m

Added PermanentError type, IsPermanent() helper.

.dockerignore

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

.editorconfig

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

.gitea/workflows/check.yml

@@ -0,0 +1,9 @@
+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

@@ -0,0 +1,45 @@
+# OS
+.DS_Store
+Thumbs.db
+
+# Editors
+*.swp
+*.swo
+*~
+*.bak
+.idea/
+.vscode/
+*.sublime-*
+
+# Node
+node_modules/
+
+# Environment / secrets
+.env
+.env.*
+*.pem
+*.key
+
+# Go build artifacts
+backend/bin/
+*.exe
+*.exe~
+*.dll
+*.so
+*.dylib
+*.test
+*.out
+vendor/
+tmp/
+
+# Frontend build output
+frontend/dist/
+frontend/build/
+frontend/.vite/
+
+# Prompts directory (local tooling, not part of the project)
+Prompts/
+
+# Logs
+*.log
+.claude

.prettierignore

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

.prettierrc

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

Dockerfile

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

LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2026 Steven Jannette
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

Makefile

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

README.md

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

REPO_POLICIES.md

@@ -0,0 +1,188 @@
+---
+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

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

backend-go/cmd/api/main.go

@@ -1,98 +0,0 @@
-package main
-
-import (
-	"fmt"
-	"log"
-	"net/http"
-	"os"
-
-	"github.com/joho/godotenv"
-	"github.com/kjannette/koin-ping/backend-go/internal/config"
-	"github.com/kjannette/koin-ping/backend-go/internal/database"
-	"github.com/kjannette/koin-ping/backend-go/internal/firebase"
-	"github.com/kjannette/koin-ping/backend-go/internal/handlers"
-	"github.com/kjannette/koin-ping/backend-go/internal/middleware"
-	"github.com/kjannette/koin-ping/backend-go/internal/models"
-)
-
-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)
-	}
-	defer database.Close()
-
-	if err := firebase.Init(cfg.FirebaseProjectID); err != nil {
-		log.Fatalf("Failed to initialize Firebase: %v", err)
-	}
-
-	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)
-
-	if err := http.ListenAndServe(addr, handler); err != nil {
-		log.Fatalf("Server failed: %v", err)
-		os.Exit(1)
-	}
-}
-
-func corsMiddleware(next http.Handler) http.Handler {
-	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		w.Header().Set("Access-Control-Allow-Origin", "*")
-		w.Header().Set("Access-Control-Allow-Methods", "GET, POST, PUT, PATCH, DELETE, OPTIONS")
-		w.Header().Set("Access-Control-Allow-Headers", "Content-Type, Authorization")
-
-		if r.Method == http.MethodOptions {
-			w.WriteHeader(http.StatusNoContent)
-			return
-		}
-
-		next.ServeHTTP(w, r)
-	})
-}

backend-go/internal/config/config.go

@@ -1,81 +0,0 @@
-package config
-
-import (
-	"fmt"
-	"os"
-	"strconv"
-	"strings"
-)
-
-type Config struct {
-	Port              int
-	APIBasePath       string
-	DatabaseURL       string
-	DBHost            string
-	DBPort            int
-	DBUser            string
-	DBPassword        string
-	DBName            string
-	FirebaseProjectID string
-	EthRPCURL         string
-	PollIntervalMS    int
-	NodeEnv           string
-}
-
-func Load() (*Config, error) {
-	cfg := &Config{
-		Port:           getEnvInt("PORT", 3001),
-		APIBasePath:    getEnv("API_BASE_PATH", "/v1"),
-		DatabaseURL:    os.Getenv("DATABASE_URL"),
-		DBHost:         getEnv("DB_HOST", "localhost"),
-		DBPort:         getEnvInt("DB_PORT", 5432),
-		DBUser:         os.Getenv("DB_USER"),
-		DBPassword:     os.Getenv("DB_PASSWORD"),
-		DBName:         os.Getenv("DB_NAME"),
-		FirebaseProjectID: os.Getenv("FIREBASE_PROJECT_ID"),
-		EthRPCURL:      os.Getenv("ETH_RPC_URL"),
-		PollIntervalMS: getEnvInt("POLL_INTERVAL_MS", 60000),
-		NodeEnv:        getEnv("NODE_ENV", "development"),
-	}
-
-	if cfg.PollIntervalMS < 1000 {
-		return nil, fmt.Errorf("POLL_INTERVAL_MS must be >= 1000, got %d", cfg.PollIntervalMS)
-	}
-
-	return cfg, nil
-}
-
-func (c *Config) DSN() string {
-	if c.DatabaseURL != "" {
-		// pgx defaults to sslmode=prefer, which fails against local Postgres.
-		// Append sslmode=disable if not already specified.
-		if !strings.Contains(c.DatabaseURL, "sslmode=") {
-			sep := "?"
-			if strings.Contains(c.DatabaseURL, "?") {
-				sep = "&"
-			}
-			return c.DatabaseURL + sep + "sslmode=disable"
-		}
-		return c.DatabaseURL
-	}
-	return fmt.Sprintf(
-		"host=%s port=%d user=%s password=%s dbname=%s sslmode=disable",
-		c.DBHost, c.DBPort, c.DBUser, c.DBPassword, c.DBName,
-	)
-}
-
-func getEnv(key, fallback string) string {
-	if v := os.Getenv(key); v != "" {
-		return v
-	}
-	return fallback
-}
-
-func getEnvInt(key string, fallback int) int {
-	if v := os.Getenv(key); v != "" {
-		if n, err := strconv.Atoi(v); err == nil {
-			return n
-		}
-	}
-	return fallback
-}

backend-go/internal/domain/types.go

@@ -1,115 +0,0 @@
-package domain
-
-import "time"
-
-type Address struct {
-	ID        int       `json:"id"`
-	UserID    string    `json:"user_id"`
-	Address   string    `json:"address"`
-	Label     *string   `json:"label"`
-	CreatedAt time.Time `json:"created_at"`
-}
-
-type AlertType string
-
-const (
-	AlertIncomingTx    AlertType = "incoming_tx"
-	AlertOutgoingTx    AlertType = "outgoing_tx"
-	AlertLargeTransfer AlertType = "large_transfer"
-	AlertBalanceBelow  AlertType = "balance_below"
-)
-
-var ValidAlertTypes = []AlertType{
-	AlertIncomingTx,
-	AlertOutgoingTx,
-	AlertLargeTransfer,
-	AlertBalanceBelow,
-}
-
-var ThresholdRequiredTypes = []AlertType{
-	AlertLargeTransfer,
-	AlertBalanceBelow,
-}
-
-func IsValidAlertType(t string) bool {
-	for _, v := range ValidAlertTypes {
-		if string(v) == t {
-			return true
-		}
-	}
-	return false
-}
-
-func IsThresholdRequired(t AlertType) bool {
-	for _, v := range ThresholdRequiredTypes {
-		if v == t {
-			return true
-		}
-	}
-	return false
-}
-
-type AlertRule struct {
-	ID        int       `json:"id"`
-	AddressID int       `json:"address_id"`
-	Type      AlertType `json:"type"`
-	Threshold *float64  `json:"threshold"`
-	Enabled   bool      `json:"enabled"`
-	CreatedAt time.Time `json:"created_at"`
-}
-
-type AlertEvent struct {
-	ID          int       `json:"id"`
-	AlertRuleID int       `json:"alert_rule_id"`
-	Message     string    `json:"message"`
-	AddressLabel *string  `json:"address_label"`
-	TxHash      *string   `json:"tx_hash"`
-	Timestamp   time.Time `json:"timestamp"`
-}
-
-type AddressCheckpoint struct {
-	AddressID        int       `json:"address_id"`
-	LastCheckedBlock int       `json:"last_checked_block"`
-	LastCheckedAt    time.Time `json:"last_checked_at"`
-}
-
-type CheckpointDetail struct {
-	AddressID        int       `json:"address_id"`
-	Address          string    `json:"address"`
-	Label            *string   `json:"label"`
-	LastCheckedBlock int       `json:"last_checked_block"`
-	LastCheckedAt    time.Time `json:"last_checked_at"`
-}
-
-type NotificationConfig struct {
-	UserID              string  `json:"user_id"`
-	DiscordWebhookURL   *string `json:"discord_webhook_url"`
-	TelegramChatID      *string `json:"telegram_chat_id"`
-	TelegramBotToken    *string `json:"telegram_bot_token,omitempty"`
-	Email               *string `json:"email"`
-	NotificationEnabled bool    `json:"notification_enabled"`
-	CreatedAt           *time.Time `json:"created_at,omitempty"`
-	UpdatedAt           *time.Time `json:"updated_at,omitempty"`
-}
-
-type NormalizedTx struct {
-	Hash           string `json:"hash"`
-	From           string `json:"from"`
-	To             *string `json:"to"`
-	Value          string `json:"value"` // Wei as string for precision
-	BlockNumber    int    `json:"block_number"`
-	BlockTimestamp int64  `json:"block_timestamp"`
-}
-
-type Direction string
-
-const (
-	DirectionIncoming Direction = "incoming"
-	DirectionOutgoing Direction = "outgoing"
-)
-
-type ObservedTx struct {
-	NormalizedTx
-	AddressID int       `json:"address_id"`
-	Direction Direction `json:"direction"`
-}

backend-go/internal/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

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

backend-go/internal/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/.golangci.yml

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

backend/ENV_TEMPLATE.md

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

backend/README.md

@@ -0,0 +1,20 @@
+Start DB:
+
+brew services start postgresql@15
+
+From the backend directory, you have a few options:
+
+Option 1: Single command (both API + poller)
+cd /Users/kjannette/workspace/koin_ping_0.2.0/backendmake dev-all
+
+Option 2: Two separate terminals
+Terminal 1 (API server):
+cd /Users/kjannette/workspace/koin_ping_0.2.0/backend go run ./cmd/api
+Terminal 2 (Poller):
+cd /Users/kjannette/workspace/koin_ping_0.2.0/backend go run ./cmd/poller
+
+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).
+make poller — Builds and runs the poller.
+make poller-dev — Runs the poller with auto-reload.
+make dev-all — Runs both the API and poller concurrently.

