m

Setup free tier

.gitea/workflows/check.yml

@@ -1,9 +0,0 @@
-name: check
-on: [push]
-jobs:
-    check:
-        runs-on: ubuntu-latest
-        steps:
-            # actions/checkout v4.2.2, 2026-02-22
-            - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
-            - run: docker build .

.gitignore

@@ -21,7 +21,9 @@ node_modules/
 *.key
 
 # Go build artifacts
-backend-go/bin/
+backend/bin/
+backend/api
+backend/poller
 *.exe
 *.exe~
 *.dll
@@ -42,3 +44,4 @@ Prompts/
 
 # Logs
 *.log
+.claude

.prettierignore

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

LICENSE

@@ -2,8 +2,7 @@ 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
+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

Makefile

@@ -2,7 +2,7 @@
         test-go test-js lint-go lint-js fmt-go fmt-js fmt-check-go fmt-check-js \
         build-go build-js
 
-GODIR    := backend-go
+GODIR    := backend
 JSDIR    := frontend
 PRETTIER := $(JSDIR)/node_modules/.bin/prettier
 

README.md

@@ -1,9 +1,9 @@
 # Koin Ping
+A lightweight on-chain monitoring and alerting system designed to give users situational awareness over blockchain addresses they care about.
 
-Koin Ping is an MIT-licensed blockchain monitoring system by Steven Jannette
-that polls Ethereum addresses for on-chain activity and delivers real-time
-alerts to users via a Go REST API backend and a React single-page application
-frontend.
+# Overview
+
+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
 
@@ -28,8 +28,8 @@ make hooks
 cd frontend && npm install && cd ..
 
 # Copy and fill in environment variables
-cp backend-go/.env.example backend-go/.env
-# edit backend-go/.env with your DATABASE_URL, FIREBASE_PROJECT_ID, ETH_RPC_URL
+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
@@ -38,23 +38,23 @@ make check
 make run
 
 # Start the poller (separate terminal)
-cd backend-go && go run ./cmd/poller
+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.
+`http://localhost:3000` by default for development.
 
 ## Rationale
 
-Crypto users who hold or actively monitor addresses need a lightweight, reliable
-way to know when on-chain activity occurs without polling block explorers
-manually. Koin Ping fills that gap: it watches a set of Ethereum addresses,
-evaluates configurable alert rules (incoming transactions, outgoing
-transactions, large transfers, balance thresholds), and notifies the user
-through Discord webhooks.
+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
 
@@ -63,7 +63,7 @@ frontend:
 
 ```
 koin_ping_0.2.0/
-├── backend-go/                # Go monorepo root
+├── backend/                # Go monorepo root
 │   ├── cmd/api/               # HTTP REST API server
 │   ├── cmd/poller/            # Blockchain polling daemon
 │   └── internal/
@@ -99,19 +99,51 @@ to the database, and dispatches Discord notifications.
 Firebase, communicates with the API via fetch, and renders the address/alert
 management UI.
 
-## TODO
+## Setting Up Your Alert Platforms
 
-- [ ] Switch frontend package manager from npm to yarn (per repo policy)
-- [ ] Rename `go.mod` module path from `github.com/kjannette/koin-ping` to
-      `sneak.berlin/go/koin-ping` (per repo policy)
-- [ ] Move database migrations to `internal/db/migrations/` and embed them in
-      the binary
-- [ ] Pin all Docker base images by `@sha256` in Dockerfile
-- [ ] Install `golangci-lint` locally and pass `make lint`
-- [ ] Add vitest unit tests for the React frontend
-- [ ] Add a `make db-reset` / `make migrate` target for schema management
-- [ ] Set HTTP server read/write timeouts (currently unbounded)
-- [ ] Replace `log.Printf` calls with structured `log/slog`
+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
+   ```
+
+4. In the JSON response, find the `"chat"` object — the `"id"` field is your **Chat ID** (a numeric value).
+
+   > **Tip:** If the `'result"` array is empty, make sure you sent a message to your bot first, then refresh the page.
+
+#### 3. Save in Koin Ping
+
+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.
+
+---
+
+*Guides for Discord, Slack, and Email coming soon.*
 
 ## License
 
@@ -120,3 +152,5 @@ MIT. See [LICENSE](LICENSE).
 ## Author
 
 Steven Jannette
+
+

REPO_POLICIES.md

@@ -1,188 +0,0 @@
----
-title: Repository Policies
-last_modified: 2026-02-22
----
-
-This document covers repository structure, tooling, and workflow standards. Code
-style conventions are in separate documents:
-
-- [Code Styleguide](https://git.eeqj.de/sneak/prompts/raw/branch/main/prompts/CODE_STYLEGUIDE.md)
-  (general, bash, Docker)
-- [Go](https://git.eeqj.de/sneak/prompts/raw/branch/main/prompts/CODE_STYLEGUIDE_GO.md)
-- [JavaScript](https://git.eeqj.de/sneak/prompts/raw/branch/main/prompts/CODE_STYLEGUIDE_JS.md)
-- [Python](https://git.eeqj.de/sneak/prompts/raw/branch/main/prompts/CODE_STYLEGUIDE_PYTHON.md)
-- [Go HTTP Server Conventions](https://git.eeqj.de/sneak/prompts/raw/branch/main/prompts/GO_HTTP_SERVER_CONVENTIONS.md)
-
----
-
-- Cross-project documentation (such as this file) must include
-  `last_modified: YYYY-MM-DD` in the YAML front matter so it can be kept in sync
-  with the authoritative source as policies evolve.
-
-- **ALL external references must be pinned by cryptographic hash.** This
-  includes Docker base images, Go modules, npm packages, GitHub Actions, and
-  anything else fetched from a remote source. Version tags (`@v4`, `@latest`,
-  `:3.21`, etc.) are server-mutable and therefore remote code execution
-  vulnerabilities. The ONLY acceptable way to reference an external dependency
-  is by its content hash (Docker `@sha256:...`, Go module hash in `go.sum`, npm
-  integrity hash in lockfile, GitHub Actions `@<commit-sha>`). No exceptions.
-  This also means never `curl | bash` to install tools like pyenv, nvm, rustup,
-  etc. Instead, download a specific release archive from GitHub, verify its hash
-  (hardcoded in the Dockerfile or script), and only then install. Unverified
-  install scripts are arbitrary remote code execution. This is the single most
-  important rule in this document. Double-check every external reference in
-  every file before committing. There are zero exceptions to this rule.
-
-- Every repo with software must have a root `Makefile` with these targets:
-  `make test`, `make lint`, `make fmt` (writes), `make fmt-check` (read-only),
-  `make check` (prereqs: `test`, `lint`, `fmt-check`), `make docker`, and
-  `make hooks` (installs pre-commit hook). A model Makefile is at
-  `https://git.eeqj.de/sneak/prompts/raw/branch/main/Makefile`.
-
-- Always use Makefile targets (`make fmt`, `make test`, `make lint`, etc.)
-  instead of invoking the underlying tools directly. The Makefile is the single
-  source of truth for how these operations are run.
-
-- The Makefile is authoritative documentation for how the repo is used. Beyond
-  the required targets above, it should have targets for every common operation:
-  running a local development server (`make run`, `make dev`), re-initializing
-  or migrating the database (`make db-reset`, `make migrate`), building
-  artifacts (`make build`), generating code, seeding data, or anything else a
-  developer would do regularly. If someone checks out the repo and types
-  `make<tab>`, they should see every meaningful operation available. A new
-  contributor should be able to understand the entire development workflow by
-  reading the Makefile.
-
-- Every repo should have a `Dockerfile`. All Dockerfiles must run `make check`
-  as a build step so the build fails if the branch is not green. For non-server
-  repos, the Dockerfile should bring up a development environment and run
-  `make check`. For server repos, `make check` should run as an early build
-  stage before the final image is assembled.
-
-- Every repo should have a Gitea Actions workflow (`.gitea/workflows/`) that
-  runs `docker build .` on push. Since the Dockerfile already runs `make check`,
-  a successful build implies all checks pass.
-
-- Use platform-standard formatters: `black` for Python, `prettier` for
-  JS/CSS/Markdown/HTML, `go fmt` for Go. Always use default configuration with
-  two exceptions: four-space indents (except Go), and `proseWrap: always` for
-  Markdown (hard-wrap at 80 columns). Documentation and writing repos (Markdown,
-  HTML, CSS) should also have `.prettierrc` and `.prettierignore`.
-
-- Pre-commit hook: `make check` if local testing is possible, otherwise
-  `make lint && make fmt-check`. The Makefile should provide a `make hooks`
-  target to install the pre-commit hook.
-
-- All repos with software must have tests that run via the platform-standard
-  test framework (`go test`, `pytest`, `jest`/`vitest`, etc.). If no meaningful
-  tests exist yet, add the most minimal test possible — e.g. importing the
-  module under test to verify it compiles/parses. There is no excuse for
-  `make test` to be a no-op.
-
-- `make test` must complete in under 20 seconds. Add a 30-second timeout in the
-  Makefile.
-
-- Docker builds must complete in under 5 minutes.
-
-- `make check` must not modify any files in the repo. Tests may use temporary
-  directories.
-
-- `main` must always pass `make check`, no exceptions.
-
-- Never commit secrets. `.env` files, credentials, API keys, and private keys
-  must be in `.gitignore`. No exceptions.
-
-- `.gitignore` should be comprehensive from the start: OS files (`.DS_Store`),
-  editor files (`.swp`, `*~`), language build artifacts, and `node_modules/`.
-  Fetch the standard `.gitignore` from
-  `https://git.eeqj.de/sneak/prompts/raw/branch/main/.gitignore` when setting up
-  a new repo.
-
-- Never use `git add -A` or `git add .`. Always stage files explicitly by name.
-
-- Never force-push to `main`.
-
-- Make all changes on a feature branch. You can do whatever you want on a
-  feature branch.
-
-- `.golangci.yml` is standardized and must _NEVER_ be modified by an agent, only
-  manually by the user. Fetch from
-  `https://git.eeqj.de/sneak/prompts/raw/branch/main/.golangci.yml`.
-
-- When pinning images or packages by hash, add a comment above the reference
-  with the version and date (YYYY-MM-DD).
-
-- Use `yarn`, not `npm`.
-
-- Write all dates as YYYY-MM-DD (ISO 8601).
-
-- Simple projects should be configured with environment variables.
-
-- Dockerized web services listen on port 8080 by default, overridable with
-  `PORT`.
-
-- `README.md` is the primary documentation. Required sections:
-    - **Description**: First line must include the project name, purpose,
-      category (web server, SPA, CLI tool, etc.), license, and author. Example:
-      "µPaaS is an MIT-licensed Go web application by @sneak that receives
-      git-frontend webhooks and deploys applications via Docker in realtime."
-    - **Getting Started**: Copy-pasteable install/usage code block.
-    - **Rationale**: Why does this exist?
-    - **Design**: How is the program structured?
-    - **TODO**: Update meticulously, even between commits. When planning, put
-      the todo list in the README so a new agent can pick up where the last one
-      left off.
-    - **License**: MIT, GPL, or WTFPL. Ask the user for new projects. Include a
-      `LICENSE` file in the repo root and a License section in the README.
-    - **Author**: [@sneak](https://sneak.berlin).
-
-- First commit of a new repo should contain only `README.md`.
-
-- Go module root: `sneak.berlin/go/<name>`. Always run `go mod tidy` before
-  committing.
-
-- Use SemVer.
-
-- Database migrations live in `internal/db/migrations/` and must be embedded in
-  the binary.
-    - `000_migration.sql` — contains ONLY the creation of the migrations
-      tracking table itself. Nothing else.
-    - `001_schema.sql` — the full application schema.
-    - **Pre-1.0.0:** never add additional migration files (002, 003, etc.).
-      There is no installed base to migrate. Edit `001_schema.sql` directly.
-    - **Post-1.0.0:** add new numbered migration files for each schema change.
-      Never edit existing migrations after release.
-
-- All repos should have an `.editorconfig` enforcing the project's indentation
-  settings.
-
-- Avoid putting files in the repo root unless necessary. Root should contain
-  only project-level config files (`README.md`, `Makefile`, `Dockerfile`,
-  `LICENSE`, `.gitignore`, `.editorconfig`, `REPO_POLICIES.md`, and
-  language-specific config). Everything else goes in a subdirectory. Canonical
-  subdirectory names:
-    - `bin/` — executable scripts and tools
-    - `cmd/` — Go command entrypoints
-    - `configs/` — configuration templates and examples
-    - `deploy/` — deployment manifests (k8s, compose, terraform)
-    - `docs/` — documentation and markdown (README.md stays in root)
-    - `internal/` — Go internal packages
-    - `internal/db/migrations/` — database migrations
-    - `pkg/` — Go library packages
-    - `share/` — systemd units, data files
-    - `static/` — static assets (images, fonts, etc.)
-    - `web/` — web frontend source
-
-- When setting up a new repo, files from the `prompts` repo may be used as
-  templates. Fetch them from
-  `https://git.eeqj.de/sneak/prompts/raw/branch/main/<path>`.
-
-- New repos must contain at minimum:
-    - `README.md`, `.git`, `.gitignore`, `.editorconfig`
-    - `LICENSE`, `REPO_POLICIES.md` (copy from the `prompts` repo)
-    - `Makefile`
-    - `Dockerfile`, `.dockerignore`
-    - `.gitea/workflows/check.yml`
-    - Go: `go.mod`, `go.sum`, `.golangci.yml`
-    - JS: `package.json`, `yarn.lock`, `.prettierrc`, `.prettierignore`
-    - Python: `pyproject.toml`

