+		`UPDATE addresses SET label = $3 WHERE id = $1 AND user_id = $2
+		 RETURNING id, user_id, address, label, created_at`,
+		id, userID, label,
+	).Scan(&a.ID, &a.UserID, &a.Address, &a.Label, &a.CreatedAt)
+	if err != nil {
+		if errors.Is(err, pgx.ErrNoRows) {
+			return nil, nil
+		}
+		return nil, err
+	}
+	return &a, nil
+}
+
+func (m *AddressModel) CountByUser(ctx context.Context, userID string) (int, error) {
+	var count int
+	err := m.pool.QueryRow(ctx,
+		`SELECT COUNT(*) FROM addresses WHERE user_id = $1`,
+		userID,
+	).Scan(&count)
+	return count, err
+}
+
 func (m *AddressModel) Remove(ctx context.Context, id int, userID string) (bool, error) {
 	tag, err := m.pool.Exec(ctx,
 		`DELETE FROM addresses WHERE id = $1 AND user_id = $2`,

backend/internal/models/alert_event.go

@@ -2,9 +2,11 @@ package models
 
 import (
 	"context"
+	"errors"
 
+	"github.com/jackc/pgx/v5"
 	"github.com/jackc/pgx/v5/pgxpool"
-	"github.com/kjannette/koin-ping/backend-go/internal/domain"
+	"github.com/kjannette/koin-ping/backend/internal/domain"
 )
 
 type AlertEventModel struct {
@@ -71,10 +73,15 @@ func (m *AlertEventModel) Create(ctx context.Context, alertRuleID int, message s
 	err := m.pool.QueryRow(ctx,
 		`INSERT INTO alert_events (alert_rule_id, message, address_label, tx_hash)
 		 VALUES ($1, $2, $3, $4)
+		 ON CONFLICT DO NOTHING
 		 RETURNING id, alert_rule_id, message, address_label, tx_hash, timestamp`,
 		alertRuleID, message, addressLabel, txHash,
 	).Scan(&e.ID, &e.AlertRuleID, &e.Message, &e.AddressLabel, &e.TxHash, &e.Timestamp)
 	if err != nil {
+		if errors.Is(err, pgx.ErrNoRows) {
+			// Duplicate silently skipped by ON CONFLICT DO NOTHING
+			return nil, nil
+		}
 		return nil, err
 	}
 	return &e, nil

backend/internal/models/alert_rule.go

@@ -0,0 +1,142 @@
+package models
+
+import (
+	"context"
+	"errors"
+
+	"github.com/jackc/pgx/v5"
+	"github.com/jackc/pgx/v5/pgxpool"
+	"github.com/kjannette/koin-ping/backend/internal/domain"
+)
+
+type AlertRuleModel struct {
+	pool *pgxpool.Pool
+}
+
+func NewAlertRuleModel(pool *pgxpool.Pool) *AlertRuleModel {
+	return &AlertRuleModel{pool: pool}
+}
+
+func (m *AlertRuleModel) Create(ctx context.Context, addressID int, alertType domain.AlertType, threshold, minimum, maximum *float64) (*domain.AlertRule, error) {
+	var r domain.AlertRule
+	err := m.pool.QueryRow(ctx,
+		`INSERT INTO alert_rules (address_id, type, threshold, minimum, maximum, enabled)
+		 VALUES ($1, $2, $3, $4, $5, TRUE)
+		 RETURNING id, address_id, type, threshold, minimum, maximum, enabled, created_at`,
+		addressID, alertType.String(), threshold, minimum, maximum,
+	).Scan(&r.ID, &r.AddressID, &r.Type, &r.Threshold, &r.Minimum, &r.Maximum, &r.Enabled, &r.CreatedAt)
+	if err != nil {
+		return nil, err
+	}
+	return &r, nil
+}
+
+func (m *AlertRuleModel) ListByAddress(ctx context.Context, addressID int) ([]domain.AlertRule, error) {
+	rows, err := m.pool.Query(ctx,
+		`SELECT id, address_id, type, threshold, minimum, maximum, enabled, created_at
+		 FROM alert_rules
+		 WHERE address_id = $1
+		 ORDER BY created_at DESC`,
+		addressID,
+	)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	var rules []domain.AlertRule
+	for rows.Next() {
+		var r domain.AlertRule
+		if err := rows.Scan(&r.ID, &r.AddressID, &r.Type, &r.Threshold, &r.Minimum, &r.Maximum, &r.Enabled, &r.CreatedAt); err != nil {
+			return nil, err
+		}
+		rules = append(rules, r)
+	}
+	return rules, rows.Err()
+}
+
+func (m *AlertRuleModel) FindByID(ctx context.Context, id int, userID *string) (*domain.AlertRule, error) {
+	var r domain.AlertRule
+	var err error
+
+	if userID != nil {
+		err = m.pool.QueryRow(ctx,
+			`SELECT ar.id, ar.address_id, ar.type, ar.threshold, ar.minimum, ar.maximum, ar.enabled, ar.created_at
+			 FROM alert_rules ar
+			 JOIN addresses a ON a.id = ar.address_id
+			 WHERE ar.id = $1 AND a.user_id = $2`,
+			id, *userID,
+		).Scan(&r.ID, &r.AddressID, &r.Type, &r.Threshold, &r.Minimum, &r.Maximum, &r.Enabled, &r.CreatedAt)
+	} else {
+		err = m.pool.QueryRow(ctx,
+			`SELECT id, address_id, type, threshold, minimum, maximum, enabled, created_at
+			 FROM alert_rules
+			 WHERE id = $1`,
+			id,
+		).Scan(&r.ID, &r.AddressID, &r.Type, &r.Threshold, &r.Minimum, &r.Maximum, &r.Enabled, &r.CreatedAt)
+	}
+
+	if err != nil {
+		if errors.Is(err, pgx.ErrNoRows) {
+			return nil, nil
+		}
+		return nil, err
+	}
+	return &r, nil
+}
+
+func (m *AlertRuleModel) UpdateEnabled(ctx context.Context, id int, enabled bool) (*domain.AlertRule, error) {
+	var r domain.AlertRule
+	err := m.pool.QueryRow(ctx,
+		`UPDATE alert_rules
+		 SET enabled = $2
+		 WHERE id = $1
+		 RETURNING id, address_id, type, threshold, minimum, maximum, enabled, created_at`,
+		id, enabled,
+	).Scan(&r.ID, &r.AddressID, &r.Type, &r.Threshold, &r.Minimum, &r.Maximum, &r.Enabled, &r.CreatedAt)
+	if err != nil {
+		if errors.Is(err, pgx.ErrNoRows) {
+			return nil, nil
+		}
+		return nil, err
+	}
+	return &r, nil
+}
+
+func (m *AlertRuleModel) UpdateThresholds(ctx context.Context, id int, minimum, maximum *float64) (*domain.AlertRule, error) {
+	var r domain.AlertRule
+	err := m.pool.QueryRow(ctx,
+		`UPDATE alert_rules
+		 SET minimum = $2, maximum = $3
+		 WHERE id = $1
+		 RETURNING id, address_id, type, threshold, minimum, maximum, enabled, created_at`,
+		id, minimum, maximum,
+	).Scan(&r.ID, &r.AddressID, &r.Type, &r.Threshold, &r.Minimum, &r.Maximum, &r.Enabled, &r.CreatedAt)
+	if err != nil {
+		if errors.Is(err, pgx.ErrNoRows) {
+			return nil, nil
+		}
+		return nil, err
+	}
+	return &r, nil
+}
+
+func (m *AlertRuleModel) CountDistinctTypesByAddress(ctx context.Context, addressID int) (int, error) {
+	var count int
+	err := m.pool.QueryRow(ctx,
+		`SELECT COUNT(DISTINCT type) FROM alert_rules WHERE address_id = $1`,
+		addressID,
+	).Scan(&count)
+	return count, err
+}
+
+func (m *AlertRuleModel) Remove(ctx context.Context, id int) (bool, error) {
+	tag, err := m.pool.Exec(ctx,
+		`DELETE FROM alert_rules WHERE id = $1`,
+		id,
+	)
+	if err != nil {
+		return false, err
+	}
+	return tag.RowsAffected() > 0, nil
+}

backend/internal/models/checkpoint.go

@@ -2,9 +2,12 @@ package models
 
 import (
 	"context"
+	"errors"
+	"time"
 
+	"github.com/jackc/pgx/v5"
 	"github.com/jackc/pgx/v5/pgxpool"
-	"github.com/kjannette/koin-ping/backend-go/internal/domain"
+	"github.com/kjannette/koin-ping/backend/internal/domain"
 )
 
 type CheckpointModel struct {
@@ -15,6 +18,20 @@ func NewCheckpointModel(pool *pgxpool.Pool) *CheckpointModel {
 	return &CheckpointModel{pool: pool}
 }
 
+// GetLatestBlock returns the highest last_checked_block and its timestamp across all addresses.
+// Returns nil, nil, nil when no checkpoints exist yet.
+func (m *CheckpointModel) GetLatestBlock(ctx context.Context) (*int, *time.Time, error) {
+	var block *int
+	var checkedAt *time.Time
+	err := m.pool.QueryRow(ctx,
+		`SELECT MAX(last_checked_block), MAX(last_checked_at) FROM address_checkpoints`,
+	).Scan(&block, &checkedAt)
+	if err != nil {
+		return nil, nil, err
+	}
+	return block, checkedAt, nil
+}
+
 // GetLastCheckedBlock returns the last checked block for an address, or -1 if never checked.
 func (m *CheckpointModel) GetLastCheckedBlock(ctx context.Context, addressID int) (int, bool, error) {
 	var block int
@@ -23,7 +40,7 @@ func (m *CheckpointModel) GetLastCheckedBlock(ctx context.Context, addressID int
 		addressID,
 	).Scan(&block)
 	if err != nil {
-		if err.Error() == "no rows in result set" {
+		if errors.Is(err, pgx.ErrNoRows) {
 			return 0, false, nil
 		}
 		return 0, false, err

backend/internal/models/notification_config.go

@@ -0,0 +1,103 @@
+package models
+
+import (
+	"context"
+	"errors"
+
+	"github.com/jackc/pgx/v5"
+	"github.com/jackc/pgx/v5/pgxpool"
+	"github.com/kjannette/koin-ping/backend/internal/domain"
+)
+
+type NotificationConfigModel struct {
+	pool *pgxpool.Pool
+}
+
+func NewNotificationConfigModel(pool *pgxpool.Pool) *NotificationConfigModel {
+	return &NotificationConfigModel{pool: pool}
+}
+
+func (m *NotificationConfigModel) GetConfig(ctx context.Context, userID string) (*domain.NotificationConfig, error) {
+	var c domain.NotificationConfig
+	err := m.pool.QueryRow(ctx,
+		`SELECT user_id, discord_webhook_url, telegram_chat_id, telegram_bot_token,
+		        email, slack_webhook_url, notification_enabled, created_at, updated_at
+		 FROM user_notification_configs
+		 WHERE user_id = $1`,
+		userID,
+	).Scan(&c.UserID, &c.DiscordWebhookURL, &c.TelegramChatID, &c.TelegramBotToken,
+		&c.Email, &c.SlackWebhookURL, &c.NotificationEnabled, &c.CreatedAt, &c.UpdatedAt)
+	if err != nil {
+		if errors.Is(err, pgx.ErrNoRows) {
+			return nil, nil
+		}
+		return nil, err
+	}
+	return &c, nil
+}
+
+func (m *NotificationConfigModel) UpsertConfig(ctx context.Context, userID string, cfg domain.NotificationConfig) (*domain.NotificationConfig, error) {
+	var c domain.NotificationConfig
+	err := m.pool.QueryRow(ctx,
+		`INSERT INTO user_notification_configs
+		   (user_id, discord_webhook_url, telegram_chat_id, telegram_bot_token,
+		    email, slack_webhook_url, notification_enabled, updated_at)
+		 VALUES ($1, $2, $3, $4, $5, $6, $7, NOW())
+		 ON CONFLICT (user_id)
+		 DO UPDATE SET
+		   discord_webhook_url = $2,
+		   telegram_chat_id = $3,
+		   telegram_bot_token = $4,
+		   email = $5,
+		   slack_webhook_url = $6,
+		   notification_enabled = $7,
+		   updated_at = NOW()
+		 RETURNING user_id, discord_webhook_url, telegram_chat_id, telegram_bot_token,
+		           email, slack_webhook_url, notification_enabled, created_at, updated_at`,
+		userID, cfg.DiscordWebhookURL, cfg.TelegramChatID, cfg.TelegramBotToken,
+		cfg.Email, cfg.SlackWebhookURL, cfg.NotificationEnabled,
+	).Scan(&c.UserID, &c.DiscordWebhookURL, &c.TelegramChatID, &c.TelegramBotToken,
+		&c.Email, &c.SlackWebhookURL, &c.NotificationEnabled, &c.CreatedAt, &c.UpdatedAt)
+	if err != nil {
+		return nil, err
+	}
+	return &c, nil
+}
+
+func (m *NotificationConfigModel) Remove(ctx context.Context, userID string) (bool, error) {
+	tag, err := m.pool.Exec(ctx,
+		`DELETE FROM user_notification_configs WHERE user_id = $1`,
+		userID,
+	)
+	if err != nil {
+		return false, err
+	}
+	return tag.RowsAffected() > 0, nil
+}
+
+func (m *NotificationConfigModel) ListEnabled(ctx context.Context) ([]domain.NotificationConfig, error) {
+	rows, err := m.pool.Query(ctx,
+		`SELECT nc.user_id, nc.discord_webhook_url, nc.telegram_chat_id, nc.telegram_bot_token,
+		        nc.email, nc.slack_webhook_url
+		 FROM user_notification_configs nc
+		 JOIN users u ON u.id = nc.user_id
+		 WHERE nc.notification_enabled = TRUE
+		   AND u.subscription_status IN ('active', 'trialing')`,
+	)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	var configs []domain.NotificationConfig
+	for rows.Next() {
+		var c domain.NotificationConfig
+		if err := rows.Scan(&c.UserID, &c.DiscordWebhookURL, &c.TelegramChatID,
+			&c.TelegramBotToken, &c.Email, &c.SlackWebhookURL); err != nil {
+			return nil, err
+		}
+		c.NotificationEnabled = true
+		configs = append(configs, c)
+	}
+	return configs, rows.Err()
+}