backend/cmd/api/main.go

@@ -0,0 +1,164 @@
+// 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)
+	alertRuleHandler := handlers.NewAlertRuleHandler(alertRuleModel, addressModel)
+	alertEventHandler := handlers.NewAlertEventHandler(alertEventModel)
+	notifConfigHandler := handlers.NewNotificationConfigHandler(notifConfigModel, cfg)
+	emailDigestHandler := handlers.NewEmailDigestHandler(emailDigestSvc, notifConfigModel)
+	statusHandler := handlers.NewStatusHandler(checkpointModel)
+	stripeHandler := handlers.NewStripeHandler(userModel, 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)
+
+	// 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)))
+
+	// Authenticated + subscribed routes — addresses
+	mux.Handle("POST "+b+"/addresses",
+		authAndSub(http.HandlerFunc(addressHandler.Create)))
+	mux.Handle("GET "+b+"/addresses",
+		authAndSub(http.HandlerFunc(addressHandler.List)))
+	mux.Handle("DELETE "+b+"/addresses/{addressId}",
+		authAndSub(http.HandlerFunc(addressHandler.Remove)))
+	mux.Handle("PATCH "+b+"/addresses/{addressId}",
+		authAndSub(http.HandlerFunc(addressHandler.UpdateLabel)))
+
+	// Authenticated + subscribed routes — alert rules
+	mux.Handle("POST "+b+"/addresses/{addressId}/alerts",
+		authAndSub(http.HandlerFunc(alertRuleHandler.Create)))
+	mux.Handle("GET "+b+"/addresses/{addressId}/alerts",
+		authAndSub(http.HandlerFunc(alertRuleHandler.ListByAddress)))
+	mux.Handle("PATCH "+b+"/alerts/{alertId}",
+		authAndSub(http.HandlerFunc(alertRuleHandler.UpdateStatus)))
+	mux.Handle("DELETE "+b+"/alerts/{alertId}",
+		authAndSub(http.HandlerFunc(alertRuleHandler.Remove)))
+
+	// Authenticated + subscribed routes — alert events
+	mux.Handle("GET "+b+"/alert-events",
+		authAndSub(http.HandlerFunc(alertEventHandler.List)))
+
+	// Authenticated + subscribed routes — notification config
+	mux.Handle("GET "+b+"/notification-config",
+		authAndSub(http.HandlerFunc(notifConfigHandler.GetConfig)))
+	mux.Handle("PUT "+b+"/notification-config",
+		authAndSub(http.HandlerFunc(notifConfigHandler.UpdateConfig)))
+	mux.Handle("DELETE "+b+"/notification-config",
+		authAndSub(http.HandlerFunc(notifConfigHandler.DeleteConfig)))
+	mux.Handle("POST "+b+"/notification-config/test",
+		authAndSub(http.HandlerFunc(notifConfigHandler.TestChannels)))
+
+	// Authenticated + subscribed routes — email digest
+	mux.Handle("POST "+b+"/email/setup",
+		authAndSub(http.HandlerFunc(emailDigestHandler.SetupEmail)))
+	mux.Handle("POST "+b+"/email/digest",
+		authAndSub(http.HandlerFunc(emailDigestHandler.SendDigest)))
+
+	handler := corsMiddleware(mux)
+
+	addr := fmt.Sprintf(":%d", cfg.Port)
+	log.Printf("Server running on port %d", cfg.Port)
+	log.Printf("API base path: %s", cfg.APIBasePath)
+	log.Printf("Environment: %s", cfg.NodeEnv)
+
+	server := &http.Server{
+		Addr:         addr,
+		Handler:      handler,
+		ReadTimeout:  serverReadTimeoutSeconds * time.Second,
+		WriteTimeout: serverWriteTimeoutSeconds * time.Second,
+	}
+	if err := server.ListenAndServe(); err != nil {
+		log.Fatalf("Server failed: %v", err)
+	}
+}
+
+func corsMiddleware(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Access-Control-Allow-Origin", "*")
+		w.Header().Set("Access-Control-Allow-Methods", "GET, POST, PUT, PATCH, DELETE, OPTIONS")
+		w.Header().Set("Access-Control-Allow-Headers", "Content-Type, Authorization")
+
+		if r.Method == http.MethodOptions {
+			w.WriteHeader(http.StatusNoContent)
+
+			return
+		}
+
+		next.ServeHTTP(w, r)
+	})
+}

backend/cmd/poller/main.go

@@ -1,3 +1,4 @@
+// Package main is the entry point for the blockchain observer poller.
 package main
 
 import (
@@ -11,13 +12,21 @@ import (
 	"time"
 
 	"github.com/joho/godotenv"
-	"github.com/kjannette/koin-ping/backend-go/internal/config"
+	"github.com/kjannette/koin-ping/backend/internal/config"
-	"github.com/kjannette/koin-ping/backend-go/internal/database"
+	"github.com/kjannette/koin-ping/backend/internal/database"
-	"github.com/kjannette/koin-ping/backend-go/internal/models"
+	"github.com/kjannette/koin-ping/backend/internal/models"
-	"github.com/kjannette/koin-ping/backend-go/internal/protocols/ethereum"
+	"github.com/kjannette/koin-ping/backend/internal/protocols/ethereum"
-	"github.com/kjannette/koin-ping/backend-go/internal/services"
+	"github.com/kjannette/koin-ping/backend/internal/services"
 )
 
+const (
+	// separatorWidth is the number of characters in log separator lines.
+	separatorWidth = 60
+	// msPerSecond converts milliseconds to seconds.
+	msPerSecond = 1000
+)
+
+//nolint:funlen
 func main() {
 	_ = godotenv.Load()
 
@@ -34,13 +43,14 @@ func main() {
 	if err != nil {
 		log.Fatalf("Failed to connect to database: %v", err)
 	}
-	defer database.Close()
 
 	eth, err := ethereum.NewJsonRpcEthereum(cfg.EthRPCURL)
 	if err != nil {
 		log.Fatalf("Failed to create Ethereum observer: %v", err)
 	}
 
+	defer database.Close()
+
 	addressModel := models.NewAddressModel(pool)
 	alertRuleModel := models.NewAlertRuleModel(pool)
 	alertEventModel := models.NewAlertEventModel(pool)
@@ -48,7 +58,11 @@ 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, notifConfigModel,
+		cfg.ResendAPIKey, cfg.EmailFrom,
+	)
+	digestSvc := services.NewEmailDigestService(cfg.ResendAPIKey, cfg.EmailFrom, alertEventModel, notifConfigModel)
 
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
@@ -58,53 +72,74 @@ func main() {
 	go func() {
 		<-sigCh
 		log.Println()
-		log.Println(strings.Repeat("=", 60))
+		log.Println(strings.Repeat("=", separatorWidth))
 		log.Println("Shutting down poller gracefully...")
-		log.Println(strings.Repeat("=", 60))
+		log.Println(strings.Repeat("=", separatorWidth))
 		cancel()
 	}()
 
 	interval := time.Duration(cfg.PollIntervalMS) * time.Millisecond
+	digestInterval := time.Duration(cfg.DigestIntervalHours) * time.Hour
 
-	log.Println(strings.Repeat("=", 60))
+	log.Println(strings.Repeat("=", separatorWidth))
 	log.Println("Koin Ping Observer Poller Starting")
-	log.Println(strings.Repeat("=", 60))
+	log.Println(strings.Repeat("=", separatorWidth))
 	log.Printf("RPC URL: %s", cfg.EthRPCURL)
-	log.Printf("Poll Interval: %dms (%ds)", cfg.PollIntervalMS, cfg.PollIntervalMS/1000)
+	log.Printf("Poll Interval: %dms (%ds)", cfg.PollIntervalMS, cfg.PollIntervalMS/msPerSecond)
-	log.Println(strings.Repeat("=", 60))
+	log.Printf("Digest Interval: %dh", cfg.DigestIntervalHours)
+	log.Println(strings.Repeat("=", separatorWidth))
 
 	runCycle(ctx, observer, evaluator)
 
 	ticker := time.NewTicker(interval)
 	defer ticker.Stop()
 
+	digestTicker := time.NewTicker(digestInterval)
+	defer digestTicker.Stop()
+
 	for {
 		select {
 		case <-ctx.Done():
 			log.Println("Poller stopped")
+
 			return
 		case <-ticker.C:
 			runCycle(ctx, observer, evaluator)
+		case <-digestTicker.C:
+			sent, digestErr := digestSvc.SendDigestsForAllUsers(ctx)
+			if digestErr != nil {
+				log.Printf("Email digest failed: %v", digestErr)
+			} else {
+				log.Printf("Sent %d email digests", sent)
+			}
 		}
 	}
 }
 
-func runCycle(ctx context.Context, observer *services.ObserverService, evaluator *services.EvaluatorService) {
+func runCycle(
+	ctx context.Context,
+	observer *services.ObserverService,
+	evaluator *services.EvaluatorService,
+) {
 	startTime := time.Now()
 	log.Printf("[%s] Starting observation cycle...", time.Now().UTC().Format(time.RFC3339))
 
 	observations, err := observer.RunOnce(ctx)
 	if err != nil {
 		log.Printf("[%s] Observation cycle failed: %v", time.Now().UTC().Format(time.RFC3339), err)
+
 		return
 	}
 
 	alertsFired, err := evaluator.Evaluate(ctx, observations)
 	if err != nil {
 		log.Printf("[%s] Evaluation failed: %v", time.Now().UTC().Format(time.RFC3339), err)
+
 		return
 	}
 
+	evaluator.WaitForNotifications()
+
 	duration := time.Since(startTime)
 	log.Printf("[%s] Cycle complete: %d observations, %d alerts fired in %s",
 		time.Now().UTC().Format(time.RFC3339),

backend/go.mod

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

backend/go.sum

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

backend/infra/migrations/003_add_slack_webhook.sql

@@ -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/schema.sql

@@ -4,15 +4,28 @@ 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_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)
 );
 
@@ -51,17 +64,20 @@ 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

@@ -0,0 +1,111 @@
+//loads environment-based configuration.
+package config
+
+import (
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+)
+
+const (
+	defaultPort = 3001
+	defaultDBPort = 5432
+	defaultPollIntervalMS = 60000
+	minPollIntervalMS = 1000
+	defaultDigestIntervalHours = 24
+)
+
+type Config struct {
+	Port              int
+	APIBasePath       string
+	DatabaseURL       string
+	DBHost            string
+	DBPort            int
+	DBUser            string
+	DBPassword        string
+	DBName            string
+	FirebaseProjectID string
+	EthRPCURL         string
+	PollIntervalMS    int
+	NodeEnv           string
+	ResendAPIKey         string
+	EmailFrom            string
+	DigestIntervalHours  int
+	StripeSecretKey      string
+	StripeWebhookSecret  string
+	StripePriceID        string
+	StripePublishableKey string
+	FrontendURL          string
+}
+
+// Load reads configuration from environment variables and returns a Config.
+func Load() (*Config, error) {
+	cfg := &Config{
+		Port:              getEnvInt("PORT", defaultPort),
+		APIBasePath:       getEnv("API_BASE_PATH", "/v1"),
+		DatabaseURL:       os.Getenv("DATABASE_URL"),
+		DBHost:            getEnv("DB_HOST", "localhost"),
+		DBPort:            getEnvInt("DB_PORT", defaultDBPort),
+		DBUser:            os.Getenv("DB_USER"),
+		DBPassword:        os.Getenv("DB_PASSWORD"),
+		DBName:            os.Getenv("DB_NAME"),
+		FirebaseProjectID: os.Getenv("FIREBASE_PROJECT_ID"),
+		EthRPCURL:         os.Getenv("ETH_RPC_URL"),
+		PollIntervalMS:    getEnvInt("POLL_INTERVAL_MS", defaultPollIntervalMS),
+		NodeEnv:           getEnv("NODE_ENV", "development"),
+		ResendAPIKey:        os.Getenv("RESEND_API_KEY"),
+		EmailFrom:           getEnv("EMAIL_FROM", "Koin Ping <alerts@koinping.com>"),
+		DigestIntervalHours:  getEnvInt("DIGEST_INTERVAL_HOURS", defaultDigestIntervalHours),
+		StripeSecretKey:      os.Getenv("STRIPE_SECRET_KEY"),
+		StripeWebhookSecret:  os.Getenv("STRIPE_WEBHOOK_SECRET"),
+		StripePriceID:        os.Getenv("STRIPE_PRICE_ID"),
+		StripePublishableKey: os.Getenv("STRIPE_PUBLISHABLE_KEY"),
+		FrontendURL:          getEnv("FRONTEND_URL", "http://localhost:3000"),
+	}
+
+	if cfg.PollIntervalMS < minPollIntervalMS {
+		return nil, fmt.Errorf("POLL_INTERVAL_MS must be >= 1000, got %d", cfg.PollIntervalMS) //nolint:err113
+	}
+
+	return cfg, nil
+}
+
+func (c *Config) DSN() string {
+	if c.DatabaseURL != "" {
+		// Append sslmode=disable if not already specified.
+		if !strings.Contains(c.DatabaseURL, "sslmode=") {
+			sep := "?"
+			if strings.Contains(c.DatabaseURL, "?") {
+				sep = "&"
+			}
+
+			return c.DatabaseURL + sep + "sslmode=disable"
+		}
+
+		return c.DatabaseURL
+	}
+
+	return fmt.Sprintf(
+		"host=%s port=%d user=%s password=%s dbname=%s sslmode=disable",
+		c.DBHost, c.DBPort, c.DBUser, c.DBPassword, c.DBName,
+	)
+}
+
+func getEnv(key, fallback string) string {
+	if v := os.Getenv(key); v != "" {
+		return v
+	}
+
+	return fallback
+}
+
+func getEnvInt(key string, fallback int) int {
+	if v := os.Getenv(key); v != "" {
+		if n, err := strconv.Atoi(v); err == nil {
+			return n
+		}
+	}
+
+	return fallback
+}

