API/src/services/notification.service.ts

import Event from '../model/event.model';
import User from '../model/user.model';
import sendMail from '../util/mailer.util';
import Queue from 'bull';
import { REDIS_URL } from '../config/env.config';

// Create Bull queues for async job processing
const emailQueue = new Queue('email-notifications', REDIS_URL || 'redis://localhost:6379');
const reminderQueue = new Queue('event-reminders', REDIS_URL || 'redis://localhost:6379');

// ==================== EMAIL QUEUE PROCESSOR ====================
emailQueue.process(async (job) => {
  const { to, subject, text, html } = job.data;
  await sendMail({ to, subject, text, html });
});

// ==================== REMINDER QUEUE PROCESSOR ====================
reminderQueue.process(async (job) => {
  const { eventId } = job.data;
  await processEventReminder(eventId);
});

// ==================== QUEUE EVENT REMINDER (Stateless) ====================
export const queueEventReminder = async (eventId: string, sendAt: Date) => {
  const delay = sendAt.getTime() - Date.now();
  
  if (delay > 0) {
    await reminderQueue.add(
      { eventId },
      { delay, attempts: 3, backoff: { type: 'exponential', delay: 2000 } }
    );
  }
};

// ==================== PROCESS EVENT REMINDER ====================
async function processEventReminder(eventId: string) {
  try {
    const event = await Event.findById(eventId)
      .populate('participants.user', 'email username')
      .populate('organization', 'username');
    
    if (!event || event.reminderSent) return;
    
    for (const participant of event.participants) {
      const user = participant.user as any;
      
      await emailQueue.add({
        to: user.email,
        subject: `Reminder: ${event.title} - Tomorrow`,
        text: `Reminder: ${event.title} starts tomorrow at ${event.startDate.toLocaleString()}`,
        html: generateReminderHTML(event, user)
      });
    }
    
    event.reminderSent = true;
    await event.save();
    
    console.log(`Reminder sent for event: ${event.title}`);
  } catch (err) {
    console.error('Error sending reminder:', err);
    throw err; // Bull will retry
  }
}

function generateReminderHTML(event: any, user: any): string {
  return `
    <div style="font-family: Arial, sans-serif; padding: 20px;">
      <h2>Event Reminder</h2>
      <p>Hi ${user.username},</p>
      <p>This is a reminder that you're registered for:</p>
      <div style="background: #f5f5f5; padding: 15px; border-radius: 8px; margin: 20px 0;">
        <h3 style="margin: 0 0 10px 0;">${event.title}</h3>
        <p><strong>Code:</strong> ${event.code}</p>
        <p><strong>Start:</strong> ${event.startDate.toLocaleString()}</p>
      </div>
    </div>
  `;
}

// ==================== SCHEDULE ALL UPCOMING REMINDERS (Run on startup) ====================
export async function scheduleUpcomingReminders() {
  const now = new Date();
  const sevenDaysFromNow = new Date(now.getTime() + 7 * 24 * 60 * 60 * 1000);
  
  const upcomingEvents = await Event.find({
    status: 'published',
    reminderSent: false,
    startDate: { $gte: now, $lte: sevenDaysFromNow }
  });
  
  for (const event of upcomingEvents) {
    const reminderTime = new Date(event.startDate.getTime() - 24 * 60 * 60 * 1000);
    await queueEventReminder(event._id.toString(), reminderTime);
  }
  
  console.log(`Scheduled ${upcomingEvents.length} event reminders`);
}

export const sendEventUpdateNotification = async (eventId: string, updateMessage: string) => {
  const event = await Event.findById(eventId).populate('participants.user', 'email username');
  
  if (!event) return;
  
  for (const participant of event.participants) {
    const user = participant.user as any;
    await emailQueue.add({
      to: user.email,
      subject: `Update: ${event.title}`,
      text: updateMessage,
      html: `<div><h2>Event Update</h2><p>${updateMessage}</p></div>`
    });
  }
};

export const sendWaitlistPromotionNotification = async (eventId: string, userId: string) => {
  const event = await Event.findById(eventId);
  const user = await User.findById(userId);
  
  if (!event || !user) return;
  
  await emailQueue.add({
    to: user.email,
    subject: `Spot Available: ${event.title}`,
    text: `Good news! A spot has opened up for ${event.title}`,
    html: `<div><h2>Good News!</h2><p>You've been registered for ${event.title}</p></div>`
  });
};