backend/internal/models/user.go

@@ -0,0 +1,111 @@
+package models
+
+import (
+	"context"
+	"errors"
+
+	"github.com/jackc/pgx/v5"
+	"github.com/jackc/pgx/v5/pgxpool"
+	"github.com/kjannette/koin-ping/backend/internal/domain"
+)
+
+type UserModel struct {
+	pool *pgxpool.Pool
+}
+
+func NewUserModel(pool *pgxpool.Pool) *UserModel {
+	return &UserModel{pool: pool}
+}
+
+const userColumns = `id, firebase_uid, email, display_name,
+	stripe_customer_id, stripe_subscription_id, subscription_status,
+	subscription_tier, subscription_created_at, created_at, updated_at`
+
+func scanUser(row pgx.Row) (*domain.User, error) {
+	var u domain.User
+	err := row.Scan(
+		&u.ID, &u.FirebaseUID, &u.Email, &u.DisplayName,
+		&u.StripeCustomerID, &u.StripeSubscriptionID, &u.SubscriptionStatus,
+		&u.SubscriptionTier, &u.SubscriptionCreatedAt, &u.CreatedAt, &u.UpdatedAt,
+	)
+	if err != nil {
+		if errors.Is(err, pgx.ErrNoRows) {
+			return nil, nil //nolint:nilnil
+		}
+		return nil, err
+	}
+	return &u, nil
+}
+
+// FindOrCreateByFirebaseUID returns the local user for a Firebase UID,
+// creating one if it doesn't exist yet. On conflict (returning user) the
+// updated_at timestamp is refreshed.
+func (m *UserModel) FindOrCreateByFirebaseUID(ctx context.Context, firebaseUID, email string) (*domain.User, error) {
+	row := m.pool.QueryRow(ctx,
+		`INSERT INTO users (firebase_uid, email)
+		 VALUES ($1, $2)
+		 ON CONFLICT (firebase_uid) DO UPDATE SET updated_at = NOW()
+		 RETURNING `+userColumns,
+		firebaseUID, email,
+	)
+	return scanUser(row)
+}
+
+func (m *UserModel) GetByID(ctx context.Context, id string) (*domain.User, error) {
+	row := m.pool.QueryRow(ctx,
+		`SELECT `+userColumns+` FROM users WHERE id = $1`, id,
+	)
+	return scanUser(row)
+}
+
+func (m *UserModel) UpdateStripeCustomer(ctx context.Context, userID, stripeCustomerID string) error {
+	_, err := m.pool.Exec(ctx,
+		`UPDATE users SET stripe_customer_id = $2, updated_at = NOW() WHERE id = $1`,
+		userID, stripeCustomerID,
+	)
+	return err
+}
+
+func (m *UserModel) ActivateSubscription(ctx context.Context, stripeCustomerID, subscriptionID, status string, tier domain.SubscriptionTier) error {
+	_, err := m.pool.Exec(ctx,
+		`UPDATE users
+		 SET stripe_subscription_id = $2,
+		     subscription_status = $3,
+		     subscription_tier = $4,
+		     subscription_created_at = COALESCE(subscription_created_at, NOW()),
+		     updated_at = NOW()
+		 WHERE stripe_customer_id = $1`,
+		stripeCustomerID, subscriptionID, status, string(tier),
+	)
+	return err
+}
+
+func (m *UserModel) UpdateSubscriptionTier(ctx context.Context, userID string, tier domain.SubscriptionTier) error {
+	_, err := m.pool.Exec(ctx,
+		`UPDATE users SET subscription_tier = $2, updated_at = NOW() WHERE id = $1`,
+		userID, string(tier),
+	)
+	return err
+}
+
+func (m *UserModel) ActivateFreeTier(ctx context.Context, userID string) error {
+	_, err := m.pool.Exec(ctx,
+		`UPDATE users
+		 SET subscription_status = 'active',
+		     subscription_tier = 'free',
+		     subscription_created_at = COALESCE(subscription_created_at, NOW()),
+		     updated_at = NOW()
+		 WHERE id = $1`,
+		userID,
+	)
+	return err
+}
+
+func (m *UserModel) UpdateSubscriptionStatus(ctx context.Context, stripeCustomerID, status string) error {
+	_, err := m.pool.Exec(ctx,
+		`UPDATE users SET subscription_status = $2, updated_at = NOW()
+		 WHERE stripe_customer_id = $1`,
+		stripeCustomerID, status,
+	)
+	return err
+}

backend/internal/notifications/discord.go

@@ -2,6 +2,7 @@ package notifications
 
 import (
 	"bytes"
+	"context"
 	"encoding/json"
 	"fmt"
 	"log"
@@ -9,11 +10,28 @@ import (
 	"time"
 )
 
-type AlertMetadata struct {
-	TxHash       string
-	AddressLabel string
-	AlertType    string
-	Address      string
+const (
+	// discordHTTPTimeoutSeconds is the timeout for Discord webhook requests.
+	discordHTTPTimeoutSeconds = 10
+
+	// Alert color codes for Discord embeds.
+	colorGreen  = 0x00ff00
+	colorOrange = 0xff9900
+	colorRed    = 0xff0000
+	colorBlue   = 0x0099ff
+)
+
+var discordHTTPClient = &http.Client{ //nolint:gochecknoglobals
+	Timeout: discordHTTPTimeoutSeconds * time.Second,
+}
+
+//  sends alert notifications via a Discord webhook.
+type DiscordNotifier struct {
+	WebhookURL string
+}
+func (d *DiscordNotifier) Send(_ context.Context, message string, meta AlertMetadata) error {
+	_, err := SendDiscordNotification(d.WebhookURL, message, meta)
+	return err
 }
 
 type discordEmbed struct {
@@ -73,7 +91,9 @@ func SendDiscordNotification(webhookURL, message string, meta AlertMetadata) (bo
 		return false, fmt.Errorf("marshal discord payload: %w", err)
 	}
 
-	resp, err := http.Post(webhookURL, "application/json", bytes.NewReader(body))
+	resp, err := discordHTTPClient.Post(
+		webhookURL, "application/json", bytes.NewReader(body),
+	)
 	if err != nil {
 		log.Printf("Failed to send Discord notification: %v", err)
 		return false, err
@@ -81,8 +101,12 @@ func SendDiscordNotification(webhookURL, message string, meta AlertMetadata) (bo
 	defer resp.Body.Close()
 
 	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
+		err := fmt.Errorf("discord webhook failed: HTTP %d", resp.StatusCode)
 		log.Printf("Discord webhook failed: HTTP %d", resp.StatusCode)
-		return false, fmt.Errorf("discord webhook failed: HTTP %d", resp.StatusCode)
+		if isPermanentStatusCode(resp.StatusCode) {
+			return false, &PermanentError{Err: err}
+		}
+		return false, err
 	}
 
 	return true, nil
@@ -98,7 +122,9 @@ func TestDiscordWebhook(webhookURL string) (bool, error) {
 		return false, err
 	}
 
-	resp, err := http.Post(webhookURL, "application/json", bytes.NewReader(body))
+	resp, err := discordHTTPClient.Post(
+		webhookURL, "application/json", bytes.NewReader(body),
+	)
 	if err != nil {
 		log.Printf("Discord webhook test failed: %v", err)
 		return false, err
@@ -111,14 +137,14 @@ func TestDiscordWebhook(webhookURL string) (bool, error) {
 func colorForAlertType(alertType string) int {
 	switch alertType {
 	case "incoming_tx":
-		return 0x00ff00 // Green
+		return colorGreen
 	case "outgoing_tx":
-		return 0xff9900 // Orange
+		return colorOrange
 	case "large_transfer":
-		return 0xff0000 // Red
+		return colorRed
 	case "balance_below":
-		return 0xff0000 // Red
+		return colorRed
 	default:
-		return 0x0099ff // Blue
+		return colorBlue
 	}
 }

backend/internal/notifications/email.go

@@ -0,0 +1,158 @@
+package notifications
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"log"
+	"net/http"
+	"time"
+)
+
+type EmailNotifier struct {
+	APIKey string
+	From   string
+	To     string
+}
+
+func (e *EmailNotifier) Send(_ context.Context, message string, meta AlertMetadata) error {
+	_, err := SendEmailNotification(e.APIKey, e.From, e.To, message, meta)
+	return err
+}
+
+const emailHTTPTimeoutSeconds = 10
+
+var emailHTTPClient = &http.Client{ //nolint:gochecknoglobals
+	Timeout: emailHTTPTimeoutSeconds * time.Second,
+}
+
+type resendPayload struct {
+	From    string `json:"from"`
+	To      string `json:"to"`
+	Subject string `json:"subject"`
+	HTML    string `json:"html"`
+}
+
+func SendEmailNotification(apiKey, fromAddress, toAddress, message string, meta AlertMetadata) (bool, error) {
+	if apiKey == "" {
+		log.Printf("Skipping email notification: RESEND_API_KEY not configured")
+		return false, nil
+	}
+
+	subject := fmt.Sprintf("Koin Ping Alert: %s", alertTypeLabel(meta.AlertType))
+
+	txLink := ""
+	if meta.TxHash != "" {
+		txLink = fmt.Sprintf(
+			`<p><a href="https://etherscan.io/tx/%s">View on Etherscan</a></p>`,
+			meta.TxHash,
+		)
+	}
+
+	html := fmt.Sprintf(`
+<div style="font-family: sans-serif; max-width: 600px; margin: 0 auto;">
+  <h2 style="color: #333;">Koin Ping Alert</h2>
+  <p style="font-size: 16px;">%s</p>
+  <table style="margin: 16px 0; border-collapse: collapse;">
+    <tr>
+      <td style="padding: 4px 12px 4px 0; color: #666;">Address</td>
+      <td style="padding: 4px 0;">%s</td>
+    </tr>
+    <tr>
+      <td style="padding: 4px 12px 4px 0; color: #666;">Blockchain</td>
+      <td style="padding: 4px 0; font-family: monospace; font-size: 13px;">%s</td>
+    </tr>
+  </table>
+  %s
+  <hr style="border: none; border-top: 1px solid #eee; margin: 24px 0;" />
+  <p style="font-size: 12px; color: #999;">Sent by Koin Ping</p>
+</div>`,
+		message, meta.AddressLabel, meta.Address, txLink)
+
+	payload := resendPayload{
+		From:    fromAddress,
+		To:      toAddress,
+		Subject: subject,
+		HTML:    html,
+	}
+
+	body, err := json.Marshal(payload)
+	if err != nil {
+		return false, fmt.Errorf("marshal email payload: %w", err)
+	}
+
+	req, err := http.NewRequest(http.MethodPost, "https://api.resend.com/emails", bytes.NewReader(body))
+	if err != nil {
+		return false, fmt.Errorf("create email request: %w", err)
+	}
+	req.Header.Set("Content-Type", "application/json")
+	req.Header.Set("Authorization", "Bearer "+apiKey)
+
+	resp, err := emailHTTPClient.Do(req)
+	if err != nil {
+		log.Printf("Failed to send email notification: %v", err)
+		return false, err
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
+		err := fmt.Errorf("resend API failed: HTTP %d", resp.StatusCode)
+		log.Printf("Resend API failed: HTTP %d", resp.StatusCode)
+		if isPermanentStatusCode(resp.StatusCode) {
+			return false, &PermanentError{Err: err}
+		}
+		return false, err
+	}
+
+	return true, nil
+}
+
+func TestEmailNotification(apiKey, fromAddress, toAddress string) (bool, error) {
+	if apiKey == "" {
+		return false, fmt.Errorf("email not configured: RESEND_API_KEY not set") //nolint:err113
+	}
+
+	payload := resendPayload{
+		From:    fromAddress,
+		To:      toAddress,
+		Subject: "Koin Ping — Test Notification",
+		HTML:    `<p>Your email alerts are configured correctly!</p><p style="font-size:12px;color:#999;">Sent by Koin Ping</p>`,
+	}
+
+	body, err := json.Marshal(payload)
+	if err != nil {
+		return false, err
+	}
+
+	req, err := http.NewRequest(http.MethodPost, "https://api.resend.com/emails", bytes.NewReader(body))
+	if err != nil {
+		return false, err
+	}
+	req.Header.Set("Content-Type", "application/json")
+	req.Header.Set("Authorization", "Bearer "+apiKey)
+
+	resp, err := emailHTTPClient.Do(req)
+	if err != nil {
+		log.Printf("Email test failed: %v", err)
+		return false, err
+	}
+	defer resp.Body.Close()
+
+	return resp.StatusCode >= 200 && resp.StatusCode < 300, nil
+}
+
+func alertTypeLabel(alertType string) string {
+	switch alertType {
+	case "incoming_tx":
+		return "Incoming Transaction"
+	case "outgoing_tx":
+		return "Outgoing Transaction"
+	case "large_transfer":
+		return "Large Transfer"
+	case "balance_below":
+		return "Balance Below Threshold"
+	default:
+		return "Alert"
+	}
+}

backend/internal/notifications/notifier.go

@@ -0,0 +1,38 @@
+package notifications
+
+import (
+	"context"
+	"errors"
+	"net/http"
+)
+
+// AlertMetadata holds context about the alert being sent.
+type AlertMetadata struct {
+	TxHash       string
+	AddressLabel string
+	AlertType    string
+	Address      string
+}
+
+type Notifier interface {
+	Send(ctx context.Context, message string, meta AlertMetadata) error
+}
+
+// PermanentError wraps errors that should not be retried (e.g. 401, 403, 404).
+type PermanentError struct{ Err error }
+
+func (e *PermanentError) Error() string { return e.Err.Error() }
+func (e *PermanentError) Unwrap() error { return e.Err }
+
+func IsPermanent(err error) bool {
+	var p *PermanentError
+	return errors.As(err, &p)
+}
+
+func isPermanentStatusCode(code int) bool {
+	return code == http.StatusUnauthorized ||
+		code == http.StatusForbidden ||
+		code == http.StatusNotFound ||
+		code == http.StatusMethodNotAllowed ||
+		code == http.StatusGone
+}