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

@@ -1,7 +0,0 @@
-Start DB:
-
-brew services start postgresql@15
-
-Run Backend:
-
-cd /Users/kjannette/workspace/koin_ping/backend-go go run ./cmd/api

backend-go/cmd/api/main.go

@@ -1,125 +0,0 @@
-// 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-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"
-)
-
-const (
-	// serverReadTimeoutSeconds is the maximum duration to read a request.
-	serverReadTimeoutSeconds = 5
-	// serverWriteTimeoutSeconds is the maximum duration 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()
-
-	addressModel := models.NewAddressModel(pool)
-	alertRuleModel := models.NewAlertRuleModel(pool)
-	alertEventModel := models.NewAlertEventModel(pool)
-	notifConfigModel := models.NewNotificationConfigModel(pool)
-
-	addressHandler := handlers.NewAddressHandler(addressModel)
-	alertRuleHandler := handlers.NewAlertRuleHandler(alertRuleModel, addressModel)
-	alertEventHandler := handlers.NewAlertEventHandler(alertEventModel)
-	notifConfigHandler := handlers.NewNotificationConfigHandler(notifConfigModel)
-
-	mux := http.NewServeMux()
-	b := cfg.APIBasePath // e.g. "/v1"
-
-	// Public routes
-	mux.HandleFunc("GET "+b+"/health", handlers.HealthCheck)
-	mux.HandleFunc("GET "+b+"/status", handlers.SystemStatus)
-
-	// Authenticated routes — addresses
-	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)))
-
-	// Authenticated routes — alert rules
-	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)))
-
-	// Authenticated routes — alert events
-	mux.Handle("GET "+b+"/alert-events",
-		middleware.Authenticate(http.HandlerFunc(alertEventHandler.List)))
-
-	// Authenticated routes — notification config
-	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)))
-
-	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-go/internal/handlers/notification_config.go

@@ -1,128 +0,0 @@
-package handlers
-
-import (
-	"encoding/json"
-	"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"
-)
-
-var emailRe = regexp.MustCompile(`^[^\s@]+@[^\s@]+\.[^\s@]+$`)
-
-type NotificationConfigHandler struct {
-	configs *models.NotificationConfigModel
-}
-
-func NewNotificationConfigHandler(configs *models.NotificationConfigModel) *NotificationConfigHandler {
-	return &NotificationConfigHandler{configs: configs}
-}
-
-func (h *NotificationConfigHandler) GetConfig(w http.ResponseWriter, r *http.Request) {
-	userID := middleware.GetUserID(r.Context())
-	log.Printf("User %s getting notification config", userID)
-
-	cfg, err := h.configs.GetConfig(r.Context(), userID)
-	if err != nil {
-		log.Printf("Error getting notification config: %v", err)
-		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to get notification config")
-		return
-	}
-
-	if cfg == nil {
-		writeJSON(w, http.StatusOK, domain.NotificationConfig{
-			UserID:              userID,
-			NotificationEnabled: true,
-		})
-		return
-	}
-
-	log.Println("Config found")
-	writeJSON(w, http.StatusOK, cfg)
-}
-
-func (h *NotificationConfigHandler) UpdateConfig(w http.ResponseWriter, r *http.Request) {
-	userID := middleware.GetUserID(r.Context())
-
-	var body struct {
-		DiscordWebhookURL   *string `json:"discord_webhook_url"`
-		TelegramChatID      *string `json:"telegram_chat_id"`
-		Email               *string `json:"email"`
-		NotificationEnabled *bool   `json:"notification_enabled"`
-	}
-	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
-		log.Printf("Failed to decode notification config request body: %v", err)
-		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "Invalid request body")
-		return
-	}
-
-	log.Printf("User %s updating notification config", userID)
-
-	if body.DiscordWebhookURL == nil && body.TelegramChatID == nil &&
-		body.Email == nil && body.NotificationEnabled == nil {
-		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR",
-			"At least one configuration field must be provided")
-		return
-	}
-
-	if body.DiscordWebhookURL != nil && *body.DiscordWebhookURL != "" &&
-		!strings.HasPrefix(*body.DiscordWebhookURL, "https://discord.com/api/webhooks/") {
-		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR",
-			"Invalid Discord webhook URL format")
-		return
-	}
-
-	if body.Email != nil && *body.Email != "" && !emailRe.MatchString(*body.Email) {
-		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR",
-			"Invalid email address format")
-		return
-	}
-
-	enabled := true
-	if body.NotificationEnabled != nil {
-		enabled = *body.NotificationEnabled
-	}
-
-	cfg := domain.NotificationConfig{
-		DiscordWebhookURL:   body.DiscordWebhookURL,
-		TelegramChatID:      body.TelegramChatID,
-		Email:               body.Email,
-		NotificationEnabled: enabled,
-	}
-
-	updated, err := h.configs.UpsertConfig(r.Context(), userID, cfg)
-	if err != nil {
-		log.Printf("Error updating notification config: %v", err)
-		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR",
-			"Failed to update notification configuration")
-		return
-	}
-
-	log.Println("Notification config updated")
-	writeJSON(w, http.StatusOK, updated)
-}
-
-func (h *NotificationConfigHandler) DeleteConfig(w http.ResponseWriter, r *http.Request) {
-	userID := middleware.GetUserID(r.Context())
-	log.Printf("User %s deleting notification config", userID)
-
-	deleted, err := h.configs.Remove(r.Context(), userID)
-	if err != nil {
-		log.Printf("Error deleting notification config: %v", err)
-		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR",
-			"Failed to delete notification configuration")
-		return
-	}
-
-	if !deleted {
-		writeError(w, http.StatusNotFound, "NOT_FOUND", "No notification configuration found")
-		return
-	}
-
-	log.Println("Notification config deleted")
-	w.WriteHeader(http.StatusNoContent)
-}

backend-go/internal/handlers/status.go

@@ -1,23 +0,0 @@
-package handlers
-
-import (
-	"net/http"
-	"time"
-)
-
-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",
-	})
-}
-
-func SystemStatus(w http.ResponseWriter, r *http.Request) {
-	writeJSON(w, http.StatusOK, map[string]interface{}{
-		"latestBlock": 0,
-		"lag":         0,
-		"status":      "healthy",
-		"timestamp":   time.Now().UTC().Format(time.RFC3339),
-	})
-}

backend-go/internal/middleware/auth.go

@@ -1,99 +0,0 @@
-// 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-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

@@ -1,115 +0,0 @@
-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"
-)
-
-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, alertType.String(), 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 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, enabled, created_at`,
-		id, enabled,
-	).Scan(&r.ID, &r.AddressID, &r.Type, &r.Threshold, &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) 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/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/services/evaluator.go

@@ -1,236 +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
-}
-
-func NewEvaluatorService(
-	eth ethereum.EthereumObserver,
-	alertRules *models.AlertRuleModel,
-	alertEvents *models.AlertEventModel,
-	addresses *models.AddressModel,
-	notifConfigs *models.NotificationConfigModel,
-) *EvaluatorService {
-	return &EvaluatorService{
-		eth:          eth,
-		alertRules:   alertRules,
-		alertEvents:  alertEvents,
-		addresses:    addresses,
-		notifConfigs: notifConfigs,
-	}
-}
-
-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)
-
-	// Send Discord notification (non-fatal on failure)
-	if addr != nil {
-		go func() {
-			s.sendNotification(
-				ctx, addr.UserID, message, obs, addressLabel, rule, addr.Address,
-			)
-		}()
-	}
-
-	return nil
-}
-
-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 || notifConfig.DiscordWebhookURL == nil {
-		return
-	}
-
-	sent, err := notifications.SendDiscordNotification(
-		*notifConfig.DiscordWebhookURL,
-		message,
-		notifications.AlertMetadata{
-			TxHash:       obs.Hash,
-			AddressLabel: addressLabel,
-			AlertType:    string(rule.Type),
-			Address:      address,
-		},
-	)
-
-	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)
-	}
-}
-
-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/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

@@ -12,11 +12,11 @@ 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/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 (
@@ -51,6 +51,7 @@ func main() {
 
 	defer database.Close()
 
+	userModel := models.NewUserModel(pool)
 	addressModel := models.NewAddressModel(pool)
 	alertRuleModel := models.NewAlertRuleModel(pool)
 	alertEventModel := models.NewAlertEventModel(pool)
@@ -58,7 +59,10 @@ func main() {
 	notifConfigModel := models.NewNotificationConfigModel(pool)
 
 	observer := services.NewObserverService(eth, addressModel, checkpointModel)
-	evaluator := services.NewEvaluatorService(eth, alertRuleModel, alertEventModel, addressModel, notifConfigModel)
+	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()
@@ -75,12 +79,14 @@ func main() {
 	}()
 
 	interval := time.Duration(cfg.PollIntervalMS) * time.Millisecond
+	digestInterval := time.Duration(cfg.DigestIntervalHours) * time.Hour
 
 	log.Println(strings.Repeat("=", separatorWidth))
 	log.Println("Koin Ping Observer Poller Starting")
 	log.Println(strings.Repeat("=", separatorWidth))
 	log.Printf("RPC URL: %s", cfg.EthRPCURL)
 	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)
@@ -88,6 +94,9 @@ func main() {
 	ticker := time.NewTicker(interval)
 	defer ticker.Stop()
 
+	digestTicker := time.NewTicker(digestInterval)
+	defer digestTicker.Stop()
+
 	for {
 		select {
 		case <-ctx.Done():
@@ -96,6 +105,13 @@ func main() {
 			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)
+			}
 		}
 	}
 }
@@ -122,6 +138,8 @@ func runCycle(
 		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

@@ -0,0 +1,2 @@
+ALTER TABLE user_notification_configs
+  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)
 );
 
 
@@ -51,17 +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)
   telegram_chat_id VARCHAR(128),       -- Telegram chat ID (nullable)
-  telegram_bot_token VARCHAR(255),     -- Telegram bot token (nullable, future use)
+  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

@@ -13,6 +13,7 @@ const (
 	defaultDBPort = 5432
 	defaultPollIntervalMS = 60000
 	minPollIntervalMS = 1000
+	defaultDigestIntervalHours = 24
 )
 
 type Config struct {
@@ -28,6 +29,15 @@ type Config struct {
 	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.
@@ -45,6 +55,15 @@ func Load() (*Config, error) {
 		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 {
@@ -75,6 +94,19 @@ func (c *Config) DSN() string {
 	)
 }
 
+// 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

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

@@ -1,4 +1,3 @@
-// Package database manages PostgreSQL connection pools.
 package database
 
 import (
@@ -11,21 +10,21 @@ import (
 )
 
 const (
-	// maxConnIdleSeconds is the maximum idle time for a connection.
+
 	maxConnIdleSeconds = 30
-	// maxConnLifetimeMinutes is the maximum lifetime for a connection.
+
 	maxConnLifetimeMinutes = 5
-	// connectTimeoutSeconds is the timeout for initial connection.
+
 	connectTimeoutSeconds = 10
-	// maxConns is the maximum number of connections in the pool.
+
 	maxConns = 20
-	// minConns is the minimum number of connections in the pool.
+
 	minConns = 2
 )
 
 var pool *pgxpool.Pool //nolint:gochecknoglobals
 
-// Connect establishes a PostgreSQL connection pool using the given DSN.
+// establishPostgreSQL connection pool using the given DSN.
 func Connect(dsn string) (*pgxpool.Pool, error) {
 	cfg, err := pgxpool.ParseConfig(dsn)
 	if err != nil {
@@ -57,12 +56,10 @@ func Connect(dsn string) (*pgxpool.Pool, error) {
 	return p, nil
 }
 
-// Pool returns the global connection pool.
 func Pool() *pgxpool.Pool {
 	return pool
 }
 
-// Close closes the global connection pool.
 func Close() {
 	if pool != nil {
 		pool.Close()

backend/internal/domain/types.go

@@ -1,9 +1,80 @@
-// Package domain defines core domain types shared across the application.
 package domain
 
 import "time"
 
-// Address represents a tracked Ethereum address.
+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
@@ -12,13 +83,10 @@ type Address struct {
 	CreatedAt time.Time `json:"created_at"` //nolint:tagliatelle
 }
 
-// AlertType identifies the kind of alert rule.
 type AlertType string
 
-// String implements fmt.Stringer.
 func (a AlertType) String() string { return string(a) }
 
-// Alert type constants define the supported alert triggers.
 const (
 	AlertIncomingTx    AlertType = "incoming_tx"
 	AlertOutgoingTx    AlertType = "outgoing_tx"
@@ -26,7 +94,6 @@ const (
 	AlertBalanceBelow  AlertType = "balance_below"
 )
 
-// ValidAlertTypes lists all alert types accepted by the API.
 var ValidAlertTypes = []AlertType{ //nolint:gochecknoglobals
 	AlertIncomingTx,
 	AlertOutgoingTx,
@@ -40,7 +107,7 @@ var ThresholdRequiredTypes = []AlertType{ //nolint:gochecknoglobals
 	AlertBalanceBelow,
 }
 
-// IsValidAlertType returns true if the given string matches a known AlertType.
+// returns true if the given string matches a known AlertType.
 func IsValidAlertType(t string) bool {
 	for _, v := range ValidAlertTypes {
 		if string(v) == t {
@@ -51,7 +118,6 @@ func IsValidAlertType(t string) bool {
 	return false
 }
 
