zod-backend/src/common/modules/notification/services/messaging/messaging-system-factory.service.ts

import { Injectable, Logger, Optional } from '@nestjs/common';
import { NotificationScope, requiresGuaranteedDelivery } from '../../enums/notification-scope.enum';
import { IMessagingSystem } from '../../interfaces/messaging-system.interface';
import { RedisPubSubMessagingService } from './redis-pubsub-messaging.service';

/**
 * Messaging System Factory
 * 
 * Determines which messaging system to use based on notification requirements.
 * 
 * - Regular notifications → Redis PubSub (fast, 2-5ms)
 * - Critical notifications → RabbitMQ/Kafka (guaranteed delivery, 20-50ms)
 * 
 * Usage:
 * ```typescript
 * const system = factory.getMessagingSystem(NotificationScope.CHILD_SPENDING);
 * await system.publish('NOTIFICATION_CREATED', payload);
 * ```
 */
@Injectable()
export class MessagingSystemFactory {
  private readonly logger = new Logger(MessagingSystemFactory.name);

  constructor(
    private readonly redisPubSubService: RedisPubSubMessagingService,
  ) {}

  /**
   * Get the appropriate messaging system based on notification scope
   * 
   * @param scope - Notification scope
   * @returns Messaging system to use
   */
  getMessagingSystem(scope: NotificationScope): IMessagingSystem {
    const needsGuaranteedDelivery = requiresGuaranteedDelivery(scope);
    
    if (needsGuaranteedDelivery) {
      this.logger.warn(
        `[Factory] Critical notification ${scope} requires guaranteed delivery, ` +
        `but RabbitMQ not configured. Falling back to Redis PubSub.`
      );
      return this.redisPubSubService;
    } else {
      this.logger.debug(`[Factory] Using Redis PubSub for notification: ${scope}`);
      return this.redisPubSubService;
    }
  }

  /**
   * Get default messaging system (Redis PubSub)
   * 
   * @returns Default messaging system
   */
  getDefaultMessagingSystem(): IMessagingSystem {
    return this.redisPubSubService;
  }
}