backend/internal/notifications/slack.go

@@ -0,0 +1,132 @@
+package notifications
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"log"
+	"net/http"
+	"time"
+)
+
+// SlackNotifier sends alert notifications via a Slack webhook.
+type SlackNotifier struct {
+	WebhookURL string
+}
+
+// Send implements Notifier for Slack.
+func (s *SlackNotifier) Send(_ context.Context, message string, meta AlertMetadata) error {
+	_, err := SendSlackNotification(s.WebhookURL, message, meta)
+	return err
+}
+
+const slackHTTPTimeoutSeconds = 10
+
+var slackHTTPClient = &http.Client{ //nolint:gochecknoglobals
+	Timeout: slackHTTPTimeoutSeconds * time.Second,
+}
+
+type slackAttachment struct {
+	Color  string        `json:"color"`
+	Title  string        `json:"title"`
+	Text   string        `json:"text"`
+	Fields []slackField  `json:"fields"`
+	Footer string        `json:"footer"`
+	Ts     int64         `json:"ts"`
+}
+
+type slackField struct {
+	Title string `json:"title"`
+	Value string `json:"value"`
+	Short bool   `json:"short"`
+}
+
+type slackPayload struct {
+	Text        string            `json:"text,omitempty"`
+	Attachments []slackAttachment `json:"attachments,omitempty"`
+}
+
+func SendSlackNotification(webhookURL, message string, meta AlertMetadata) (bool, error) {
+	fields := []slackField{
+		{Title: "Address", Value: meta.AddressLabel, Short: true},
+		{Title: "Blockchain Address", Value: fmt.Sprintf("`%s`", meta.Address), Short: false},
+	}
+
+	if meta.TxHash != "" {
+		fields = append(fields, slackField{
+			Title: "Transaction",
+			Value: fmt.Sprintf("<https://etherscan.io/tx/%s|View on Etherscan>", meta.TxHash),
+			Short: false,
+		})
+	}
+
+	payload := slackPayload{
+		Attachments: []slackAttachment{
+			{
+				Color:  slackColorForAlertType(meta.AlertType),
+				Title:  "Koin Ping Alert",
+				Text:   message,
+				Fields: fields,
+				Footer: "Koin Ping",
+				Ts:     time.Now().Unix(),
+			},
+		},
+	}
+
+	body, err := json.Marshal(payload)
+	if err != nil {
+		return false, fmt.Errorf("marshal slack payload: %w", err)
+	}
+
+	resp, err := slackHTTPClient.Post(webhookURL, "application/json", bytes.NewReader(body))
+	if err != nil {
+		log.Printf("Failed to send Slack notification: %v", err)
+		return false, err
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
+		err := fmt.Errorf("slack webhook failed: HTTP %d", resp.StatusCode)
+		log.Printf("Slack webhook failed: HTTP %d", resp.StatusCode)
+		if isPermanentStatusCode(resp.StatusCode) {
+			return false, &PermanentError{Err: err}
+		}
+		return false, err
+	}
+
+	return true, nil
+}
+
+func TestSlackWebhook(webhookURL string) (bool, error) {
+	payload := slackPayload{
+		Text: "Koin Ping test notification — Your Slack alerts are configured correctly!",
+	}
+
+	body, err := json.Marshal(payload)
+	if err != nil {
+		return false, err
+	}
+
+	resp, err := slackHTTPClient.Post(webhookURL, "application/json", bytes.NewReader(body))
+	if err != nil {
+		log.Printf("Slack webhook test failed: %v", err)
+		return false, err
+	}
+	defer resp.Body.Close()
+
+	return resp.StatusCode >= 200 && resp.StatusCode < 300, nil
+}
+
+func slackColorForAlertType(alertType string) string {
+	switch alertType {
+	case "incoming_tx":
+		return "#00ff00"
+	case "outgoing_tx":
+		return "#ff9900"
+	case "large_transfer", "balance_below":
+		return "#ff0000"
+	default:
+		return "#0099ff"
+	}
+}

backend/internal/notifications/telegram.go

@@ -0,0 +1,126 @@
+package notifications
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"log"
+	"net/http"
+	"time"
+)
+
+// TelegramNotifier sends alert notifications via Telegram.
+type TelegramNotifier struct {
+	BotToken string
+	ChatID   string
+}
+
+// Send implements Notifier for Telegram.
+func (t *TelegramNotifier) Send(_ context.Context, message string, meta AlertMetadata) error {
+	_, err := SendTelegramNotification(t.BotToken, t.ChatID, message, meta)
+	return err
+}
+
+const telegramHTTPTimeoutSeconds = 10
+
+var telegramHTTPClient = &http.Client{ //nolint:gochecknoglobals
+	Timeout: telegramHTTPTimeoutSeconds * time.Second,
+}
+
+type telegramPayload struct {
+	ChatID    string `json:"chat_id"`
+	Text      string `json:"text"`
+	ParseMode string `json:"parse_mode"`
+}
+
+func SendTelegramNotification(botToken, chatID, message string, meta AlertMetadata) (bool, error) {
+	text := fmt.Sprintf("*Koin Ping Alert*\n\n%s\n\n*Address:* %s\n`%s`",
+		escapeMarkdown(message), escapeMarkdown(meta.AddressLabel), meta.Address)
+
+	if meta.TxHash != "" {
+		text += fmt.Sprintf("\n\n[View on Etherscan](https://etherscan.io/tx/%s)", meta.TxHash)
+	}
+
+	payload := telegramPayload{
+		ChatID:    chatID,
+		Text:      text,
+		ParseMode: "Markdown",
+	}
+
+	body, err := json.Marshal(payload)
+	if err != nil {
+		return false, fmt.Errorf("marshal telegram payload: %w", err)
+	}
+
+	url := fmt.Sprintf("https://api.telegram.org/bot%s/sendMessage", botToken)
+
+	resp, err := telegramHTTPClient.Post(url, "application/json", bytes.NewReader(body))
+	if err != nil {
+		log.Printf("Failed to send Telegram notification: %v", err)
+		return false, err
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
+		err := fmt.Errorf("telegram API failed: HTTP %d", resp.StatusCode)
+		log.Printf("Telegram API failed: HTTP %d", resp.StatusCode)
+		if isPermanentStatusCode(resp.StatusCode) {
+			return false, &PermanentError{Err: err}
+		}
+		return false, err
+	}
+
+	return true, nil
+}
+
+func TestTelegramWebhook(botToken, chatID string) (bool, error) {
+	payload := telegramPayload{
+		ChatID:    chatID,
+		Text:      "Koin Ping test notification — Your Telegram alerts are configured correctly!",
+		ParseMode: "Markdown",
+	}
+
+	body, err := json.Marshal(payload)
+	if err != nil {
+		return false, err
+	}
+
+	url := fmt.Sprintf("https://api.telegram.org/bot%s/sendMessage", botToken)
+
+	resp, err := telegramHTTPClient.Post(url, "application/json", bytes.NewReader(body))
+	if err != nil {
+		log.Printf("Telegram test failed: %v", err)
+		return false, err
+	}
+	defer resp.Body.Close()
+
+	return resp.StatusCode >= 200 && resp.StatusCode < 300, nil
+}
+
+func escapeMarkdown(s string) string {
+	replacer := []struct{ old, new string }{
+		{"_", "\\_"}, {"*", "\\*"}, {"[", "\\["}, {"]", "\\]"},
+		{"(", "\\("}, {")", "\\)"}, {"~", "\\~"}, {"`", "\\`"},
+		{">", "\\>"}, {"#", "\\#"}, {"+", "\\+"}, {"-", "\\-"},
+		{"=", "\\="}, {"|", "\\|"}, {"{", "\\{"}, {"}", "\\}"},
+		{".", "\\."}, {"!", "\\!"},
+	}
+	result := s
+	for _, r := range replacer {
+		result = replaceAll(result, r.old, r.new)
+	}
+	return result
+}
+
+func replaceAll(s, old, new string) string {
+	out := ""
+	for i := 0; i < len(s); i++ {
+		if string(s[i]) == old {
+			out += new
+		} else {
+			out += string(s[i])
+		}
+	}
+	return out
+}