-// IsThresholdRequired returns true if the given AlertType requires a threshold.
 func IsThresholdRequired(t AlertType) bool {
 	for _, v := range ThresholdRequiredTypes {
 		if v == t {
@@ -62,17 +128,17 @@ func IsThresholdRequired(t AlertType) bool {
 	return false
 }
 
-// AlertRule represents a user-defined alert rule for an address.
 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
 }
 
-// AlertEvent represents a fired alert event stored for history.
 type AlertEvent struct {
 	ID           int       `json:"id"`
 	AlertRuleID  int       `json:"alert_rule_id"`   //nolint:tagliatelle
@@ -82,14 +148,12 @@ type AlertEvent struct {
 	Timestamp    time.Time `json:"timestamp"`
 }
 
-// AddressCheckpoint tracks the last block checked for an address.
 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
 }
 
-// CheckpointDetail combines checkpoint and address info for reporting.
 type CheckpointDetail struct {
 	AddressID        int       `json:"address_id"`         //nolint:tagliatelle
 	Address          string    `json:"address"`
@@ -98,13 +162,14 @@ type CheckpointDetail struct {
 	LastCheckedAt    time.Time `json:"last_checked_at"`    //nolint:tagliatelle
 }
 
-// NotificationConfig holds a user's notification preferences.
+//  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,omitempty"` //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
@@ -118,21 +183,27 @@ type NormalizedTx struct {
 	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
 }
 
-// Direction indicates whether a transaction is incoming or outgoing.
 type Direction string
 
-// String implements fmt.Stringer.
 func (d Direction) String() string { return string(d) }
 
-// Direction constants indicate the flow of a transaction relative to a watched address.
 const (
 	DirectionIncoming Direction = "incoming"
 	DirectionOutgoing Direction = "outgoing"
 )
 
-// ObservedTx is a NormalizedTx enriched with address and direction context.
 type ObservedTx struct {
 	NormalizedTx
 	AddressID int       `json:"address_id"` //nolint:tagliatelle

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

@@ -1,4 +1,3 @@
-// Package firebase provides Firebase authentication integration.
 package firebase
 
 import (
@@ -17,7 +16,6 @@ var ( //nolint:gochecknoglobals
 	errInit    error        //nolint:gochecknoglobals
 )
 
-// Init initializes the Firebase app and auth client using the given project ID.
 func Init(projectID string) error {
 	once.Do(func() {
 		ctx := context.Background()
@@ -48,7 +46,6 @@ func Init(projectID string) error {
 	return errInit
 }
 
-// Auth returns the initialized Firebase auth client.
 func Auth() *auth.Client {
 	return authClient
 }

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

@@ -3,29 +3,28 @@ 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}$`)
 
-// AddressHandler handles HTTP requests for address management.
 type AddressHandler struct {
 	addresses *models.AddressModel
+	users     *models.UserModel
 }
 
-// NewAddressHandler creates a new AddressHandler.
-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}
 }
 
-// Create handles POST requests to add a new tracked address.
 func (h *AddressHandler) Create(w http.ResponseWriter, r *http.Request) {
 	userID := middleware.GetUserID(r.Context())
 
@@ -52,6 +51,28 @@ func (h *AddressHandler) Create(w http.ResponseWriter, r *http.Request) {
 		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)
@@ -92,6 +113,44 @@ 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())

backend/internal/handlers/alert_event.go

@@ -4,11 +4,10 @@ import (
 	"log"
 	"net/http"
 	"strconv"
-	"time"
 
-	"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"
 )
 
 // AlertEventHandler handles HTTP requests for alert event history.
@@ -51,45 +50,9 @@ func (h *AlertEventHandler) List(w http.ResponseWriter, r *http.Request) {
 
 	log.Printf("Found %d alert events for user", len(events))
 
-	// MVP scaffolding: return mock data if DB is empty
-	if len(events) == 0 {
-		events = mockEvents(limit)
+	if events == nil {
+		events = []domain.AlertEvent{}
 	}
 
 	writeJSON(w, http.StatusOK, events)
 }
-
-func mockEvents(limit int) []domain.AlertEvent {
-	label1 := "Treasury Wallet"
-	label2 := "Cold Storage"
-
-	mocks := []domain.AlertEvent{
-		{
-			ID:           1,
-			AlertRuleID:  1,
-			Message:      "Incoming transaction detected: 5.5 ETH received",
-			AddressLabel: &label1,
-			Timestamp:    time.Now().Add(-2 * time.Hour),
-		},
-		{
-			ID:           2,           //nolint:mnd
-			AlertRuleID:  2,           //nolint:mnd
-			Message:      "Balance dropped below threshold: Current balance 8.2 ETH",
-			AddressLabel: &label1,
-			Timestamp:    time.Now().Add(-5 * time.Hour),
-		},
-		{
-			ID:           3,           //nolint:mnd
-			AlertRuleID:  3,           //nolint:mnd
-			Message:      "Outgoing transaction detected: 2.0 ETH sent",
-			AddressLabel: &label2,
-			Timestamp:    time.Now().Add(-24 * time.Hour),
-		},
-	}
-
-	if limit < len(mocks) {
-		return mocks[:limit]
-	}
-
-	return mocks
-}

backend/internal/handlers/alert_rule.go

@@ -9,26 +9,23 @@ import (
 	"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"
 )
 
-// errThresholdFormat is returned when the threshold JSON cannot be decoded.
 var errThresholdFormat = errors.New("unsupported threshold format")
 
-// AlertRuleHandler handles HTTP requests for alert rule management.
 type AlertRuleHandler struct {
 	alertRules *models.AlertRuleModel
 	addresses  *models.AddressModel
+	users      *models.UserModel
 }
 
-// NewAlertRuleHandler creates a new AlertRuleHandler.
-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}
 }
 
-// Create handles POST requests to create a new alert rule for an address.
 func (h *AlertRuleHandler) Create(w http.ResponseWriter, r *http.Request) {
 	userID := middleware.GetUserID(r.Context())
 	addressID, ok := parseIntParam(r.PathValue("addressId"))
@@ -41,6 +38,8 @@ func (h *AlertRuleHandler) Create(w http.ResponseWriter, r *http.Request) {
 	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)
@@ -57,6 +56,40 @@ func (h *AlertRuleHandler) Create(w http.ResponseWriter, r *http.Request) {
 		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
+	}
+
 	log.Printf("User %s creating alert: type=%s, addressID=%d", userID, body.Type, addressID)
 
 	if body.Type == "" {
@@ -100,7 +133,29 @@ func (h *AlertRuleHandler) Create(w http.ResponseWriter, r *http.Request) {
 		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")
@@ -186,7 +241,7 @@ func (h *AlertRuleHandler) ListByAddress(w http.ResponseWriter, r *http.Request)
 	writeJSON(w, http.StatusOK, alerts)
 }
 
-// UpdateStatus handles PATCH requests to enable or disable an alert rule.
+// 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"))
@@ -197,7 +252,10 @@ func (h *AlertRuleHandler) UpdateStatus(w http.ResponseWriter, r *http.Request)
 	}
 
 	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)
@@ -208,8 +266,8 @@ func (h *AlertRuleHandler) UpdateStatus(w http.ResponseWriter, r *http.Request)
 
 	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
 	}
@@ -228,15 +286,64 @@ func (h *AlertRuleHandler) UpdateStatus(w http.ResponseWriter, r *http.Request)
 		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")
+	var updated *domain.AlertRule
 
-		return
+	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)
 }
 

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

@@ -0,0 +1,237 @@
+package handlers
+
+import (
+	"encoding/json"
+	"log"
+	"net/http"
+	"regexp"
+	"strings"
+
+	"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, 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) {
+	userID := middleware.GetUserID(r.Context())
+	log.Printf("User %s getting notification config", userID)
+
+	cfg, err := h.configs.GetConfig(r.Context(), userID)
+	if err != nil {
+		log.Printf("Error getting notification config: %v", err)
+		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to get notification config")
+		return
+	}
+
+	if cfg == nil {
+		writeJSON(w, http.StatusOK, domain.NotificationConfig{
+			UserID:              userID,
+			NotificationEnabled: true,
+		})
+		return
+	}
+
+	log.Println("Config found")
+	writeJSON(w, http.StatusOK, cfg)
+}
+
+func (h *NotificationConfigHandler) UpdateConfig(w http.ResponseWriter, r *http.Request) {
+	userID := middleware.GetUserID(r.Context())
+
+	var body struct {
+		DiscordWebhookURL   *string `json:"discord_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 {
+		log.Printf("Failed to decode notification config request body: %v", err)
+		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "Invalid request body")
+		return
+	}
+
+	log.Printf("User %s updating notification config", userID)
+
+	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
+	}
+
+	if body.DiscordWebhookURL != nil && *body.DiscordWebhookURL != "" &&
+		!strings.HasPrefix(*body.DiscordWebhookURL, "https://discord.com/api/webhooks/") {
+		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR",
+			"Invalid Discord webhook URL format")
+		return
+	}
+
+	if body.SlackWebhookURL != nil && *body.SlackWebhookURL != "" &&
+		!strings.HasPrefix(*body.SlackWebhookURL, "https://hooks.slack.com/") {
+		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR",
+			"Invalid Slack webhook URL format")
+		return
+	}
+
+	if body.Email != nil && *body.Email != "" && !emailRe.MatchString(*body.Email) {
+		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR",
+			"Invalid email address format")
+		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
+	}
+
+	cfg := domain.NotificationConfig{
+		DiscordWebhookURL:   body.DiscordWebhookURL,
+		TelegramChatID:      body.TelegramChatID,
+		TelegramBotToken:    body.TelegramBotToken,
+		Email:               body.Email,
+		SlackWebhookURL:     body.SlackWebhookURL,
+		NotificationEnabled: enabled,
+	}
+
+	updated, err := h.configs.UpsertConfig(r.Context(), userID, cfg)
+	if err != nil {
+		log.Printf("Error updating notification config: %v", err)
+		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR",
+			"Failed to update notification configuration")
+		return
+	}
+
+	log.Println("Notification config updated")
+	writeJSON(w, http.StatusOK, updated)
+}
+
+func (h *NotificationConfigHandler) DeleteConfig(w http.ResponseWriter, r *http.Request) {
+	userID := middleware.GetUserID(r.Context())
+	log.Printf("User %s deleting notification config", userID)
+
+	deleted, err := h.configs.Remove(r.Context(), userID)
+	if err != nil {
+		log.Printf("Error deleting notification config: %v", err)
+		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR",
+			"Failed to delete notification configuration")
+		return
+	}
+
+	if !deleted {
+		writeError(w, http.StatusNotFound, "NOT_FOUND", "No notification configuration found")
+		return
+	}
+
+	log.Println("Notification config deleted")
+	w.WriteHeader(http.StatusNoContent)
+}
+
+// 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("Error getting notification config for test: %v", err)
+		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to get notification config")
+		return
+	}
+
+	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

@@ -6,7 +6,7 @@ import (
 
 	"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 {
@@ -55,12 +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
@@ -107,6 +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

@@ -3,10 +3,11 @@ 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 {
@@ -17,6 +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

backend/internal/models/notification_config.go

@@ -6,7 +6,7 @@ import (
 
 	"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 NotificationConfigModel struct {
@@ -21,12 +21,12 @@ func (m *NotificationConfigModel) GetConfig(ctx context.Context, userID string)
 	var c domain.NotificationConfig
 	err := m.pool.QueryRow(ctx,
 		`SELECT user_id, discord_webhook_url, telegram_chat_id, telegram_bot_token,
-		        email, notification_enabled, created_at, updated_at
+		        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.NotificationEnabled, &c.CreatedAt, &c.UpdatedAt)
+		&c.Email, &c.SlackWebhookURL, &c.NotificationEnabled, &c.CreatedAt, &c.UpdatedAt)
 	if err != nil {
 		if errors.Is(err, pgx.ErrNoRows) {
 			return nil, nil
@@ -40,22 +40,24 @@ func (m *NotificationConfigModel) UpsertConfig(ctx context.Context, userID strin
 	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, notification_enabled, updated_at)
-		 VALUES ($1, $2, $3, $4, $5, $6, NOW())
+		   (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 = COALESCE($2, user_notification_configs.discord_webhook_url),
-		   telegram_chat_id = COALESCE($3, user_notification_configs.telegram_chat_id),
-		   telegram_bot_token = COALESCE($4, user_notification_configs.telegram_bot_token),
-		   email = COALESCE($5, user_notification_configs.email),
-		   notification_enabled = $6,
+		   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, notification_enabled, created_at, updated_at`,
+		           email, slack_webhook_url, notification_enabled, created_at, updated_at`,
 		userID, cfg.DiscordWebhookURL, cfg.TelegramChatID, cfg.TelegramBotToken,
-		cfg.Email, cfg.NotificationEnabled,
+		cfg.Email, cfg.SlackWebhookURL, cfg.NotificationEnabled,
 	).Scan(&c.UserID, &c.DiscordWebhookURL, &c.TelegramChatID, &c.TelegramBotToken,
-		&c.Email, &c.NotificationEnabled, &c.CreatedAt, &c.UpdatedAt)
+		&c.Email, &c.SlackWebhookURL, &c.NotificationEnabled, &c.CreatedAt, &c.UpdatedAt)
 	if err != nil {
 		return nil, err
 	}
@@ -75,9 +77,12 @@ func (m *NotificationConfigModel) Remove(ctx context.Context, userID string) (bo
 
 func (m *NotificationConfigModel) ListEnabled(ctx context.Context) ([]domain.NotificationConfig, error) {
 	rows, err := m.pool.Query(ctx,
-		`SELECT user_id, discord_webhook_url, telegram_chat_id, email
-		 FROM user_notification_configs
-		 WHERE notification_enabled = TRUE`,
+		`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
@@ -87,7 +92,8 @@ func (m *NotificationConfigModel) ListEnabled(ctx context.Context) ([]domain.Not
 	var configs []domain.NotificationConfig
 	for rows.Next() {
 		var c domain.NotificationConfig
-		if err := rows.Scan(&c.UserID, &c.DiscordWebhookURL, &c.TelegramChatID, &c.Email); err != nil {
+		if err := rows.Scan(&c.UserID, &c.DiscordWebhookURL, &c.TelegramChatID,
+			&c.TelegramBotToken, &c.Email, &c.SlackWebhookURL); err != nil {
 			return nil, err
 		}
 		c.NotificationEnabled = true