backend/internal/database/postgres.go

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

backend/internal/domain/types.go

@@ -0,0 +1,149 @@
+package domain
+
+import "time"
+
+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
+	SubscriptionCreatedAt *time.Time `json:"subscription_created_at,omitempty"` //nolint:tagliatelle
+	CreatedAt             time.Time  `json:"created_at"`             //nolint:tagliatelle
+	UpdatedAt             time.Time  `json:"updated_at"`             //nolint:tagliatelle
+}
+
+type Address struct {
+	ID        int       `json:"id"`
+	UserID    string    `json:"user_id"`    //nolint:tagliatelle
+	Address   string    `json:"address"`
+	Label     *string   `json:"label"`
+	CreatedAt time.Time `json:"created_at"` //nolint:tagliatelle
+}
+
+type AlertType string
+
+func (a AlertType) String() string { return string(a) }
+
+const (
+	AlertIncomingTx    AlertType = "incoming_tx"
+	AlertOutgoingTx    AlertType = "outgoing_tx"
+	AlertLargeTransfer AlertType = "large_transfer"
+	AlertBalanceBelow  AlertType = "balance_below"
+)
+
+var ValidAlertTypes = []AlertType{ //nolint:gochecknoglobals
+	AlertIncomingTx,
+	AlertOutgoingTx,
+	AlertLargeTransfer,
+	AlertBalanceBelow,
+}
+
+// ThresholdRequiredTypes lists alert types that require a threshold value.
+var ThresholdRequiredTypes = []AlertType{ //nolint:gochecknoglobals
+	AlertLargeTransfer,
+	AlertBalanceBelow,
+}
+
+// returns true if the given string matches a known AlertType.
+func IsValidAlertType(t string) bool {
+	for _, v := range ValidAlertTypes {
+		if string(v) == t {
+			return true
+		}
+	}
+
+	return false
+}
+
+func IsThresholdRequired(t AlertType) bool {
+	for _, v := range ThresholdRequiredTypes {
+		if v == t {
+			return true
+		}
+	}
+
+	return false
+}
+
+type AlertRule struct {
+	ID        int       `json:"id"`
+	AddressID int       `json:"address_id"` //nolint:tagliatelle
+	Type      AlertType `json:"type"`
+	Threshold *float64  `json:"threshold"`
+	Enabled   bool      `json:"enabled"`
+	CreatedAt time.Time `json:"created_at"` //nolint:tagliatelle
+}
+
+type AlertEvent struct {
+	ID           int       `json:"id"`
+	AlertRuleID  int       `json:"alert_rule_id"`   //nolint:tagliatelle
+	Message      string    `json:"message"`
+	AddressLabel *string   `json:"address_label"`   //nolint:tagliatelle
+	TxHash       *string   `json:"tx_hash"`         //nolint:tagliatelle
+	Timestamp    time.Time `json:"timestamp"`
+}
+
+type AddressCheckpoint struct {
+	AddressID        int       `json:"address_id"`         //nolint:tagliatelle
+	LastCheckedBlock int       `json:"last_checked_block"` //nolint:tagliatelle
+	LastCheckedAt    time.Time `json:"last_checked_at"`    //nolint:tagliatelle
+}
+
+type CheckpointDetail struct {
+	AddressID        int       `json:"address_id"`         //nolint:tagliatelle
+	Address          string    `json:"address"`
+	Label            *string   `json:"label"`
+	LastCheckedBlock int       `json:"last_checked_block"` //nolint:tagliatelle
+	LastCheckedAt    time.Time `json:"last_checked_at"`    //nolint:tagliatelle
+}
+
+//  holds a user's notification preferences.
+type NotificationConfig struct {
+	UserID              string     `json:"user_id"`              //nolint:tagliatelle
+	DiscordWebhookURL   *string    `json:"discord_webhook_url"`  //nolint:tagliatelle
+	TelegramChatID      *string    `json:"telegram_chat_id"`     //nolint:tagliatelle
+	TelegramBotToken    *string    `json:"telegram_bot_token"`   //nolint:tagliatelle
+	Email               *string    `json:"email"`
+	SlackWebhookURL     *string    `json:"slack_webhook_url"`    //nolint:tagliatelle
+	NotificationEnabled bool       `json:"notification_enabled"` //nolint:tagliatelle
+	CreatedAt           *time.Time `json:"created_at,omitempty"` //nolint:tagliatelle
+	UpdatedAt           *time.Time `json:"updated_at,omitempty"` //nolint:tagliatelle
+}
+
+// NormalizedTx is a blockchain transaction normalized for internal use.
+type NormalizedTx struct {
+	Hash           string  `json:"hash"`
+	From           string  `json:"from"`
+	To             *string `json:"to"`
+	Value          string  `json:"value"` // Wei as string for precision
+	BlockNumber    int     `json:"block_number"`    //nolint:tagliatelle
+	BlockTimestamp int64   `json:"block_timestamp"` //nolint:tagliatelle
+
+	// ERC-20 token transfer fields (nil for native ETH transfers)
+	TokenContract *string `json:"token_contract,omitempty"` //nolint:tagliatelle
+	TokenSymbol   *string `json:"token_symbol,omitempty"`   //nolint:tagliatelle
+	TokenDecimals *int    `json:"token_decimals,omitempty"` //nolint:tagliatelle
+	TokenValue    *string `json:"token_value,omitempty"`    //nolint:tagliatelle
+}
+
+func (tx NormalizedTx) IsTokenTransfer() bool {
+	return tx.TokenContract != nil
+}
+
+type Direction string
+
+func (d Direction) String() string { return string(d) }
+
+const (
+	DirectionIncoming Direction = "incoming"
+	DirectionOutgoing Direction = "outgoing"
+)
+
+type ObservedTx struct {
+	NormalizedTx
+	AddressID int       `json:"address_id"` //nolint:tagliatelle
+	Direction Direction `json:"direction"`
+}

backend/internal/firebase/admin.go

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

backend/internal/handlers/address.go

@@ -1,3 +1,4 @@
+// Package handlers implements HTTP request handlers for the API.
 package handlers
 
 import (
@@ -7,9 +8,9 @@ import (
 	"regexp"
 	"strings"
 
-	"github.com/kjannette/koin-ping/backend-go/internal/domain"
+	"github.com/kjannette/koin-ping/backend/internal/domain"
-	"github.com/kjannette/koin-ping/backend-go/internal/middleware"
+	"github.com/kjannette/koin-ping/backend/internal/middleware"
-	"github.com/kjannette/koin-ping/backend-go/internal/models"
+	"github.com/kjannette/koin-ping/backend/internal/models"
 )
 
 var ethAddressRe = regexp.MustCompile(`^0x[a-fA-F0-9]{40}$`)
@@ -32,16 +33,19 @@ func (h *AddressHandler) Create(w http.ResponseWriter, r *http.Request) {
 	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
 		log.Printf("Failed to decode address request body: %v", err)
 		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "Invalid request body")
+
 		return
 	}
 
 	if body.Address == "" {
 		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "Address is required")
+
 		return
 	}
 
 	if !ethAddressRe.MatchString(body.Address) {
 		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "Invalid Ethereum address format")
+
 		return
 	}
 
@@ -51,10 +55,12 @@ func (h *AddressHandler) Create(w http.ResponseWriter, r *http.Request) {
 	if err != nil {
 		if strings.Contains(err.Error(), "23505") || strings.Contains(err.Error(), "unique") {
 			writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "You are already tracking this address")
+
 			return
 		}
 		log.Printf("Error creating address: %v", err)
 		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to create address")
+
 		return
 	}
 
@@ -62,6 +68,7 @@ func (h *AddressHandler) Create(w http.ResponseWriter, r *http.Request) {
 	writeJSON(w, http.StatusCreated, addr)
 }
 
+// List handles GET requests to list all tracked addresses for the current user.
 func (h *AddressHandler) List(w http.ResponseWriter, r *http.Request) {
 	userID := middleware.GetUserID(r.Context())
 	log.Printf("User %s listing addresses", userID)
@@ -70,6 +77,7 @@ func (h *AddressHandler) List(w http.ResponseWriter, r *http.Request) {
 	if err != nil {
 		log.Printf("Error listing addresses: %v", err)
 		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to list addresses")
+
 		return
 	}
 
@@ -81,11 +89,51 @@ func (h *AddressHandler) List(w http.ResponseWriter, r *http.Request) {
 	writeJSON(w, http.StatusOK, addresses)
 }
 
+//  handles PATCH requests to update an address label.
+func (h *AddressHandler) UpdateLabel(w http.ResponseWriter, r *http.Request) {
+	userID := middleware.GetUserID(r.Context())
+	addressID, ok := parseIntParam(r.PathValue("addressId"))
+	if !ok {
+		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "Invalid address ID")
+
+		return
+	}
+
+	var body struct {
+		Label *string `json:"label"`
+	}
+	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "Invalid request body")
+
+		return
+	}
+
+	log.Printf("User %s updating label for address ID: %d", userID, addressID)
+
+	addr, err := h.addresses.UpdateLabel(r.Context(), addressID, userID, body.Label)
+	if err != nil {
+		log.Printf("Error updating address label: %v", err)
+		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to update address")
+
+		return
+	}
+
+	if addr == nil {
+		writeError(w, http.StatusNotFound, "NOT_FOUND", "Address not found")
+
+		return
+	}
+
+	writeJSON(w, http.StatusOK, addr)
+}
+
+// Remove handles DELETE requests to remove a tracked address.
 func (h *AddressHandler) Remove(w http.ResponseWriter, r *http.Request) {
 	userID := middleware.GetUserID(r.Context())
 	addressID, ok := parseIntParam(r.PathValue("addressId"))
 	if !ok {
 		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "Invalid address ID")
+
 		return
 	}
 
@@ -95,12 +143,14 @@ func (h *AddressHandler) Remove(w http.ResponseWriter, r *http.Request) {
 	if err != nil {
 		log.Printf("Error deleting address: %v", err)
 		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to delete address")
+
 		return
 	}
 
 	if !deleted {
 		log.Printf("Address %d not found or not owned by user", addressID)
 		writeError(w, http.StatusNotFound, "NOT_FOUND", "Address not found")
+
 		return
 	}
 

backend/internal/handlers/alert_event.go

@@ -4,21 +4,23 @@ import (
 	"log"
 	"net/http"
 	"strconv"
-	"time"
 
-	"github.com/kjannette/koin-ping/backend-go/internal/domain"
+	"github.com/kjannette/koin-ping/backend/internal/domain"
-	"github.com/kjannette/koin-ping/backend-go/internal/middleware"
+	"github.com/kjannette/koin-ping/backend/internal/middleware"
-	"github.com/kjannette/koin-ping/backend-go/internal/models"
+	"github.com/kjannette/koin-ping/backend/internal/models"
 )
 
+// AlertEventHandler handles HTTP requests for alert event history.
 type AlertEventHandler struct {
 	alertEvents *models.AlertEventModel
 }
 
+// NewAlertEventHandler creates a new AlertEventHandler.
 func NewAlertEventHandler(alertEvents *models.AlertEventModel) *AlertEventHandler {
 	return &AlertEventHandler{alertEvents: alertEvents}
 }
 
+// List handles GET requests to list recent alert events for the current user.
 func (h *AlertEventHandler) List(w http.ResponseWriter, r *http.Request) {
 	userID := middleware.GetUserID(r.Context())
 
@@ -34,6 +36,7 @@ func (h *AlertEventHandler) List(w http.ResponseWriter, r *http.Request) {
 
 	if limit < 1 || limit > 100 {
 		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "Limit must be between 1 and 100")
+
 		return
 	}
 
@@ -41,49 +44,15 @@ func (h *AlertEventHandler) List(w http.ResponseWriter, r *http.Request) {
 	if err != nil {
 		log.Printf("Error listing alert events: %v", err)
 		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to list alert events")
+
 		return
 	}
 
 	log.Printf("Found %d alert events for user", len(events))
 
-	// MVP scaffolding: return mock data if DB is empty
+	if events == nil {
-	if len(events) == 0 {
+		events = []domain.AlertEvent{}
-		events = mockEvents(limit)
 	}
 
 	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,
-			AlertRuleID:  2,
-			Message:      "Balance dropped below threshold: Current balance 8.2 ETH",
-			AddressLabel: &label1,
-			Timestamp:    time.Now().Add(-5 * time.Hour),
-		},
-		{
-			ID:           3,
-			AlertRuleID:  3,
-			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