backend/internal/protocols/ethereum/jsonrpc.go

@@ -0,0 +1,421 @@
+package ethereum
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"log"
+	"math/big"
+	"net/http"
+	"strings"
+	"time"
+
+	"github.com/kjannette/koin-ping/backend/internal/domain"
+)
+
+const (
+	rpcTimeoutMS      = 30000
+	rpcMaxRetries     = 3
+	rpcRetryBaseMS    = 2000
+	rpcMinIntervalMS  = 1000
+)
+
+type JsonRpcEthereum struct {
+	rpcURL     string
+	client     *http.Client
+	lastCallAt time.Time
+}
+
+func NewJsonRpcEthereum(rpcURL string) (*JsonRpcEthereum, error) {
+	if rpcURL == "" {
+		return nil, fmt.Errorf("JsonRpcEthereum requires a valid RPC URL")
+	}
+	return &JsonRpcEthereum{
+		rpcURL: rpcURL,
+		client: &http.Client{
+			Timeout: time.Duration(rpcTimeoutMS) * time.Millisecond,
+		},
+	}, nil
+}
+
+type rpcRequest struct {
+	JSONRPC string        `json:"jsonrpc"`
+	ID      int64         `json:"id"`
+	Method  string        `json:"method"`
+	Params  []interface{} `json:"params"`
+}
+
+type rpcResponse struct {
+	JSONRPC string          `json:"jsonrpc"`
+	ID      int64           `json:"id"`
+	Result  json.RawMessage `json:"result"`
+	Error   *rpcError       `json:"error"`
+}
+
+type rpcError struct {
+	Code    int    `json:"code"`
+	Message string `json:"message"`
+}
+
+func (j *JsonRpcEthereum) callRPC(ctx context.Context, method string, params ...interface{}) (json.RawMessage, error) {
+	j.throttle(ctx)
+
+	if params == nil {
+		params = []interface{}{}
+	}
+
+	body, err := json.Marshal(rpcRequest{
+		JSONRPC: "2.0",
+		ID:      time.Now().UnixMilli(),
+		Method:  method,
+		Params:  params,
+	})
+	if err != nil {
+		return nil, fmt.Errorf("marshal RPC request: %w", err)
+	}
+
+	result, callErr := j.callWithRetry(ctx, method, body)
+	j.lastCallAt = time.Now()
+
+	return result, callErr
+}
+
+func (j *JsonRpcEthereum) throttle(ctx context.Context) {
+	if j.lastCallAt.IsZero() {
+		return
+	}
+	minInterval := time.Duration(rpcMinIntervalMS) * time.Millisecond
+	elapsed := time.Since(j.lastCallAt)
+	if elapsed >= minInterval {
+		return
+	}
+	select {
+	case <-ctx.Done():
+	case <-time.After(minInterval - elapsed):
+	}
+}
+
+// callWithRetry executes a JSON-RPC POST with exponential backoff on transient errors.
+// It retries on network errors, HTTP 429, and HTTP 5xx. It does NOT retry on RPC-level
+// errors or other 4xx responses (those are permanent failures).
+func (j *JsonRpcEthereum) callWithRetry(ctx context.Context, method string, body []byte) (json.RawMessage, error) {
+	var lastErr error
+	for attempt := range rpcMaxRetries {
+		if attempt > 0 {
+			wait := time.Duration(rpcRetryBaseMS*(1<<(attempt-1))) * time.Millisecond
+			select {
+			case <-ctx.Done():
+				return nil, ctx.Err()
+			case <-time.After(wait):
+			}
+			log.Printf("Retrying RPC call [%s] (attempt %d/%d)", method, attempt+1, rpcMaxRetries)
+		}
+
+		result, err := j.doRPCCall(ctx, method, body)
+		if err == nil {
+			return result, nil
+		}
+
+		lastErr = err
+
+		// Permanent errors: do not retry
+		if isPermanentRPCError(err) {
+			return nil, err
+		}
+
+		log.Printf("Transient RPC error [%s] (attempt %d/%d): %v", method, attempt+1, rpcMaxRetries, err)
+	}
+
+	return nil, lastErr
+}
+
+func (j *JsonRpcEthereum) doRPCCall(ctx context.Context, method string, body []byte) (json.RawMessage, error) {
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, j.rpcURL, bytes.NewReader(body))
+	if err != nil {
+		return nil, fmt.Errorf("create RPC request: %w", err)
+	}
+	req.Header.Set("Content-Type", "application/json")
+
+	resp, err := j.client.Do(req)
+	if err != nil {
+		return nil, fmt.Errorf("RPC call failed [%s]: %w", method, err)
+	}
+	defer resp.Body.Close()
+
+	// 429 and 5xx are transient; other non-200 are permanent.
+	if resp.StatusCode != http.StatusOK {
+		err := fmt.Errorf("HTTP %d: %s for %s", resp.StatusCode, resp.Status, method)
+		if resp.StatusCode == http.StatusTooManyRequests || resp.StatusCode >= 500 { //nolint:mnd
+			return nil, err // transient — will be retried
+		}
+		return nil, &permanentRPCError{err}
+	}
+
+	var rpcResp rpcResponse
+	if err := json.NewDecoder(resp.Body).Decode(&rpcResp); err != nil {
+		return nil, fmt.Errorf("decode RPC response: %w", err)
+	}
+
+	if rpcResp.Error != nil {
+		// RPC-level errors are permanent (bad params, unsupported method, etc.)
+		return nil, &permanentRPCError{
+			fmt.Errorf("RPC Error [%s]: %s (code: %d)", method, rpcResp.Error.Message, rpcResp.Error.Code),
+		}
+	}
+
+	return rpcResp.Result, nil
+}
+
+type permanentRPCError struct{ cause error }
+
+func (e *permanentRPCError) Error() string { return e.cause.Error() }
+func (e *permanentRPCError) Unwrap() error { return e.cause }
+
+func isPermanentRPCError(err error) bool {
+	var p *permanentRPCError
+	return errors.As(err, &p)
+}
+
+func (j *JsonRpcEthereum) GetLatestBlockNumber(ctx context.Context) (int, error) {
+	result, err := j.callRPC(ctx, "eth_blockNumber")
+	if err != nil {
+		return 0, err
+	}
+
+	var hexBlock string
+	if err := json.Unmarshal(result, &hexBlock); err != nil {
+		return 0, fmt.Errorf("unmarshal block number: %w", err)
+	}
+
+	return hexToInt(hexBlock)
+}
+
+type rpcBlock struct {
+	Timestamp    string  `json:"timestamp"`
+	Transactions []rpcTx `json:"transactions"`
+}
+
+type rpcTx struct {
+	Hash        string  `json:"hash"`
+	From        string  `json:"from"`
+	To          *string `json:"to"`
+	Value       string  `json:"value"`
+	BlockNumber string  `json:"blockNumber"`
+}
+
+func (j *JsonRpcEthereum) GetBlockTransactions(ctx context.Context, blockNumber int) ([]domain.NormalizedTx, error) {
+	hexBlock := fmt.Sprintf("0x%x", blockNumber)
+
+	result, err := j.callRPC(ctx, "eth_getBlockByNumber", hexBlock, true)
+	if err != nil {
+		return nil, err
+	}
+
+	if string(result) == "null" {
+		return nil, nil
+	}
+
+	var block rpcBlock
+	if err := json.Unmarshal(result, &block); err != nil {
+		return nil, fmt.Errorf("unmarshal block: %w", err)
+	}
+
+	blockTimestamp, err := hexToInt64(block.Timestamp)
+	if err != nil {
+		return nil, fmt.Errorf("parse block timestamp: %w", err)
+	}
+
+	txs := make([]domain.NormalizedTx, 0, len(block.Transactions))
+	for _, tx := range block.Transactions {
+		bn, _ := hexToInt(tx.BlockNumber)
+
+		var toLower *string
+		if tx.To != nil {
+			s := strings.ToLower(*tx.To)
+			toLower = &s
+		}
+
+		txs = append(txs, domain.NormalizedTx{
+			Hash:           tx.Hash,
+			From:           strings.ToLower(tx.From),
+			To:             toLower,
+			Value:          hexToDecimalString(tx.Value),
+			BlockNumber:    bn,
+			BlockTimestamp: blockTimestamp,
+		})
+	}
+
+	return txs, nil
+}
+
+func (j *JsonRpcEthereum) GetBalance(ctx context.Context, address string) (string, error) {
+	result, err := j.callRPC(ctx, "eth_getBalance", address, "latest")
+	if err != nil {
+		return "", err
+	}
+
+	var hexBalance string
+	if err := json.Unmarshal(result, &hexBalance); err != nil {
+		return "", fmt.Errorf("unmarshal balance: %w", err)
+	}
+
+	return hexToDecimalString(hexBalance), nil
+}
+
+const erc20TransferTopic = "0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef"
+
+const minTransferTopics = 3
+
+type rpcLog struct {
+	Address     string   `json:"address"`
+	Topics      []string `json:"topics"`
+	Data        string   `json:"data"`
+	BlockNumber string   `json:"blockNumber"`
+	TxHash      string   `json:"transactionHash"`
+}
+
+// GetTokenTransfers fetches ERC-20 Transfer events for a given address
+// across a block range, covering both incoming and outgoing transfers.
+func (j *JsonRpcEthereum) GetTokenTransfers(ctx context.Context, fromBlock, toBlock int, address string) ([]domain.NormalizedTx, error) {
+	paddedAddr := padAddress(address)
+	hexFrom := fmt.Sprintf("0x%x", fromBlock)
+	hexTo := fmt.Sprintf("0x%x", toBlock)
+
+	incomingLogs, err := j.getTransferLogs(ctx, hexFrom, hexTo, "", paddedAddr)
+	if err != nil {
+		return nil, fmt.Errorf("fetch incoming token transfers: %w", err)
+	}
+
+	outgoingLogs, err := j.getTransferLogs(ctx, hexFrom, hexTo, paddedAddr, "")
+	if err != nil {
+		return nil, fmt.Errorf("fetch outgoing token transfers: %w", err)
+	}
+
+	seen := make(map[string]bool)
+	var txs []domain.NormalizedTx
+
+	for _, entry := range append(incomingLogs, outgoingLogs...) {
+		key := entry.TxHash + "|" + entry.Address + "|" + entry.Data
+		if seen[key] {
+			continue
+		}
+		seen[key] = true
+
+		tx, parseErr := parseTransferLog(entry)
+		if parseErr != nil {
+			log.Printf("Skipping unparseable transfer log in tx %s: %v", entry.TxHash, parseErr)
+			continue
+		}
+		txs = append(txs, tx)
+	}
+
+	return txs, nil
+}
+
+func (j *JsonRpcEthereum) getTransferLogs(ctx context.Context, fromBlock, toBlock, fromAddr, toAddr string) ([]rpcLog, error) {
+	topics := make([]interface{}, minTransferTopics)
+	topics[0] = erc20TransferTopic
+
+	if fromAddr != "" {
+		topics[1] = fromAddr
+	}
+	if toAddr != "" {
+		topics[2] = toAddr
+	}
+
+	filter := map[string]interface{}{
+		"fromBlock": fromBlock,
+		"toBlock":   toBlock,
+		"topics":    topics,
+	}
+
+	result, err := j.callRPC(ctx, "eth_getLogs", filter)
+	if err != nil {
+		return nil, err
+	}
+
+	var logs []rpcLog
+	if err := json.Unmarshal(result, &logs); err != nil {
+		return nil, fmt.Errorf("unmarshal logs: %w", err)
+	}
+
+	return logs, nil
+}
+
+func parseTransferLog(entry rpcLog) (domain.NormalizedTx, error) {
+	if len(entry.Topics) < minTransferTopics {
+		return domain.NormalizedTx{}, fmt.Errorf("transfer log has %d topics, expected >= 3", len(entry.Topics))
+	}
+
+	from := topicToAddress(entry.Topics[1])
+	to := topicToAddress(entry.Topics[2])
+	tokenValue := hexToDecimalString(entry.Data)
+	blockNumber, _ := hexToInt(entry.BlockNumber)
+
+	contractAddr := strings.ToLower(entry.Address)
+	tokenInfo, known := LookupToken(contractAddr)
+
+	tx := domain.NormalizedTx{
+		Hash:          entry.TxHash,
+		From:          from,
+		To:            &to,
+		Value:         "0",
+		BlockNumber:   blockNumber,
+		TokenContract: &contractAddr,
+		TokenValue:    &tokenValue,
+	}
+
+	if known {
+		tx.TokenSymbol = &tokenInfo.Symbol
+		tx.TokenDecimals = &tokenInfo.Decimals
+	}
+
+	return tx, nil
+}
+
+func padAddress(addr string) string {
+	clean := strings.TrimPrefix(strings.ToLower(addr), "0x")
+	const addressHexLen = 64
+	return "0x" + strings.Repeat("0", addressHexLen-len(clean)) + clean
+}
+
+func topicToAddress(topic string) string {
+	clean := strings.TrimPrefix(topic, "0x")
+	const ethAddrLen = 40
+	if len(clean) > ethAddrLen {
+		clean = clean[len(clean)-ethAddrLen:]
+	}
+	return "0x" + strings.ToLower(clean)
+}
+
+func hexToInt(hex string) (int, error) {
+	hex = strings.TrimPrefix(hex, "0x")
+	n, ok := new(big.Int).SetString(hex, 16)
+	if !ok {
+		return 0, fmt.Errorf("invalid hex: %s", hex)
+	}
+	return int(n.Int64()), nil
+}
+
+func hexToInt64(hex string) (int64, error) {
+	hex = strings.TrimPrefix(hex, "0x")
+	n, ok := new(big.Int).SetString(hex, 16)
+	if !ok {
+		return 0, fmt.Errorf("invalid hex: %s", hex)
+	}
+	return n.Int64(), nil
+}
+
+func hexToDecimalString(hex string) string {
+	if hex == "" || hex == "0x" || hex == "0x0" {
+		return "0"
+	}
+	clean := strings.TrimPrefix(hex, "0x")
+	n, ok := new(big.Int).SetString(clean, 16)
+	if !ok {
+		return "0"
+	}
+	return n.String()
+}

backend/internal/protocols/ethereum/observer.go

@@ -3,7 +3,7 @@ package ethereum
 import (
 	"context"
 
-	"github.com/kjannette/koin-ping/backend-go/internal/domain"
+	"github.com/kjannette/koin-ping/backend/internal/domain"
 )
 
 // EthereumObserver defines the interface for blockchain interaction.
@@ -12,4 +12,5 @@ type EthereumObserver interface {
 	GetLatestBlockNumber(ctx context.Context) (int, error)
 	GetBlockTransactions(ctx context.Context, blockNumber int) ([]domain.NormalizedTx, error)
 	GetBalance(ctx context.Context, address string) (string, error)
+	GetTokenTransfers(ctx context.Context, fromBlock, toBlock int, address string) ([]domain.NormalizedTx, error)
 }

backend/internal/protocols/ethereum/tokens.go

@@ -0,0 +1,34 @@
+package ethereum
+
+import "strings"
+
+// TokenInfo holds metadata for a known ERC-20 token contract.
+type TokenInfo struct {
+	Symbol   string
+	Decimals int
+}
+
+//nolint:gochecknoglobals
+var wellKnownTokens = map[string]TokenInfo{
+	"0xdac17f958d2ee523a2206206994597c13d831ec7": {Symbol: "USDT", Decimals: 6},
+	"0xa0b86991c6218b36c1d19d4a2e9eb0ce3606eb48": {Symbol: "USDC", Decimals: 6},
+	"0x6b175474e89094c44da98b954eedeac495271d0f": {Symbol: "DAI", Decimals: 18},
+	"0xc02aaa39b223fe8d0a0e5c4f27ead9083c756cc2": {Symbol: "WETH", Decimals: 18},
+	"0x2260fac5e5542a773aa44fbcfedf7c193bc2c599": {Symbol: "WBTC", Decimals: 8},
+	"0x514910771af9ca656af840dff83e8264ecf986ca": {Symbol: "LINK", Decimals: 18},
+	"0x1f9840a85d5af5bf1d1762f925bdaddc4201f984": {Symbol: "UNI", Decimals: 18},
+	"0x7fc66500c84a76ad7e9c93437bfc5ac33e2ddae9": {Symbol: "AAVE", Decimals: 18},
+	"0x95ad61b0a150d79219dcf64e1e6cc01f0b64c4ce": {Symbol: "SHIB", Decimals: 18},
+	"0x6982508145454ce325ddbe47a25d4ec3d2311933": {Symbol: "PEPE", Decimals: 18},
+	"0xb8c77482e45f1f44de1745f52c74426c631bdd52": {Symbol: "BNB", Decimals: 18},
+	"0x4fabb145d64652a948d72533023f6e7a623c7c53": {Symbol: "BUSD", Decimals: 18},
+	"0x75231f58b43240c9718dd58b4967c5114342a86c": {Symbol: "OKB", Decimals: 18},
+	"0x582d872a1b094fc48f5de31d3b73f2d9be47def1": {Symbol: "TON", Decimals: 9},
+	"0x4d224452801aced8b2f0aebe155379bb5d594381": {Symbol: "APE", Decimals: 18},
+}
+
+// LookupToken returns metadata for a known token contract, if found.
+func LookupToken(contractAddress string) (TokenInfo, bool) {
+	info, ok := wellKnownTokens[strings.ToLower(contractAddress)]
+	return info, ok
+}

