import { Router } from 'express';
import crypto from 'crypto';
import { getDb } from '../config/database.js';
import { authenticateToken } from '../middleware/auth.js';
import { log } from '../config/logger.js';
import {
  isFederationEnabled,
  getFederationDomain,
  signPayload,
  verifyPayload,
  discoverInstance,
  parseAddress,
} from '../config/federation.js';
import { rateLimit } from 'express-rate-limit';

const router = Router();

// Rate limit for federation calendar receive
const calendarFederationLimiter = rateLimit({
  windowMs: 15 * 60 * 1000,
  max: 100,
  standardHeaders: true,
  legacyHeaders: false,
  message: { error: 'Too many requests. Please try again later.' },
});

// ── GET /api/calendar/events — List events for the current user ─────────────
router.get('/events', authenticateToken, async (req, res) => {
  try {
    const db = getDb();
    const { from, to } = req.query;

    let sql = `
      SELECT ce.*, COALESCE(NULLIF(u.display_name,''), u.name) as organizer_name
      FROM calendar_events ce
      JOIN users u ON ce.user_id = u.id
      WHERE (ce.user_id = ? OR ce.id IN (
        SELECT event_id FROM calendar_event_shares WHERE user_id = ?
      ))
    `;
    const params = [req.user.id, req.user.id];

    if (from) {
      sql += ' AND ce.end_time >= ?';
      params.push(from);
    }
    if (to) {
      sql += ' AND ce.start_time <= ?';
      params.push(to);
    }

    sql += ' ORDER BY ce.start_time ASC';
    const events = await db.all(sql, params);

    // Mark shared events
    for (const ev of events) {
      ev.is_owner = ev.user_id === req.user.id;
    }

    res.json({ events });
  } catch (err) {
    log.server.error(`Calendar list error: ${err.message}`);
    res.status(500).json({ error: 'Events could not be loaded' });
  }
});

// ── GET /api/calendar/events/:id — Get single event ─────────────────────────
router.get('/events/:id', authenticateToken, async (req, res) => {
  try {
    const db = getDb();
    const event = await db.get(`
      SELECT ce.*, COALESCE(NULLIF(u.display_name,''), u.name) as organizer_name
      FROM calendar_events ce
      JOIN users u ON ce.user_id = u.id
      WHERE ce.id = ?
    `, [req.params.id]);

    if (!event) return res.status(404).json({ error: 'Event not found' });

    // Check access
    if (event.user_id !== req.user.id) {
      const share = await db.get('SELECT id FROM calendar_event_shares WHERE event_id = ? AND user_id = ?', [event.id, req.user.id]);
      if (!share) return res.status(403).json({ error: 'No permission' });
    }

    // Get shared users
    const sharedUsers = await db.all(`
      SELECT u.id, u.name, u.display_name, u.email, u.avatar_color, u.avatar_image
      FROM calendar_event_shares ces
      JOIN users u ON ces.user_id = u.id
      WHERE ces.event_id = ?
    `, [event.id]);

    event.is_owner = event.user_id === req.user.id;
    res.json({ event, sharedUsers });
  } catch (err) {
    log.server.error(`Calendar get event error: ${err.message}`);
    res.status(500).json({ error: 'Event could not be loaded' });
  }
});

// ── POST /api/calendar/events — Create event ────────────────────────────────
router.post('/events', authenticateToken, async (req, res) => {
  try {
    const { title, description, start_time, end_time, room_uid, color } = req.body;

    if (!title || !title.trim()) return res.status(400).json({ error: 'Title is required' });
    if (!start_time || !end_time) return res.status(400).json({ error: 'Start and end time are required' });
    if (title.length > 200) return res.status(400).json({ error: 'Title must not exceed 200 characters' });
    if (description && description.length > 5000) return res.status(400).json({ error: 'Description must not exceed 5000 characters' });

    const startDate = new Date(start_time);
    const endDate = new Date(end_time);
    if (isNaN(startDate.getTime()) || isNaN(endDate.getTime())) {
      return res.status(400).json({ error: 'Invalid date format' });
    }
    if (endDate <= startDate) {
      return res.status(400).json({ error: 'End time must be after start time' });
    }