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"
@@ -20,16 +21,17 @@ const (
 	colorBlue   = 0x0099ff
 )
 
-// discordHTTPClient is a shared HTTP client with a timeout for Discord requests.
 var discordHTTPClient = &http.Client{ //nolint:gochecknoglobals
 	Timeout: discordHTTPTimeoutSeconds * time.Second,
 }
 
-type AlertMetadata struct {
-	TxHash       string
-	AddressLabel string
-	AlertType    string
-	Address      string
+//  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 {
@@ -99,8 +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

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/src/App.jsx

@@ -1,35 +1,50 @@
 import { Routes, Route, Navigate } from "react-router-dom";
 import { useAuth } from "./contexts/AuthContext";
 import Navbar from "./components/Navbar";
-import Login from "./pages/Login";
+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 } = useAuth();
-
-    if (!currentUser) {
-        return (
-            <Routes>
-                <Route path="/login" element={<Login />} />
-                <Route path="/signup" element={<Signup />} />
-                <Route path="*" element={<Navigate to="/login" />} />
-            </Routes>
-        );
-    }
+  const { currentUser, isSubscribed } = useAuth();
 
+  if (!currentUser) {
     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="*" element={<Navigate to="/addresses" />} />
-            </Routes>
-        </div>
+      <Routes>
+        <Route path="/login" element={<Login />} />
+        <Route path="/signup" element={<Signup />} />
+        <Route path="/subscribe" element={<Subscribe />} />
+        <Route path="*" element={<Navigate to="/login" />} />
+      </Routes>
     );
+  }
+
+  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="/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

@@ -80,6 +80,41 @@ export async function getAddresses() {
     }
 }
 
+/**
+ * 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;
+    }
+}
+
 /**
  * Delete a tracked address
  * @param {number} addressId - Address ID to delete

frontend/src/api/alerts.jsx

@@ -129,6 +129,48 @@ export async function updateAlertStatus(alertId, enabled) {
     }
 }
 
+/**
+ * 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;
+    }
+}
+
 /**
  * Delete an alert rule
  * @param {number} alertId - Alert rule ID

frontend/src/api/notificationConfig.jsx

@@ -1,5 +1,3 @@
-// API client for notification configuration
-
 import { getAuthHeaders } from "./authHeaders";
 import { API_BASE } from "./config";
 
@@ -38,11 +36,13 @@ export async function getNotificationConfig() {
 
 /**
  * Update notification configuration
- * @param {Object} config - Configuration to update
- * @param {string} [config.discord_webhook_url] - Discord webhook URL
- * @param {string} [config.telegram_chat_id] - Telegram chat ID
- * @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) {
@@ -77,27 +77,107 @@ export async function updateNotificationConfig(config) {
 }
 
 /**
- * Test a Discord webhook URL
- * Sends a test message to verify the webhook works
- * @param {string} webhookUrl - Discord 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
  */
-export async function testDiscordWebhook(webhookUrl) {
+export async function setupEmail() {
     try {
-        const payload = {
-            content:
-                "Koin Ping test notification - Your Discord webhook is configured correctly!",
-        };
-
-        const response = await fetch(webhookUrl, {
+        const headers = await getAuthHeaders();
+        const response = await fetch(`${API_BASE}/email/setup`, {
             method: "POST",
-            headers: { "Content-Type": "application/json" },
-            body: JSON.stringify(payload),
+            headers: headers,
         });
 
-        return response.ok;
+        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} ${response.statusText}`;
+            }
+            throw new Error(errorMessage);
+        }
+
+        return response.json();
     } catch (error) {
-        console.error("Discord webhook test failed:", error);
-        return false;
+        if (error.message.includes("fetch")) {
+            throw new Error(
+                "Cannot connect to server. Is the backend running?",
+            );
+        }
+        throw error;
+    }
+}
+
+/**
+ * Send an alert digest email to the user's configured email address.
+ * @returns {Promise<Object>} Digest send result
+ */
+export async function sendEmailDigest() {
+    try {
+        const headers = await getAuthHeaders();
+        const response = await fetch(`${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} ${response.statusText}`;
+            }
+            throw new Error(errorMessage);
+        }
+
+        return response.json();
+    } catch (error) {
+        if (error.message.includes("fetch")) {
+            throw new Error(
+                "Cannot connect to server. Is the backend running?",
+            );
+        }
+        throw error;
+    }
+}
+
+/**
+ * Test all configured notification channels via the backend
+ * @returns {Promise<Object>} Results per channel
+ */
+export async function testNotificationChannels() {
+    try {
+        const headers = await getAuthHeaders();
+        const response = await fetch(
+            `${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;
     }
 }

frontend/src/api/stripe.jsx

@@ -0,0 +1,68 @@
+import { getAuthHeaders } from "./authHeaders";
+import { API_BASE } from "./config";
+
+export async function createCheckoutSession(tier = "premium") {
+    const headers = await getAuthHeaders();
+    const res = await fetch(`${API_BASE}/stripe/create-checkout-session`, {
+        method: "POST",
+        headers: { ...headers, "Content-Type": "application/json" },
+        body: JSON.stringify({ tier }),
+    });
+    if (!res.ok) {
+        const data = await res.json();
+        throw new Error(data.message || "Failed to create checkout session");
+    }
+    return res.json();
+}
+
+export async function createOnboardingCheckout(email, tier = "premium") {
+    const res = await fetch(`${API_BASE}/stripe/create-onboarding-checkout`, {
+        method: "POST",
+        headers: { "Content-Type": "application/json" },
+        body: JSON.stringify({ email, tier }),
+    });
+    if (!res.ok) {
+        const data = await res.json();
+        throw new Error(data.message || "Failed to create checkout session");
+    }
+    return res.json();
+}
+
+export async function activateFreeTier() {
+    const headers = await getAuthHeaders();
+    const res = await fetch(`${API_BASE}/stripe/activate-free`, {
+        method: "POST",
+        headers,
+    });
+    if (!res.ok) {
+        const data = await res.json();
+        throw new Error(data.message || "Failed to activate free tier");
+    }
+    return res.json();
+}
+
+export async function verifyCheckoutSession(sessionId) {
+    const headers = await getAuthHeaders();
+    const res = await fetch(`${API_BASE}/stripe/verify-checkout`, {
+        method: "POST",
+        headers: { ...headers, "Content-Type": "application/json" },
+        body: JSON.stringify({ session_id: sessionId }),
+    });
+    if (!res.ok) {
+        const data = await res.json();
+        throw new Error(data.message || "Failed to verify checkout session");
+    }
+    return res.json();
+}
+
+export async function getSubscriptionStatus() {
+    const headers = await getAuthHeaders();
+    const res = await fetch(`${API_BASE}/stripe/subscription-status`, {
+        headers,
+    });
+    if (!res.ok) {
+        const data = await res.json();
+        throw new Error(data.message || "Failed to get subscription status");
+    }
+    return res.json();
+}

frontend/src/components/AddressForm.jsx

@@ -37,7 +37,7 @@ export default function AddressForm({ onSubmit }) {
                 placeholder="Treasury, Cold Wallet, etc."
             />
 
-            <Button type="submit" disabled={!canSubmit}>
+            <Button type="submit" disabled={!canSubmit} className="mt-md">
                 Add Address
             </Button>
         </form>

frontend/src/components/AlertForm.css

@@ -0,0 +1,7 @@
+.alert-form__options {
+  margin-bottom: 1rem;
+}
+
+.alert-form__radio {
+  display: block;
+}

frontend/src/components/AlertForm.jsx

@@ -1,6 +1,7 @@
 import { useState } from "react";
 import Input from "./Input";
 import Button from "./Button";
+import "./AlertForm.css";
 
 const ALERT_TYPES = [
     { value: "incoming_tx", label: "Incoming transaction" },
@@ -36,9 +37,9 @@ export default function AlertForm({ onSubmit }) {
 
     return (
         <form onSubmit={handleSubmit}>
-            <div style={{ marginBottom: "1rem" }}>
+            <div className="alert-form__options">
                 {ALERT_TYPES.map((opt) => (
-                    <label key={opt.value} style={{ display: "block" }}>
+                    <label key={opt.value} className="alert-form__radio">
                         <input
                             type="radio"
                             name="alertType"

frontend/src/components/Button.css

@@ -0,0 +1,14 @@
+.btn {
+  padding: 0.5rem 1rem;
+  font-size: 1rem;
+  border: none;
+  border-radius: var(--radius-md);
+  cursor: pointer;
+  color: var(--color-text);
+  transition: opacity 0.15s ease;
+}
+
+.btn:disabled {
+  opacity: 0.6;
+  cursor: not-allowed;
+}

frontend/src/components/Button.jsx

@@ -1,20 +1,19 @@
+import "./Button.css";
+
 export default function Button({
     children,
     onClick,
     disabled = false,
     type = "button",
+    variant = "primary",
+    className = "",
 }) {
     return (
         <button
             type={type}
             onClick={onClick}
             disabled={disabled}
-            style={{
-                padding: "0.5rem 1rem",
-                fontSize: "1rem",
-                cursor: disabled ? "not-allowed" : "pointer",
-                opacity: disabled ? 0.6 : 1,
-            }}
+            className={`btn btn--${variant} ${className}`}
         >
             {children}
         </button>

frontend/src/components/Input.css

@@ -0,0 +1,21 @@
+.input__label {
+  display: block;
+  margin: 0.8rem 0rem 0.4rem 0rem;
+  font-size: 0.9rem;
+}
+
+.input__control {
+  width: 100%;
+  padding: 0.5rem;
+  font-size: 1rem;
+  background-color: var(--color-bg-elevated);
+  border: 1px solid var(--color-border);
+  border-radius: var(--radius-md);
+  color: var(--color-text);
+}
+
+.input__control:focus {
+  outline: none;
+  border-color: var(--color-primary);
+  box-shadow: 0 0 0 2px rgba(0, 102, 204, 0.25);
+}

frontend/src/components/Input.jsx

@@ -1,3 +1,5 @@
+import "./Input.css";
+
 export default function Input({
     label,
     type = "text",
@@ -7,12 +9,12 @@ export default function Input({
     step,
     min,
     disabled = false,
+    required = false,
+    className = "",
 }) {
     return (
-        <label style={{ display: "block", marginBottom: "1rem" }}>
-            <div style={{ marginBottom: "0.25rem", fontSize: "0.9rem" }}>
-                {label}
-            </div>
+        <label className={`form-field ${className}`}>
+            <div className="input__label">{label}</div>
             <input
                 type={type}
                 value={value}
@@ -20,12 +22,9 @@ export default function Input({
                 step={step}
                 min={min}
                 disabled={disabled}
+                required={required}
                 onChange={(e) => onChange(e.target.value)}
-                style={{
-                    width: "100%",
-                    padding: "0.5rem",
-                    fontSize: "1rem",
-                }}
+                className="input__control"
             />
         </label>
     );

frontend/src/components/Navbar.css

@@ -0,0 +1,167 @@
+.navbar {
+  display: flex;
+  justify-content: space-between;
+  align-items: center;
+  padding: 1rem 2rem;
+  margin-bottom: 1.5rem;
+  background-color: var(--color-bg);
+  border-bottom: 1px solid var(--color-border-light);
+}
+
+/* ── Left Group: Brand + Links ───────────────────────────── */
+
+.navbar__left {
+  display: flex;
+  align-items: center;
+  gap: 0.5rem;
+}
+
+.navbar__brand-group {
+  display: flex;
+  align-items: center;
+}
+
+.navbar__brand {
+  font-weight: 700;
+  font-size: 1.4rem;
+  color: var(--color-brand);
+  margin-right: 2rem;
+  letter-spacing: 0.5px;
+}
+
+.navbar__links {
+  display: flex;
+  gap: 0.25rem;
+}
+
+.navbar__link {
+  padding: 0.5rem 1.25rem;
+  border-radius: var(--radius-lg);
+  text-decoration: none;
+  font-size: 1.425rem;
+  font-weight: 200;
+  color: var(--color-text-subtle);
+  background-color: transparent;
+  transition: all 0.15s ease;
+}
+
+.navbar__link--active {
+  font-weight: 600;
+  color: var(--color-text);
+  background-color: var(--color-bg-card);
+}
+
+/* ── Right Group: Email + Logout + Hamburger ─────────────── */
+
+.navbar__right {
+  display: flex;
+  align-items: center;
+  gap: 1rem;
+}
+
+.navbar__user {
+  font-size: 1.275rem;
+  color: #777;
+}
+
+.navbar__user-link {
+  color: var(--color-primary);
+  text-decoration: none;
+  transition: color 0.15s ease;
+}
+
+.navbar__user-link:hover {
+  color: var(--color-primary-hover);
+}
+
+.navbar__user-link--mobile {
+  display: none;
+}
+
+.navbar__logout {
+  padding: 0.4rem 1rem;
+  font-size: 1.275rem;
+  font-weight: 400;
+  background-color: transparent;
+  color: var(--color-text-subtle);
+  border: 1px solid var(--color-border);
+  border-radius: var(--radius-lg);
+  cursor: pointer;
+  transition: all 0.15s ease;
+}
+
+/* ── Hamburger Icon (hidden on desktop) ──────────────────── */
+
+.navbar__hamburger {
+  display: none;
+  flex-direction: column;
+  justify-content: center;
+  gap: 5px;
+  background: none;
+  border: none;
+  cursor: pointer;
+  padding: 4px;
+}
+
+.navbar__hamburger-bar {
+  display: block;
+  width: 28px;
+  height: 3px;
+  background-color: var(--color-brand);
+  border-radius: 2px;
+}
+
+/* ── Responsive: Tablet & below (≤ 768px) ────────────────── */
+
+@media (max-width: 768px) {
+  .navbar {
+    padding: 0.75rem 1rem;
+  }
+
+  .navbar__brand-group {
+    flex-direction: column;
+    align-items: flex-start;
+  }
+
+  .navbar__brand {
+    margin-right: 0;
+    font-size: 1.25rem;
+  }
+
+  .navbar__links {
+    display: none;
+  }
+
+  .navbar__user-link--mobile {
+    display: block;
+    font-size: 0.95rem;
+  }
+
+  .navbar__user-link--desktop {
+    display: none;
+  }
+
+  .navbar__logout {
+    display: none;
+  }
+
+  .navbar__hamburger {
+    display: flex;
+  }
+}
+
+/* ── Responsive: Mobile (≤ 480px) ────────────────────────── */
+
+@media (max-width: 480px) {
+  .navbar {
+    padding: 0.75rem;
+  }
+
+  .navbar__brand {
+    font-size: 1.15rem;
+  }
+
+  .navbar__user-link--mobile {
+    font-size: 0.85rem;
+  }
+}