backend/internal/services/email_digest.go

@@ -0,0 +1,196 @@
+package services
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"log"
+	"net/http"
+	"time"
+
+	"github.com/kjannette/koin-ping/backend/internal/models"
+)
+
+const (
+	resendAPIURL          = "https://api.resend.com/emails"
+	emailHTTPTimeout      = 10 * time.Second
+	defaultDigestMaxItems = 50
+)
+
+var digestHTTPClient = &http.Client{Timeout: emailHTTPTimeout} //nolint:gochecknoglobals
+
+// handles email setup and digest sending via Resend.
+type EmailDigestService struct {
+	apiKey      string
+	fromAddress string
+	alertEvents *models.AlertEventModel
+	notifCfgs   *models.NotificationConfigModel
+}
+
+func NewEmailDigestService(
+	apiKey, fromAddress string,
+	alertEvents *models.AlertEventModel,
+	notifCfgs *models.NotificationConfigModel,
+) *EmailDigestService {
+	return &EmailDigestService{
+		apiKey:      apiKey,
+		fromAddress: fromAddress,
+		alertEvents: alertEvents,
+		notifCfgs:   notifCfgs,
+	}
+}
+
+// Configured returns true when the Resend API key is present.
+func (s *EmailDigestService) Configured() bool {
+	return s.apiKey != ""
+}
+
+// SetupEmail validates the email works by sending a welcome/confirmation
+// message via Resend. Called when a user saves their email in notification settings.
+func (s *EmailDigestService) SetupEmail(toAddress string) error {
+	if !s.Configured() {
+		return fmt.Errorf("email service not configured: RESEND_API_KEY not set") //nolint:err113
+	}
+
+	html := `
+<div style="font-family: sans-serif; max-width: 600px; margin: 0 auto;">
+  <h2 style="color: #333;">Welcome to Koin Ping Email Alerts</h2>
+  <p>Your email has been successfully configured for alert notifications.</p>
+  <p>You will receive alert digests at this address when events are triggered
+     on your watched addresses.</p>
+  <hr style="border: none; border-top: 1px solid #eee; margin: 24px 0;" />
+  <p style="font-size: 12px; color: #999;">Sent by Koin Ping</p>
+</div>`
+
+	return s.send(toAddress, "Koin Ping — Email Alerts Configured", html)
+}
+
+func (s *EmailDigestService) SendDigest(ctx context.Context, userID, toAddress string) error {
+	if !s.Configured() {
+		return fmt.Errorf("email service not configured: RESEND_API_KEY not set") //nolint:err113
+	}
+
+	events, err := s.alertEvents.ListRecentByUser(ctx, userID, defaultDigestMaxItems)
+	if err != nil {
+		return fmt.Errorf("fetch alert events: %w", err)
+	}
+
+	if len(events) == 0 {
+		log.Printf("No recent alerts for user %s — skipping digest", userID)
+		return nil
+	}
+
+	var rows string
+	for _, e := range events {
+		label := "—"
+		if e.AddressLabel != nil {
+			label = *e.AddressLabel
+		}
+		txLink := "—"
+		if e.TxHash != nil {
+			txLink = fmt.Sprintf(
+				`<a href="https://etherscan.io/tx/%s" style="color:#0066cc;">%s…</a>`,
+				*e.TxHash, (*e.TxHash)[:10],
+			)
+		}
+		rows += fmt.Sprintf(`
+      <tr>
+        <td style="padding:6px 8px; border-bottom:1px solid #eee;">%s</td>
+        <td style="padding:6px 8px; border-bottom:1px solid #eee;">%s</td>
+        <td style="padding:6px 8px; border-bottom:1px solid #eee;">%s</td>
+        <td style="padding:6px 8px; border-bottom:1px solid #eee; font-size:12px; color:#666;">%s</td>
+      </tr>`,
+			label, e.Message, txLink,
+			e.Timestamp.Format("Jan 2 15:04 UTC"),
+		)
+	}
+
+	html := fmt.Sprintf(`
+<div style="font-family: sans-serif; max-width: 700px; margin: 0 auto;">
+  <h2 style="color: #333;">Koin Ping — Alert Digest</h2>
+  <p>Here are your recent alerts (%d total):</p>
+  <table style="width:100%%; border-collapse:collapse; font-size:14px;">
+    <thead>
+      <tr style="background:#f5f5f5;">
+        <th style="padding:8px; text-align:left;">Address</th>
+        <th style="padding:8px; text-align:left;">Alert</th>
+        <th style="padding:8px; text-align:left;">Tx</th>
+        <th style="padding:8px; text-align:left;">Time</th>
+      </tr>
+    </thead>
+    <tbody>%s</tbody>
+  </table>
+  <hr style="border:none; border-top:1px solid #eee; margin:24px 0;" />
+  <p style="font-size:12px; color:#999;">Sent by Koin Ping</p>
+</div>`, len(events), rows)
+
+	subject := fmt.Sprintf("Koin Ping Digest — %d alerts", len(events))
+
+	return s.send(toAddress, subject, html)
+}
+
+func (s *EmailDigestService) SendDigestsForAllUsers(ctx context.Context) (int, error) {
+	if !s.Configured() {
+		return 0, nil
+	}
+
+	configs, err := s.notifCfgs.ListEnabled(ctx)
+	if err != nil {
+		return 0, fmt.Errorf("list enabled configs: %w", err)
+	}
+
+	sent := 0
+	for _, cfg := range configs {
+		if cfg.Email == nil || *cfg.Email == "" {
+			continue
+		}
+		if err := s.SendDigest(ctx, cfg.UserID, *cfg.Email); err != nil {
+			log.Printf("Failed to send digest to user %s: %v", cfg.UserID, err)
+			continue
+		}
+		sent++
+	}
+
+	return sent, nil
+}
+
+type resendEmailPayload struct {
+	From    string `json:"from"`
+	To      string `json:"to"`
+	Subject string `json:"subject"`
+	HTML    string `json:"html"`
+}
+
+func (s *EmailDigestService) send(to, subject, html string) error {
+	payload := resendEmailPayload{
+		From:    s.fromAddress,
+		To:      to,
+		Subject: subject,
+		HTML:    html,
+	}
+
+	body, err := json.Marshal(payload)
+	if err != nil {
+		return fmt.Errorf("marshal email payload: %w", err)
+	}
+
+	req, err := http.NewRequest(http.MethodPost, resendAPIURL, bytes.NewReader(body))
+	if err != nil {
+		return fmt.Errorf("create request: %w", err)
+	}
+	req.Header.Set("Content-Type", "application/json")
+	req.Header.Set("Authorization", "Bearer "+s.apiKey)
+
+	resp, err := digestHTTPClient.Do(req)
+	if err != nil {
+		return fmt.Errorf("send email via Resend: %w", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
+		return fmt.Errorf("Resend API returned HTTP %d", resp.StatusCode) //nolint:err113
+	}
+
+	return nil
+}

backend/internal/services/evaluator.go

@@ -0,0 +1,406 @@
+package services
+
+import (
+	"context"
+	"fmt"
+	"log"
+	"sync"
+	"time"
+
+	"golang.org/x/sync/semaphore"
+
+	"github.com/kjannette/koin-ping/backend/internal/domain"
+	"github.com/kjannette/koin-ping/backend/internal/models"
+	"github.com/kjannette/koin-ping/backend/internal/notifications"
+	"github.com/kjannette/koin-ping/backend/internal/protocols/ethereum"
+	"github.com/kjannette/koin-ping/backend/internal/wei"
+)
+
+const (
+	notificationTimeout    = 30 * time.Second
+	notificationMaxRetries = 3
+	notificationRetryBase  = time.Second
+	maxConcurrentNotifications = 5
+)
+
+type EvaluatorService struct {
+	eth          ethereum.EthereumObserver
+	alertRules   *models.AlertRuleModel
+	alertEvents  *models.AlertEventModel
+	addresses    *models.AddressModel
+	users        *models.UserModel
+	notifConfigs *models.NotificationConfigModel
+	notifSem     *semaphore.Weighted
+	notifWg      sync.WaitGroup
+}
+
+func NewEvaluatorService(
+	eth ethereum.EthereumObserver,
+	alertRules *models.AlertRuleModel,
+	alertEvents *models.AlertEventModel,
+	addresses *models.AddressModel,
+	users *models.UserModel,
+	notifConfigs *models.NotificationConfigModel,
+) *EvaluatorService {
+	return &EvaluatorService{
+		eth:          eth,
+		alertRules:   alertRules,
+		alertEvents:  alertEvents,
+		addresses:    addresses,
+		users:        users,
+		notifConfigs: notifConfigs,
+		notifSem:     semaphore.NewWeighted(maxConcurrentNotifications),
+	}
+}
+
+func (s *EvaluatorService) Evaluate(ctx context.Context, observations []domain.ObservedTx) (int, error) {
+	alertsFired := 0
+
+	for _, obs := range observations {
+		fired, err := s.evaluateObservation(ctx, obs)
+		if err != nil {
+			log.Printf("Error evaluating observation for address ID %d: %v", obs.AddressID, err)
+			continue
+		}
+		alertsFired += fired
+	}
+
+	return alertsFired, nil
+}
+
+func (s *EvaluatorService) evaluateObservation(ctx context.Context, obs domain.ObservedTx) (int, error) {
+	rules, err := s.alertRules.ListByAddress(ctx, obs.AddressID)
+	if err != nil {
+		return 0, err
+	}
+
+	alertsFired := 0
+	for _, rule := range rules {
+		if !rule.Enabled {
+			continue
+		}
+
+		matches, err := s.ruleMatches(ctx, rule, obs)
+		if err != nil {
+			log.Printf("Error matching rule %d: %v", rule.ID, err)
+			continue
+		}
+
+		if matches {
+			if err := s.fireAlert(ctx, rule, obs); err != nil {
+				log.Printf("Error firing alert for rule %d: %v", rule.ID, err)
+				continue
+			}
+			alertsFired++
+		}
+	}
+
+	return alertsFired, nil
+}
+
+func (s *EvaluatorService) ruleMatches(ctx context.Context, rule domain.AlertRule, obs domain.ObservedTx) (bool, error) {
+	switch rule.Type {
+	case domain.AlertIncomingTx:
+		return s.matchesDirectionalTx(rule, obs, domain.DirectionIncoming)
+	case domain.AlertOutgoingTx:
+		return s.matchesDirectionalTx(rule, obs, domain.DirectionOutgoing)
+	case domain.AlertLargeTransfer:
+		return s.matchesLargeTransfer(rule, obs)
+	case domain.AlertBalanceBelow:
+		return s.matchesBalanceBelow(ctx, rule, obs)
+	default:
+		log.Printf("Unknown rule type: %s", rule.Type)
+		return false, nil
+	}
+}
+
+func (s *EvaluatorService) matchesDirectionalTx(rule domain.AlertRule, obs domain.ObservedTx, expected domain.Direction) (bool, error) {
+	if obs.Direction != expected {
+		return false, nil
+	}
+
+	if rule.Minimum != nil {
+		minWei, err := wei.FromEth(*rule.Minimum)
+		if err != nil {
+			return false, err
+		}
+		aboveMin, err := wei.GreaterThanOrEqual(obs.Value, minWei)
+		if err != nil {
+			return false, err
+		}
+		if !aboveMin {
+			return false, nil
+		}
+	}
+
+	if rule.Maximum != nil {
+		maxWei, err := wei.FromEth(*rule.Maximum)
+		if err != nil {
+			return false, err
+		}
+		belowMax, err := wei.LessThanOrEqual(obs.Value, maxWei)
+		if err != nil {
+			return false, err
+		}
+		if !belowMax {
+			return false, nil
+		}
+	}
+
+	return true, nil
+}
+
+func (s *EvaluatorService) matchesLargeTransfer(rule domain.AlertRule, obs domain.ObservedTx) (bool, error) {
+	if rule.Threshold == nil {
+		return false, nil
+	}
+
+	thresholdWei, err := wei.FromEth(*rule.Threshold)
+	if err != nil {
+		return false, err
+	}
+
+	return wei.GreaterThanOrEqual(obs.Value, thresholdWei)
+}
+
+// matchesBalanceBelow only triggers after outgoing transactions, since incoming
+// transactions increase balance and can't cause it to drop below threshold.
+func (s *EvaluatorService) matchesBalanceBelow(ctx context.Context, rule domain.AlertRule, obs domain.ObservedTx) (bool, error) {
+	if rule.Threshold == nil {
+		return false, nil
+	}
+
+	if obs.Direction != domain.DirectionOutgoing {
+		return false, nil
+	}
+
+	addr, err := s.addresses.FindByID(ctx, obs.AddressID, nil)
+	if err != nil {
+		return false, err
+	}
+	if addr == nil {
+		log.Printf("Address ID %d not found", obs.AddressID)
+		return false, nil
+	}
+
+	balanceWei, err := s.eth.GetBalance(ctx, addr.Address)
+	if err != nil {
+		return false, err
+	}
+
+	thresholdWei, err := wei.FromEth(*rule.Threshold)
+	if err != nil {
+		return false, err
+	}
+
+	return wei.LessThan(balanceWei, thresholdWei)
+}
+
+func (s *EvaluatorService) fireAlert(ctx context.Context, rule domain.AlertRule, obs domain.ObservedTx) error {
+	addr, err := s.addresses.FindByID(ctx, obs.AddressID, nil)
+	if err != nil {
+		return err
+	}
+
+	addressLabel := "Unknown"
+	if addr != nil {
+		if addr.Label != nil {
+			addressLabel = *addr.Label
+		} else {
+			addressLabel = addr.Address
+		}
+	}
+
+	message := s.buildMessage(rule, obs)
+	txHash := &obs.Hash
+
+	event, err := s.alertEvents.Create(ctx, rule.ID, message, &addressLabel, txHash)
+	if err != nil {
+		return err
+	}
+
+	if event == nil {
+		log.Printf("[ALERT DEDUP] Rule %d (%s) - duplicate event skipped for TX: %s", rule.ID, rule.Type, obs.Hash)
+		return nil
+	}
+
+	log.Printf("[ALERT FIRED] Rule %d (%s) - %s - TX: %s", rule.ID, rule.Type, message, obs.Hash)
+
+	if addr != nil {
+		userID := addr.UserID
+		address := addr.Address
+		if err := s.notifSem.Acquire(ctx, 1); err != nil {
+			log.Printf("Failed to acquire notification semaphore for rule %d: %v", rule.ID, err)
+			return nil
+		}
+		s.notifWg.Add(1)
+		go func() {
+			defer s.notifSem.Release(1)
+			defer s.notifWg.Done()
+			notifCtx, cancel := context.WithTimeout(context.Background(), notificationTimeout)
+			defer cancel()
+			s.sendNotification(notifCtx, userID, message, obs, addressLabel, rule, address)
+		}()
+	}
+
+	return nil
+}
+
+// WaitForNotifications blocks until all in-flight notification goroutines finish.
+func (s *EvaluatorService) WaitForNotifications() {
+	s.notifWg.Wait()
+}
+
+func (s *EvaluatorService) buildNotifiers(cfg *domain.NotificationConfig, limits domain.TierLimits) []notifications.Notifier {
+	var notifiers []notifications.Notifier
+
+	if limits.ChannelAllowed("discord") &&
+		cfg.DiscordWebhookURL != nil && *cfg.DiscordWebhookURL != "" {
+		notifiers = append(notifiers, &notifications.DiscordNotifier{WebhookURL: *cfg.DiscordWebhookURL})
+	}
+
+	if limits.ChannelAllowed("telegram") &&
+		cfg.TelegramBotToken != nil && *cfg.TelegramBotToken != "" &&
+		cfg.TelegramChatID != nil && *cfg.TelegramChatID != "" {
+		notifiers = append(notifiers, &notifications.TelegramNotifier{
+			BotToken: *cfg.TelegramBotToken,
+			ChatID:   *cfg.TelegramChatID,
+		})
+	}
+
+	if limits.ChannelAllowed("slack") &&
+		cfg.SlackWebhookURL != nil && *cfg.SlackWebhookURL != "" {
+		notifiers = append(notifiers, &notifications.SlackNotifier{WebhookURL: *cfg.SlackWebhookURL})
+	}
+
+	// Email is delivered exclusively via the daily digest service, never real-time.
+
+	return notifiers
+}
+
+func sendWithRetry(ctx context.Context, n notifications.Notifier, message string, meta notifications.AlertMetadata) error {
+	var lastErr error
+	for attempt := range notificationMaxRetries {
+		if attempt > 0 {
+			wait := notificationRetryBase * time.Duration(1<<(attempt-1))
+			select {
+			case <-ctx.Done():
+				return ctx.Err()
+			case <-time.After(wait):
+			}
+		}
+
+		if err := n.Send(ctx, message, meta); err != nil {
+			lastErr = err
+
+			if notifications.IsPermanent(err) {
+				log.Printf("Permanent notification failure, skipping retries: %v", err)
+				return err
+			}
+
+			log.Printf("Notification attempt %d/%d failed: %v", attempt+1, notificationMaxRetries, err)
+			continue
+		}
+
+		return nil
+	}
+
+	return lastErr
+}
+
+func (s *EvaluatorService) sendNotification(ctx context.Context, userID, message string, obs domain.ObservedTx, addressLabel string, rule domain.AlertRule, address string) {
+	notifConfig, err := s.notifConfigs.GetConfig(ctx, userID)
+	if err != nil {
+		log.Printf("Failed to get notification config: %v", err)
+		return
+	}
+
+	if notifConfig == nil || !notifConfig.NotificationEnabled {
+		return
+	}
+
+	user, err := s.users.GetByID(ctx, userID)
+	if err != nil || user == nil {
+		log.Printf("Failed to load user %s for tier check in notification: %v", userID, err)
+		return
+	}
+	limits := domain.GetTierLimits(user.SubscriptionTier)
+
+	meta := notifications.AlertMetadata{
+		TxHash:       obs.Hash,
+		AddressLabel: addressLabel,
+		AlertType:    string(rule.Type),
+		Address:      address,
+	}
+
+	for _, n := range s.buildNotifiers(notifConfig, limits) {
+		if err := sendWithRetry(ctx, n, message, meta); err != nil {
+			log.Printf("Notification channel failed for user %s after retries: %v", userID, err)
+		} else {
+			log.Printf("Notification sent to user %s via %T", userID, n)
+		}
+	}
+}
+
+func (s *EvaluatorService) buildMessage(rule domain.AlertRule, obs domain.ObservedTx) string {
+	if obs.IsTokenTransfer() {
+		return s.buildTokenMessage(rule, obs)
+	}
+
+	switch rule.Type {
+	case domain.AlertIncomingTx:
+		ethStr, _ := wei.FormatAsEth(obs.Value, 4)
+		return fmt.Sprintf("Incoming transaction: %s received", ethStr)
+	case domain.AlertOutgoingTx:
+		ethStr, _ := wei.FormatAsEth(obs.Value, 4)
+		return fmt.Sprintf("Outgoing transaction: %s sent", ethStr)
+	case domain.AlertLargeTransfer:
+		ethStr, _ := wei.FormatAsEth(obs.Value, 4)
+		threshold := float64(0)
+		if rule.Threshold != nil {
+			threshold = *rule.Threshold
+		}
+		return fmt.Sprintf("Large transfer detected: %s (threshold: %g ETH)", ethStr, threshold)
+	case domain.AlertBalanceBelow:
+		threshold := float64(0)
+		if rule.Threshold != nil {
+			threshold = *rule.Threshold
+		}
+		return fmt.Sprintf("Balance dropped below threshold of %g ETH", threshold)
+	default:
+		return "Alert triggered"
+	}
+}
+
+const defaultTokenDecimals = 18
+
+func (s *EvaluatorService) buildTokenMessage(rule domain.AlertRule, obs domain.ObservedTx) string {
+	symbol := "tokens"
+	if obs.TokenSymbol != nil {
+		symbol = *obs.TokenSymbol
+	}
+
+	amount := "unknown"
+	if obs.TokenValue != nil {
+		decimals := defaultTokenDecimals
+		if obs.TokenDecimals != nil {
+			decimals = *obs.TokenDecimals
+		}
+		amount = wei.FormatTokenAmount(*obs.TokenValue, decimals)
+	}
+
+	switch rule.Type {
+	case domain.AlertIncomingTx:
+		return fmt.Sprintf("Incoming transfer: %s %s received", amount, symbol)
+	case domain.AlertOutgoingTx:
+		return fmt.Sprintf("Outgoing transfer: %s %s sent", amount, symbol)
+	case domain.AlertLargeTransfer:
+		threshold := float64(0)
+		if rule.Threshold != nil {
+			threshold = *rule.Threshold
+		}
+		return fmt.Sprintf("Large token transfer: %s %s (threshold: %g)", amount, symbol, threshold)
+	default:
+		return fmt.Sprintf("Token transfer: %s %s", amount, symbol)
+	}
+}