    // Verify room exists if specified
    const db = getDb();
    if (room_uid) {
      const room = await db.get('SELECT id FROM rooms WHERE uid = ?', [room_uid]);
      if (!room) return res.status(400).json({ error: 'Linked room not found' });
    }

    const uid = crypto.randomBytes(12).toString('hex');
    const result = await db.run(`
      INSERT INTO calendar_events (uid, title, description, start_time, end_time, room_uid, user_id, color)
      VALUES (?, ?, ?, ?, ?, ?, ?, ?)
    `, [
      uid,
      title.trim(),
      description || null,
      startDate.toISOString(),
      endDate.toISOString(),
      room_uid || null,
      req.user.id,
      color || '#6366f1',
    ]);

    const event = await db.get('SELECT * FROM calendar_events WHERE id = ?', [result.lastInsertRowid]);
    res.status(201).json({ event });
  } catch (err) {
    log.server.error(`Calendar create error: ${err.message}`);
    res.status(500).json({ error: 'Event could not be created' });
  }
});

// ── PUT /api/calendar/events/:id — Update event ─────────────────────────────
router.put('/events/:id', authenticateToken, async (req, res) => {
  try {
    const db = getDb();
    const event = await db.get('SELECT * FROM calendar_events WHERE id = ? AND user_id = ?', [req.params.id, req.user.id]);
    if (!event) return res.status(404).json({ error: 'Event not found or no permission' });

    const { title, description, start_time, end_time, room_uid, color } = req.body;

    if (title && title.length > 200) return res.status(400).json({ error: 'Title must not exceed 200 characters' });
    if (description && description.length > 5000) return res.status(400).json({ error: 'Description must not exceed 5000 characters' });

    if (start_time && end_time) {
      const s = new Date(start_time);
      const e = new Date(end_time);
      if (isNaN(s.getTime()) || isNaN(e.getTime())) return res.status(400).json({ error: 'Invalid date format' });
      if (e <= s) return res.status(400).json({ error: 'End time must be after start time' });
    }

    if (room_uid) {
      const room = await db.get('SELECT id FROM rooms WHERE uid = ?', [room_uid]);
      if (!room) return res.status(400).json({ error: 'Linked room not found' });
    }

    await db.run(`
      UPDATE calendar_events SET
        title = COALESCE(?, title),
        description = ?,
        start_time = COALESCE(?, start_time),
        end_time = COALESCE(?, end_time),
        room_uid = ?,
        color = COALESCE(?, color),
        updated_at = CURRENT_TIMESTAMP
      WHERE id = ?
    `, [
      title || null,
      description !== undefined ? description : event.description,
      start_time || null,
      end_time || null,
      room_uid !== undefined ? (room_uid || null) : event.room_uid,
      color || null,
      req.params.id,
    ]);

    const updated = await db.get('SELECT * FROM calendar_events WHERE id = ?', [req.params.id]);
    res.json({ event: updated });
  } catch (err) {
    log.server.error(`Calendar update error: ${err.message}`);
    res.status(500).json({ error: 'Event could not be updated' });
  }
});

// ── DELETE /api/calendar/events/:id — Delete event ──────────────────────────
router.delete('/events/:id', authenticateToken, async (req, res) => {
  try {
    const db = getDb();
    const event = await db.get('SELECT * FROM calendar_events WHERE id = ? AND user_id = ?', [req.params.id, req.user.id]);
    if (!event) return res.status(404).json({ error: 'Event not found or no permission' });

    await db.run('DELETE FROM calendar_events WHERE id = ?', [req.params.id]);
    res.json({ message: 'Event deleted' });
  } catch (err) {
    log.server.error(`Calendar delete error: ${err.message}`);
    res.status(500).json({ error: 'Event could not be deleted' });
  }
});