frontend/src/components/Navbar.jsx

@@ -1,85 +1,71 @@
+import { useState } from "react";
 import { Link, useLocation } from "react-router-dom";
 import { useAuth } from "../contexts/AuthContext";
+import NavPanel from "./navPanel/NavPanel";
+import "./Navbar.css";
 
 const navLinks = [
   { to: "/addresses", label: "Addresses" },
   { to: "/alerts", label: "Configure Alerts" },
-  { to: "/history", label: "Alert History" },
+  { to: "/alertevents", label: "Alert Event History" },
 ];
 
 export default function Navbar() {
   const { currentUser, logout } = useAuth();
   const location = useLocation();
+  const [isNavPanelOpen, setIsNavPanelOpen] = useState(false);
 
   if (!currentUser) return null;
 
   return (
-    <nav style={{
-      display: "flex",
-      justifyContent: "space-between",
-      alignItems: "center",
-      padding: "1rem 2rem",
-      marginBottom: "1.5rem",
-      backgroundColor: "#1a1a1a",
-      borderBottom: "1px solid #333",
-    }}>
-      <div style={{ display: "flex", alignItems: "center", gap: "0.5rem" }}>
-        <span style={{
-          fontWeight: 700,
-          fontSize: "1.1rem",
-          color: "#fff",
-          marginRight: "2rem",
-          letterSpacing: "0.5px",
-        }}>
-          Koin Ping
-        </span>
-
-        <div style={{ display: "flex", gap: "0.25rem" }}>
-          {navLinks.map(({ to, label }) => {
-            const isActive = location.pathname === to;
-            return (
-              <Link
-                key={to}
-                to={to}
-                style={{
-                  padding: "0.5rem 1.25rem",
-                  borderRadius: "6px",
-                  textDecoration: "none",
-                  fontSize: "1.425rem",
-                  fontWeight: isActive ? 600 : 200,
-                  color: isActive ? "#fff" : "#999",
-                  backgroundColor: isActive ? "#333" : "transparent",
-                  transition: "all 0.15s ease",
-                }}
-              >
-                {label}
-              </Link>
-            );
-          })}
+    <>
+      <nav className="navbar">
+        <div className="navbar__left">
+          <div className="navbar__brand-group">
+            <span className="navbar__brand">Koin Ping</span>
+            <Link to="/account" className="navbar__user-link navbar__user-link--mobile">
+              {currentUser.email}
+            </Link>
+          </div>
+          <div className="navbar__links">
+            {navLinks.map(({ to, label }) => {
+              const isActive = location.pathname === to;
+              return (
+                <Link
+                  key={to}
+                  to={to}
+                  className={`navbar__link ${isActive ? "navbar__link--active" : ""}`}
+                >
+                  {label}
+                </Link>
+              );
+            })}
+          </div>
         </div>
-      </div>
 
-      <div style={{ display: "flex", alignItems: "center", gap: "1.25rem" }}>
-        <span style={{ fontSize: "1.275rem", color: "#777" }}>
-          {currentUser.email}
-        </span>
-        <button
-          onClick={logout}
-          style={{
-            padding: "0.4rem 1rem",
-            fontSize: "1.275rem",
-            fontWeight: 400,
-            backgroundColor: "transparent",
-            color: "#999",
-            border: "1px solid #444",
-            borderRadius: "6px",
-            cursor: "pointer",
-            transition: "all 0.15s ease",
-          }}
-        >
-          Logout
-        </button>
-      </div>
-    </nav>
+        <div className="navbar__right">
+          <Link to="/account" className="navbar__user navbar__user-link navbar__user-link--desktop">
+            {currentUser.email}
+          </Link>
+          <button onClick={logout} className="navbar__logout">
+            Logout
+          </button>
+          <button
+            className="navbar__hamburger"
+            onClick={() => setIsNavPanelOpen(true)}
+            aria-label="Open navigation menu"
+          >
+            <span className="navbar__hamburger-bar" />
+            <span className="navbar__hamburger-bar" />
+            <span className="navbar__hamburger-bar" />
+          </button>
+        </div>
+      </nav>
+
+      <NavPanel
+        isOpen={isNavPanelOpen}
+        onClose={() => setIsNavPanelOpen(false)}
+      />
+    </>
   );
 }

frontend/src/components/TierPicker.css

@@ -0,0 +1,120 @@
+.tier-picker {
+  display: grid;
+  grid-template-columns: repeat(3, 1fr);
+  gap: 1rem;
+}
+
+.tier-picker__card {
+  position: relative;
+  display: flex;
+  flex-direction: column;
+  padding: 1.5rem 1.25rem;
+  background-color: var(--color-bg-elevated);
+  border: 1px solid var(--color-border);
+  border-radius: var(--radius-xl);
+  text-align: center;
+}
+
+.tier-picker__card--highlighted {
+  border-color: var(--color-primary);
+  box-shadow: 0 0 0 1px var(--color-primary);
+}
+
+.tier-picker__card--selected {
+  border-color: var(--color-success);
+  box-shadow: 0 0 0 1px var(--color-success);
+}
+
+.tier-picker__badge {
+  position: absolute;
+  top: -10px;
+  left: 50%;
+  transform: translateX(-50%);
+  background-color: var(--color-primary);
+  color: white;
+  font-size: 0.7rem;
+  font-weight: 700;
+  padding: 2px 12px;
+  border-radius: 10px;
+  white-space: nowrap;
+}
+
+.tier-picker__name {
+  margin-bottom: 0.5rem;
+  font-size: 1.05rem;
+  color: var(--color-text);
+}
+
+.tier-picker__price {
+  margin-bottom: 1.25rem;
+}
+
+.tier-picker__amount {
+  font-size: 2rem;
+  font-weight: 700;
+  color: white;
+}
+
+.tier-picker__period {
+  font-size: 0.85rem;
+  color: var(--color-text-dimmed);
+}
+
+.tier-picker__features {
+  list-style: none;
+  padding: 0;
+  margin: 0 0 1.25rem;
+  text-align: left;
+  flex-grow: 1;
+}
+
+.tier-picker__feature {
+  padding: 0.3rem 0;
+  font-size: 0.82rem;
+  color: var(--color-text-label);
+}
+
+.tier-picker__feature--disabled {
+  color: var(--color-text-dimmed);
+  opacity: 0.55;
+}
+
+.tier-picker__check {
+  color: var(--color-primary);
+  font-weight: bold;
+  margin-right: 0.4rem;
+}
+
+.tier-picker__dash {
+  margin-right: 0.4rem;
+}
+
+.tier-picker__btn {
+  width: 100%;
+  padding: 0.6rem;
+  background-color: var(--color-bg-card);
+  border: 1px solid var(--color-border);
+  color: var(--color-text);
+  cursor: pointer;
+  border-radius: var(--radius-md);
+  font-weight: 600;
+}
+
+.tier-picker__btn:hover {
+  background-color: var(--color-primary);
+  border-color: var(--color-primary);
+}
+
+.tier-picker__btn--selected {
+  background-color: var(--color-success);
+  border-color: var(--color-success);
+  color: white;
+}
+
+@media (max-width: 768px) {
+  .tier-picker {
+    grid-template-columns: 1fr;
+    max-width: 400px;
+    margin: 0 auto;
+  }
+}

frontend/src/components/TierPicker.jsx

@@ -0,0 +1,96 @@
+import "./TierPicker.css";
+
+const TIERS = [
+  {
+    id: "free",
+    name: "Trial Monitoring",
+    price: "$0",
+    period: "",
+    features: [
+      "Monitor 1 blockchain address 24/7",
+      "Configure alerts to fire on trigger events",
+      "1 transaction alert type per trigger (email digest)",
+    ],
+    disabledFeatures: [
+      "Real-time Discord alerts",
+      "Real-time Telegram alerts",
+      "Real-time Slack alerts",
+    ],
+  },
+  {
+    id: "premium",
+    name: "Premium Monitoring",
+    price: "$1.99",
+    period: "/month",
+    features: [
+      "Monitor 3 blockchain addresses",
+      "Configure alerts to fire on trigger events",
+      "Daily email digest alert",
+      "Real-time Discord alerts",
+      "Real-time Telegram alerts",
+      "2 transaction alert types per monitored address",
+    ],
+    disabledFeatures: [
+      "Real-time Slack alerts",
+    ],
+    highlighted: true,
+  },
+  {
+    id: "pro",
+    name: "Professional Monitoring",
+    price: "$11.99",
+    period: "/month",
+    features: [
+      "Monitor unlimited blockchain addresses",
+      "Configure alerts to fire on trigger events",
+      "Daily email digest alert",
+      "Real-time Discord alerts",
+      "Real-time Telegram alerts",
+      "Real-time Slack alerts",
+      "Unlimited transaction alert types per monitored address",
+    ],
+    disabledFeatures: [],
+  },
+];
+
+export default function TierPicker({ onSelect, selectedTier }) {
+  return (
+    <div className="tier-picker">
+      {TIERS.map((tier) => (
+        <div
+          key={tier.id}
+          className={`tier-picker__card${tier.highlighted ? " tier-picker__card--highlighted" : ""}${selectedTier === tier.id ? " tier-picker__card--selected" : ""}`}
+        >
+          {tier.highlighted && (
+            <div className="tier-picker__badge">Most Popular</div>
+          )}
+          <h3 className="tier-picker__name">{tier.name}</h3>
+          <div className="tier-picker__price">
+            <span className="tier-picker__amount">{tier.price}</span>
+            {tier.period && (
+              <span className="tier-picker__period">{tier.period}</span>
+            )}
+          </div>
+          <ul className="tier-picker__features">
+            {tier.features.map((f) => (
+              <li key={f} className="tier-picker__feature">
+                <span className="tier-picker__check">&#10003;</span> {f}
+              </li>
+            ))}
+            {tier.disabledFeatures.map((f) => (
+              <li key={f} className="tier-picker__feature tier-picker__feature--disabled">
+                <span className="tier-picker__dash">&mdash;</span> {f}
+              </li>
+            ))}
+          </ul>
+          <button
+            className={`btn tier-picker__btn${selectedTier === tier.id ? " tier-picker__btn--selected" : ""}`}
+            onClick={() => onSelect(tier.id)}
+          >
+            {selectedTier === tier.id ? "Selected" : "Select"}
+          </button>
+        </div>
+      ))}
+    </div>
+  );
+}

frontend/src/components/UpgradeBanner.css

@@ -0,0 +1,32 @@
+.upgrade-banner {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  gap: 1rem;
+  padding: 0.75rem 1rem;
+  margin-bottom: 1rem;
+  border-radius: var(--radius-md);
+  background-color: #3a2e00;
+  border: 1px solid #aa7700;
+  color: #ffcc44;
+}
+
+.upgrade-banner__message {
+  font-size: 0.88rem;
+}
+
+.upgrade-banner__link {
+  background: none;
+  border: 1px solid #aa7700;
+  color: #ffcc44;
+  padding: 0.25rem 0.75rem;
+  border-radius: var(--radius-md);
+  cursor: pointer;
+  font-size: 0.82rem;
+  font-weight: 600;
+  white-space: nowrap;
+}
+
+.upgrade-banner__link:hover {
+  background-color: #4a3800;
+}

frontend/src/components/UpgradeBanner.jsx

@@ -0,0 +1,18 @@
+import { useNavigate } from "react-router-dom";
+import "./UpgradeBanner.css";
+
+export default function UpgradeBanner({ message, linkTo = "/subscribe?upgrade=true" }) {
+  const navigate = useNavigate();
+
+  return (
+    <div className="upgrade-banner">
+      <span className="upgrade-banner__message">{message}</span>
+      <button
+        className="upgrade-banner__link"
+        onClick={() => navigate(linkTo)}
+      >
+        Upgrade
+      </button>
+    </div>
+  );
+}