backend/internal/services/observer.go

@@ -5,9 +5,9 @@ import (
 	"log"
 	"strings"
 
-	"github.com/kjannette/koin-ping/backend-go/internal/domain"
-	"github.com/kjannette/koin-ping/backend-go/internal/models"
-	"github.com/kjannette/koin-ping/backend-go/internal/protocols/ethereum"
+	"github.com/kjannette/koin-ping/backend/internal/domain"
+	"github.com/kjannette/koin-ping/backend/internal/models"
+	"github.com/kjannette/koin-ping/backend/internal/protocols/ethereum"
 )
 
 const maxBlocksPerRun = 100
@@ -80,6 +80,15 @@ func (s *ObserverService) observeAddress(ctx context.Context, addr domain.Addres
 		}
 	}
 
+	tokenTxs, err := s.eth.GetTokenTransfers(ctx, startBlock, endBlock, addr.Address)
+	if err != nil {
+		log.Printf("Error fetching token transfers for %s: %v", addr.Address, err)
+	} else {
+		for _, tx := range tokenTxs {
+			observations = append(observations, createObservedTx(tx, addr))
+		}
+	}
+
 	if _, err := s.checkpoint.UpdateLastCheckedBlock(ctx, addr.ID, endBlock); err != nil {
 		return nil, err
 	}

backend/internal/wei/converter.go

@@ -90,6 +90,14 @@ func LessThan(weiA, weiB string) (bool, error) {
 	return cmp < 0, nil
 }
 
+func LessThanOrEqual(weiA, weiB string) (bool, error) {
+	cmp, err := Compare(weiA, weiB)
+	if err != nil {
+		return false, err
+	}
+	return cmp <= 0, nil
+}
+
 // FormatAsEth formats a Wei string as "X.XXXX ETH".
 func FormatAsEth(weiString string, decimals int) (string, error) {
 	eth, err := ToEth(weiString)
@@ -98,3 +106,54 @@ func FormatAsEth(weiString string, decimals int) (string, error) {
 	}
 	return fmt.Sprintf("%.*f ETH", decimals, eth), nil
 }
+
+// FormatTokenAmount formats a raw token amount using the token's decimal places.
+// For example, 1000000 USDT (6 decimals) becomes "1".
+func FormatTokenAmount(rawValue string, tokenDecimals int) string {
+	if rawValue == "" || rawValue == "0" {
+		return "0"
+	}
+
+	n, ok := new(big.Int).SetString(rawValue, 10)
+	if !ok {
+		return "0"
+	}
+
+	divisor := new(big.Int).Exp(big.NewInt(10), big.NewInt(int64(tokenDecimals)), nil) //nolint:mnd
+	whole := new(big.Int).Div(n, divisor)
+	remainder := new(big.Int).Mod(n, divisor)
+
+	if remainder.Sign() == 0 {
+		return addThousandsSeparators(whole.String())
+	}
+
+	fracStr := fmt.Sprintf("%0*s", tokenDecimals, remainder.String())
+	fracStr = strings.TrimRight(fracStr, "0")
+	const maxDisplayDecimals = 4
+	if len(fracStr) > maxDisplayDecimals {
+		fracStr = fracStr[:maxDisplayDecimals]
+	}
+
+	return addThousandsSeparators(whole.String()) + "." + fracStr
+}
+
+func addThousandsSeparators(s string) string {
+	if len(s) <= 3 { //nolint:mnd
+		return s
+	}
+
+	var result strings.Builder
+	offset := len(s) % 3 //nolint:mnd
+	if offset > 0 {
+		result.WriteString(s[:offset])
+	}
+
+	for i := offset; i < len(s); i += 3 { //nolint:mnd
+		if result.Len() > 0 {
+			result.WriteByte(',')
+		}
+		result.WriteString(s[i : i+3]) //nolint:mnd
+	}
+
+	return result.String()
+}

frontend/README.md

@@ -5,24 +5,27 @@ React + Vite frontend for the on-chain monitoring and alerting system.
 ## Getting Started
 
 1. Install dependencies:
-   ```bash
-   npm install
-   ```
+
+    ```bash
+    npm install
+    ```
 
 2. Run the development server:
-   ```bash
-   npm run dev
-   ```
+
+    ```bash
+    npm run dev
+    ```
 
 3. Build for production:
-   ```bash
-   npm run build
-   ```
+
+    ```bash
+    npm run build
+    ```
 
 4. Preview production build:
-   ```bash
-   npm run preview
-   ```
+    ```bash
+    npm run preview
+    ```
 
 ## Project Structure
 
@@ -34,5 +37,5 @@ React + Vite frontend for the on-chain monitoring and alerting system.
 
 ## Development
 
-The frontend runs on port 3000 and proxies API requests to the backend running on port 5000.
-
+The frontend runs on port 3000 and proxies API requests to the backend running
+on port 5000.

frontend/package.json

@@ -1,32 +1,36 @@
 {
-  "name": "frontend",
-  "version": "1.0.0",
-  "description": "koin_ping blockchain monoitor UI",
-  "main": "index.js",
-  "scripts": {
-    "dev": "vite",
-    "build": "vite build",
-    "preview": "vite preview"
-  },
-  "keywords": [
-    "cryptocurrency",
-    "blockchain",
-    "blockchain event moitoring"
-  ],
-  "author": "Steven Jannette",
-  "license": "MIT",
-  "type": "module",
-  "dependencies": {
-    "firebase": "^12.7.0",
-    "react": "^19.2.3",
-    "react-dom": "^19.2.3",
-    "react-router-dom": "^7.11.0"
-  },
-  "devDependencies": {
-    "@types/react": "^19.2.7",
-    "@types/react-dom": "^19.2.3",
-    "@vitejs/plugin-react": "^5.1.2",
-    "typescript": "^5.9.3",
-    "vite": "^7.3.0"
-  }
+    "name": "frontend",
+    "version": "1.0.0",
+    "description": "koin_ping blockchain monitor UI",
+    "main": "index.js",
+    "scripts": {
+        "dev": "vite",
+        "build": "vite build",
+        "preview": "vite preview",
+        "test": "vite build",
+        "lint": "prettier --check 'src/**/*.{js,jsx,ts,tsx,css}'",
+        "fmt": "prettier --write 'src/**/*.{js,jsx,ts,tsx,css}'"
+    },
+    "keywords": [
+        "cryptocurrency",
+        "blockchain",
+        "blockchain event monitoring"
+    ],
+    "author": "Steven Jannette",
+    "license": "MIT",
+    "type": "module",
+    "dependencies": {
+        "firebase": "^12.7.0",
+        "react": "^19.2.3",
+        "react-dom": "^19.2.3",
+        "react-router-dom": "^7.11.0"
+    },
+    "devDependencies": {
+        "@types/react": "^19.2.7",
+        "@types/react-dom": "^19.2.3",
+        "@vitejs/plugin-react": "^5.1.2",
+        "prettier": "^3.8.1",
+        "typescript": "^5.9.3",
+        "vite": "^7.3.0"
+    }
 }

frontend/prettierrc

@@ -0,0 +1,4 @@
+{
+    "tabWidth": 4,
+    "proseWrap": "always"
+}

frontend/src/App.jsx

@@ -1,60 +1,48 @@
-import { Routes, Route, Link, Navigate } from "react-router-dom";
+import { Routes, Route, Navigate } from "react-router-dom";
 import { useAuth } from "./contexts/AuthContext";
-import Login from "./pages/Login";
+import Navbar from "./components/Navbar";
+import Login from "./pages/login/Login";
 import Signup from "./pages/Signup";
-import Addresses from "./pages/Addresses";
-import Alerts from "./pages/Alerts";
-import AlertHistory from "./pages/AlertHistory";
+import Subscribe from "./pages/subscribe/Subscribe";
+import Addresses from "./pages/addresses/Addresses";
+import Alerts from "./pages/alerts/Alerts";
+import AlertHistory from "./pages/alertHistory/AlertHistory";
+import Account from "./pages/user_account/Account";
 
 export default function App() {
-  const { currentUser, logout } = useAuth();
+  const { currentUser, isSubscribed } = useAuth();
 
-  // Show login/signup routes if not authenticated
   if (!currentUser) {
     return (
       <Routes>
         <Route path="/login" element={<Login />} />
         <Route path="/signup" element={<Signup />} />
+        <Route path="/subscribe" element={<Subscribe />} />
         <Route path="*" element={<Navigate to="/login" />} />
       </Routes>
     );
   }
 
-  // Show main app if authenticated
-  return (
-    <div style={{ padding: "1rem" }}>
-      <nav style={{ marginBottom: "1rem", display: "flex", justifyContent: "space-between", alignItems: "center" }}>
-        <div>
-          <Link to="/addresses">Addresses</Link>{" | "}
-          <Link to="/alerts">Alerts</Link>{" | "}
-          <Link to="/history">History</Link>
-        </div>
-        <div style={{ display: "flex", alignItems: "center", gap: "1rem" }}>
-          <span style={{ fontSize: "0.9rem", color: "#999" }}>
-            {currentUser.email}
-          </span>
-          <button
-            onClick={logout}
-            style={{
-              padding: "0.5rem 1rem",
-              fontSize: "0.9rem",
-              backgroundColor: "#333",
-              color: "white",
-              border: "1px solid #555",
-              borderRadius: "4px",
-              cursor: "pointer"
-            }}
-          >
-            Logout
-          </button>
-        </div>
-      </nav>
+  if (!isSubscribed) {
+    return (
+      <Routes>
+        <Route path="/subscribe" element={<Subscribe />} />
+        <Route path="/account" element={<><Navbar /><Account /></>} />
+        <Route path="*" element={<Navigate to="/subscribe" />} />
+      </Routes>
+    );
+  }
 
