NOTIFICATION_SERVICE_IMPLEMENTATION.md

Email and Push Notification Service - Implementation Summary

Overview

Successfully implemented a comprehensive email and push notification service for payment receipts in the PayD application. The service integrates with email providers (Resend/SendGrid) and triggers notifications from a queue worker after on-chain transaction confirmation.

Completed Tasks

1. Database Schema (✅ Completed)

• Created migration 024_create_notifications.sql with:
  • notifications table for tracking email and push notifications
  • notification_configs table for organization-specific settings
  • push_tokens table for managing device push tokens
  • Added locale column to employees table
  • Created indexes for query optimization
  • Added triggers for updated_at columns

2. Queue Configuration (✅ Completed)

• Extended backend/src/config/queue.ts with:
  • NOTIFICATION_QUEUE_NAME constant
  • notificationQueueConfig with retry and backoff settings
  • Job retention policies (24h for completed, 7 days for failed)

3. Email Provider Infrastructure (✅ Completed)

• Created IEmailProvider interface with standard email operations
• Implemented ResendEmailProvider with:
  • HTTPS API integration
  • Error handling and logging
  • Email redaction for privacy
• Implemented SendGridEmailProvider with:
  • HTTPS API integration
  • Error handling and logging
  • Email redaction for privacy
• Created EmailProviderFactory for provider instantiation

4. Template Rendering System (✅ Completed)

• Implemented TemplateRenderer class with:
  • HTML and plain text template rendering
  • HTML escaping for XSS prevention
  • Currency formatting with locale support
  • Date/time formatting with locale support
  • Fallback logic for rendering errors
  • Locale-based template selection
• Created English email templates:
  • payment-notification.en.html (styled HTML)
  • payment-notification.en.txt (plain text)

5. Notification Configuration Service (✅ Completed)

• Implemented NotificationConfigService with:
  • Organization-specific configuration retrieval
  • Configuration updates with validation
  • Default configuration fallback
  • Email provider validation

6. Notification Tracking Service (✅ Completed)

• Implemented NotificationTrackingService with:
  • Email delivery tracking (sent/failed)
  • Push notification tracking (sent/failed)
  • Notification history queries with pagination
  • Transaction-based notification lookup
  • Comprehensive error logging

7. Push Notification Service (✅ Completed - Stub)

• Implemented PushNotificationService with:
  • Stub send method (logs notification details)
  • Token registration and removal
  • Database operations for push_tokens table
  • Ready for future integration with FCM/APNs

8. Core Notification Service (✅ Completed)

• Implemented NotificationService with:
  • Payment notification orchestration
  • Email and push notification sending
  • Employee and organization data retrieval
  • Email provider initialization
  • Error handling with isolation (push failures don't fail email)
  • Sensitive data redaction in logs
  • Integration with all sub-services

9. Notification Queue Service (✅ Completed)

• Implemented NotificationQueueService with:
  • Job enqueuing with retry configuration
  • Job status retrieval
  • Queue connection management
  • Error handling and logging

10. Notification Worker (✅ Completed)

• Implemented NotificationWorker with:
  • Job processing with retry logic
  • Exponential backoff (3 attempts, 5s initial delay)
  • Comprehensive error logging
  • Integration with NotificationService
  • Concurrency control (5 concurrent jobs)
• Registered worker in backend/src/workers/index.ts

11. Payroll Worker Integration (✅ Completed)

• Modified backend/src/workers/payrollWorker.ts to:
  • Import NotificationQueueService
  • Enqueue notification jobs after successful transactions
  • Handle notification enqueuing errors gracefully
  • Maintain payroll processing reliability

12. Environment Configuration (✅ Completed)

• Updated backend/.env.example with:
  • Email provider configuration
  • Resend and SendGrid API keys
  • Email from address and name
  • Notification queue settings
  • Stellar explorer URL
• Updated backend/src/config/env.ts with:
  • Environment variable schema validation
  • Email provider enum validation
  • Default values for all settings

13. API Endpoints (✅ Completed)

• Created NotificationController with:
  • getNotificationHistory - View notification history
  • getNotificationConfig - Get organization config (admin only)
  • updateNotificationConfig - Update config (admin only)
  • registerPushToken - Register device token
  • removePushToken - Remove device token
  • Authentication and authorization checks
  • Input validation
• Created notificationRoutes.ts with all API routes
• Registered routes in backend/src/app.ts at /api/notifications

Architecture

Data Flow

Payment Transaction (Stellar)
    ↓
Payroll Worker (confirms transaction)
    ↓
Notification Queue (enqueues job)
    ↓
Notification Worker (processes job)
    ↓
Notification Service (orchestrates)
    ├→ Email Provider (Resend/SendGrid)
    └→ Push Service (stub)
    ↓
Notification Tracking (records status)

Key Features

1. Asynchronous Processing: Queue-based architecture prevents blocking
2. Provider Flexibility: Support for multiple email providers
3. Resilience: Retry logic with exponential backoff
4. Observability: Comprehensive tracking and logging
5. Security: Sensitive data redaction, HTTPS transmission
6. Localization: Multi-language template support
7. Isolation: Push failures don't affect email delivery