@@ -2,17 +2,20 @@ package handlers
 
 import (
 	"encoding/json"
+	"errors"
 	"fmt"
 	"log"
 	"net/http"
 	"strconv"
 	"strings"
 
-	"github.com/kjannette/koin-ping/backend-go/internal/domain"
+	"github.com/kjannette/koin-ping/backend/internal/domain"
-	"github.com/kjannette/koin-ping/backend-go/internal/middleware"
+	"github.com/kjannette/koin-ping/backend/internal/middleware"
-	"github.com/kjannette/koin-ping/backend-go/internal/models"
+	"github.com/kjannette/koin-ping/backend/internal/models"
 )
 
+var errThresholdFormat = errors.New("unsupported threshold format")
+
 type AlertRuleHandler struct {
 	alertRules *models.AlertRuleModel
 	addresses  *models.AddressModel
@@ -27,6 +30,7 @@ func (h *AlertRuleHandler) Create(w http.ResponseWriter, r *http.Request) {
 	addressID, ok := parseIntParam(r.PathValue("addressId"))
 	if !ok {
 		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "Invalid address ID")
+
 		return
 	}
 
@@ -37,6 +41,7 @@ func (h *AlertRuleHandler) Create(w http.ResponseWriter, r *http.Request) {
 	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
 		log.Printf("Failed to decode alert request body: %v", err)
 		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "Invalid request body")
+
 		return
 	}
 
@@ -44,6 +49,7 @@ func (h *AlertRuleHandler) Create(w http.ResponseWriter, r *http.Request) {
 	if err != nil {
 		log.Printf("Failed to parse threshold: %v", err)
 		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "threshold must be a valid number")
+
 		return
 	}
 
@@ -51,16 +57,18 @@ func (h *AlertRuleHandler) Create(w http.ResponseWriter, r *http.Request) {
 
 	if body.Type == "" {
 		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "Alert type is required")
+
 		return
 	}
 
 	if !domain.IsValidAlertType(body.Type) {
 		types := make([]string, len(domain.ValidAlertTypes))
 		for i, t := range domain.ValidAlertTypes {
-			types[i] = string(t)
+			types[i] = t.String()
 		}
 		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR",
-			fmt.Sprintf("Invalid alert type. Must be one of: %s", strings.Join(types, ", ")))
+			"Invalid alert type. Must be one of: "+strings.Join(types, ", "))
+
 		return
 	}
 
@@ -69,6 +77,7 @@ func (h *AlertRuleHandler) Create(w http.ResponseWriter, r *http.Request) {
 		if threshold == nil || *threshold <= 0 {
 			writeError(w, http.StatusBadRequest, "VALIDATION_ERROR",
 				fmt.Sprintf("Alert type '%s' requires a positive threshold value", body.Type))
+
 			return
 		}
 	}
@@ -77,11 +86,13 @@ func (h *AlertRuleHandler) Create(w http.ResponseWriter, r *http.Request) {
 	if err != nil {
 		log.Printf("Error finding address: %v", err)
 		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to create alert rule")
+
 		return
 	}
 	if addr == nil {
 		log.Printf("Address %d not found or not owned by user", addressID)
 		writeError(w, http.StatusNotFound, "NOT_FOUND", "Address not found")
+
 		return
 	}
 
@@ -89,6 +100,7 @@ func (h *AlertRuleHandler) Create(w http.ResponseWriter, r *http.Request) {
 	if err != nil {
 		log.Printf("Error creating alert rule: %v", err)
 		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to create alert rule")
+
 		return
 	}
 
@@ -98,12 +110,12 @@ func (h *AlertRuleHandler) Create(w http.ResponseWriter, r *http.Request) {
 
 func parseThreshold(raw json.RawMessage) (*float64, error) {
 	if len(raw) == 0 {
-		return nil, nil
+		return nil, nil //nolint:nilnil
 	}
 
 	// Check null before number -- json.Unmarshal treats null as valid for float64 (sets to 0).
 	if string(raw) == "null" {
-		return nil, nil
+		return nil, nil //nolint:nilnil
 	}
 
 	var asNumber float64
@@ -115,23 +127,26 @@ func parseThreshold(raw json.RawMessage) (*float64, error) {
 	if err := json.Unmarshal(raw, &asString); err == nil {
 		asString = strings.TrimSpace(asString)
 		if asString == "" {
-			return nil, nil
+			return nil, nil //nolint:nilnil
 		}
 		parsed, parseErr := strconv.ParseFloat(asString, 64)
 		if parseErr != nil {
 			return nil, parseErr
 		}
+
 		return &parsed, nil
 	}
 
-	return nil, fmt.Errorf("unsupported threshold format")
+	return nil, errThresholdFormat
 }
 
+// ListByAddress handles GET requests to list alert rules for an address.
 func (h *AlertRuleHandler) ListByAddress(w http.ResponseWriter, r *http.Request) {
 	userID := middleware.GetUserID(r.Context())
 	addressID, ok := parseIntParam(r.PathValue("addressId"))
 	if !ok {
 		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "Invalid address ID")
+
 		return
 	}
 
@@ -141,11 +156,13 @@ func (h *AlertRuleHandler) ListByAddress(w http.ResponseWriter, r *http.Request)
 	if err != nil {
 		log.Printf("Error finding address: %v", err)
 		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to list alerts")
+
 		return
 	}
 	if addr == nil {
 		log.Printf("Address %d not found or not owned by user", addressID)
 		writeError(w, http.StatusNotFound, "NOT_FOUND", "Address not found")
+
 		return
 	}
 
@@ -153,6 +170,7 @@ func (h *AlertRuleHandler) ListByAddress(w http.ResponseWriter, r *http.Request)
 	if err != nil {
 		log.Printf("Error listing alerts: %v", err)
 		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to list alerts")
+
 		return
 	}
 
@@ -164,11 +182,13 @@ 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.
 func (h *AlertRuleHandler) UpdateStatus(w http.ResponseWriter, r *http.Request) {
 	userID := middleware.GetUserID(r.Context())
 	alertID, ok := parseIntParam(r.PathValue("alertId"))
 	if !ok {
 		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "Invalid alert ID")
+
 		return
 	}
 
@@ -178,6 +198,7 @@ func (h *AlertRuleHandler) UpdateStatus(w http.ResponseWriter, r *http.Request)
 	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
 		log.Printf("Failed to decode update request body: %v", err)
 		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "Invalid request body")
+
 		return
 	}
 
@@ -185,6 +206,7 @@ func (h *AlertRuleHandler) UpdateStatus(w http.ResponseWriter, r *http.Request)
 
 	if body.Enabled == nil {
 		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "enabled must be a boolean value")
+
 		return
 	}
 
@@ -192,11 +214,13 @@ func (h *AlertRuleHandler) UpdateStatus(w http.ResponseWriter, r *http.Request)
 	if err != nil {
 		log.Printf("Error finding alert: %v", err)
 		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to update alert")
+
 		return
 	}
 	if alert == nil {
 		log.Printf("Alert %d not found or not owned by user", alertID)
 		writeError(w, http.StatusNotFound, "NOT_FOUND", "Alert rule not found")
+
 		return
 	}
 
@@ -204,6 +228,7 @@ func (h *AlertRuleHandler) UpdateStatus(w http.ResponseWriter, r *http.Request)
 	if err != nil {
 		log.Printf("Error updating alert: %v", err)
 		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to update alert")
+
 		return
 	}
 
@@ -211,11 +236,13 @@ func (h *AlertRuleHandler) UpdateStatus(w http.ResponseWriter, r *http.Request)
 	writeJSON(w, http.StatusOK, updated)
 }
 
+// Remove handles DELETE requests to remove an alert rule.
 func (h *AlertRuleHandler) Remove(w http.ResponseWriter, r *http.Request) {
 	userID := middleware.GetUserID(r.Context())
 	alertID, ok := parseIntParam(r.PathValue("alertId"))
 	if !ok {
 		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "Invalid alert ID")
+
 		return
 	}
 
@@ -225,17 +252,20 @@ func (h *AlertRuleHandler) Remove(w http.ResponseWriter, r *http.Request) {
 	if err != nil {
 		log.Printf("Error finding alert: %v", err)
 		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to delete alert")
+
 		return
 	}
 	if alert == nil {
 		log.Printf("Alert %d not found or not owned by user", alertID)
 		writeError(w, http.StatusNotFound, "NOT_FOUND", "Alert rule not found")
+
 		return
 	}
 
 	if _, err := h.alertRules.Remove(r.Context(), alertID); err != nil {
 		log.Printf("Error deleting alert: %v", err)
 		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to delete alert")
+
 		return
 	}
 

backend/internal/handlers/alert_rule_test.go

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

backend/internal/handlers/email_digest.go

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

backend/internal/handlers/notification_config.go

@@ -7,19 +7,22 @@ import (
 	"regexp"
 	"strings"
 
-	"github.com/kjannette/koin-ping/backend-go/internal/domain"
+	"github.com/kjannette/koin-ping/backend/internal/config"
-	"github.com/kjannette/koin-ping/backend-go/internal/middleware"
+	"github.com/kjannette/koin-ping/backend/internal/domain"
-	"github.com/kjannette/koin-ping/backend-go/internal/models"
+	"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
+	cfg     *config.Config
 }
 
-func NewNotificationConfigHandler(configs *models.NotificationConfigModel) *NotificationConfigHandler {
+func NewNotificationConfigHandler(configs *models.NotificationConfigModel, cfg *config.Config) *NotificationConfigHandler {
-	return &NotificationConfigHandler{configs: configs}
+	return &NotificationConfigHandler{configs: configs, cfg: cfg}
 }
 
 func (h *NotificationConfigHandler) GetConfig(w http.ResponseWriter, r *http.Request) {
@@ -51,7 +54,9 @@ func (h *NotificationConfigHandler) UpdateConfig(w http.ResponseWriter, r *http.
 	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 {
@@ -63,7 +68,8 @@ func (h *NotificationConfigHandler) UpdateConfig(w http.ResponseWriter, r *http.
 	log.Printf("User %s updating notification config", userID)
 
 	if body.DiscordWebhookURL == nil && body.TelegramChatID == nil &&
-		body.Email == nil && body.NotificationEnabled == 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
@@ -76,6 +82,13 @@ func (h *NotificationConfigHandler) UpdateConfig(w http.ResponseWriter, r *http.
 		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")
@@ -90,7 +103,9 @@ func (h *NotificationConfigHandler) UpdateConfig(w http.ResponseWriter, r *http.
 	cfg := domain.NotificationConfig{
 		DiscordWebhookURL:   body.DiscordWebhookURL,
 		TelegramChatID:      body.TelegramChatID,
+		TelegramBotToken:    body.TelegramBotToken,
 		Email:               body.Email,
+		SlackWebhookURL:     body.SlackWebhookURL,
 		NotificationEnabled: enabled,
 	}
 
@@ -126,3 +141,76 @@ func (h *NotificationConfigHandler) DeleteConfig(w http.ResponseWriter, r *http.
 	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 +1,254 @@
+package handlers
+
+import (
+	"encoding/json"
+	"io"
+	"log"
+	"net/http"
+
+	"github.com/stripe/stripe-go/v82"
+	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/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}
+}
+
+// CreateCheckoutSession creates a Stripe Checkout session for the monthly subscription.
+func (h *StripeHandler) CreateCheckoutSession(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
+	}
+
+	params := &stripe.CheckoutSessionParams{
+		Mode: stripe.String(string(stripe.CheckoutSessionModeSubscription)),
+		LineItems: []*stripe.CheckoutSessionLineItemParams{
+			{
+				Price:    stripe.String(h.cfg.StripePriceID),
+				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),
+	}
+
+	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_created_at": user.SubscriptionCreatedAt,
+	})
+}
+
+// VerifyCheckoutSession retrieves a completed checkout session from Stripe,
+// confirms payment, and activates the user's subscription in the database.
+// This is the primary activation path; webhooks serve as a backup.
+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 != 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
+	}
+
+	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"); err != nil {
+			log.Printf("VerifyCheckout: failed to activate subscription: %v", err)
+		}
+	}
+
+	log.Printf("Checkout verified for user %s, customer %s, subscription %s", userID, customerID, subscriptionID)
+	writeJSON(w, http.StatusOK, map[string]string{"subscription_status": "active"})
+}
+
+// HandleWebhook processes incoming Stripe webhook events.
+// This endpoint must NOT require authentication (Stripe calls it directly).
+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
+	}
+
+	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"); err != nil {
+			log.Printf("Failed to activate subscription: %v", err)
+		}
+	}
+
+	log.Printf("Checkout completed for user %s, customer %s, subscription %s", userID, customerID, subscriptionID)
+}
+
+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)
+	if err := h.users.ActivateSubscription(r.Context(), customerID, sub.ID, status); err != nil {
+		log.Printf("Failed to update subscription status: %v", err)
+	}
+
+	log.Printf("Subscription %s updated to %s for customer %s", sub.ID, status, 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 +1,152 @@
+// 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"
+)
+
+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)
+
+			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 ""
+}

backend/internal/models/address.go

@@ -2,9 +2,11 @@ package models
 
 import (
 	"context"
+	"errors"
 