+  return (
+    <div>
+      <Navbar />
       <Routes>
         <Route path="/" element={<Addresses />} />
         <Route path="/addresses" element={<Addresses />} />
         <Route path="/alerts" element={<Alerts />} />
-        <Route path="/history" element={<AlertHistory />} />
+        <Route path="/alertevents" element={<AlertHistory />} />
+        <Route path="/account" element={<Account />} />
+        <Route path="/subscribe" element={<Subscribe />} />
         <Route path="*" element={<Navigate to="/addresses" />} />
       </Routes>
     </div>

frontend/src/api/account.js

@@ -0,0 +1,25 @@
+import { getAuthHeaders } from "./authHeaders";
+import { API_BASE } from "./config";
+
+export async function getAccount() {
+    const headers = await getAuthHeaders();
+    const res = await fetch(`${API_BASE}/user/account`, { headers });
+    if (!res.ok) {
+        const data = await res.json();
+        throw new Error(data.message || "Failed to load account");
+    }
+    return res.json();
+}
+
+export async function createPortalSession() {
+    const headers = await getAuthHeaders();
+    const res = await fetch(`${API_BASE}/stripe/create-portal-session`, {
+        method: "POST",
+        headers,
+    });
+    if (!res.ok) {
+        const data = await res.json();
+        throw new Error(data.message || "Failed to create portal session");
+    }
+    return res.json();
+}

frontend/src/api/addresses.jsx

@@ -1,7 +1,7 @@
 // API client for address management
 
-import { getAuthHeaders, getAuthHeadersSimple } from './authHeaders';
-import { API_BASE } from './config';
+import { getAuthHeaders, getAuthHeadersSimple } from "./authHeaders";
+import { API_BASE } from "./config";
 
 /**
  * Create a new blockchain address to monitor
@@ -11,35 +11,37 @@ import { API_BASE } from './config';
  * @returns {Promise<Object>} Created address with id and metadata
  */
 export async function createAddress(data) {
-  try {
-  const headers = await getAuthHeaders();
-  const response = await fetch(`${API_BASE}/addresses`, {
-    method: 'POST',
-    headers: headers,
-    body: JSON.stringify(data)
-  });
+    try {
+        const headers = await getAuthHeaders();
+        const response = await fetch(`${API_BASE}/addresses`, {
+            method: "POST",
+            headers: headers,
+            body: JSON.stringify(data),
+        });
 
-  if (!response.ok) {
-      // Try to parse error response, but handle if it's not JSON
-      let errorMessage = 'Failed to create address';
-      try {
-    const error = await response.json();
-        errorMessage = error.message || errorMessage;
-      } catch {
-        // If JSON parse fails, use status text
-        errorMessage = `Server error: ${response.status} ${response.statusText}`;
-      }
-      throw new Error(errorMessage);
-  }
+        if (!response.ok) {
+            // Try to parse error response, but handle if it's not JSON
+            let errorMessage = "Failed to create address";
+            try {
+                const error = await response.json();
+                errorMessage = error.message || errorMessage;
+            } catch {
+                // If JSON parse fails, use status text
+                errorMessage = `Server error: ${response.status} ${response.statusText}`;
+            }
+            throw new Error(errorMessage);
+        }
 
-  return response.json();
-  } catch (error) {
-    // Handle network errors
-    if (error.message.includes('fetch')) {
-      throw new Error('Cannot connect to server. Is the backend running?');
+        return response.json();
+    } catch (error) {
+        // Handle network errors
+        if (error.message.includes("fetch")) {
+            throw new Error(
+                "Cannot connect to server. Is the backend running?",
+            );
+        }
+        throw error;
     }
-    throw error;
-  }
 }
 
 /**
@@ -47,33 +49,70 @@ export async function createAddress(data) {
  * @returns {Promise<Array>} List of all addresses
  */
 export async function getAddresses() {
-  try {
-  const headers = await getAuthHeadersSimple();
-  const response = await fetch(`${API_BASE}/addresses`, {
-    headers: headers
-  });
+    try {
+        const headers = await getAuthHeadersSimple();
+        const response = await fetch(`${API_BASE}/addresses`, {
+            headers: headers,
+        });
 
-  if (!response.ok) {
-      // Try to parse error response, but handle if it's not JSON
-      let errorMessage = 'Failed to fetch addresses';
-      try {
-    const error = await response.json();
-        errorMessage = error.message || errorMessage;
-      } catch {
-        // If JSON parse fails, use status text
-        errorMessage = `Server error: ${response.status} ${response.statusText}`;
-      }
-      throw new Error(errorMessage);
-  }
+        if (!response.ok) {
+            // Try to parse error response, but handle if it's not JSON
+            let errorMessage = "Failed to fetch addresses";
+            try {
+                const error = await response.json();
+                errorMessage = error.message || errorMessage;
+            } catch {
+                // If JSON parse fails, use status text
+                errorMessage = `Server error: ${response.status} ${response.statusText}`;
+            }
+            throw new Error(errorMessage);
+        }
 
-  return response.json();
-  } catch (error) {
-    // Handle network errors or JSON parse errors
-    if (error.message.includes('fetch')) {
-      throw new Error('Cannot connect to server. Is the backend running?');
+        return response.json();
+    } catch (error) {
+        // Handle network errors or JSON parse errors
+        if (error.message.includes("fetch")) {
+            throw new Error(
+                "Cannot connect to server. Is the backend running?",
+            );
+        }
+        throw error;
+    }
+}
+
+/**
+ * Update an address (e.g. change its label)
+ * @param {number} addressId - Address ID to update
+ * @param {Object} data - Fields to update (e.g. { label: "New Label" })
+ * @returns {Promise<Object>} Updated address
+ */
+export async function updateAddress(addressId, data) {
+    try {
+        const headers = await getAuthHeaders();
+        const response = await fetch(`${API_BASE}/addresses/${addressId}`, {
+            method: "PATCH",
+            headers: headers,
+            body: JSON.stringify(data),
+        });
+
+        if (!response.ok) {
+            let errorMessage = "Failed to update address";
+            try {
+                const error = await response.json();
+                errorMessage = error.message || errorMessage;
+            } catch {
+                errorMessage = `Server error: ${response.status} ${response.statusText}`;
+            }
+            throw new Error(errorMessage);
+        }
+
+        return response.json();
+    } catch (error) {
+        if (error.message.includes("fetch")) {
+            throw new Error("Cannot connect to server. Is the backend running?");
+        }
+        throw error;
     }
-    throw error;
-  }
 }
 
 /**
@@ -82,31 +121,32 @@ export async function getAddresses() {
  * @returns {Promise<void>}
  */
 export async function deleteAddress(addressId) {
-  try {
-  const headers = await getAuthHeadersSimple();
-  const response = await fetch(`${API_BASE}/addresses/${addressId}`, {
-    method: 'DELETE',
-    headers: headers
-  });
+    try {
+        const headers = await getAuthHeadersSimple();
+        const response = await fetch(`${API_BASE}/addresses/${addressId}`, {
+            method: "DELETE",
+            headers: headers,
+        });
 
-  if (!response.ok && response.status !== 204) {
-      // Try to parse error response, but handle if it's not JSON
-      let errorMessage = 'Failed to delete address';
-      try {
-    const error = await response.json();
-        errorMessage = error.message || errorMessage;
-      } catch {
-        // If JSON parse fails, use status text
-        errorMessage = `Server error: ${response.status} ${response.statusText}`;
-      }
-      throw new Error(errorMessage);
+        if (!response.ok && response.status !== 204) {
+            // Try to parse error response, but handle if it's not JSON
+            let errorMessage = "Failed to delete address";
+            try {
+                const error = await response.json();
+                errorMessage = error.message || errorMessage;
+            } catch {
+                // If JSON parse fails, use status text
+                errorMessage = `Server error: ${response.status} ${response.statusText}`;
+            }
+            throw new Error(errorMessage);
+        }
+    } catch (error) {
+        // Handle network errors
+        if (error.message.includes("fetch")) {
+            throw new Error(
+                "Cannot connect to server. Is the backend running?",
+            );
+        }
+        throw error;
     }
-  } catch (error) {
-    // Handle network errors
-    if (error.message.includes('fetch')) {
-      throw new Error('Cannot connect to server. Is the backend running?');
-    }
-    throw error;
-  }
 }
-

frontend/src/api/alertEvents.jsx

@@ -1,35 +1,37 @@
 // API client for alert event history
 
-import { getAuthHeadersSimple } from './authHeaders';
-import { API_BASE } from './config';
+import { getAuthHeadersSimple } from "./authHeaders";
+import { API_BASE } from "./config";
 
 /**
  * Get all alert events (history)
  * @returns {Promise<Array>} List of alert events, sorted by most recent first
  */
 export async function getAlertEvents() {
-  try {
-  const headers = await getAuthHeadersSimple();
-  const response = await fetch(`${API_BASE}/alert-events`, {
-    headers: headers
-  });
+    try {
+        const headers = await getAuthHeadersSimple();
+        const response = await fetch(`${API_BASE}/alert-events`, {
+            headers: headers,
+        });
 
-  if (!response.ok) {
-      let errorMessage = 'Failed to fetch alert events';
-      try {
-    const error = await response.json();
-        errorMessage = error.message || errorMessage;
-      } catch {
-        errorMessage = `Server error: ${response.status} ${response.statusText}`;
-      }
-      throw new Error(errorMessage);
-  }
+        if (!response.ok) {
+            let errorMessage = "Failed to fetch alert events";
+            try {
+                const error = await response.json();
+                errorMessage = error.message || errorMessage;
+            } catch {
+                errorMessage = `Server error: ${response.status} ${response.statusText}`;
+            }
+            throw new Error(errorMessage);
+        }
 
-  return response.json();
-  } catch (error) {
-    if (error.message.includes('fetch')) {
-      throw new Error('Cannot connect to server. Is the backend running?');
+        return response.json();
+    } catch (error) {
+        if (error.message.includes("fetch")) {
+            throw new Error(
+                "Cannot connect to server. Is the backend running?",
+            );
+        }
+        throw error;
     }
-    throw error;
-  }
 }

frontend/src/api/alerts.jsx

@@ -1,16 +1,16 @@
 // API client for alert rule management
 
-import { getAuthHeaders, getAuthHeadersSimple } from './authHeaders';
-import { API_BASE } from './config';
+import { getAuthHeaders, getAuthHeadersSimple } from "./authHeaders";
+import { API_BASE } from "./config";
 
 /**
  * Alert types supported by the system
  */
 export const ALERT_TYPES = {
-  INCOMING_TX: 'incoming_tx',
-  OUTGOING_TX: 'outgoing_tx',
-  LARGE_TRANSFER: 'large_transfer',
-  BALANCE_BELOW: 'balance_below'
+    INCOMING_TX: "incoming_tx",
+    OUTGOING_TX: "outgoing_tx",
+    LARGE_TRANSFER: "large_transfer",
+    BALANCE_BELOW: "balance_below",
 };
 
 /**
@@ -22,32 +22,37 @@ export const ALERT_TYPES = {
  * @returns {Promise<Object>} Created alert rule
  */
 export async function createAlert(addressId, data) {
-  try {
-  const headers = await getAuthHeaders();
-  const response = await fetch(`${API_BASE}/addresses/${addressId}/alerts`, {
-    method: 'POST',
-    headers: headers,
-    body: JSON.stringify(data)
-  });
+    try {
+        const headers = await getAuthHeaders();
+        const response = await fetch(
+            `${API_BASE}/addresses/${addressId}/alerts`,
+            {
+                method: "POST",
+                headers: headers,
+                body: JSON.stringify(data),
+            },
+        );
 
-  if (!response.ok) {
-      let errorMessage = 'Failed to create alert rule';
-      try {
-    const error = await response.json();
-        errorMessage = error.message || errorMessage;
-      } catch {
-        errorMessage = `Server error: ${response.status} ${response.statusText}`;
-      }
-      throw new Error(errorMessage);
-  }
+        if (!response.ok) {
+            let errorMessage = "Failed to create alert rule";
+            try {
+                const error = await response.json();
+                errorMessage = error.message || errorMessage;
+            } catch {
+                errorMessage = `Server error: ${response.status} ${response.statusText}`;
+            }
+            throw new Error(errorMessage);
+        }
 
-  return response.json();
-  } catch (error) {
-    if (error.message.includes('fetch')) {
-      throw new Error('Cannot connect to server. Is the backend running?');
+        return response.json();
+    } catch (error) {
+        if (error.message.includes("fetch")) {
+            throw new Error(
+                "Cannot connect to server. Is the backend running?",
+            );
+        }
+        throw error;
     }
-    throw error;
-  }
 }
 
 /**
@@ -56,30 +61,35 @@ export async function createAlert(addressId, data) {
  * @returns {Promise<Array>} List of alert rules
  */
 export async function getAlerts(addressId) {
-  try {
-  const headers = await getAuthHeadersSimple();
-  const response = await fetch(`${API_BASE}/addresses/${addressId}/alerts`, {
-    headers: headers
-  });
+    try {
+        const headers = await getAuthHeadersSimple();
+        const response = await fetch(
+            `${API_BASE}/addresses/${addressId}/alerts`,
+            {
+                headers: headers,
+            },
+        );
 
-  if (!response.ok) {
-      let errorMessage = 'Failed to fetch alert rules';
-      try {
-    const error = await response.json();
-        errorMessage = error.message || errorMessage;
-      } catch {
-        errorMessage = `Server error: ${response.status} ${response.statusText}`;
-      }
-      throw new Error(errorMessage);
-  }
+        if (!response.ok) {
+            let errorMessage = "Failed to fetch alert rules";
+            try {
+                const error = await response.json();
+                errorMessage = error.message || errorMessage;
+            } catch {
+                errorMessage = `Server error: ${response.status} ${response.statusText}`;
+            }
+            throw new Error(errorMessage);
+        }
 
-  return response.json();
-  } catch (error) {
-    if (error.message.includes('fetch')) {
-      throw new Error('Cannot connect to server. Is the backend running?');
+        return response.json();
+    } catch (error) {
+        if (error.message.includes("fetch")) {
+            throw new Error(
+                "Cannot connect to server. Is the backend running?",
+            );
+        }
+        throw error;
     }
-    throw error;
-  }
 }
 