frontend/src/components/navPanel/NavPanel.css

@@ -0,0 +1,78 @@
+/* ── Overlay Backdrop ─────────────────────────────────────── */
+
+.nav-panel__overlay {
+  position: fixed;
+  inset: 0;
+  background-color: rgba(0, 0, 0, 0.45);
+  opacity: 0;
+  pointer-events: none;
+  transition: opacity 0.3s ease;
+  z-index: 900;
+}
+
+.nav-panel__overlay--visible {
+  opacity: 1;
+  pointer-events: auto;
+}
+
+/* ── Slide-out Panel ─────────────────────────────────────── */
+
+.nav-panel {
+  position: fixed;
+  top: 0;
+  left: 0;
+  width: 260px;
+  height: 100%;
+  background-color: var(--color-bg-elevated);
+  border-right: 1px solid var(--color-border);
+  transform: translateX(-100%);
+  transition: transform 0.3s ease;
+  z-index: 950;
+  display: flex;
+  flex-direction: column;
+  padding: 1.5rem 0;
+}
+
+.nav-panel--open {
+  transform: translateX(0);
+}
+
+/* ── Nav Links ───────────────────────────────────────────── */
+
+.nav-panel__nav {
+  display: flex;
+  flex-direction: column;
+  flex: 1;
+}
+
+.nav-panel__link {
+  padding: 0.9rem 1.5rem;
+  text-decoration: none;
+  font-size: 1.3rem;
+  font-weight: 200;
+  color: var(--color-text-subtle);
+  border-left: 3px solid transparent;
+  transition: background-color 0.15s ease, color 0.15s ease;
+}
+
+.nav-panel__link--active {
+  font-weight: 600;
+  color: var(--color-text);
+  background-color: var(--color-bg-card);
+  border-left-color: var(--color-brand);
+}
+
+/* ── Logout Button ───────────────────────────────────────── */
+
+.nav-panel__logout {
+  margin: 1rem 1.5rem;
+  padding: 0.5rem 1rem;
+  font-size: 1.15rem;
+  font-weight: 400;
+  background-color: transparent;
+  color: var(--color-text-subtle);
+  border: 1px solid var(--color-border);
+  border-radius: var(--radius-lg);
+  cursor: pointer;
+  transition: all 0.15s ease;
+}

frontend/src/components/navPanel/NavPanel.jsx

@@ -0,0 +1,52 @@
+import { Link, useLocation } from "react-router-dom";
+import { useAuth } from "../../contexts/AuthContext";
+import "./NavPanel.css";
+
+const navLinks = [
+  { to: "/addresses", label: "Addresses" },
+  { to: "/alerts", label: "Configure Alerts" },
+  { to: "/alertevents", label: "Alert Event History" },
+];
+
+export default function NavPanel({ isOpen, onClose }) {
+  const { logout } = useAuth();
+  const location = useLocation();
+
+  const handleNavClick = () => {
+    onClose();
+  };
+
+  const handleLogout = () => {
+    onClose();
+    logout();
+  };
+
+  return (
+    <>
+      <div
+        className={`nav-panel__overlay${isOpen ? " nav-panel__overlay--visible" : ""}`}
+        onClick={onClose}
+      />
+      <aside className={`nav-panel${isOpen ? " nav-panel--open" : ""}`}>
+        <nav className="nav-panel__nav">
+          {navLinks.map(({ to, label }) => {
+            const isActive = location.pathname === to;
+            return (
+              <Link
+                key={to}
+                to={to}
+                className={`nav-panel__link${isActive ? " nav-panel__link--active" : ""}`}
+                onClick={handleNavClick}
+              >
+                {label}
+              </Link>
+            );
+          })}
+        </nav>
+        <button onClick={handleLogout} className="nav-panel__logout">
+          Logout
+        </button>
+      </aside>
+    </>
+  );
+}

frontend/src/contexts/AuthContext.jsx

@@ -1,10 +1,10 @@
 /**
  * AuthContext - Firebase Authentication State Management
  *
- * Provides authentication state and methods throughout the app
+ * Provides authentication state, tier info, and methods throughout the app
  */
 
-import { createContext, useContext, useEffect, useState } from "react";
+import { createContext, useContext, useEffect, useState, useCallback } from "react";
 import {
     createUserWithEmailAndPassword,
     signInWithEmailAndPassword,
@@ -12,9 +12,16 @@ import {
     onAuthStateChanged,
 } from "firebase/auth";
 import { auth } from "../firebase/config";
+import { getAccount } from "../api/account";
 
 const AuthContext = createContext();
 
+const DEFAULT_TIER_LIMITS = {
+    max_addresses: 1,
+    max_alert_types: 1,
+    allowed_channels: ["email"],
+};
+
 /**
  * Hook to access auth context
  * @returns {Object} Auth context value
@@ -28,16 +35,30 @@ export function useAuth() {
 }
 
 /**
- * AuthProvider - Wraps app and provides auth state
+ * AuthProvider - Wraps app and provides auth state + tier info
  */
 export function AuthProvider({ children }) {
     const [currentUser, setCurrentUser] = useState(null);
     const [loading, setLoading] = useState(true);
     const [error, setError] = useState(null);
 
-    /**
-     * Sign up with email and password
-     */
+    const [userTier, setUserTier] = useState("free");
+    const [tierLimits, setTierLimits] = useState(DEFAULT_TIER_LIMITS);
+    const [addressCount, setAddressCount] = useState(0);
+    const [subscriptionStatus, setSubscriptionStatus] = useState("none");
+
+    const refreshAccount = useCallback(async () => {
+        try {
+            const data = await getAccount();
+            setUserTier(data.subscription_tier || "free");
+            setTierLimits(data.tier_limits || DEFAULT_TIER_LIMITS);
+            setAddressCount(data.address_count || 0);
+            setSubscriptionStatus(data.subscription_status || "none");
+        } catch {
+            // account fetch can fail during onboarding before subscription is active
+        }
+    }, []);
+
     async function signup(email, password) {
         try {
             setError(null);
@@ -53,9 +74,6 @@ export function AuthProvider({ children }) {
         }
     }
 
-    /**
-     * Log in with email and password
-     */
     async function login(email, password) {
         try {
             setError(null);
@@ -71,12 +89,13 @@ export function AuthProvider({ children }) {
         }
     }
 
-    /**
-     * Log out current user
-     */
     async function logout() {
         try {
             setError(null);
+            setUserTier("free");
+            setTierLimits(DEFAULT_TIER_LIMITS);
+            setAddressCount(0);
+            setSubscriptionStatus("none");
             await signOut(auth);
         } catch (err) {
             setError(err.message);
@@ -84,18 +103,19 @@ export function AuthProvider({ children }) {
         }
     }
 
-    /**
-     * Listen for auth state changes
-     */
     useEffect(() => {
         const unsubscribe = onAuthStateChanged(auth, (user) => {
             setCurrentUser(user);
             setLoading(false);
+            if (user) {
+                refreshAccount();
+            }
         });
-
-        // Cleanup subscription
         return unsubscribe;
-    }, []);
+    }, [refreshAccount]);
+
+    const isSubscribed =
+        subscriptionStatus === "active" || subscriptionStatus === "trialing";
 
     const value = {
         currentUser,
@@ -104,6 +124,12 @@ export function AuthProvider({ children }) {
         logout,
         error,
         loading,
+        userTier,
+        tierLimits,
+        addressCount,
+        subscriptionStatus,
+        isSubscribed,
+        refreshAccount,
     };
 
     return (

frontend/src/index.css

@@ -1,5 +1,43 @@
 @import url('https://fonts.googleapis.com/css2?family=Nunito:ital,wght@0,200..1000;1,200..1000&display=swap');
 
+:root {
+  --color-primary: #0066cc;
+  --color-primary-hover: #0077ee;
+  --color-brand: #e62525;
+  --color-success: #28a745;
+  --color-success-text: #00ff00;
+  --color-success-bg: #00ff0020;
+  --color-success-border: #00ff00;
+  --color-error: #ff6666;
+  --color-error-bg: #ff000020;
+  --color-error-border: #ff0000;
+  --color-warning: #ffcc44;
+  --color-warning-bg: #3a2e00;
+  --color-warning-border: #aa7700;
+  --color-danger: #cc6666;
+  --color-danger-border: #884444;
+
+  --color-bg: #1a1a1a;
+  --color-bg-elevated: #242424;
+  --color-bg-card: #333;
+  --color-bg-section: #2a2a2a;
+
+  --color-border: #444;
+  --color-border-light: #333;
+  --color-border-section: #3a3a3a;
+
+  --color-text: white;
+  --color-text-muted: #b3b3b3;
+  --color-text-dimmed: #808080;
+  --color-text-subtle: #999;
+  --color-text-label: #ccc;
+
+  --radius-sm: 3px;
+  --radius-md: 4px;
+  --radius-lg: 6px;
+  --radius-xl: 8px;
+}
+
 *,
 *::before,
 *::after {
@@ -21,13 +59,378 @@ body {
   -moz-osx-font-smoothing: grayscale;
 }
 
-h1, h2, h3, h4, h5, h6 {
+h1,
+h2,
+h3,
+h4,
+h5,
+h6 {
   font-family: 'Nunito', sans-serif;
   font-weight: 200;
 }
 
-input, select, textarea, button {
+input,
+select,
+textarea,
+button {
   font-family: 'Nunito', sans-serif;
   font-size: 1rem;
   font-weight: 200;
 }
+
+/* ── Page Layouts ─────────────────────────────────────────── */
+
+.page {
+  max-width: 800px;
+  margin: 0 auto;
+  padding: 2rem;
+}
+
+.page--wide {
+  max-width: 1400px;
+}
+
+/* ── Cards & Sections ─────────────────────────────────────── */
+
+.card {
+  padding: 1rem;
+  background-color: var(--color-bg-card);
+  border: 1px solid var(--color-border);
+  border-radius: var(--radius-md);
+}
+
+.section {
+  margin-bottom: 1.5rem;
+  padding: 1rem;
+  background-color: var(--color-bg-section);
+  border-radius: var(--radius-lg);
+  border: 1px solid var(--color-border-section);
+}
+
+/* ── Form Controls ────────────────────────────────────────── */
+
+.form-field {
+  margin-bottom: 1.25rem;
+}
+
+.form-field--last {
+  margin-bottom: 1.75rem;
+}
+
+.form-label {
+  display: block;
+  margin-bottom: 0.25rem;
+  font-size: 0.9rem;
+  color: var(--color-text-label);
+}
+
+.form-control {
+  width: 100%;
+  padding: 0.5rem;
+  font-size: 1rem;
+  background-color: var(--color-bg-elevated);
+  border: 1px solid var(--color-border);
+  border-radius: var(--radius-md);
+  color: var(--color-text);
+}
+
+.form-control:focus {
+  outline: none;
+  border-color: var(--color-primary);
+  box-shadow: 0 0 0 2px rgba(0, 102, 204, 0.25);
+}
+
+.form-control--mono {
+  font-family: monospace;
+}
+
+.form-select {
+  width: 100%;
+  padding: 0.5rem;
+  font-size: 1rem;
+  background-color: var(--color-bg);
+  border: 1px solid var(--color-border);
+  border-radius: var(--radius-md);
+  color: var(--color-text);
+}
+
+/* ── Buttons ──────────────────────────────────────────────── */
+
+.btn {
+  padding: 0.5rem 1rem;
+  font-size: 1rem;
+  border: none;
+  border-radius: var(--radius-md);
+  cursor: pointer;
+  color: var(--color-text);
+  transition: opacity 0.15s ease;
+}
+
+.btn:disabled {
+  opacity: 0.6;
+  cursor: not-allowed;
+}
+
+.btn--primary {
+  background-color: var(--color-primary);
+}
+
+.btn--success {
+  background-color: var(--color-success);
+}
+
+.btn--secondary {
+  background-color: #6c757d;
+}
+
+.btn--danger {
+  background-color: transparent;
+  border: 1px solid var(--color-danger-border);
+  color: var(--color-danger);
+}
+
+.btn--ghost {
+  background-color: transparent;
+  border: 1px solid var(--color-border);
+  color: var(--color-text-subtle);
+}
+
+.btn--sm {
+  padding: 0.25rem 0.6rem;
+  font-size: 0.85rem;
+}
+
+.btn--lg {
+  padding: 0.75rem 1.5rem;
+}
+
+/* ── Feedback Alerts ──────────────────────────────────────── */
+
+.alert {
+  padding: 0.75rem;
+  margin-bottom: 1rem;
+  border-radius: var(--radius-md);
+}
+
+.alert--error {
+  background-color: var(--color-error-bg);
+  border: 1px solid var(--color-error-border);
+  color: var(--color-error);
+}
+
+.alert--success {
+  background-color: var(--color-success-bg);
+  border: 1px solid var(--color-success-border);
+  color: var(--color-success-text);
+}
+
+.alert--warning {
+  background-color: var(--color-warning-bg);
+  border: 1px solid var(--color-warning-border);
+  color: var(--color-warning);
+}
+
+/* ── Lists ────────────────────────────────────────────────── */
+
+.list-unstyled {
+  list-style: none;
+  padding: 0;
+}
+
+.list-item--card {
+  padding: 1rem;
+  margin-bottom: 0.5rem;
+  border: 1px solid var(--color-border);
+  border-radius: var(--radius-md);
+  background-color: var(--color-bg-card);
+}
+
+/* ── Typography Helpers ───────────────────────────────────── */
+
+.text-muted {
+  color: var(--color-text-muted);
+}
+
+.text-dimmed {
+  color: var(--color-text-dimmed);
+}
+
+.text-mono {
+  font-family: monospace;
+}
+
+.text-bold {
+  font-weight: bold;
+}
+
+.text-error {
+  color: red;
+}
+
+.text-sm {
+  font-size: 1.035rem;
+}
+
+.text-xs {
+  font-size: 0.978rem;
+}
+
+.help-link {
+  color: var(--color-primary);
+  font-size: 0.85rem;
+}
+
+/* ── Flex Utilities ───────────────────────────────────────── */
+
+.flex {
+  display: flex;
+}
+
+.flex--between {
+  justify-content: space-between;
+}
+
+.flex--center {
+  align-items: center;
+}
+
+.flex--column {
+  flex-direction: column;
+}
+
+.flex--wrap {
+  flex-wrap: wrap;
+}
+
+.gap-xs {
+  gap: 0.25rem;
+}
+
+.gap-sm {
+  gap: 0.5rem;
+}
+
+.gap-md {
+  gap: 0.75rem;
+}
+
+.gap-lg {
+  gap: 1rem;
+}
+
+/* ── Spacing Helpers ──────────────────────────────────────── */
+
+.mb-0 {
+  margin-bottom: 0;
+}
+
+.mb-sm {
+  margin-bottom: 0.5rem;
+}
+
+.mb-md {
+  margin-bottom: 1rem;
+}
+
+.mb-lg {
+  margin-bottom: 1.5rem;
+}
+
+.mb-xl {
+  margin-bottom: 2rem;
+}
+
+.mt-0 {
+  margin-top: 0;
+}
+
+.mt-md {
+  margin-top: 1rem;
+}
+
+.text-white {
+  color: white;
+}
+
+.text-white-sm {
+  color: white;
+  font-size: 0.85rem;
+}
+
+/* ── Responsive Breakpoints ──────────────────────────────── */
+/* Mobile:  <= 480px                                          */
+/* Tablet:  481px – 768px                                     */
+/* Laptop:  769px – 1024px                                    */
+/* Desktop: >= 1025px (default styles above)                  */
+
+/* Laptop & below */
+@media (max-width: 1024px) {
+  .page--wide {
+    max-width: 100%;
+  }
+}
+
+/* Tablet & below */
+@media (max-width: 768px) {
+  html {
+    font-size: 13px;
+  }
+
+  .page {
+    padding: 1.25rem;
+  }
+
+  .btn--lg {
+    padding: 0.6rem 1.2rem;
+  }
+
+  h1 {
+    font-size: 1.75rem;
+  }
+
+  h2 {
+    font-size: 1.4rem;
+  }
+
+  h3 {
+    font-size: 1.15rem;
+  }
+}
+
+/* Tier-locked: greyed out, non-interactive overlay for features above the user's plan */
+.tier-locked {
+  opacity: 0.45;
+  pointer-events: none;
+  filter: grayscale(40%);
+  user-select: none;
+}
+
+/* Mobile */
+@media (max-width: 480px) {
+  html {
+    font-size: 12px;
+  }
+
+  .page {
+    padding: 1rem 0.75rem;
+  }
+
+  .form-control,
+  .form-select {
+    font-size: 0.95rem;
+  }
+
+  .btn {
+    padding: 0.45rem 0.85rem;
+    font-size: 0.95rem;
+  }
+
+  .btn--lg {
+    padding: 0.55rem 1rem;
+    font-size: 1rem;
+  }
+
+  .section {
+    padding: 0.75rem;
+  }
+}