+	"github.com/jackc/pgx/v5"
 	"github.com/jackc/pgx/v5/pgxpool"
-	"github.com/kjannette/koin-ping/backend-go/internal/domain"
+	"github.com/kjannette/koin-ping/backend/internal/domain"
 )
 
 type AddressModel struct {
@@ -97,7 +99,25 @@ func (m *AddressModel) FindByID(ctx context.Context, id int, userID *string) (*d
 	}
 
 	if err != nil {
-		if err.Error() == "no rows in result set" {
+		if errors.Is(err, pgx.ErrNoRows) {
+			return nil, nil
+		}
+		return nil, err
+	}
+	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

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

@@ -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 AlertRuleModel struct {
@@ -21,7 +23,7 @@ func (m *AlertRuleModel) Create(ctx context.Context, addressID int, alertType do
 		`INSERT INTO alert_rules (address_id, type, threshold, enabled)
 		 VALUES ($1, $2, $3, TRUE)
 		 RETURNING id, address_id, type, threshold, enabled, created_at`,
-		addressID, string(alertType), threshold,
+		addressID, alertType.String(), threshold,
 	).Scan(&r.ID, &r.AddressID, &r.Type, &r.Threshold, &r.Enabled, &r.CreatedAt)
 	if err != nil {
 		return nil, err
@@ -75,7 +77,7 @@ func (m *AlertRuleModel) FindByID(ctx context.Context, id int, userID *string) (
 	}
 
 	if err != nil {
-		if err.Error() == "no rows in result set" {
+		if errors.Is(err, pgx.ErrNoRows) {
 			return nil, nil
 		}
 		return nil, err
@@ -93,7 +95,7 @@ func (m *AlertRuleModel) UpdateEnabled(ctx context.Context, id int, enabled bool
 		id, enabled,
 	).Scan(&r.ID, &r.AddressID, &r.Type, &r.Threshold, &r.Enabled, &r.CreatedAt)
 	if err != nil {
-		if err.Error() == "no rows in result set" {
+		if errors.Is(err, pgx.ErrNoRows) {
 			return nil, nil
 		}
 		return nil, err

backend/internal/models/checkpoint.go

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

backend/internal/models/notification_config.go

@@ -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 NotificationConfigModel struct {
@@ -19,14 +21,14 @@ 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 err.Error() == "no rows in result set" {
+		if errors.Is(err, pgx.ErrNoRows) {
 			return nil, nil
 		}
 		return nil, err
@@ -38,22 +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)
+		   (user_id, discord_webhook_url, telegram_chat_id, telegram_bot_token,
-		 VALUES ($1, $2, $3, $4, $5, $6, NOW())
+		    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),
+		   discord_webhook_url = $2,
-		   telegram_chat_id = COALESCE($3, user_notification_configs.telegram_chat_id),
+		   telegram_chat_id = $3,
-		   telegram_bot_token = COALESCE($4, user_notification_configs.telegram_bot_token),
+		   telegram_bot_token = $4,
-		   email = COALESCE($5, user_notification_configs.email),
+		   email = $5,
-		   notification_enabled = $6,
+		   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
 	}
@@ -73,7 +77,8 @@ 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
+		`SELECT user_id, discord_webhook_url, telegram_chat_id, telegram_bot_token,
+		        email, slack_webhook_url
 		 FROM user_notification_configs
 		 WHERE notification_enabled = TRUE`,
 	)
@@ -85,7 +90,8 @@ 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 +1,89 @@
+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_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.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) error {
+	_, err := m.pool.Exec(ctx,
+		`UPDATE users
+		 SET stripe_subscription_id = $2,
+		     subscription_status = $3,
+		     subscription_created_at = COALESCE(subscription_created_at, NOW()),
+		     updated_at = NOW()
+		 WHERE stripe_customer_id = $1`,
+		stripeCustomerID, subscriptionID, status,
+	)
+	return err
+}
+
+func (m *UserModel) UpdateSubscriptionStatus(ctx context.Context, stripeCustomerID, status string) error {
+	_, err := m.pool.Exec(ctx,
+		`UPDATE users SET subscription_status = $2, updated_at = NOW()
+		 WHERE stripe_customer_id = $1`,
+		stripeCustomerID, status,
+	)
+	return err
+}

backend/internal/notifications/discord.go

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

backend/internal/notifications/email.go

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

backend/internal/notifications/notifier.go

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

backend/internal/notifications/slack.go

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

backend/internal/notifications/telegram.go

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

backend/internal/protocols/ethereum/jsonrpc.go

@@ -0,0 +1,399 @@
+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
+)
+
+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)
+	}
+
+	return j.callWithRetry(ctx, method, body)
+}
+
+// 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

@@ -4,12 +4,23 @@ import (
 	"context"
 	"fmt"
 	"log"
+	"sync"
+	"time"
 
-	"github.com/kjannette/koin-ping/backend-go/internal/domain"
+	"golang.org/x/sync/semaphore"
-	"github.com/kjannette/koin-ping/backend-go/internal/models"
+
-	"github.com/kjannette/koin-ping/backend-go/internal/notifications"
+	"github.com/kjannette/koin-ping/backend/internal/domain"
-	"github.com/kjannette/koin-ping/backend-go/internal/protocols/ethereum"
+	"github.com/kjannette/koin-ping/backend/internal/models"
-	"github.com/kjannette/koin-ping/backend-go/internal/wei"
+	"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 {
@@ -18,6 +29,10 @@ type EvaluatorService struct {
 	alertEvents  *models.AlertEventModel
 	addresses    *models.AddressModel
 	notifConfigs *models.NotificationConfigModel
+	resendAPIKey string
+	emailFrom    string
+	notifSem     *semaphore.Weighted
+	notifWg      sync.WaitGroup
 }
 
 func NewEvaluatorService(
@@ -26,6 +41,8 @@ func NewEvaluatorService(
 	alertEvents *models.AlertEventModel,
 	addresses *models.AddressModel,
 	notifConfigs *models.NotificationConfigModel,
+	resendAPIKey string,
+	emailFrom string,
 ) *EvaluatorService {
 	return &EvaluatorService{
 		eth:          eth,
@@ -33,6 +50,9 @@ func NewEvaluatorService(
 		alertEvents:  alertEvents,
 		addresses:    addresses,
 		notifConfigs: notifConfigs,
+		resendAPIKey: resendAPIKey,
+		emailFrom:    emailFrom,
+		notifSem:     semaphore.NewWeighted(maxConcurrentNotifications),
 	}
 }
 
@@ -161,21 +181,103 @@ func (s *EvaluatorService) fireAlert(ctx context.Context, rule domain.AlertRule,
 	message := s.buildMessage(rule, obs)
 	txHash := &obs.Hash
 
-	_, err = s.alertEvents.Create(ctx, rule.ID, message, &addressLabel, txHash)
+	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)
 
-	// Send Discord notification (non-fatal on failure)
 	if addr != nil {
-		go s.sendNotification(ctx, addr.UserID, message, obs, addressLabel, rule, addr.Address)
+		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) []notifications.Notifier {
+	var notifiers []notifications.Notifier
+
+	if cfg.DiscordWebhookURL != nil && *cfg.DiscordWebhookURL != "" {
+		notifiers = append(notifiers, &notifications.DiscordNotifier{WebhookURL: *cfg.DiscordWebhookURL})
+	}
+
+	if cfg.TelegramBotToken != nil && *cfg.TelegramBotToken != "" &&
+		cfg.TelegramChatID != nil && *cfg.TelegramChatID != "" {
+		notifiers = append(notifiers, &notifications.TelegramNotifier{
+			BotToken: *cfg.TelegramBotToken,
+			ChatID:   *cfg.TelegramChatID,
+		})
+	}
+
+	if cfg.SlackWebhookURL != nil && *cfg.SlackWebhookURL != "" {
+		notifiers = append(notifiers, &notifications.SlackNotifier{WebhookURL: *cfg.SlackWebhookURL})
+	}
+
+	if cfg.Email != nil && *cfg.Email != "" {
+		notifiers = append(notifiers, &notifications.EmailNotifier{
+			APIKey: s.resendAPIKey,
+			From:   s.emailFrom,
+			To:     *cfg.Email,
+		})
+	}
+
+	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 {
@@ -183,29 +285,31 @@ func (s *EvaluatorService) sendNotification(ctx context.Context, userID, message
 		return
 	}
 
-	if notifConfig == nil || !notifConfig.NotificationEnabled || notifConfig.DiscordWebhookURL == nil {
+	if notifConfig == nil || !notifConfig.NotificationEnabled {
 		return
 	}
 
-	sent, err := notifications.SendDiscordNotification(
+	meta := notifications.AlertMetadata{
-		*notifConfig.DiscordWebhookURL,
+		TxHash:       obs.Hash,
-		message,
+		AddressLabel: addressLabel,
-		notifications.AlertMetadata{
+		AlertType:    string(rule.Type),
-			TxHash:       obs.Hash,
+		Address:      address,
-			AddressLabel: addressLabel,
+	}
-			AlertType:    string(rule.Type),
-			Address:      address,
-		},
-	)
 
-	if err != nil || !sent {
+	for _, n := range s.buildNotifiers(notifConfig) {
-		log.Printf("Discord notification failed for user %s: %v", userID, err)
+		if err := sendWithRetry(ctx, n, message, meta); err != nil {
-	} else {
+			log.Printf("Notification channel failed for user %s after retries: %v", userID, err)
-		log.Printf("Discord notification sent to user %s", userID)
+		} 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)
@@ -230,3 +334,36 @@ func (s *EvaluatorService) buildMessage(rule domain.AlertRule, obs domain.Observ
 		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/internal/domain"
-	"github.com/kjannette/koin-ping/backend-go/internal/models"
+	"github.com/kjannette/koin-ping/backend/internal/models"
-	"github.com/kjannette/koin-ping/backend-go/internal/protocols/ethereum"
+	"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

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

frontend/README.md

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

frontend/package.json

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

frontend/prettierrc

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

frontend/src/App.jsx

@@ -1,60 +1,36 @@
-import { Routes, Route, Link, Navigate } from "react-router-dom";
+import { Routes, Route, Navigate } from "react-router-dom";
 import { useAuth } from "./contexts/AuthContext";
-import Login from "./pages/Login";
+import Navbar from "./components/Navbar";
+import Login from "./pages/login/Login";
 import Signup from "./pages/Signup";
-import Addresses from "./pages/Addresses";
+import Subscribe from "./pages/subscribe/subscribe";
-import Alerts from "./pages/Alerts";
+import Addresses from "./pages/addresses/Addresses";
-import AlertHistory from "./pages/AlertHistory";
+import Alerts from "./pages/alerts/Alerts";
+import AlertHistory from "./pages/alertHistory/AlertHistory";
 
 export default function App() {
-  const { currentUser, logout } = useAuth();
+  const { currentUser } = useAuth();
 
-  // Show login/signup routes if not authenticated
   if (!currentUser) {
     return (
       <Routes>
         <Route path="/login" element={<Login />} />
         <Route path="/signup" element={<Signup />} />
+        <Route path="/subscribe" element={<Subscribe />} />
         <Route path="*" element={<Navigate to="/login" />} />
       </Routes>
     );
   }
 