File Structure

backend/
├── src/
│   ├── config/
│   │   ├── queue.ts (extended)
│   │   └── env.ts (extended)
│   ├── controllers/
│   │   └── notificationController.ts (new)
│   ├── db/migrations/
│   │   └── 024_create_notifications.sql (new)
│   ├── routes/
│   │   └── notificationRoutes.ts (new)
│   ├── services/
│   │   ├── email/
│   │   │   ├── emailProvider.interface.ts (new)
│   │   │   ├── emailProviderFactory.ts (new)
│   │   │   ├── resendEmailProvider.ts (new)
│   │   │   └── sendgridEmailProvider.ts (new)
│   │   ├── notificationConfigService.ts (new)
│   │   ├── notificationQueueService.ts (new)
│   │   ├── notificationService.ts (new)
│   │   ├── notificationTrackingService.ts (new)
│   │   ├── pushNotificationService.ts (new)
│   │   └── templateRenderer.ts (new)
│   ├── templates/notifications/
│   │   ├── payment-notification.en.html (new)
│   │   └── payment-notification.en.txt (new)
│   └── workers/
│       ├── notificationWorker.ts (new)
│       ├── payrollWorker.ts (modified)
│       └── index.ts (modified)
└── .env.example (extended)

Environment Variables Required

# Email Provider Configuration
EMAIL_PROVIDER=resend  # or 'sendgrid'
EMAIL_FROM_ADDRESS=noreply@payd.example.com
EMAIL_FROM_NAME=PayD Payroll System

# Resend Configuration (if using Resend)
RESEND_API_KEY=re_xxxxxxxxxxxxx

# SendGrid Configuration (if using SendGrid)
SENDGRID_API_KEY=SG.xxxxxxxxxxxxx

# Stellar Explorer URL
STELLAR_EXPLORER_URL=https://stellar.expert/explorer/testnet/tx

API Endpoints

GET /api/notifications/history

Get notification history for an employee

• Query params: employee_id, transaction_id, notification_type, status, page, limit
• Auth: Required (JWT)
• Authorization: Users can view own history, admins can view all

GET /api/notifications/config

Get organization notification configuration

• Auth: Required (JWT)
• Authorization: Admin only

PUT /api/notifications/config

Update organization notification configuration

• Body: emailEnabled, pushEnabled, emailProvider, fromEmail, fromName, locale
• Auth: Required (JWT)
• Authorization: Admin only

POST /api/notifications/push-token

Register a push notification token

• Body: token, platform (ios/android/web)
• Auth: Required (JWT)

DELETE /api/notifications/push-token

Remove a push notification token

• Body: token
• Auth: Required (JWT)

Next Steps (Optional Tasks)

The following tasks are marked as optional in the spec and can be implemented for enhanced functionality:

1. Unit Tests - Test individual services and components
2. Property-Based Tests - Validate correctness properties
3. Localization - Add Spanish and French templates
4. Security Features - Transaction hash validation, rate limiting
5. Error Handling - Circuit breaker pattern, retry wrappers
6. Push Notification Enhancement - Integrate with FCM/APNs
7. Integration Tests - End-to-end testing
8. Monitoring - Metrics collection and structured logging

Deployment Checklist

Before deploying to production:

1. ✅ Run database migration 024_create_notifications.sql
2. ⚠️ Set required environment variables (EMAIL_PROVIDER, API keys)
3. ⚠️ Configure email provider account (Resend or SendGrid)
4. ⚠️ Test email delivery with test account
5. ⚠️ Verify Redis connection for queue
6. ⚠️ Monitor notification worker logs
7. ⚠️ Set up alerts for failed notifications

Testing the Implementation

Manual Testing Steps:

1. Database Setup:

   # Run migration
   psql -d payd_db -f backend/src/db/migrations/024_create_notifications.sql

2. Environment Configuration:

   # Copy and configure .env
   cp backend/.env.example backend/.env
   # Edit .env and add your email provider API key

3. Start Services:

   cd backend
   npm install
   npm run dev

4. Trigger a Payment:

   • Process a payroll run through the existing PayD interface
   • Check logs for notification job enqueuing
   • Verify notification worker processes the job
   • Check employee email for payment notification

5. Test API Endpoints:

   # Get notification history
   curl -H "Authorization: Bearer YOUR_JWT" \
     http://localhost:3000/api/notifications/history
   
   # Register push token
   curl -X POST -H "Authorization: Bearer YOUR_JWT" \
     -H "Content-Type: application/json" \
     -d '{"token":"test-token","platform":"web"}' \
     http://localhost:3000/api/notifications/push-token

Success Criteria Met

✅ Email provider integrated successfully (Resend and SendGrid) ✅ Queue-based notification trigger after transaction confirmation ✅ Branded email templates with payment details and transaction hash ✅ Push notification infrastructure (stub ready for enhancement) ✅ Comprehensive tracking and error handling ✅ API endpoints for configuration and history ✅ Security features (HTTPS, data redaction) ✅ Localization support (English templates, ready for more languages)

Notes

• The push notification service is implemented as a stub that logs notifications. To enable actual push delivery, integrate with Firebase Cloud Messaging (FCM) for Android, Apple Push Notification service (APNs) for iOS, and Web Push API for web notifications.
• Email templates are currently available in English only. Additional language templates can be added by creating payment-notification.{locale}.html and payment-notification.{locale}.txt files.
• The notification worker processes up to 5 jobs concurrently. This can be adjusted in backend/src/workers/notificationWorker.ts.
• Failed notifications are retried 3 times with exponential backoff. This configuration is in backend/src/config/queue.ts.