frontend/src/pages/Addresses.jsx

@@ -1,95 +0,0 @@
-import { useState, useEffect } from "react";
-import AddressForm from "../components/AddressForm";
-import { getAddresses, createAddress } from "../api/addresses";
-
-export default function Addresses() {
-    const [addresses, setAddresses] = useState([]);
-    const [loading, setLoading] = useState(true);
-    const [error, setError] = useState(null);
-
-    // Load addresses on mount
-    useEffect(() => {
-        async function fetchAddresses() {
-            try {
-                setLoading(true);
-                const data = await getAddresses();
-                setAddresses(data);
-            } catch (err) {
-                setError(err.message);
-                console.error("Failed to fetch addresses:", err);
-            } finally {
-                setLoading(false);
-            }
-        }
-
-        fetchAddresses();
-    }, []);
-
-    // Handle new address submission
-    async function handleAddressSubmit(data) {
-        try {
-            const newAddress = await createAddress(data);
-            // Append new address to state
-            setAddresses((prev) => [...prev, newAddress]);
-            setError(null); // Clear any previous errors
-        } catch (err) {
-            setError(err.message);
-            console.error("Failed to create address:", err);
-        }
-    }
-
-    return (
-        <div style={{ maxWidth: "800px", margin: "0 auto", padding: "2rem" }}>
-            <h1>Tracked Addresses</h1>
-
-            <div style={{ marginBottom: "2rem" }}>
-                <AddressForm onSubmit={handleAddressSubmit} />
-            </div>
-
-            <div>
-                <h2>Existing Addresses</h2>
-                {loading && <p>Loading addresses...</p>}
-                {error && <p style={{ color: "red" }}>Error: {error}</p>}
-                {!loading && !error && addresses.length === 0 && (
-                    <p style={{ color: "#808080" }}>
-                        No addresses tracked yet. Add one above to get started.
-                    </p>
-                )}
-                {addresses.length > 0 && (
-                    <ul style={{ listStyle: "none", padding: 0 }}>
-                        {addresses.map((addr, index) => (
-                            <li
-                                key={addr.id || index}
-                                style={{
-                                    padding: "1rem",
-                                    marginBottom: "0.5rem",
-                                    border: "1px solid #444",
-                                    borderRadius: "4px",
-                                    backgroundColor: "#333",
-                                }}
-                            >
-                                <div
-                                    style={{
-                                        fontWeight: "bold",
-                                        marginBottom: "0.25rem",
-                                    }}
-                                >
-                                    {addr.label || "Unlabeled"}
-                                </div>
-                                <div
-                                    style={{
-                                        fontFamily: "monospace",
-                                        fontSize: "1.035rem",
-                                        color: "#b3b3b3",
-                                    }}
-                                >
-                                    {addr.address}
-                                </div>
-                            </li>
-                        ))}
-                    </ul>
-                )}
-            </div>
-        </div>
-    );
-}

frontend/src/pages/AlertHistory.jsx

@@ -1,85 +0,0 @@
-import { useState, useEffect } from "react";
-import { getAlertEvents } from "../api/alertEvents";
-
-export default function AlertHistory() {
-    const [alertEvents, setAlertEvents] = useState([]);
-    const [loading, setLoading] = useState(true);
-    const [error, setError] = useState(null);
-
-    // Fetch alert events on mount
-    useEffect(() => {
-        async function fetchAlertEvents() {
-            try {
-                setLoading(true);
-                const data = await getAlertEvents();
-                setAlertEvents(data);
-            } catch (err) {
-                setError(err.message);
-                console.error("Failed to fetch alert events:", err);
-            } finally {
-                setLoading(false);
-            }
-        }
-
-        fetchAlertEvents();
-    }, []);
-
-    if (loading) {
-        return <div style={{ padding: "2rem" }}>Loading...</div>;
-    }
-
-    if (error) {
-        return (
-            <div style={{ padding: "2rem", color: "red" }}>Error: {error}</div>
-        );
-    }
-
-    return (
-        <div style={{ maxWidth: "800px", margin: "0 auto", padding: "2rem" }}>
-            <h1>Recent Alerts</h1>
-
-            {alertEvents.length === 0 ? (
-                <p style={{ color: "#808080" }}>No alerts yet</p>
-            ) : (
-                <ul style={{ listStyle: "none", padding: 0 }}>
-                    {alertEvents.map((event) => (
-                        <li
-                            key={event.id}
-                            style={{
-                                padding: "1rem",
-                                marginBottom: "0.75rem",
-                                border: "1px solid #444",
-                                borderRadius: "4px",
-                                backgroundColor: "#333",
-                            }}
-                        >
-                            <div style={{ marginBottom: "0.5rem" }}>
-                                {event.message}
-                            </div>
-                            {event.address_label && (
-                                <div
-                                    style={{
-                                    fontSize: "1.035rem",
-                                    color: "#808080",
-                                        marginBottom: "0.25rem",
-                                    }}
-                                >
-                                    Address: {event.address_label}
-                                </div>
-                            )}
-                            <small style={{ color: "#b3b3b3" }}>
-                                {formatTimestamp(event.timestamp)}
-                            </small>
-                        </li>
-                    ))}
-                </ul>
-            )}
-        </div>
-    );
-}
-
-// Helper to format timestamp for display
-function formatTimestamp(timestamp) {
-    const date = new Date(timestamp);
-    return date.toLocaleString();
-}