-  // Show main app if authenticated
   return (
-    <div style={{ padding: "1rem" }}>
+    <div>
-      <nav style={{ marginBottom: "1rem", display: "flex", justifyContent: "space-between", alignItems: "center" }}>
+      <Navbar />
-        <div>
-          <Link to="/addresses">Addresses</Link>{" | "}
-          <Link to="/alerts">Alerts</Link>{" | "}
-          <Link to="/history">History</Link>
-        </div>
-        <div style={{ display: "flex", alignItems: "center", gap: "1rem" }}>
-          <span style={{ fontSize: "0.9rem", color: "#999" }}>
-            {currentUser.email}
-          </span>
-          <button
-            onClick={logout}
-            style={{
-              padding: "0.5rem 1rem",
-              fontSize: "0.9rem",
-              backgroundColor: "#333",
-              color: "white",
-              border: "1px solid #555",
-              borderRadius: "4px",
-              cursor: "pointer"
-            }}
-          >
-            Logout
-          </button>
-        </div>
-      </nav>
-
       <Routes>
         <Route path="/" element={<Addresses />} />
         <Route path="/addresses" element={<Addresses />} />
         <Route path="/alerts" element={<Alerts />} />
-        <Route path="/history" element={<AlertHistory />} />
+        <Route path="/alertevents" element={<AlertHistory />} />
+        <Route path="/subscribe" element={<Subscribe />} />
         <Route path="*" element={<Navigate to="/addresses" />} />
       </Routes>
     </div>

frontend/src/api/addresses.jsx

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

frontend/src/api/alertEvents.jsx

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

frontend/src/api/alerts.jsx

@@ -1,16 +1,16 @@
 // API client for alert rule management
 
-import { getAuthHeaders, getAuthHeadersSimple } from './authHeaders';
+import { getAuthHeaders, getAuthHeadersSimple } from "./authHeaders";
-import { API_BASE } from './config';
+import { API_BASE } from "./config";
 
 /**
  * Alert types supported by the system
  */
 export const ALERT_TYPES = {
-  INCOMING_TX: 'incoming_tx',
+    INCOMING_TX: "incoming_tx",
-  OUTGOING_TX: 'outgoing_tx',
+    OUTGOING_TX: "outgoing_tx",
-  LARGE_TRANSFER: 'large_transfer',
+    LARGE_TRANSFER: "large_transfer",
-  BALANCE_BELOW: 'balance_below'
+    BALANCE_BELOW: "balance_below",
 };
 
 /**
@@ -22,32 +22,37 @@ export const ALERT_TYPES = {
  * @returns {Promise<Object>} Created alert rule
  */
 export async function createAlert(addressId, data) {
-  try {
+    try {
-  const headers = await getAuthHeaders();
+        const headers = await getAuthHeaders();
-  const response = await fetch(`${API_BASE}/addresses/${addressId}/alerts`, {
+        const response = await fetch(
-    method: 'POST',
+            `${API_BASE}/addresses/${addressId}/alerts`,
-    headers: headers,
+            {
-    body: JSON.stringify(data)
+                method: "POST",
-  });
+                headers: headers,
+                body: JSON.stringify(data),
+            },
+        );
 
-  if (!response.ok) {
+        if (!response.ok) {
-      let errorMessage = 'Failed to create alert rule';
+            let errorMessage = "Failed to create alert rule";
-      try {
+            try {
-    const error = await response.json();
+                const error = await response.json();
-        errorMessage = error.message || errorMessage;
+                errorMessage = error.message || errorMessage;
-      } catch {
+            } catch {
-        errorMessage = `Server error: ${response.status} ${response.statusText}`;
+                errorMessage = `Server error: ${response.status} ${response.statusText}`;
-      }
+            }
-      throw new Error(errorMessage);
+            throw new Error(errorMessage);
-  }
+        }
 
-  return response.json();
+        return response.json();
-  } catch (error) {
+    } catch (error) {
-    if (error.message.includes('fetch')) {
+        if (error.message.includes("fetch")) {
-      throw new Error('Cannot connect to server. Is the backend running?');
+            throw new Error(
+                "Cannot connect to server. Is the backend running?",
+            );
+        }
+        throw error;
     }
-    throw error;
-  }
 }
 
 /**
@@ -56,30 +61,35 @@ export async function createAlert(addressId, data) {
  * @returns {Promise<Array>} List of alert rules
  */
 export async function getAlerts(addressId) {
-  try {
+    try {
-  const headers = await getAuthHeadersSimple();
+        const headers = await getAuthHeadersSimple();
-  const response = await fetch(`${API_BASE}/addresses/${addressId}/alerts`, {
+        const response = await fetch(
-    headers: headers
+            `${API_BASE}/addresses/${addressId}/alerts`,
-  });
+            {
+                headers: headers,
+            },
+        );
 
-  if (!response.ok) {
+        if (!response.ok) {
-      let errorMessage = 'Failed to fetch alert rules';
+            let errorMessage = "Failed to fetch alert rules";
-      try {
+            try {
-    const error = await response.json();
+                const error = await response.json();
-        errorMessage = error.message || errorMessage;
+                errorMessage = error.message || errorMessage;
-      } catch {
+            } catch {
-        errorMessage = `Server error: ${response.status} ${response.statusText}`;
+                errorMessage = `Server error: ${response.status} ${response.statusText}`;
-      }
+            }
-      throw new Error(errorMessage);
+            throw new Error(errorMessage);
-  }
+        }
 
-  return response.json();
+        return response.json();
-  } catch (error) {
+    } catch (error) {
-    if (error.message.includes('fetch')) {
+        if (error.message.includes("fetch")) {
-      throw new Error('Cannot connect to server. Is the backend running?');
+            throw new Error(
+                "Cannot connect to server. Is the backend running?",
+            );
+        }
+        throw error;
     }
-    throw error;
-  }
 }
 
 /**
@@ -89,32 +99,34 @@ export async function getAlerts(addressId) {
  * @returns {Promise<Object>} Updated alert rule
  */
 export async function updateAlertStatus(alertId, enabled) {
-  try {
+    try {
-  const headers = await getAuthHeaders();
+        const headers = await getAuthHeaders();
-  const response = await fetch(`${API_BASE}/alerts/${alertId}`, {
+        const response = await fetch(`${API_BASE}/alerts/${alertId}`, {
-    method: 'PATCH',
+            method: "PATCH",
-    headers: headers,
+            headers: headers,
-    body: JSON.stringify({ enabled })
+            body: JSON.stringify({ enabled }),
-  });
+        });
 
-  if (!response.ok) {
+        if (!response.ok) {
-      let errorMessage = 'Failed to update alert rule';
+            let errorMessage = "Failed to update alert rule";
-      try {
+            try {
-    const error = await response.json();
+                const error = await response.json();
-        errorMessage = error.message || errorMessage;
+                errorMessage = error.message || errorMessage;
-      } catch {
+            } catch {
-        errorMessage = `Server error: ${response.status} ${response.statusText}`;
+                errorMessage = `Server error: ${response.status} ${response.statusText}`;
-      }
+            }
-      throw new Error(errorMessage);
+            throw new Error(errorMessage);
-  }
+        }
 
-  return response.json();
+        return response.json();
-  } catch (error) {
+    } catch (error) {
-    if (error.message.includes('fetch')) {
+        if (error.message.includes("fetch")) {
-      throw new Error('Cannot connect to server. Is the backend running?');
+            throw new Error(
+                "Cannot connect to server. Is the backend running?",
+            );
+        }
+        throw error;
     }
-    throw error;
-  }
 }
 
 /**
@@ -123,27 +135,29 @@ export async function updateAlertStatus(alertId, enabled) {
  * @returns {Promise<void>}
  */
 export async function deleteAlert(alertId) {
-  try {
+    try {
-  const headers = await getAuthHeadersSimple();
+        const headers = await getAuthHeadersSimple();
-  const response = await fetch(`${API_BASE}/alerts/${alertId}`, {
+        const response = await fetch(`${API_BASE}/alerts/${alertId}`, {
-    method: 'DELETE',
+            method: "DELETE",
-    headers: headers
+            headers: headers,
-  });
+        });
 
-  if (!response.ok && response.status !== 204) {
+        if (!response.ok && response.status !== 204) {
-      let errorMessage = 'Failed to delete alert rule';
+            let errorMessage = "Failed to delete alert rule";
-      try {
+            try {
-    const error = await response.json();
+                const error = await response.json();
-        errorMessage = error.message || errorMessage;
+                errorMessage = error.message || errorMessage;
-      } catch {
+            } catch {
-        errorMessage = `Server error: ${response.status} ${response.statusText}`;
+                errorMessage = `Server error: ${response.status} ${response.statusText}`;
-      }
+            }
-      throw new Error(errorMessage);
+            throw new Error(errorMessage);
+        }
+    } catch (error) {
+        if (error.message.includes("fetch")) {
+            throw new Error(
+                "Cannot connect to server. Is the backend running?",
+            );
+        }
+        throw error;
     }
-  } catch (error) {
-    if (error.message.includes('fetch')) {
-      throw new Error('Cannot connect to server. Is the backend running?');
-    }
-    throw error;
-  }
 }

frontend/src/api/authHeaders.js

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

frontend/src/api/config.js

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

frontend/src/api/notificationConfig.jsx

@@ -1,99 +1,183 @@
-// API client for notification configuration
+import { getAuthHeaders } from "./authHeaders";
-
+import { API_BASE } from "./config";
-import { getAuthHeaders } from './authHeaders';
-import { API_BASE } from './config';
 
 /**
  * Get notification configuration for current user
  * @returns {Promise<Object>} Notification config
  */
 export async function getNotificationConfig() {
-  try {
+    try {
-    const headers = await getAuthHeaders();
+        const headers = await getAuthHeaders();
-    const response = await fetch(`${API_BASE}/notification-config`, {
+        const response = await fetch(`${API_BASE}/notification-config`, {
-      headers: headers
+            headers: headers,
-    });
+        });
 
-    if (!response.ok) {
+        if (!response.ok) {
-      let errorMessage = 'Failed to fetch notification config';
+            let errorMessage = "Failed to fetch notification config";
-      try {
+            try {
-        const error = await response.json();
+                const error = await response.json();
-        errorMessage = error.message || errorMessage;
+                errorMessage = error.message || errorMessage;
-      } catch {
+            } catch {
-        errorMessage = `Server error: ${response.status} ${response.statusText}`;
+                errorMessage = `Server error: ${response.status} ${response.statusText}`;
-      }
+            }
-      throw new Error(errorMessage);
+            throw new Error(errorMessage);
-    }
+        }
 
-    return response.json();
+        return response.json();
-  } catch (error) {
+    } catch (error) {
-    if (error.message.includes('fetch')) {
+        if (error.message.includes("fetch")) {
-      throw new Error('Cannot connect to server. Is the backend running?');
+            throw new Error(
+                "Cannot connect to server. Is the backend running?",
+            );
+        }
+        throw error;
     }
-    throw error;
-  }
 }
 
 /**
  * Update notification configuration
- * @param {Object} config - Configuration to update
+ * @param {Object} config
- * @param {string} [config.discord_webhook_url] - Discord webhook URL
+ * @param {string} [config.discord_webhook_url]
- * @param {string} [config.telegram_chat_id] - Telegram chat ID
+ * @param {string} [config.telegram_chat_id]
- * @param {string} [config.email] - Email address
+ * @param {string} [config.telegram_bot_token]
- * @param {boolean} [config.notification_enabled] - Enable/disable notifications
+ * @param {string} [config.email]
+ * @param {string} [config.slack_webhook_url]
+ * @param {boolean} [config.notification_enabled]
  * @returns {Promise<Object>} Updated config
  */
 export async function updateNotificationConfig(config) {
-  try {
+    try {
-    const headers = await getAuthHeaders();
+        const headers = await getAuthHeaders();
-    const response = await fetch(`${API_BASE}/notification-config`, {
+        const response = await fetch(`${API_BASE}/notification-config`, {
-      method: 'PUT',
+            method: "PUT",
-      headers: headers,
+            headers: headers,
-      body: JSON.stringify(config)
+            body: JSON.stringify(config),
-    });
+        });
 
