stock-bot/libs/core/event-bus/src/event-bus.ts

import { EventEmitter } from 'eventemitter3';
import Redis from 'ioredis';
import { getLogger } from '@stock-bot/logger';
import type { EventBusConfig, EventBusMessage, EventHandler, EventSubscription } from './types';

/**
 * Lightweight Event Bus for inter-service communication
 * Uses Redis pub/sub for simple, real-time event distribution
 */
export class EventBus extends EventEmitter {
  private publisher: Redis;
  private subscriber: Redis;
  private readonly serviceName: string;
  private readonly logger: ReturnType<typeof getLogger>;
  private subscriptions: Map<string, EventSubscription> = new Map();
  private isConnected: boolean = false;

  constructor(config: EventBusConfig) {
    super();
    this.serviceName = config.serviceName;
    this.logger = getLogger(`event-bus:${this.serviceName}`);

    // Create Redis connections
    const redisOptions = {
      host: config.redisConfig.host,
      port: config.redisConfig.port,
      password: config.redisConfig.password,
      db: config.redisConfig.db || 0,
      lazyConnect: false,
      enableOfflineQueue: true,
      reconnectOnError: (err: Error) => {
        this.logger.error('Redis connection error:', err);
        return true;
      },
    };

    this.publisher = new Redis(redisOptions);
    this.subscriber = new Redis(redisOptions);

    this.setupRedisHandlers();
  }

  private setupRedisHandlers(): void {
    // Publisher handlers
    this.publisher.on('connect', () => {
      this.logger.info('Publisher connected to Redis');
      this.isConnected = true;
    });

    this.publisher.on('error', error => {
      this.logger.error('Publisher Redis error:', error);
    });

    // Subscriber handlers
    this.subscriber.on('connect', () => {
      this.logger.info('Subscriber connected to Redis');
      // Resubscribe to all channels on reconnect
      this.resubscribeAll();
    });

    this.subscriber.on('error', error => {
      this.logger.error('Subscriber Redis error:', error);
    });

    // Handle incoming messages
    this.subscriber.on('message', this.handleMessage.bind(this));
  }

  private handleMessage(channel: string, message: string): void {
    try {
      const eventMessage: EventBusMessage = JSON.parse(message);

      // Skip messages from self
      if (eventMessage.source === this.serviceName) {
        return;
      }

      // Extract event type from channel (remove 'events:' prefix)
      const eventType = channel.replace('events:', '');

      // Emit locally
      this.emit(eventType, eventMessage);

      // Call registered handler if exists
      const subscription = this.subscriptions.get(eventType);
      if (subscription?.handler) {
        Promise.resolve(subscription.handler(eventMessage)).catch(error => {
          this.logger.error(`Handler error for event ${eventType}:`, error);
        });
      }

      this.logger.debug(`Received event: ${eventType} from ${eventMessage.source}`);
    } catch (error) {
      this.logger.error('Failed to handle message:', { error, channel, message });
    }
  }

  /**
   * Publish an event
   */
  async publish<T = any>(type: string, data: T, metadata?: Record<string, any>): Promise<void> {
    const message: EventBusMessage<T> = {
      id: this.generateId(),
      type,
      source: this.serviceName,
      timestamp: Date.now(),
      data,
      metadata,
    };

    // Emit locally first
    this.emit(type, message);

    // Publish to Redis
    if (this.isConnected) {
      try {
        const channel = `events:${type}`;
        await this.publisher.publish(channel, JSON.stringify(message));
        this.logger.debug(`Published event: ${type}`, { messageId: message.id });
      } catch (error) {
        this.logger.error(`Failed to publish event: ${type}`, { error, messageId: message.id });
        throw error;
      }
    } else {
      this.logger.warn(`Not connected to Redis, event ${type} only emitted locally`);
    }
  }

  /**
   * Subscribe to an event
   */
  async subscribe<T = any>(eventType: string, handler: EventHandler<T>): Promise<void> {
    // Register handler
    this.subscriptions.set(eventType, { channel: `events:${eventType}`, handler });

    // Add local listener
    this.on(eventType, handler);

    // Subscribe to Redis channel
    try {
      const channel = `events:${eventType}`;
      await this.subscriber.subscribe(channel);
      this.logger.debug(`Subscribed to event: ${eventType}`);
    } catch (error) {
      this.logger.error(`Failed to subscribe to event: ${eventType}`, error);
      throw error;
    }
  }

  /**
   * Unsubscribe from an event
   */
  async unsubscribe(eventType: string, handler?: EventHandler): Promise<void> {
    // Remove specific handler or all handlers
    if (handler) {
      this.off(eventType, handler);
    } else {
      this.removeAllListeners(eventType);
    }

    // Remove from subscriptions
    this.subscriptions.delete(eventType);

    // Unsubscribe from Redis
    try {
      const channel = `events:${eventType}`;
      await this.subscriber.unsubscribe(channel);
      this.logger.debug(`Unsubscribed from event: ${eventType}`);
    } catch (error) {
      this.logger.error(`Failed to unsubscribe from event: ${eventType}`, error);
    }
  }

  /**
   * Resubscribe to all channels (used on reconnect)
   */
  private async resubscribeAll(): Promise<void> {
    for (const [eventType, subscription] of this.subscriptions.entries()) {
      try {
        await this.subscriber.subscribe(subscription.channel);
        this.logger.debug(`Resubscribed to event: ${eventType}`);
      } catch (error) {
        this.logger.error(`Failed to resubscribe to event: ${eventType}`, error);
      }
    }
  }

  /**
   * Wait for connection to be established
   */
  async waitForConnection(timeout: number = 5000): Promise<void> {
    const startTime = Date.now();

    while (!this.isConnected && Date.now() - startTime < timeout) {
      await new Promise(resolve => setTimeout(resolve, 100));
    }

    if (!this.isConnected) {
      throw new Error(`Failed to connect to Redis within ${timeout}ms`);
    }
  }

  /**
   * Close all connections
   */
  async close(): Promise<void> {
    this.isConnected = false;

    // Clear all subscriptions
    this.subscriptions.clear();
    this.removeAllListeners();

    // Close Redis connections
    await Promise.all([this.publisher.quit(), this.subscriber.quit()]);

    this.logger.info('Event bus closed');
  }

  /**
   * Generate unique message ID
   */
  private generateId(): string {
    return `${this.serviceName}-${Date.now()}-${Math.random().toString(36).substr(2, 9)}`;
  }

  /**
   * Check if connected to Redis
   */
  get connected(): boolean {
    return this.isConnected;
  }

  /**
   * Get service name
   */
  get service(): string {
    return this.serviceName;
  }
}