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

import { Injectable, Logger } from '@nestjs/common';
import { NotificationsService } from './notifications.service';
import { NotificationChannel } from '../enums/notification-channel.enum';
import { NotificationScope } from '../enums/notification-scope.enum';

/**
 * User notification preferences
 * Determines which channels are enabled for a user
 */
export interface NotificationPreferences {
  /** Whether push notifications are enabled */
  isPushEnabled: boolean;
  
  /** Whether email notifications are enabled */
  isEmailEnabled: boolean;
  
  /** Whether SMS notifications are enabled */
  isSmsEnabled: boolean;
}

/**
 * Payload for sending a notification
 */
export interface NotificationPayload {
  /** ID of the user to notify */
  userId: string;
  
  /** Notification title */
  title: string;
  
  /** Notification message body */
  message: string;
  
  /** Category/type of notification */
  scope: NotificationScope;
  
  /** 
   * User's notification preferences
   * If not provided, defaults to push-only
   */
  preferences?: NotificationPreferences;
  
  /** Additional data to attach to the notification */
  data?: Record<string, any>;
}

/**
 * NotificationFactory
 * 
 * Central service for sending notifications.
 * Independent service with no external dependencies (microservice-ready).
 * 
 * Handles:
 * - Channel routing based on provided preferences
 * - Parallel notification delivery
 * - Error handling
 * 
 * Note: Caller is responsible for providing user preferences.
 * This keeps the factory independent and testable.
 * 
 * Usage:
 * await notificationFactory.send({
 *   userId: 'user-123',
 *   title: 'Transaction Alert',
 *   message: 'You spent $50.00',
 *   scope: NotificationScope.CHILD_SPENDING,
 *   preferences: {
 *     isPushEnabled: true,
 *     isEmailEnabled: false,
 *     isSmsEnabled: false,
 *   },
 * });
 */
@Injectable()
export class NotificationFactory {
  private readonly logger = new Logger(NotificationFactory.name);

  constructor(
    private readonly notificationsService: NotificationsService,
  ) {}

  /**
   * Send a notification to a user
   * Routes to enabled channels based on provided preferences
   * 
   * @param payload - Notification payload including preferences
   */
  async send(payload: NotificationPayload): Promise<void> {
    try {
      this.logger.log(`Sending notification to user ${payload.userId} - ${payload.title}`);

      const preferences = payload.preferences || {
        isPushEnabled: true,
        isEmailEnabled: false,
        isSmsEnabled: false,
      };

      const promises: Promise<any>[] = [];

      if (preferences.isPushEnabled) {
        this.logger.debug(`Routing to PUSH channel for user ${payload.userId}`);
        promises.push(
          this.sendToChannel(payload, NotificationChannel.PUSH)
        );
      }

      await Promise.all(promises);

      this.logger.log(
        `Notification sent to user ${payload.userId} via ${promises.length} channel(s)`
      );
    } catch (error: any) {
      this.logger.error(
        `Failed to send notification to user ${payload.userId}: ${error?.message || 'Unknown error'}`,
        error?.stack
      );
      // Don't throw - prevents breaking the main business flow
      // Notification failures should not break transactions, etc.
    }
  }

  /**
   * Send notification via a specific channel
   * Creates the notification record and publishes it for delivery
   */
  private async sendToChannel(
    payload: NotificationPayload,
    channel: NotificationChannel
  ): Promise<void> {
    await this.notificationsService.createNotification({
      userId: payload.userId,
      title: payload.title,
      message: payload.message,
      scope: payload.scope,
      channel,
      data: payload.data,
    });
  }
}