# Telegram Notifications Module

## Overview

The Telegram Notifications Module provides a complete backend-only notification system for the Math Platform. It sends administrative alerts to a Telegram bot, keeping admins informed about user activities, system errors, and important events.

## Architecture

```
backend/
├── src/
│   ├── config/
│   │   └── telegram.ts                 # Telegram configuration & settings
│   ├── modules/
│   │   └── notification/
│   │       ├── notification.service.ts # Main notification service
│   │       ├── index.ts                # Module exports
│   │       └── telegram/
│   │           ├── telegram.client.ts  # HTTP client for Telegram API
│   │           └── templates/          # Message templates
│   │               ├── index.ts        # Template factory
│   │               ├── alert.template.ts
│   │               ├── progress.template.ts
│   │               └── achievement.template.ts
│   ├── workers/
│   │   └── notification-sender.worker.ts  # Async job processor
│   └── scripts/
│       └── test-telegram.ts            # Test script
```

## Features

- **Async Queue Processing**: Uses Bull with Redis for reliable job processing
- **Retry Logic**: Automatic retry with exponential backoff on failures
- **Rich Templates**: Pre-built templates for different notification types
- **Type Safety**: Full TypeScript support with proper interfaces
- **Error Handling**: Comprehensive error handling and logging
- **Rate Limiting**: Built-in rate limiting to avoid Telegram API limits
- **Health Checks**: Monitor notification system health

## Configuration

### Environment Variables

```env
# Telegram Configuration
TELEGRAM_BOT_TOKEN="your-telegram-bot-token-here"
TELEGRAM_ADMIN_CHAT_ID="your-chat-id-here"
TELEGRAM_ENABLED=true

# Optional Configuration
TELEGRAM_API_URL="https://api.telegram.org"
TELEGRAM_TIMEOUT=10000
TELEGRAM_MAX_RETRIES=3
TELEGRAM_RETRY_DELAY=1000
TELEGRAM_PARSE_MODE="HTML"
TELEGRAM_DISABLE_WEB_PAGE_PREVIEW=true
TELEGRAM_MIN_PRIORITY="NORMAL"
```

### Priority Levels

Notifications can be filtered by priority:

- `LOW`: Informational notifications (user activity, exercise completion)
- `NORMAL`: Regular notifications (module completion, achievements)
- `HIGH`: Important notifications (errors, performance issues)
- `URGENT`: Critical notifications (security alerts)

## Usage

### Basic Notifications

```typescript
import { notificationService } from './modules/notification';

// System Notification
await notificationService.sendSystemNotification(
  'Server Started',
  'The application server has started successfully',
  { port: 3001, environment: 'production' }
);

// User Registration
await notificationService.notifyNewUser({
  userId: 'user-123',
  anonymousId: 'anon-456',
  username: 'john_doe',
  email: 'john@example.com',
  registeredAt: new Date().toISOString(),
  ipAddress: '192.168.1.1',
});

// Error Notification
await notificationService.notifySystemError({
  errorType: 'DatabaseError',
  errorMessage: 'Failed to connect to database',
  stackTrace: 'Error: ...',
  path: '/api/users',
  method: 'POST',
  statusCode: 500,
});
```

### Advanced Usage

```typescript
// Module Completion
await notificationService.notifyModuleCompleted({
  userId: 'user-123',
  anonymousId: 'anon-456',
  moduleName: 'Vectores y Espacios Vectoriales',
  moduleType: 'FUNDAMENTOS',
  finalScore: 95,
  totalPoints: 1250,
  exercisesCompleted: 45,
  timeSpentMinutes: 120,
  startedAt: startDate.toISOString(),
  completedAt: new Date().toISOString(),
});

// Achievement Notification
await notificationService.notifyTop10Entry({
  userId: 'user-123',
  anonymousId: 'anon-456',
  position: 5,
  points: 2500,
  exercisesCompleted: 120,
  streak: 15,
});

// Daily Summary (scheduled task)
await notificationService.sendDailySummary(new Date());
```

## Templates

### Available Templates

1. **System Notifications**: General system alerts
2. **User Registration**: New user signups
3. **User Activity**: User actions and events
4. **Exercise Completion**: Exercise finished
5. **Module Completion**: Module finished
6. **Achievements**: Badges and milestones
7. **Error Notifications**: System errors
8. **Security Alerts**: Security events
9. **Performance Monitoring**: Performance metrics

### Creating Custom Templates

```typescript
import { TelegramTemplateFactory } from './modules/notification/telegram/templates';

// Format message using template factory
const { content, messageType, priority } = TelegramTemplateFactory.formatMessage(
  TelegramMessageType.SYSTEM,
  {
    title: 'Custom Alert',
    message: 'Something important happened',
    details: { key: 'value' }
  }
);

// Send custom notification
await notificationService.sendNotification(
  TelegramMessageType.SYSTEM,
  data,
  { priority: TelegramPriority.HIGH }
);
```

## Worker & Queue

### Queue Management

```typescript
import {
  getNotificationQueue,
  getQueueStats,
  pauseQueue,
  resumeQueue
} from './modules/notification';

// Get queue statistics
const stats = await getQueueStats();
console.log(stats);
// { waiting: 5, active: 2, completed: 100, failed: 3, ... }

// Pause queue (maintenance)
await pauseQueue();

// Resume queue
await resumeQueue();
```