// ── POST /api/calendar/events/:id/share — Share event with local user ───────
router.post('/events/:id/share', authenticateToken, async (req, res) => {
  try {
    const { user_id } = req.body;
    if (!user_id) return res.status(400).json({ error: 'User ID is required' });

    const db = getDb();
    const event = await db.get('SELECT * FROM calendar_events WHERE id = ? AND user_id = ?', [req.params.id, req.user.id]);
    if (!event) return res.status(404).json({ error: 'Event not found or no permission' });
    if (user_id === req.user.id) return res.status(400).json({ error: 'Cannot share with yourself' });

    const existing = await db.get('SELECT id FROM calendar_event_shares WHERE event_id = ? AND user_id = ?', [event.id, user_id]);
    if (existing) return res.status(400).json({ error: 'Already shared with this user' });

    await db.run('INSERT INTO calendar_event_shares (event_id, user_id) VALUES (?, ?)', [event.id, user_id]);

    const sharedUsers = await db.all(`
      SELECT u.id, u.name, u.display_name, u.email, u.avatar_color, u.avatar_image
      FROM calendar_event_shares ces
      JOIN users u ON ces.user_id = u.id
      WHERE ces.event_id = ?
    `, [event.id]);

    res.json({ sharedUsers });
  } catch (err) {
    log.server.error(`Calendar share error: ${err.message}`);
    res.status(500).json({ error: 'Could not share event' });
  }
});

// ── DELETE /api/calendar/events/:id/share/:userId — Remove share ────────────
router.delete('/events/:id/share/:userId', authenticateToken, async (req, res) => {
  try {
    const db = getDb();
    const event = await db.get('SELECT * FROM calendar_events WHERE id = ? AND user_id = ?', [req.params.id, req.user.id]);
    if (!event) return res.status(404).json({ error: 'Event not found or no permission' });

    await db.run('DELETE FROM calendar_event_shares WHERE event_id = ? AND user_id = ?', [event.id, parseInt(req.params.userId)]);

    const sharedUsers = await db.all(`
      SELECT u.id, u.name, u.display_name, u.email, u.avatar_color, u.avatar_image
      FROM calendar_event_shares ces
      JOIN users u ON ces.user_id = u.id
      WHERE ces.event_id = ?
    `, [event.id]);

    res.json({ sharedUsers });
  } catch (err) {
    log.server.error(`Calendar unshare error: ${err.message}`);
    res.status(500).json({ error: 'Could not remove share' });
  }
});

// ── GET /api/calendar/events/:id/ics — Download event as ICS ────────────────
router.get('/events/:id/ics', authenticateToken, async (req, res) => {
  try {
    const db = getDb();
    const event = await db.get(`
      SELECT ce.*, COALESCE(NULLIF(u.display_name,''), u.name) as organizer_name, u.email as organizer_email
      FROM calendar_events ce
      JOIN users u ON ce.user_id = u.id
      WHERE ce.id = ?
    `, [req.params.id]);

    if (!event) return res.status(404).json({ error: 'Event not found' });

    // Check access
    if (event.user_id !== req.user.id) {
      const share = await db.get('SELECT id FROM calendar_event_shares WHERE event_id = ? AND user_id = ?', [event.id, req.user.id]);
      if (!share) return res.status(403).json({ error: 'No permission' });
    }

    // Build room join URL if linked
    const baseUrl = process.env.APP_URL || `${req.protocol}://${req.get('host')}`;
    let location = '';
    if (event.room_uid) {
      location = `${baseUrl}/join/${event.room_uid}`;
    }

    const ics = generateICS(event, location, baseUrl);

    res.setHeader('Content-Type', 'text/calendar; charset=utf-8');
    res.setHeader('Content-Disposition', `attachment; filename="${encodeURIComponent(event.title)}.ics"`);
    res.send(ics);
  } catch (err) {
    log.server.error(`ICS download error: ${err.message}`);
    res.status(500).json({ error: 'Could not generate ICS file' });
  }
});