-    if (!response.ok) {
+        if (!response.ok) {
-      let errorMessage = 'Failed to update notification config';
+            let errorMessage = "Failed to update notification config";
-      try {
+            try {
-        const error = await response.json();
+                const error = await response.json();
-        errorMessage = error.message || errorMessage;
+                errorMessage = error.message || errorMessage;
-      } catch {
+            } catch {
-        errorMessage = `Server error: ${response.status} ${response.statusText}`;
+                errorMessage = `Server error: ${response.status} ${response.statusText}`;
-      }
+            }
-      throw new Error(errorMessage);
+            throw new Error(errorMessage);
-    }
+        }
 
-    return response.json();
+        return response.json();
-  } catch (error) {
+    } catch (error) {
-    if (error.message.includes('fetch')) {
+        if (error.message.includes("fetch")) {
-      throw new Error('Cannot connect to server. Is the backend running?');
+            throw new Error(
+                "Cannot connect to server. Is the backend running?",
+            );
+        }
+        throw error;
     }
-    throw error;
-  }
 }
 
 /**
- * Test a Discord webhook URL
+ * Set up email notifications via Resend.
- * Sends a test message to verify the webhook works
+ * Reads the user's saved email from their config and sends a confirmation.
- * @param {string} webhookUrl - Discord webhook URL to test
+ * @returns {Promise<Object>} Setup result
- * @returns {Promise<boolean>} True if test successful
  */
-export async function testDiscordWebhook(webhookUrl) {
+export async function setupEmail() {
-  try {
+    try {
-    const payload = {
+        const headers = await getAuthHeaders();
-      content: 'Koin Ping test notification - Your Discord webhook is configured correctly!',
+        const response = await fetch(`${API_BASE}/email/setup`, {
-    };
+            method: "POST",
+            headers: headers,
+        });
 
-    const response = await fetch(webhookUrl, {
+        if (!response.ok) {
-      method: 'POST',
+            let errorMessage = "Failed to set up email";
-      headers: { 'Content-Type': 'application/json' },
+            try {
-      body: JSON.stringify(payload)
+                const error = await response.json();
-    });
+                errorMessage = error.message || errorMessage;
+            } catch {
+                errorMessage = `Server error: ${response.status} ${response.statusText}`;
+            }
+            throw new Error(errorMessage);
+        }
 
-    return response.ok;
+        return response.json();
-  } catch (error) {
+    } catch (error) {
-    console.error('Discord webhook test failed:', error);
+        if (error.message.includes("fetch")) {
-    return false;
+            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/status.jsx

@@ -1,18 +1,18 @@
 // API client for system status
 
-import { API_BASE } from './config';
+import { API_BASE } from "./config";
 
 /**
  * Get system status including latest processed block and health
  * @returns {Promise<Object>} System status
  */
 export async function getSystemStatus() {
-  const response = await fetch(`${API_BASE}/status`);
+    const response = await fetch(`${API_BASE}/status`);
 
-  if (!response.ok) {
+    if (!response.ok) {
-    const error = await response.json();
+        const error = await response.json();
-    throw new Error(error.message || 'Failed to fetch system status');
+        throw new Error(error.message || "Failed to fetch system status");
-  }
+    }
 
-  return response.json();
+    return response.json();
 }

frontend/src/api/stripe.jsx

@@ -0,0 +1,41 @@
+import { getAuthHeaders } from "./authHeaders";
+import { API_BASE } from "./config";
+
+export async function createCheckoutSession() {
+    const headers = await getAuthHeaders();
+    const res = await fetch(`${API_BASE}/stripe/create-checkout-session`, {
+        method: "POST",
+        headers,
+    });
+    if (!res.ok) {
+        const data = await res.json();
+        throw new Error(data.message || "Failed to create checkout session");
+    }
+    return res.json();
+}
+
+export async function verifyCheckoutSession(sessionId) {
+    const headers = await getAuthHeaders();
+    const res = await fetch(`${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

@@ -3,43 +3,43 @@ import Input from "./Input";
 import Button from "./Button";
 
 export default function AddressForm({ onSubmit }) {
-  const [address, setAddress] = useState("");
+    const [address, setAddress] = useState("");
-  const [label, setLabel] = useState("");
+    const [label, setLabel] = useState("");
 
-  const canSubmit = address.trim().length > 0;
+    const canSubmit = address.trim().length > 0;
 
-  function handleSubmit(e) {
+    function handleSubmit(e) {
-    e.preventDefault();
+        e.preventDefault();
-    if (!canSubmit) return;
+        if (!canSubmit) return;
 
-    onSubmit({
+        onSubmit({
-      address: address.trim(),
+            address: address.trim(),
-      label: label.trim(),
+            label: label.trim(),
-    });
+        });
 
-    setAddress("");
+        setAddress("");
-    setLabel("");
+        setLabel("");
-  }
+    }
 
-  return (
+    return (
-    <form onSubmit={handleSubmit}>
+        <form onSubmit={handleSubmit}>
-      <Input
+            <Input
-        label="Blockchain Address"
+                label="Blockchain Address"
-        value={address}
+                value={address}
-        onChange={setAddress}
+                onChange={setAddress}
-        placeholder="0x..."
+                placeholder="0x..."
-      />
+            />
 
-      <Input
+            <Input
-        label="Label (optional)"
+                label="Label (optional)"
-        value={label}
+                value={label}
-        onChange={setLabel}
+                onChange={setLabel}
-        placeholder="Treasury, Cold Wallet, etc."
+                placeholder="Treasury, Cold Wallet, etc."
-      />
+            />
 
-      <Button type="submit" disabled={!canSubmit}>
+            <Button type="submit" disabled={!canSubmit} className="mt-md">
-        Add Address
+                Add Address
-      </Button>
+            </Button>
-    </form>
+        </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

@@ -1,71 +1,72 @@
 import { useState } from "react";
 import Input from "./Input";
 import Button from "./Button";
+import "./AlertForm.css";
 
 const ALERT_TYPES = [
-  { value: "incoming_tx", label: "Incoming transaction" },
+    { value: "incoming_tx", label: "Incoming transaction" },
-  { value: "outgoing_tx", label: "Outgoing transaction" },
+    { value: "outgoing_tx", label: "Outgoing transaction" },
-  { value: "large_transfer", label: "Large transfer" },
+    { value: "large_transfer", label: "Large transfer" },
-  { value: "balance_below", label: "Balance below threshold" },
+    { value: "balance_below", label: "Balance below threshold" },
 ];
 
 export default function AlertForm({ onSubmit }) {
-  const [type, setType] = useState("incoming_tx");
+    const [type, setType] = useState("incoming_tx");
-  const [threshold, setThreshold] = useState("");
+    const [threshold, setThreshold] = useState("");
 
-  const needsThreshold =
+    const needsThreshold =
-    type === "large_transfer" || type === "balance_below";
+        type === "large_transfer" || type === "balance_below";
 
-  const canSubmit = needsThreshold
+    const canSubmit = needsThreshold
-    ? threshold.trim() !== "" && 
+        ? threshold.trim() !== "" &&
-      !isNaN(Number(threshold)) && 
+          !isNaN(Number(threshold)) &&
-      Number(threshold) > 0
+          Number(threshold) > 0
-    : true;
+        : true;
 
-  function handleSubmit(e) {
+    function handleSubmit(e) {
-    e.preventDefault();
+        e.preventDefault();
-    if (!canSubmit) return;
+        if (!canSubmit) return;
 
-    onSubmit({
+        onSubmit({
-      type,
+            type,
-      threshold: needsThreshold ? Number(threshold) : undefined,
+            threshold: needsThreshold ? Number(threshold) : undefined,
-    });
+        });
 
-    setThreshold("");
+        setThreshold("");
-  }
+    }
 
-  return (
+    return (
-    <form onSubmit={handleSubmit}>
+        <form onSubmit={handleSubmit}>
-      <div style={{ marginBottom: "1rem" }}>
+            <div className="alert-form__options">
-        {ALERT_TYPES.map((opt) => (
+                {ALERT_TYPES.map((opt) => (
-          <label key={opt.value} style={{ display: "block" }}>
+                    <label key={opt.value} className="alert-form__radio">
-            <input
+                        <input
-              type="radio"
+                            type="radio"
-              name="alertType"
+                            name="alertType"
-              value={opt.value}
+                            value={opt.value}
-              checked={type === opt.value}
+                            checked={type === opt.value}
-              onChange={() => setType(opt.value)}
+                            onChange={() => setType(opt.value)}
-            />
+                        />{" "}
-            {" "}{opt.label}
+                        {opt.label}
-          </label>
+                    </label>
-        ))}
+                ))}
-      </div>
+            </div>
 
-      {needsThreshold && (
+            {needsThreshold && (
-        <Input
+                <Input
-          label="Amount (ETH)"
+                    label="Amount (ETH)"
-          type="number"
+                    type="number"
-          step="0.000001"
+                    step="0.000001"
-          min="0"
+                    min="0"
-          value={threshold}
+                    value={threshold}
-          onChange={setThreshold}
+                    onChange={setThreshold}
-          placeholder="e.g. 10"
+                    placeholder="e.g. 10"
-        />
+                />
-      )}
+            )}
 
-      <Button type="submit" disabled={!canSubmit}>
+            <Button type="submit" disabled={!canSubmit}>
-        Create Alert
+                Create Alert
-      </Button>
+            </Button>
-    </form>
+        </form>
-  );
+    );
 }

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

@@ -1,23 +1,21 @@
+import "./Button.css";
+
 export default function Button({
     children,
     onClick,
     disabled = false,
     type = "button",
-  }) {
+    variant = "primary",
+    className = "",
+}) {
     return (
-      <button
+        <button
-        type={type}
+            type={type}
-        onClick={onClick}
+            onClick={onClick}
-        disabled={disabled}
+            disabled={disabled}
-        style={{
+            className={`btn btn--${variant} ${className}`}
-          padding: "0.5rem 1rem",
+        >
-          fontSize: "1rem",
+            {children}
-          cursor: disabled ? "not-allowed" : "pointer",
+        </button>
-          opacity: disabled ? 0.6 : 1,
-        }}
-      >
-        {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",
@@ -7,27 +9,23 @@ export default function Input({
     step,
     min,
     disabled = false,
-  }) {
+    required = false,
+    className = "",
+}) {
     return (
-      <label style={{ display: "block", marginBottom: "1rem" }}>
+        <label className={`form-field ${className}`}>
-        <div style={{ marginBottom: "0.25rem", fontSize: "0.9rem" }}>
+            <div className="input__label">{label}</div>
-          {label}
+            <input
-        </div>
+                type={type}
-        <input
+                value={value}
-          type={type}
+                placeholder={placeholder}
-          value={value}
+                step={step}
-          placeholder={placeholder}
+                min={min}
-          step={step}
+                disabled={disabled}
-          min={min}
+                required={required}
-          disabled={disabled}
+                onChange={(e) => onChange(e.target.value)}
-          onChange={(e) => onChange(e.target.value)}
+                className="input__control"
-          style={{
+            />
-            width: "100%",
+        </label>
-            padding: "0.5rem",
-            fontSize: "1rem",
-          }}
-        />
-      </label>
     );
-  }
+}
-  

frontend/src/components/Navbar.css

@@ -0,0 +1,56 @@
+.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);
+}
+
+.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);
+}
+
+.navbar__user {
+  font-size: 1.275rem;
+  color: #777;
+}
+
+.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;
+}

frontend/src/components/Navbar.jsx

@@ -0,0 +1,45 @@
+import { Link, useLocation } from "react-router-dom";
+import { useAuth } from "../contexts/AuthContext";
+import "./Navbar.css";
+
+const navLinks = [
+  { to: "/addresses", label: "Addresses" },
+  { to: "/alerts", label: "Configure Alerts" },
+  { to: "/alertevents", label: "Alert Event History" },
+];
+
+export default function Navbar() {
+  const { currentUser, logout } = useAuth();
+  const location = useLocation();
+
+  if (!currentUser) return null;
+
+  return (
+    <nav className="navbar">
+      <div className="flex flex--center gap-sm">
+        <span className="navbar__brand">Koin Ping</span>
+        <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 className="flex flex--center gap-lg">
+        <span className="navbar__user">{currentUser.email}</span>
+        <button onClick={logout} className="navbar__logout">
+          Logout
+        </button>
+      </div>
+    </nav>
+  );
+}

frontend/src/contexts/AuthContext.jsx

@@ -4,14 +4,14 @@
  * Provides authentication state and methods throughout the app
  */
 