### Retry Failed Notifications

```typescript
import { retryFailedNotifications } from './modules/notification';

// Retry up to 10 failed notifications
const retriedCount = await retryFailedNotifications(10);
console.log(`Retried ${retriedCount} notifications`);
```

## Testing

### Run Test Script

```bash
# Test all Telegram notifications
npm run test:telegram

# Or directly with tsx
npx tsx src/scripts/test-telegram.ts
```

### Test Coverage

The test script validates:
- Telegram client connection
- System notifications
- User registration notifications
- Error notifications
- Module completion notifications
- Achievement notifications
- Queue statistics

## Health Monitoring

### Check Notification Health

```typescript
const health = await notificationService.healthCheck();

console.log(health);
// {
//   healthy: true,
//   telegram: true,
//   stats: {
//     total: 100,
//     pending: 5,
//     sent: 90,
//     failed: 5,
//     todaySent: 25,
//     todayFailed: 2
//   }
// }
```

### Worker Health

```typescript
import { getWorkerHealth } from './workers/notification-sender.worker';

const workerHealth = await getWorkerHealth();

console.log(workerHealth);
// {
//   healthy: true,
//   queueStats: { ... },
//   workerRunning: true
// }
```

## Error Handling

### Common Errors

1. **Rate Limiting (429)**
   - Automatic retry with exponential backoff
   - Configurable retry delay and max attempts

2. **Bot Blocked (403)**
   - User must unblock the bot in Telegram
   - Check admin chat ID is correct

3. **Invalid Token (401)**
   - Verify `TELEGRAM_BOT_TOKEN` is correct
   - Regenerate token via @BotFather if needed

4. **Chat Not Found (400)**
   - Verify `TELEGRAM_ADMIN_CHAT_ID` is correct
   - Start a conversation with the bot first

### Debugging

```typescript
import { logger } from './shared/utils/logger';

// Enable debug logging
logger.level = 'debug';

// Check Telegram configuration
import { telegramConfig } from './config/telegram';
console.log(telegramConfig.healthCheck());
```

## Production Considerations

### Security

- Never commit bot tokens to version control
- Use environment variables for sensitive data
- Implement rate limiting per notification type
- Monitor for abuse patterns

### Performance

- Use async queue for all notifications
- Don't block main thread with Telegram calls
- Implement proper error recovery
- Monitor queue depth and processing time

### Monitoring

```typescript
// Set up monitoring (example with cron)
import cron from 'node-cron';

// Check queue health every 5 minutes
cron.schedule('*/5 * * * *', async () => {
  const stats = await getQueueStats();

  if (stats.failed > 10) {
    // Alert admins about high failure rate
    await notificationService.sendSystemNotification(
      'High Notification Failure Rate',
      `${stats.failed} notifications have failed`,
      { stats }
    );
  }
});
```

## API Reference

### NotificationService

```typescript
class NotificationService {
  // Send system notification
  sendSystemNotification(title, message, details?): Promise<NotificationResult>

  // Notify new user registration
  notifyNewUser(data): Promise<CreateNotificationResult>

  // Notify module completion
  notifyModuleCompleted(data): Promise<CreateNotificationResult>

  // Notify top 10 entry
  notifyTop10Entry(data): Promise<CreateNotificationResult>

  // Notify system error
  notifySystemError(data): Promise<CreateNotificationResult>

  // Send daily summary
  sendDailySummary(date?): Promise<CreateNotificationResult>

  // Get statistics
  getStatistics(): Promise<NotificationStatistics>

  // Retry failed notifications
  retryFailedNotifications(limit?): Promise<void>

  // Health check
  healthCheck(): Promise<HealthCheckResult>
}
```

### TelegramClient

```typescript
class TelegramClient {
  // Send text message
  sendMessage(chatId, text, options?): Promise<MessageResult>

  // Send photo
  sendPhoto(chatId, photo, caption?, options?): Promise<MessageResult>

  // Send document
  sendDocument(chatId, document, caption?, options?): Promise<MessageResult>

  // Get bot info
  getMe(): Promise<TelegramBotInfo>

  // Health check
  healthCheck(): Promise<HealthCheckResult>
}
```

## Troubleshooting

### Notifications Not Sending

1. Check Telegram is enabled: `TELEGRAM_ENABLED=true`
2. Verify bot token is valid
3. Confirm admin chat ID is correct
4. Check Redis connection for worker queue
5. Review logs for error messages

### Queue Backing Up

1. Increase worker concurrency: `WORKER_CONCURRENCY=5`
2. Check for rate limiting issues
3. Verify network connectivity to Telegram API
4. Consider reducing notification frequency

### High Failure Rate

1. Check Telegram API status
2. Verify bot permissions
3. Review error messages in logs
4. Check for rate limiting (429 errors)
5. Validate message formatting

## Contributing

When adding new notification types:

1. Create template in `templates/` directory
2. Add message type to `TelegramMessageType` enum
3. Add convenience method to `NotificationService`
4. Update this documentation
5. Add tests for new notification type

## License

MIT

## Support

For issues or questions:
- Check logs in `logs/combined.log`
- Review Telegram API documentation: https://core.telegram.org/bots/api
- Test configuration using: `npm run test:telegram`