E-Commerce-Module/backend/src/services/notificationService.js

// Create a new file: src/services/notificationService.js

const nodemailer = require('nodemailer');
const config = require('../config');

/**
 * Service for handling notifications including stock alerts
 */
const notificationService = {
  /**
   * Create email transporter
   * @returns {Object} Configured nodemailer transporter
   */
  createTransporter() {
    return nodemailer.createTransport({
      host: config.email.host,
      port: config.email.port,
      auth: {
        user: config.email.user,
        pass: config.email.pass
      }
    });
  },

  /**
   * Process pending low stock notifications
   * @param {Object} pool - Database connection pool
   * @param {Function} query - Database query function
   * @returns {Promise<number>} Number of notifications processed
   */
  async processLowStockNotifications(pool, query) {
    const client = await pool.connect();
    let processedCount = 0;
    
    try {
      await client.query('BEGIN');
      
      // Get pending low stock notifications
      const pendingNotifications = await client.query(`
        SELECT id 
        FROM notification_logs 
        WHERE notification_type = 'low_stock_alert' 
        AND status = 'pending'
        LIMIT 50
      `);
      
      if (pendingNotifications.rows.length === 0) {
        await client.query('COMMIT');
        return 0;
      }
      
      // Get products with current stock below threshold
      const lowStockProducts = await client.query(`
        SELECT 
          p.id, 
          p.name, 
          p.stock_quantity, 
          p.stock_notification 
        FROM products p
        WHERE 
          p.stock_notification IS NOT NULL 
          AND p.stock_notification->>'enabled' = 'true'
          AND p.stock_notification->>'email' IS NOT NULL
          AND p.stock_quantity <= (p.stock_notification->>'threshold')::int
      `);
      
      if (lowStockProducts.rows.length === 0) {
        // Mark notifications as processed with no action
        const notificationIds = pendingNotifications.rows.map(n => n.id);
        await client.query(`
          UPDATE notification_logs
          SET status = 'completed', error_message = 'No eligible products found'
          WHERE id = ANY($1)
        `, [notificationIds]);
        
        await client.query('COMMIT');
        return 0;
      }
      
      // Initialize email transporter
      const transporter = this.createTransporter();
      
      // Send notifications for each low stock product
      console.log(JSON.stringify(lowStockProducts, null, 4))
      for (const product of lowStockProducts.rows) {
        console.log(JSON.stringify(product, null, 4))
        console.log(typeof product.stock_notification)
        const notification = JSON.parse(product.stock_notification);
        
        try {
          // Send email notification
          await transporter.sendMail({
            from: config.email.reply,
            to: notification.email,
            subject: `Low Stock Alert: ${product.name}`,
            html: this.generateLowStockEmailTemplate(product)
          });
          
          // Mark one notification as processed
          if (pendingNotifications.rows[processedCount]) {
            await client.query(`
              UPDATE notification_logs
              SET status = 'success'
              WHERE id = $1
            `, [pendingNotifications.rows[processedCount].id]);
            
            processedCount++;
          }
        } catch (error) {
          console.error(`Error sending low stock notification for product ${product.id}:`, error);
          
          // Mark notification as failed
          if (pendingNotifications.rows[processedCount]) {
            await client.query(`
              UPDATE notification_logs
              SET status = 'failed', error_message = $2
              WHERE id = $1
            `, [pendingNotifications.rows[processedCount].id, error.message]);
            
            processedCount++;
          }
        }
      }
      
      await client.query('COMMIT');
      return processedCount;
    } catch (error) {
      await client.query('ROLLBACK');
      console.error('Error processing low stock notifications:', error);
      throw error;
    } finally {
      client.release();
    }
  },
  
  /**
   * Generate email template for low stock notification
   * @param {Object} product - Product with low stock
   * @returns {string} HTML email template
   */
  generateLowStockEmailTemplate(product) {
    const stockNotification = JSON.parse(product.stock_notification);
    const threshold = stockNotification.threshold || 0;
    
    return `
      <div style="font-family: Arial, sans-serif; max-width: 600px; margin: 0 auto;">
        <div style="background-color: #f8f8f8; padding: 20px; text-align: center;">
          <h1 style="color: #ff6b6b;">Low Stock Alert</h1>
        </div>
        
        <div style="padding: 20px;">
          <p>Hello,</p>
          
          <p>This is an automated notification to inform you that the following product is running low on stock:</p>
          
          <div style="background-color: #f8f8f8; padding: 15px; margin: 20px 0; border-left: 4px solid #ff6b6b;">
            <h3 style="margin-top: 0;">${product.name}</h3>
            <p><strong>Current Stock:</strong> ${product.stock_quantity}</p>
            <p><strong>Threshold:</strong> ${threshold}</p>
          </div>
          
          <p>You might want to restock this item soon to avoid running out of inventory.</p>
          
          <div style="margin-top: 30px; border-top: 1px solid #eee; padding-top: 20px;">
            <p>This is an automated notification. You received this because you set up stock notifications for this product.</p>
          </div>
        </div>
        
        <div style="background-color: #333; color: white; padding: 15px; text-align: center; font-size: 12px;">
          <p>&copy; ${new Date().getFullYear()} Rocks, Bones & Sticks. All rights reserved.</p>
        </div>
      </div>
    `;
  }
};

module.exports = notificationService;