 /**
@@ -89,32 +99,76 @@ export async function getAlerts(addressId) {
  * @returns {Promise<Object>} Updated alert rule
  */
 export async function updateAlertStatus(alertId, enabled) {
-  try {
-  const headers = await getAuthHeaders();
-  const response = await fetch(`${API_BASE}/alerts/${alertId}`, {
-    method: 'PATCH',
-    headers: headers,
-    body: JSON.stringify({ enabled })
-  });
+    try {
+        const headers = await getAuthHeaders();
+        const response = await fetch(`${API_BASE}/alerts/${alertId}`, {
+            method: "PATCH",
+            headers: headers,
+            body: JSON.stringify({ enabled }),
+        });
 
-  if (!response.ok) {
-      let errorMessage = 'Failed to update alert rule';
-      try {
-    const error = await response.json();
-        errorMessage = error.message || errorMessage;
-      } catch {
-        errorMessage = `Server error: ${response.status} ${response.statusText}`;
-      }
-      throw new Error(errorMessage);
-  }
+        if (!response.ok) {
+            let errorMessage = "Failed to update alert rule";
+            try {
+                const error = await response.json();
+                errorMessage = error.message || errorMessage;
+            } catch {
+                errorMessage = `Server error: ${response.status} ${response.statusText}`;
+            }
+            throw new Error(errorMessage);
+        }
 
-  return response.json();
-  } catch (error) {
-    if (error.message.includes('fetch')) {
-      throw new Error('Cannot connect to server. Is the backend running?');
+        return response.json();
+    } catch (error) {
+        if (error.message.includes("fetch")) {
+            throw new Error(
+                "Cannot connect to server. Is the backend running?",
+            );
+        }
+        throw error;
+    }
+}
+
+/**
+ * Update the min/max thresholds on an alert rule
+ * @param {number} alertId - Alert rule ID
+ * @param {number|null} minimum - Minimum amount (null to clear)
+ * @param {number|null} maximum - Maximum amount (null to clear)
+ * @returns {Promise<Object>} Updated alert rule
+ */
+export async function updateAlertThresholds(alertId, minimum, maximum) {
+    try {
+        const headers = await getAuthHeaders();
+        const response = await fetch(`${API_BASE}/alerts/${alertId}`, {
+            method: "PATCH",
+            headers: headers,
+            body: JSON.stringify({
+                update_min_max: true,
+                minimum: minimum ?? null,
+                maximum: maximum ?? null,
+            }),
+        });
+
+        if (!response.ok) {
+            let errorMessage = "Failed to update alert thresholds";
+            try {
+                const error = await response.json();
+                errorMessage = error.message || errorMessage;
+            } catch {
+                errorMessage = `Server error: ${response.status} ${response.statusText}`;
+            }
+            throw new Error(errorMessage);
+        }
+
+        return response.json();
+    } catch (error) {
+        if (error.message.includes("fetch")) {
+            throw new Error(
+                "Cannot connect to server. Is the backend running?",
+            );
+        }
+        throw error;
     }
-    throw error;
-  }
 }
 
 /**
@@ -123,27 +177,29 @@ export async function updateAlertStatus(alertId, enabled) {
  * @returns {Promise<void>}
  */
 export async function deleteAlert(alertId) {
-  try {
-  const headers = await getAuthHeadersSimple();
-  const response = await fetch(`${API_BASE}/alerts/${alertId}`, {
-    method: 'DELETE',
-    headers: headers
-  });
+    try {
+        const headers = await getAuthHeadersSimple();
+        const response = await fetch(`${API_BASE}/alerts/${alertId}`, {
+            method: "DELETE",
+            headers: headers,
+        });
 
-  if (!response.ok && response.status !== 204) {
-      let errorMessage = 'Failed to delete alert rule';
-      try {
-    const error = await response.json();
-        errorMessage = error.message || errorMessage;
-      } catch {
-        errorMessage = `Server error: ${response.status} ${response.statusText}`;
-      }
-      throw new Error(errorMessage);
+        if (!response.ok && response.status !== 204) {
+            let errorMessage = "Failed to delete alert rule";
+            try {
+                const error = await response.json();
+                errorMessage = error.message || errorMessage;
+            } catch {
+                errorMessage = `Server error: ${response.status} ${response.statusText}`;
+            }
+            throw new Error(errorMessage);
+        }
+    } catch (error) {
+        if (error.message.includes("fetch")) {
+            throw new Error(
+                "Cannot connect to server. Is the backend running?",
+            );
+        }
+        throw error;
     }
-  } catch (error) {
-    if (error.message.includes('fetch')) {
-      throw new Error('Cannot connect to server. Is the backend running?');
-    }
-    throw error;
-  }
 }

frontend/src/api/authHeaders.js

@@ -5,26 +5,26 @@
  * Includes Firebase ID token in Authorization header
  */
 
-import { auth } from '../firebase/config';
+import { auth } from "../firebase/config";
 
 /**
  * Get headers with authentication token
  * @returns {Promise<Object>} Headers object with Authorization
  */
 export async function getAuthHeaders() {
-  const currentUser = auth.currentUser;
+    const currentUser = auth.currentUser;
 
-  if (!currentUser) {
-    throw new Error('No authenticated user');
-  }
+    if (!currentUser) {
+        throw new Error("No authenticated user");
+    }
 
-  // Get Firebase ID token
-  const token = await currentUser.getIdToken();
+    // Get Firebase ID token
+    const token = await currentUser.getIdToken();
 
-  return {
-    'Content-Type': 'application/json',
-    'Authorization': `Bearer ${token}`
-  };
+    return {
+        "Content-Type": "application/json",
+        Authorization: `Bearer ${token}`,
+    };
 }
 
 /**
@@ -32,16 +32,15 @@ export async function getAuthHeaders() {
  * @returns {Promise<Object>} Headers object with Authorization
  */
 export async function getAuthHeadersSimple() {
-  const currentUser = auth.currentUser;
+    const currentUser = auth.currentUser;
 
-  if (!currentUser) {
-    throw new Error('No authenticated user');
-  }
+    if (!currentUser) {
+        throw new Error("No authenticated user");
+    }
 
-  const token = await currentUser.getIdToken();
+    const token = await currentUser.getIdToken();
 
-  return {
-    'Authorization': `Bearer ${token}`
-  };
+    return {
+        Authorization: `Bearer ${token}`,
+    };
 }
-

frontend/src/api/config.js

@@ -1 +1 @@
-export const API_BASE = import.meta.env.VITE_API_BASE || '/v1';
+export const API_BASE = import.meta.env.VITE_API_BASE || "/v1";

frontend/src/api/notificationConfig.jsx

@@ -1,116 +1,183 @@
-import { getAuthHeaders } from './authHeaders';
-import { API_BASE } from './config';
+import { getAuthHeaders } from "./authHeaders";
+import { API_BASE } from "./config";
 
 /**
  * Get notification configuration for current user
  * @returns {Promise<Object>} Notification config
  */
 export async function getNotificationConfig() {
-  try {
-    const headers = await getAuthHeaders();
-    const response = await fetch(`${API_BASE}/notification-config`, {
-      headers: headers
-    });
+    try {
+        const headers = await getAuthHeaders();
+        const response = await fetch(`${API_BASE}/notification-config`, {
+            headers: headers,
+        });
 
-    if (!response.ok) {
-      let errorMessage = 'Failed to fetch notification config';
-      try {
-        const error = await response.json();
-        errorMessage = error.message || errorMessage;
-      } catch {
-        errorMessage = `Server error: ${response.status} ${response.statusText}`;
-      }
-      throw new Error(errorMessage);
-    }
+        if (!response.ok) {
+            let errorMessage = "Failed to fetch notification config";
+            try {
+                const error = await response.json();
+                errorMessage = error.message || errorMessage;
+            } catch {
+                errorMessage = `Server error: ${response.status} ${response.statusText}`;
+            }
+            throw new Error(errorMessage);
+        }
 
-    return response.json();
-  } catch (error) {
-    if (error.message.includes('fetch')) {
-      throw new Error('Cannot connect to server. Is the backend running?');
+        return response.json();
+    } catch (error) {
+        if (error.message.includes("fetch")) {
+            throw new Error(
+                "Cannot connect to server. Is the backend running?",
+            );
+        }
+        throw error;
     }
-    throw error;
-  }
 }
 
 /**
  * Update notification configuration
- * @param {Object} config - Configuration to update
- * @param {string} [config.discord_webhook_url] - Discord webhook URL
- * @param {string} [config.slack_webhook_url] - Slack webhook URL
- * @param {string} [config.email] - Email address
- * @param {boolean} [config.notification_enabled] - Enable/disable notifications
+ * @param {Object} config
+ * @param {string} [config.discord_webhook_url]
+ * @param {string} [config.telegram_chat_id]
+ * @param {string} [config.telegram_bot_token]
+ * @param {string} [config.email]
+ * @param {string} [config.slack_webhook_url]
+ * @param {boolean} [config.notification_enabled]
  * @returns {Promise<Object>} Updated config
  */
 export async function updateNotificationConfig(config) {
-  try {
-    const headers = await getAuthHeaders();
-    const response = await fetch(`${API_BASE}/notification-config`, {
-      method: 'PUT',
-      headers: headers,
-      body: JSON.stringify(config)
-    });
+    try {
+        const headers = await getAuthHeaders();
+        const response = await fetch(`${API_BASE}/notification-config`, {
+            method: "PUT",
+            headers: headers,
+            body: JSON.stringify(config),
+        });
 
-    if (!response.ok) {
-      let errorMessage = 'Failed to update notification config';
-      try {
-        const error = await response.json();
-        errorMessage = error.message || errorMessage;
-      } catch {
-        errorMessage = `Server error: ${response.status} ${response.statusText}`;
-      }
-      throw new Error(errorMessage);
-    }
+        if (!response.ok) {
+            let errorMessage = "Failed to update notification config";
+            try {
+                const error = await response.json();
+                errorMessage = error.message || errorMessage;
+            } catch {
+                errorMessage = `Server error: ${response.status} ${response.statusText}`;
+            }
+            throw new Error(errorMessage);
+        }
 
-    return response.json();
-  } catch (error) {
-    if (error.message.includes('fetch')) {
-      throw new Error('Cannot connect to server. Is the backend running?');
+        return response.json();
+    } catch (error) {
+        if (error.message.includes("fetch")) {
+            throw new Error(
+                "Cannot connect to server. Is the backend running?",
+            );
+        }
+        throw error;
     }
-    throw error;
-  }
 }
 
 /**
- * Test a webhook URL by sending a test message via the backend
- * @param {string} type - 'discord' or 'slack'
- * @param {string} webhookUrl - Webhook URL to test
- * @returns {Promise<boolean>} True if test successful
+ * Set up email notifications via Resend.
+ * Reads the user's saved email from their config and sends a confirmation.
+ * @returns {Promise<Object>} Setup result
  */
-async function testWebhook(type, webhookUrl) {
-  try {
-    const headers = await getAuthHeaders();
-    const response = await fetch(`${API_BASE}/notification-config/test`, {
-      method: 'POST',
-      headers: headers,
-      body: JSON.stringify({ type, url: webhookUrl })
-    });
+export async function setupEmail() {
+    try {
+        const headers = await getAuthHeaders();
+        const response = await fetch(`${API_BASE}/email/setup`, {
+            method: "POST",
+            headers: headers,
+        });
 
-    if (!response.ok) {
-      return false;
+        if (!response.ok) {
+            let errorMessage = "Failed to set up email";
+            try {
+                const error = await response.json();
+                errorMessage = error.message || errorMessage;
+            } catch {
+                errorMessage = `Server error: ${response.status} ${response.statusText}`;
+            }
+            throw new Error(errorMessage);
+        }
+
+        return response.json();
+    } catch (error) {
+        if (error.message.includes("fetch")) {
+            throw new Error(
+                "Cannot connect to server. Is the backend running?",
+            );
+        }
+        throw error;
     }
-
-    const result = await response.json();
-    return result.success === true;
-  } catch (error) {
-    console.error(`${type} webhook test failed:`, error);
-    return false;
-  }
 }
 
 /**
- * Test a Discord webhook URL
- * @param {string} webhookUrl - Discord webhook URL to test
- * @returns {Promise<boolean>} True if test successful
+ * Send an alert digest email to the user's configured email address.
+ * @returns {Promise<Object>} Digest send result
  */
-export async function testDiscordWebhook(webhookUrl) {
-  return testWebhook('discord', webhookUrl);
+export async function sendEmailDigest() {
+    try {
+        const headers = await getAuthHeaders();
+        const response = await fetch(`${API_BASE}/email/digest`, {
+            method: "POST",
+            headers: headers,
+        });
+
+        if (!response.ok) {
+            let errorMessage = "Failed to send digest";
+            try {
+                const error = await response.json();
+                errorMessage = error.message || errorMessage;
+            } catch {
+                errorMessage = `Server error: ${response.status} ${response.statusText}`;
+            }
+            throw new Error(errorMessage);
+        }
+
+        return response.json();
+    } catch (error) {
+        if (error.message.includes("fetch")) {
+            throw new Error(
+                "Cannot connect to server. Is the backend running?",
+            );
+        }
+        throw error;
+    }
 }
 
 /**
- * Test a Slack webhook URL
- * @param {string} webhookUrl - Slack webhook URL to test
- * @returns {Promise<boolean>} True if test successful
+ * Test all configured notification channels via the backend
+ * @returns {Promise<Object>} Results per channel
  */
-export async function testSlackWebhook(webhookUrl) {
-  return testWebhook('slack', webhookUrl);
+export async function testNotificationChannels() {
+    try {
+        const headers = await getAuthHeaders();
+        const response = await fetch(
+            `${API_BASE}/notification-config/test`,
+            {
+                method: "POST",
+                headers: headers,
+            },
+        );
+
+        if (!response.ok) {
+            let errorMessage = "Failed to test notification channels";
+            try {
+                const error = await response.json();
+                errorMessage = error.message || errorMessage;
+            } catch {
+                errorMessage = `Server error: ${response.status} ${response.statusText}`;
+            }
+            throw new Error(errorMessage);
+        }
+
+        return response.json();
+    } catch (error) {
+        if (error.message.includes("fetch")) {
+            throw new Error(
+                "Cannot connect to server. Is the backend running?",
+            );
+        }
+        throw error;
+    }
 }