const express = require('express');
const router = express.Router();
const fs = require('fs');
const path = require('path');
const { requireAuth } = require('./auth');
const eventBus = require('./eventBus');

// 💾 Local file storage helper (persistent when on HF data mount if available)
const NOTIFICATIONS_DIR = fs.existsSync('/data') ? '/data' : path.join(__dirname, '..');
const NOTIFICATIONS_FILE = path.join(NOTIFICATIONS_DIR, 'notifications.json');

// Helper to access notification logs
function readNotifications() {
  try {
    if (!fs.existsSync(NOTIFICATIONS_FILE)) {
      return [];
    }
    return JSON.parse(fs.readFileSync(NOTIFICATIONS_FILE, 'utf8'));
  } catch (e) {
    console.error('Failed to read notifications log:', e);
    return [];
  }
}

function writeNotifications(data) {
  try {
    fs.writeFileSync(NOTIFICATIONS_FILE, JSON.stringify(data, null, 2), 'utf8');
  } catch (e) {
    console.error('Failed to write notifications log:', e);
  }
}

/**
 * Centrally registers and logs a notification, then broadcasts it in real-time
 */
const initNotificationService = (io) => {
  const addNotification = (notif) => {
    const notifications = readNotifications();
    const newNotif = {
      id: `notif-${Date.now()}-${Math.random().toString(36).substr(2, 9)}`,
      organization_id: notif.organization_id || '00000000-0000-0000-0000-000000000001',
      title: notif.title,
      message: notif.message,
      type: notif.type || 'SYSTEM_ALERT',
      priority: notif.priority || 'Low',
      is_read: false,
      is_resolved: false,
      action_url: notif.action_url || '',
      created_at: new Date().toISOString()
    };
    notifications.unshift(newNotif);
    writeNotifications(notifications);
    
    // 📢 Socket.IO Room Isolation: Emit strictly to clients connected within this specific organization
    if (io) {
      io.to(`org-${newNotif.organization_id}`).emit('notification_created', newNotif);
    }
    return newNotif;
  };

  // ===================================================================
  // 📥 EVENT BUS SUBSCRIBERS (Decoupled Automated System Alerts)
  // ===================================================================

  // 1. Auto Alert for Manual Enrollments
  eventBus.subscribe('manual_admission.completed', (payload) => {
    const { student_name, student_id, course, pending_amount, installment_option, organization_id } = payload;
    
    addNotification({
      organization_id,
      title: "New admission completed 🎓",
      message: `${student_name} enrolled in ${course} (ID: ${student_id}).`,
      type: "ADMISSION_ALERT",
      priority: "Medium",
      action_url: "/admissions"
    });

    if (parseFloat(pending_amount || 0) > 0) {
      addNotification({
        organization_id,
        title: "Installment generated 💰",
        message: `Pending balance of ₹${parseFloat(pending_amount).toLocaleString()} for ${student_name} (${installment_option || 'EMI'}).`,
        type: "PAYMENT_ALERT",
        priority: "High",
        action_url: "/admissions"
      });
    }

    // AI trends trigger alert
    addNotification({
      organization_id,
      title: `${course} conversion boost 📈`,
      message: `AI Insight: ${course} enrollments showed a surge after campaign adjustments.`,
      type: "AI_INSIGHT",
      priority: "Medium",
      action_url: "/ai-insights"
    });
  });

  // 2. Alert for Payment Completions
  eventBus.subscribe('payment.completed', (payload) => {
    const { student_name, course, organization_id } = payload;
    addNotification({
      organization_id,
      title: "Fee payment completed ✅",
      message: `Received final fee payment installment from ${student_name} for course: ${course}.`,
      type: "PAYMENT_ALERT",
      priority: "Medium",
      action_url: "/admissions"
    });
  });

  // 3. Alert for Real-time counselor lead updates
  eventBus.subscribe('lead.status_changed', (payload) => {
    const { student_name, new_status, organization_id } = payload;
    
    if (new_status === 'Pending') {
      addNotification({
        organization_id,
        title: "Follow-up Overdue Alert 🔴",
        message: `Lead ${student_name} followup has expired. Action required.`,
        type: "SYSTEM_ALERT",
        priority: "High",
        action_url: "/leads"
      });
    }
  });

  return { addNotification };
};

// ===================================================================
// REST API Routes
// ===================================================================

// GET /api/notifications - Fetch all active notifications scoped by active tenant
router.get('/', requireAuth, (req, res) => {
  try {
    const notifications = readNotifications();
    const tenantNotifications = notifications.filter(n => n.organization_id === req.user.organization_id);
    res.json(tenantNotifications);
  } catch (error) {
    res.status(500).json({ error: 'Failed to fetch notification database logs' });
  }
});

// PUT /api/notifications/:id/read - Mark alert as read
router.put('/:id/read', requireAuth, (req, res) => {
  const { id } = req.params;
  try {
    const notifications = readNotifications();
    const idx = notifications.findIndex(n => n.id === id && n.organization_id === req.user.organization_id);
    if (idx !== -1) {
      notifications[idx].is_read = true;
      writeNotifications(notifications);
      return res.json({ success: true });
    }
    res.status(404).json({ error: 'Alert log not found' });
  } catch (error) {
    res.status(500).json({ error: 'Failed to update alert log status' });
  }
});

// PUT /api/notifications/:id/resolve - Resolve active notification checklist item
router.put('/:id/resolve', requireAuth, (req, res) => {
  const { id } = req.params;
  try {
    const notifications = readNotifications();
    const idx = notifications.findIndex(n => n.id === id && n.organization_id === req.user.organization_id);
    if (idx !== -1) {
      notifications[idx].is_resolved = true;
      notifications[idx].is_read = true;
      writeNotifications(notifications);
      return res.json({ success: true });
    }
    res.status(404).json({ error: 'Alert log not found' });
  } catch (error) {
    res.status(500).json({ error: 'Failed to resolve notification logs' });
  }
});

// POST /api/notifications/mark-all-read - Clear all unread notifications
router.post('/mark-all-read', requireAuth, (req, res) => {
  try {
    const notifications = readNotifications();
    notifications.forEach(n => {
      if (n.organization_id === req.user.organization_id) {
        n.is_read = true;
      }
    });
    writeNotifications(notifications);
    res.json({ success: true });
  } catch (error) {
    res.status(500).json({ error: 'Failed to mark notifications read' });
  }
});

module.exports = {
  router,
  initNotificationService
};