Feat/notification

[nafiuishaaq]

🎯 Completed Notification Service Implementation

Core Architecture

We've created a comprehensive, production-ready NestJS module that handles centralized event processing and multi-channel notifications. The service is fully integrated with the existing TruthBounty ecosystem.

📁 File Structure

notifications/
├── notifications.module.ts          # Main module definition
├── controllers/
│   └── notifications.controller.ts  # REST API endpoints
├── services/
│   ├── notifications.service.ts     # Core event processing logic
│   ├── notification-preferences.service.ts  # User preference management
│   ├── delivery-history.service.ts  # Delivery tracking and auditing
│   ├── websocket.service.ts         # Real-time WebSocket delivery
│   ├── email.service.ts             # Email delivery with templates
│   ├── webhook.service.ts           # Third-party webhook integration
│   └── notification.processor.ts    # BullMQ queue processor
├── entities/
│   ├── notification.entity.ts       # Main notification model
│   ├── notification-preference.entity.ts  # User preferences
│   └── delivery-history.entity.ts   # Delivery audit logs
├── dto/
│   ├── list-notifications.dto.ts    # Filtering/pagination DTO
│   └── update-preferences.dto.ts    # Preferences update DTO
└── interfaces/
    └── notification.types.ts        # Shared types, enums, interfaces

closes #280 

✨ Key Features Implemented

1. Centralized Event Processing

   • processIncomingEvent() handles all protocol events from blockchain indexer, governance, reputation, and rewards systems
   • Maps events to notification categories and priorities automatically
   • Checks user preferences before creating notifications

2. Multi-Channel Delivery

   • In-App: Database-stored notifications for web/mobile apps
   • WebSocket: Real-time push to connected clients with connection tracking
   • Email: HTML/text email templates with digest support
   • Webhook: Custom webhooks for third-party integrations with HMAC signatures
   • Push (ready for future implementation)

closes #285

3. User Preference Management

   • Granular channel enable/disable per user
   • Category-level notification controls
   • Email digest settings (daily/weekly)
   • Alert-specific toggles (governance, staking, rewards, security)
   • Default preferences created automatically for new users

4. Reliable Queueing with BullMQ

   • Exponential backoff retry logic (5 attempts starting at 1s delay)
   • Priority queueing (critical > high > medium > low)
   • Dead-letter queue for failed deliveries
   • 10 concurrent workers for processing
   • Automatic retry tracking and incrementing

closes #286

5. Audit & Monitoring

   • Complete delivery history tracking with timestamps
   • Success/failure metrics and statistics
   • Integration with MetricsService for observability
   • Detailed logging throughout the system

6. REST API Endpoints

   • GET /notifications - List user's notifications with filtering/pagination
   • PUT /notifications/:id/read - Mark notification as read
   • GET /preferences - Get user preferences
   • PUT /preferences - Update notification preferences

7. Database Integration

   • TypeORM entities with proper relationships
   • Notification → User (many-to-one)
   • NotificationPreference → User (one-to-one)
   • DeliveryHistory → Notification (many-to-one)
   • Cascade deletion for data integrity

🔧 Technical Highlights

• Follows NestJS best practices with proper dependency injection
• Type-safe throughout with TypeScript
• Works with existing project dependencies (Prisma, Redis, BullMQ, TypeORM)
• JWT authentication for all protected endpoints
• Class-validator for input validation
• CORS support for WebSocket connections
• Timing-safe signature verification for webhooks
• Automatic cleanup of disconnected WebSocket clients

closes #845

The service is now ready for database migrations and integration testing. All references that were previously missing (like NotificationPreferencesService, DeliveryHistoryService, etc.) are now implemented and properly imported throughout the module.

[dDevAhmed]

resolve conflict @nafiuishaaq