-import { createContext, useContext, useEffect, useState } from 'react';
+import { createContext, useContext, useEffect, useState } from "react";
 import {
-  createUserWithEmailAndPassword,
+    createUserWithEmailAndPassword,
-  signInWithEmailAndPassword,
+    signInWithEmailAndPassword,
-  signOut,
+    signOut,
-  onAuthStateChanged
+    onAuthStateChanged,
-} from 'firebase/auth';
+} from "firebase/auth";
-import { auth } from '../firebase/config';
+import { auth } from "../firebase/config";
 
 const AuthContext = createContext();
 
@@ -20,88 +20,95 @@ const AuthContext = createContext();
  * @returns {Object} Auth context value
  */
 export function useAuth() {
-  const context = useContext(AuthContext);
+    const context = useContext(AuthContext);
-  if (!context) {
+    if (!context) {
-    throw new Error('useAuth must be used within AuthProvider');
+        throw new Error("useAuth must be used within AuthProvider");
-  }
+    }
-  return context;
+    return context;
 }
 
 /**
  * AuthProvider - Wraps app and provides auth state
  */
 export function AuthProvider({ children }) {
-  const [currentUser, setCurrentUser] = useState(null);
+    const [currentUser, setCurrentUser] = useState(null);
-  const [loading, setLoading] = useState(true);
+    const [loading, setLoading] = useState(true);
-  const [error, setError] = useState(null);
+    const [error, setError] = useState(null);
 
-  /**
+    /**
-   * Sign up with email and password
+     * Sign up with email and password
-   */
+     */
-  async function signup(email, password) {
+    async function signup(email, password) {
-    try {
+        try {
-      setError(null);
+            setError(null);
-      const result = await createUserWithEmailAndPassword(auth, email, password);
+            const result = await createUserWithEmailAndPassword(
-      return result.user;
+                auth,
-    } catch (err) {
+                email,
-      setError(err.message);
+                password,
-      throw err;
+            );
+            return result.user;
+        } catch (err) {
+            setError(err.message);
+            throw err;
+        }
     }
-  }
 
-  /**
+    /**
-   * Log in with email and password
+     * Log in with email and password
-   */
+     */
-  async function login(email, password) {
+    async function login(email, password) {
-    try {
+        try {
-      setError(null);
+            setError(null);
-      const result = await signInWithEmailAndPassword(auth, email, password);
+            const result = await signInWithEmailAndPassword(
-      return result.user;
+                auth,
-    } catch (err) {
+                email,
-      setError(err.message);
+                password,
-      throw err;
+            );
+            return result.user;
+        } catch (err) {
+            setError(err.message);
+            throw err;
+        }
     }
-  }
 
-  /**
+    /**
-   * Log out current user
+     * Log out current user
-   */
+     */
-  async function logout() {
+    async function logout() {
-    try {
+        try {
-      setError(null);
+            setError(null);
-      await signOut(auth);
+            await signOut(auth);
-    } catch (err) {
+        } catch (err) {
-      setError(err.message);
+            setError(err.message);
-      throw err;
+            throw err;
+        }
     }
-  }
 
-  /**
+    /**
-   * Listen for auth state changes
+     * Listen for auth state changes
-   */
+     */
-  useEffect(() => {
+    useEffect(() => {
-    const unsubscribe = onAuthStateChanged(auth, (user) => {
+        const unsubscribe = onAuthStateChanged(auth, (user) => {
-      setCurrentUser(user);
+            setCurrentUser(user);
-      setLoading(false);
+            setLoading(false);
-    });
+        });
 
-    // Cleanup subscription
+        // Cleanup subscription
-    return unsubscribe;
+        return unsubscribe;
-  }, []);
+    }, []);
 
-  const value = {
+    const value = {
-    currentUser,
+        currentUser,
-    signup,
+        signup,
-    login,
+        login,
-    logout,
+        logout,
-    error,
+        error,
-    loading
+        loading,
-  };
+    };
 
-  return (
+    return (
-    <AuthContext.Provider value={value}>
+        <AuthContext.Provider value={value}>
-      {!loading && children}
+            {!loading && children}
-    </AuthContext.Provider>
+        </AuthContext.Provider>
-  );
+    );
 }
-

frontend/src/firebase/config.js

@@ -1,6 +1,5 @@
-
+import { initializeApp } from "firebase/app";
-import { initializeApp } from 'firebase/app';
+import { getAuth } from "firebase/auth";
-import { getAuth } from 'firebase/auth';
 import {
     firebaseApiKey,
     firebaseAuthDomain,
@@ -8,9 +7,8 @@ import {
     firebaseStorageBucket,
     firebaseMessagingSenderId,
     firebaseAppId,
-    firebaseMeasurementId
+    firebaseMeasurementId,
-} from '../secrets.js';
+} from "../secrets.js";
-
 
 const firebaseConfig = {
     apiKey: firebaseApiKey,
@@ -19,12 +17,11 @@ const firebaseConfig = {
     storageBucket: firebaseStorageBucket,
     messagingSenderId: firebaseMessagingSenderId,
     appId: firebaseAppId,
-    measurementId: firebaseMeasurementId
+    measurementId: firebaseMeasurementId,
-  };
+};
 
 const app = initializeApp(firebaseConfig);
 
 export const auth = getAuth(app);
 
 export default app;
-

frontend/src/index.css

@@ -0,0 +1,358 @@
+@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 {
+  box-sizing: border-box;
+  margin: 0;
+  padding: 0;
+}
+
+html {
+  font-size: 14px;
+}
+
+body {
+  font-family: 'Nunito', sans-serif;
+  font-size: 1.5rem;
+  font-weight: 200;
+  line-height: 1.6;
+  -webkit-font-smoothing: antialiased;
+  -moz-osx-font-smoothing: grayscale;
+}
+
+h1,
+h2,
+h3,
+h4,
+h5,
+h6 {
+  font-family: 'Nunito', sans-serif;
+  font-weight: 200;
+}
+
+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;
+}

frontend/src/main.jsx

@@ -3,13 +3,14 @@ import ReactDOM from "react-dom/client";
 import { BrowserRouter } from "react-router-dom";
 import { AuthProvider } from "./contexts/AuthContext";
 import App from "./App";
+import "./index.css";
 
 ReactDOM.createRoot(document.getElementById("root")).render(
-  <React.StrictMode>
+    <React.StrictMode>
-    <BrowserRouter>
+        <BrowserRouter>
-      <AuthProvider>
+            <AuthProvider>
-        <App />
+                <App />
-      </AuthProvider>
+            </AuthProvider>
-    </BrowserRouter>
+        </BrowserRouter>
-  </React.StrictMode>
+    </React.StrictMode>,
 );

frontend/src/pages/Addresses.jsx

@@ -1,83 +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: "#666" }}>
-            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 #ddd",
-                  borderRadius: "4px",
-                }}
-              >
-                <div style={{ fontWeight: "bold", marginBottom: "0.25rem" }}>
-                  {addr.label || "Unlabeled"}
-                </div>
-                <div style={{ fontFamily: "monospace", fontSize: "0.9rem" }}>
-                  {addr.address}
-                </div>
-              </li>
-            ))}
-          </ul>
-        )}
-      </div>
-    </div>
-  );
-}

frontend/src/pages/Alerts.jsx

@@ -1,471 +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: "#2a2a2a",
-                  borderRadius: "4px",
-                  border: "1px solid #444"
-                }}
-              >
-                <div style={{ fontSize: "0.9rem", color: "#999" }}>
-                  Managing alerts for:
-                </div>
-                <div style={{ fontWeight: "bold", marginTop: "0.25rem" }}>
-                  {selectedAddress.label || "Unlabeled"}
-                </div>
-                <div style={{ fontFamily: "monospace", fontSize: "0.9rem", color: "#999" }}>
-                  {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: "#2a2a2a",
-                          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: "0.9rem", color: "#999" }}>
-                                Threshold: {alert.threshold} ETH
-                              </div>
-                            )}
-                            <div style={{ fontSize: "0.85rem", color: "#666", 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: '#f5f5f5', 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: '0.85rem', color: '#666', 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: '0.85rem', color: '#999', 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;
-}

frontend/src/pages/Login.jsx

@@ -1,143 +0,0 @@
-/**
- * Login Page
- * 
- * Allows existing users to sign in with email and password
- */
-
-import { useState } from 'react';
-import { Link, useNavigate } from 'react-router-dom';
-import { useAuth } from '../contexts/AuthContext';
-
-export default function Login() {
-  const [email, setEmail] = useState('');
-  const [password, setPassword] = useState('');
-  const [error, setError] = useState('');
-  const [loading, setLoading] = useState(false);
-  
-  const { login } = useAuth();
-  const navigate = useNavigate();
-
-  async function handleSubmit(e) {
-    e.preventDefault();
-
-    // Validation
-    if (!email || !password) {
-      setError('Please fill in all fields');
-      return;
-    }
-
-    try {
-      setError('');
-      setLoading(true);
-      await login(email, password);
-      navigate('/addresses'); // Redirect to main app
-    } catch (err) {
-      setError('Failed to log in: ' + err.message);
-    } finally {
-      setLoading(false);
-    }
-  }
-
-  return (
-    <div style={{ 
-      maxWidth: '400px', 
-      margin: '4rem auto', 
-      padding: '2rem',
-      border: '1px solid #333',
-      borderRadius: '8px'
-    }}>
-      <h1 style={{ marginBottom: '2rem', textAlign: 'center' }}>
-        Koin Ping - Login
-      </h1>
-
-      {error && (
-        <div style={{ 
-          padding: '0.75rem', 
-          marginBottom: '1rem', 
-          backgroundColor: '#ff000020',
-          border: '1px solid #ff0000',
-          borderRadius: '4px',
-          color: '#ff6666'
-        }}>
-          {error}
-        </div>
-      )}
-
-      <form onSubmit={handleSubmit}>
-        <div style={{ marginBottom: '1rem' }}>
-          <label style={{ display: 'block', marginBottom: '0.5rem' }}>
-            Email
-          </label>
-          <input
-            type="email"
-            value={email}
-            onChange={(e) => setEmail(e.target.value)}
-            disabled={loading}
-            style={{
-              width: '100%',
-              padding: '0.5rem',
-              fontSize: '1rem',
-              backgroundColor: '#1a1a1a',
-              border: '1px solid #444',
-              borderRadius: '4px',
-              color: 'white'
-            }}
-            required
-          />
-        </div>
-
-        <div style={{ marginBottom: '1.5rem' }}>
-          <label style={{ display: 'block', marginBottom: '0.5rem' }}>
-            Password
-          </label>
-          <input
-            type="password"
-            value={password}
-            onChange={(e) => setPassword(e.target.value)}
-            disabled={loading}
-            style={{
-              width: '100%',
-              padding: '0.5rem',
-              fontSize: '1rem',
-              backgroundColor: '#1a1a1a',
-              border: '1px solid #444',
-              borderRadius: '4px',
-              color: 'white'
-            }}
-            required
-          />
-        </div>
-
-        <button
-          type="submit"
-          disabled={loading}
-          style={{
-            width: '100%',
-            padding: '0.75rem',
-            fontSize: '1rem',
-            backgroundColor: loading ? '#333' : '#0066cc',
-            color: 'white',
-            border: 'none',
-            borderRadius: '4px',
-            cursor: loading ? 'not-allowed' : 'pointer'
-          }}
-        >
-          {loading ? 'Logging in...' : 'Log In'}
-        </button>
-      </form>
-
-      <div style={{ marginTop: '1.5rem', textAlign: 'center' }}>
-        <p style={{ color: '#999' }}>
-          Don't have an account?{' '}
-          <Link 
-            to="/signup" 
-            style={{ color: '#0066cc', textDecoration: 'none' }}
-          >
-            Sign up here
-          </Link>
-        </p>
-      </div>
-    </div>
-  );
-}
-