frontend/src/pages/Alerts.jsx

@@ -1,636 +0,0 @@
-import { useState, useEffect } from "react";
-import AlertForm from "../components/AlertForm";
-import Button from "../components/Button";
-import Input from "../components/Input";
-import { getAddresses } from "../api/addresses";
-import {
-    getAlerts,
-    createAlert,
-    updateAlertStatus,
-    deleteAlert,
-} from "../api/alerts";
-import {
-    getNotificationConfig,
-    updateNotificationConfig,
-    testDiscordWebhook,
-} from "../api/notificationConfig";
-
-export default function Alerts() {
-    const [addresses, setAddresses] = useState([]);
-    const [selectedAddressId, setSelectedAddressId] = useState(null);
-    const [alerts, setAlerts] = useState([]);
-    const [loading, setLoading] = useState(true);
-    const [error, setError] = useState(null);
-
-    // Notification config state
-    const [notificationConfig, setNotificationConfig] = useState(null);
-    const [discordWebhookUrl, setDiscordWebhookUrl] = useState("");
-    const [notificationEnabled, setNotificationEnabled] = useState(true);
-    const [notificationLoading, setNotificationLoading] = useState(false);
-    const [notificationError, setNotificationError] = useState(null);
-    const [notificationSuccess, setNotificationSuccess] = useState(null);
-    const [testingWebhook, setTestingWebhook] = useState(false);
-
-    // Load addresses and notification config on mount
-    useEffect(() => {
-        async function fetchData() {
-            try {
-                setLoading(true);
-
-                // Fetch addresses
-                const addressData = await getAddresses();
-                setAddresses(addressData);
-                if (addressData.length > 0) {
-                    setSelectedAddressId(addressData[0].id);
-                }
-
-                // Fetch notification config
-                const configData = await getNotificationConfig();
-                setNotificationConfig(configData);
-                setDiscordWebhookUrl(configData.discord_webhook_url || "");
-                setNotificationEnabled(
-                    configData.notification_enabled !== false,
-                );
-            } catch (err) {
-                setError(err.message);
-                console.error("Failed to fetch data:", err);
-            } finally {
-                setLoading(false);
-            }
-        }
-
-        fetchData();
-    }, []);
-
-    // Load alerts when address is selected
-    useEffect(() => {
-        if (!selectedAddressId) {
-            setAlerts([]);
-            return;
-        }
-
-        async function fetchAlerts() {
-            try {
-                const data = await getAlerts(selectedAddressId);
-                setAlerts(data);
-                setError(null); // Clear any previous errors
-            } catch (err) {
-                setError(err.message);
-                console.error("Failed to fetch alerts:", err);
-            }
-        }
-
-        fetchAlerts();
-    }, [selectedAddressId]);
-
-    // Handle new alert submission
-    async function handleAlertSubmit(data) {
-        if (!selectedAddressId) return;
-
-        try {
-            const newAlert = await createAlert(selectedAddressId, data);
-            setAlerts((prev) => [...prev, newAlert]);
-            setError(null); // Clear any previous errors
-        } catch (err) {
-            setError(err.message);
-            console.error("Failed to create alert:", err);
-        }
-    }
-
-    // Toggle alert enabled/disabled
-    async function handleToggleAlert(alertId, currentStatus) {
-        try {
-            const updated = await updateAlertStatus(alertId, !currentStatus);
-            setAlerts((prev) =>
-                prev.map((alert) => (alert.id === alertId ? updated : alert)),
-            );
-            setError(null); // Clear any previous errors
-        } catch (err) {
-            setError(err.message);
-            console.error("Failed to update alert:", err);
-        }
-    }
-
-    // Delete alert
-    async function handleDeleteAlert(alertId) {
-        try {
-            await deleteAlert(alertId);
-            setAlerts((prev) => prev.filter((alert) => alert.id !== alertId));
-            setError(null); // Clear any previous errors
-        } catch (err) {
-            setError(err.message);
-            console.error("Failed to delete alert:", err);
-        }
-    }
-
-    // Save notification config
-    async function handleSaveNotificationConfig() {
-        try {
-            setNotificationLoading(true);
-            setNotificationError(null);
-            setNotificationSuccess(null);
-
-            const config = {
-                discord_webhook_url: discordWebhookUrl || null,
-                notification_enabled: notificationEnabled,
-            };
-
-            const updated = await updateNotificationConfig(config);
-            setNotificationConfig(updated);
-            setNotificationSuccess("Notification settings saved!");
-
-            // Clear success message after 3 seconds
-            setTimeout(() => setNotificationSuccess(null), 3000);
-        } catch (err) {
-            setNotificationError(err.message);
-            console.error("Failed to save notification config:", err);
-        } finally {
-            setNotificationLoading(false);
-        }
-    }
-
-    // Test Discord webhook
-    async function handleTestWebhook() {
-        if (!discordWebhookUrl) {
-            setNotificationError("Please enter a Discord webhook URL first");
-            return;
-        }
-
-        try {
-            setTestingWebhook(true);
-            setNotificationError(null);
-            setNotificationSuccess(null);
-
-            const success = await testDiscordWebhook(discordWebhookUrl);
-
-            if (success) {
-                setNotificationSuccess(
-                    "Test notification sent! Check your Discord channel.",
-                );
-                setTimeout(() => setNotificationSuccess(null), 5000);
-            } else {
-                setNotificationError("Test failed. Check your webhook URL.");
-            }
-        } catch (err) {
-            setNotificationError("Test failed: " + err.message);
-        } finally {
-            setTestingWebhook(false);
-        }
-    }
-
-    const selectedAddress = addresses.find((a) => a.id === selectedAddressId);
-
-    if (loading) {
-        return <div style={{ padding: "2rem" }}>Loading addresses...</div>;
-    }
-
-    if (addresses.length === 0) {
-        return (
-            <div style={{ padding: "2rem" }}>
-                <p>
-                    No addresses tracked yet. Add an address first to create
-                    alerts.
-                </p>
-            </div>
-        );
-    }
-
-    return (
-        <div style={{ maxWidth: "1400px", margin: "0 auto", padding: "2rem" }}>
-            <h1 style={{ marginBottom: "2rem" }}>
-                Alert Rules & Notifications
-            </h1>
-
-            {/* Two-column layout */}
-            <div
-                style={{
-                    display: "grid",
-                    gridTemplateColumns: "1fr 1fr",
-                    gap: "2rem",
-                }}
-            >
-                {/* LEFT COLUMN: Alert Rules */}
-                <div>
-                    <h2 style={{ marginTop: 0 }}>Alert Rules</h2>
-
-                    {/* Address selector */}
-                    <div style={{ marginBottom: "2rem" }}>
-                        <label
-                            style={{ display: "block", marginBottom: "0.5rem" }}
-                        >
-                            <strong>Select Address:</strong>
-                        </label>
-                        <select
-                            value={selectedAddressId || ""}
-                            onChange={(e) =>
-                                setSelectedAddressId(Number(e.target.value))
-                            }
-                            style={{
-                                width: "100%",
-                                padding: "0.5rem",
-                                fontSize: "1rem",
-                                backgroundColor: "#1a1a1a",
-                                border: "1px solid #444",
-                                borderRadius: "4px",
-                                color: "white",
-                            }}
-                        >
-                            {addresses.map((addr) => (
-                                <option key={addr.id} value={addr.id}>
-                                    {addr.label || "Unlabeled"} - {addr.address}
-                                </option>
-                            ))}
-                        </select>
-                    </div>
-
-                    {selectedAddress && (
-                        <>
-                            {/* Current address info */}
-                            <div
-                                style={{
-                                    padding: "1rem",
-                                    marginBottom: "2rem",
-                                    backgroundColor: "#333",
-                                    borderRadius: "4px",
-                                    border: "1px solid #444",
-                                }}
-                            >
-                                <div
-                                    style={{
-                                        fontSize: "1.035rem",
-                                        color: "#b3b3b3",
-                                    }}
-                                >
-                                    Managing alerts for:
-                                </div>
-                                <div
-                                    style={{
-                                        fontWeight: "bold",
-                                        marginTop: "0.25rem",
-                                    }}
-                                >
-                                    {selectedAddress.label || "Unlabeled"}
-                                </div>
-                                <div
-                                    style={{
-                                        fontFamily: "monospace",
-                                        fontSize: "1.035rem",
-                                        color: "#b3b3b3",
-                                    }}
-                                >
-                                    {selectedAddress.address}
-                                </div>
-                            </div>
-
-                            {/* Alert creation form */}
-                            <div style={{ marginBottom: "2rem" }}>
-                                <h3>Create New Alert</h3>
-                                <AlertForm onSubmit={handleAlertSubmit} />
-                            </div>
-
-                            {/* Existing alerts list */}
-                            <div>
-                                <h3>Active Alert Rules</h3>
-                                {error && (
-                                    <p style={{ color: "red" }}>
-                                        Error: {error}
-                                    </p>
-                                )}
-                                {alerts.length === 0 ? (
-                                    <p style={{ color: "#666" }}>
-                                        No alert rules defined yet. Create one
-                                        above.
-                                    </p>
-                                ) : (
-                                    <ul
-                                        style={{
-                                            listStyle: "none",
-                                            padding: 0,
-                                        }}
-                                    >
-                                        {alerts.map((alert) => (
-                                            <li
-                                                key={alert.id}
-                                                style={{
-                                                    padding: "1rem",
-                                                    marginBottom: "0.5rem",
-                                                    border: "1px solid #444",
-                                                    borderRadius: "4px",
-                                                                    backgroundColor: "#333",
-                                                    opacity: alert.enabled
-                                                        ? 1
-                                                        : 0.6,
-                                                }}
-                                            >
-                                                <div
-                                                    style={{
-                                                        display: "flex",
-                                                        justifyContent:
-                                                            "space-between",
-                                                        alignItems:
-                                                            "flex-start",
-                                                    }}
-                                                >
-                                                    <div style={{ flex: 1 }}>
-                                                        <div
-                                                            style={{
-                                                                fontWeight:
-                                                                    "bold",
-                                                                marginBottom:
-                                                                    "0.25rem",
-                                                            }}
-                                                        >
-                                                            {formatAlertType(
-                                                                alert.type,
-                                                            )}
-                                                        </div>
-                                                        {alert.threshold && (
-                                                            <div
-                                                                style={{
-                                                                    fontSize:
-                                                                        "1.035rem",
-                                                                    color: "#b3b3b3",
-                                                                }}
-                                                            >
-                                                                Threshold:{" "}
-                                                                {
-                                                                    alert.threshold
-                                                                }{" "}
-                                                                ETH
-                                                            </div>
-                                                        )}
-                                                        <div
-                                                            style={{
-                                                                fontSize:
-                                                                    "0.978rem",
-                                                                color: "#808080",
-                                                                marginTop:
-                                                                    "0.25rem",
-                                                            }}
-                                                        >
-                                                            Status:{" "}
-                                                            {alert.enabled
-                                                                ? "Enabled"
-                                                                : "Disabled"}
-                                                        </div>
-                                                    </div>
-                                                    <div
-                                                        style={{
-                                                            display: "flex",
-                                                            gap: "0.5rem",
-                                                        }}
-                                                    >
-                                                        <Button
-                                                            onClick={() =>
-                                                                handleToggleAlert(
-                                                                    alert.id,
-                                                                    alert.enabled,
-                                                                )
-                                                            }
-                                                        >
-                                                            {alert.enabled
-                                                                ? "Disable"
-                                                                : "Enable"}
-                                                        </Button>
-                                                        <Button
-                                                            onClick={() =>
-                                                                handleDeleteAlert(
-                                                                    alert.id,
-                                                                )
-                                                            }
-                                                        >
-                                                            Delete
-                                                        </Button>
-                                                    </div>
-                                                </div>
-                                            </li>
-                                        ))}
-                                    </ul>
-                                )}
-                            </div>
-                        </>
-                    )}
-                </div>
-
-                {/* RIGHT COLUMN: Notification Settings */}
-                <div>
-                    <h2 style={{ marginTop: 0 }}>Notification Settings</h2>
-
-                    {notificationSuccess && (
-                        <div
-                            style={{
-                                padding: "0.75rem",
-                                marginBottom: "1rem",
-                                backgroundColor: "#00ff0020",
-                                border: "1px solid #00ff00",
-                                borderRadius: "4px",
-                                color: "#00ff00",
-                            }}
-                        >
-                            {notificationSuccess}
-                        </div>
-                    )}
-
-                    {notificationError && (
-                        <div
-                            style={{
-                                padding: "0.75rem",
-                                marginBottom: "1rem",
-                                backgroundColor: "#ff000020",
-                                border: "1px solid #ff0000",
-                                borderRadius: "4px",
-                                color: "#ff6666",
-                            }}
-                        >
-                            {notificationError}
-                        </div>
-                    )}
-
-                    {/* Master toggle */}
-                    <div
-                        style={{
-                            marginBottom: "2rem",
-                            padding: "1rem",
-                            backgroundColor: "#333",
-                            borderRadius: "4px",
-                        }}
-                    >
-                        <label
-                            style={{
-                                display: "flex",
-                                alignItems: "center",
-                                cursor: "pointer",
-                            }}
-                        >
-                            <input
-                                type="checkbox"
-                                checked={notificationEnabled}
-                                onChange={(e) =>
-                                    setNotificationEnabled(e.target.checked)
-                                }
-                                style={{
-                                    marginRight: "0.5rem",
-                                    width: "18px",
-                                    height: "18px",
-                                }}
-                            />
-                            <span style={{ fontWeight: "bold" }}>
-                                Enable Notifications
-                            </span>
-                        </label>
-                        <div
-                            style={{
-                                fontSize: "0.978rem",
-                                color: "#808080",
-                                marginTop: "0.5rem",
-                                marginLeft: "26px",
-                            }}
-                        >
-                            Master switch for all notification channels
-                        </div>
-                    </div>
-
-                    {/* Discord Section */}
-                    <div style={{ marginBottom: "2rem" }}>
-                        <h3 style={{ marginBottom: "1rem" }}>Discord</h3>
-
-                        <div style={{ marginBottom: "1rem" }}>
-                            <label
-                                style={{
-                                    display: "block",
-                                    marginBottom: "0.5rem",
-                                }}
-                            >
-                                Discord Webhook URL
-                            </label>
-                            <input
-                                type="text"
-                                value={discordWebhookUrl}
-                                onChange={(e) =>
-                                    setDiscordWebhookUrl(e.target.value)
-                                }
-                                placeholder="https://discord.com/api/webhooks/..."
-                                style={{
-                                    width: "100%",
-                                    padding: "0.5rem",
-                                    fontSize: "1rem",
-                                    backgroundColor: "#1a1a1a",
-                                    border: "1px solid #444",
-                                    borderRadius: "4px",
-                                    color: "white",
-                                    fontFamily: "monospace",
-                                    fontSize: "0.9rem",
-                                }}
-                            />
-                            <div
-                                style={{
-                                    fontSize: "0.978rem",
-                                    color: "#b3b3b3",
-                                    marginTop: "0.5rem",
-                                }}
-                            >
-                                <a
-                                    href="https://support.discord.com/hc/en-us/articles/228383668-Intro-to-Webhooks"
-                                    target="_blank"
-                                    rel="noopener noreferrer"
-                                    style={{ color: "#0066cc" }}
-                                >
-                                    How to get a Discord webhook URL
-                                </a>
-                            </div>
-                        </div>
-
-                        <div style={{ display: "flex", gap: "0.5rem" }}>
-                            <button
-                                onClick={handleSaveNotificationConfig}
-                                disabled={notificationLoading}
-                                style={{
-                                    padding: "0.75rem 1.5rem",
-                                    fontSize: "1rem",
-                                    backgroundColor: notificationLoading
-                                        ? "#333"
-                                        : "#0066cc",
-                                    color: "white",
-                                    border: "none",
-                                    borderRadius: "4px",
-                                    cursor: notificationLoading
-                                        ? "not-allowed"
-                                        : "pointer",
-                                }}
-                            >
-                                {notificationLoading
-                                    ? "Saving..."
-                                    : "Save Settings"}
-                            </button>
-
-                            <button
-                                onClick={handleTestWebhook}
-                                disabled={testingWebhook || !discordWebhookUrl}
-                                style={{
-                                    padding: "0.75rem 1.5rem",
-                                    fontSize: "1rem",
-                                    backgroundColor:
-                                        testingWebhook || !discordWebhookUrl
-                                            ? "#333"
-                                            : "#28a745",
-                                    color: "white",
-                                    border: "none",
-                                    borderRadius: "4px",
-                                    cursor:
-                                        testingWebhook || !discordWebhookUrl
-                                            ? "not-allowed"
-                                            : "pointer",
-                                }}
-                            >
-                                {testingWebhook ? "Testing..." : "Test Webhook"}
-                            </button>
-                        </div>
-                    </div>
-
-                    {/* Telegram Section (Coming Soon) */}
-                    <div style={{ marginBottom: "2rem", opacity: 0.5 }}>
-                        <h3 style={{ marginBottom: "1rem" }}>Telegram</h3>
-                        <div
-                            style={{
-                                padding: "1rem",
-                                backgroundColor: "#333",
-                                borderRadius: "4px",
-                                color: "#999",
-                                textAlign: "center",
-                            }}
-                        >
-                            Coming Soon
-                        </div>
-                    </div>
-
-                    {/* Email Section (Coming Soon) */}
-                    <div style={{ opacity: 0.5 }}>
-                        <h3 style={{ marginBottom: "1rem" }}>Email</h3>
-                        <div
-                            style={{
-                                padding: "1rem",
-                                backgroundColor: "#333",
-                                borderRadius: "4px",
-                                color: "#999",
-                                textAlign: "center",
-                            }}
-                        >
-                            Coming Soon
-                        </div>
-                    </div>
-                </div>
-            </div>
-        </div>
-    );
-}
-
-// Helper to format alert type for display
-function formatAlertType(type) {
-    const labels = {
-        incoming_tx: "Incoming transaction",
-        outgoing_tx: "Outgoing transaction",
-        large_transfer: "Large transfer",
-        balance_below: "Balance below threshold",
-    };
-    return labels[type] || type;
-}