// ── POST /api/calendar/events/:id/federation — Send event to remote user ────
router.post('/events/:id/federation', authenticateToken, async (req, res) => {
  try {
    if (!isFederationEnabled()) {
      return res.status(400).json({ error: 'Federation is not configured on this instance' });
    }

    const { to } = req.body;
    if (!to) return res.status(400).json({ error: 'Remote address is required' });

    const { username, domain } = parseAddress(to);
    if (!domain) return res.status(400).json({ error: 'Remote address must be in format username@domain' });
    if (domain === getFederationDomain()) {
      return res.status(400).json({ error: 'Cannot send to your own instance. Use local sharing instead.' });
    }

    const db = getDb();
    const event = await db.get('SELECT * FROM calendar_events WHERE id = ? AND user_id = ?', [req.params.id, req.user.id]);
    if (!event) return res.status(404).json({ error: 'Event not found or no permission' });

    const baseUrl = process.env.APP_URL || `${req.protocol}://${req.get('host')}`;
    let joinUrl = null;
    if (event.room_uid) {
      joinUrl = `${baseUrl}/join/${event.room_uid}`;
    }

    const payload = {
      type: 'calendar_event',
      event_uid: event.uid,
      title: event.title,
      description: event.description || '',
      start_time: event.start_time,
      end_time: event.end_time,
      room_uid: event.room_uid || null,
      join_url: joinUrl,
      from_user: `@${req.user.name}@${getFederationDomain()}`,
      to_user: to,
      timestamp: new Date().toISOString(),
    };

    const signature = signPayload(payload);
    const { baseUrl: remoteApi } = await discoverInstance(domain);

    const response = await fetch(`${remoteApi}/calendar-event`, {
      method: 'POST',
      headers: {
        'Content-Type': 'application/json',
        'X-Federation-Signature': signature,
        'X-Federation-Origin': getFederationDomain(),
      },
      body: JSON.stringify(payload),
      signal: AbortSignal.timeout(15_000),
    });

    if (!response.ok) {
      const data = await response.json().catch(() => ({}));
      throw new Error(data.error || `Remote server responded with ${response.status}`);
    }

    res.json({ success: true });
  } catch (err) {
    log.server.error(`Calendar federation send error: ${err.message}`);
    res.status(500).json({ error: err.message || 'Could not send event to remote instance' });
  }
});

// ── POST /receive-event or /calendar-event — Receive calendar event from remote ──
// '/receive-event' when mounted at /api/calendar
// '/calendar-event' when mounted at /api/federation (for remote instance discovery)
router.post(['/receive-event', '/calendar-event'], calendarFederationLimiter, async (req, res) => {
  try {
    if (!isFederationEnabled()) {
      return res.status(400).json({ error: 'Federation is not configured on this instance' });
    }

    const signature = req.headers['x-federation-signature'];
    const payload = req.body || {};

    if (!signature) return res.status(401).json({ error: 'Missing federation signature' });

    const { event_uid, title, description, start_time, end_time, room_uid, join_url, from_user, to_user } = payload;

    if (!event_uid || !title || !start_time || !end_time || !from_user || !to_user) {
      return res.status(400).json({ error: 'Incomplete event payload' });
    }

    // Validate lengths
    if (event_uid.length > 100 || title.length > 200 || (description && description.length > 5000) ||
        from_user.length > 200 || to_user.length > 200 || (join_url && join_url.length > 2000)) {
      return res.status(400).json({ error: 'Payload fields exceed maximum allowed length' });
    }

    // Verify signature
    const { domain: senderDomain } = parseAddress(from_user);
    if (!senderDomain) return res.status(400).json({ error: 'Sender address must include a domain' });

    const { publicKey } = await discoverInstance(senderDomain);
    if (!publicKey) return res.status(400).json({ error: 'Sender instance did not provide a public key' });
    if (!verifyPayload(payload, signature, publicKey)) {
      return res.status(403).json({ error: 'Invalid federation signature' });
    }

    // Find local user
    const { username } = parseAddress(to_user);
    const db = getDb();
    const targetUser = await db.get('SELECT id, name, email FROM users WHERE LOWER(name) = LOWER(?)', [username]);
    if (!targetUser) return res.status(404).json({ error: 'User not found on this instance' });

    // Check duplicate
    const existing = await db.get('SELECT id FROM calendar_events WHERE uid = ? AND user_id = ?', [event_uid, targetUser.id]);
    if (existing) return res.json({ success: true, message: 'Event already received' });

    // Create event for the target user
    await db.run(`
      INSERT INTO calendar_events (uid, title, description, start_time, end_time, room_uid, user_id, color, federated_from, federated_join_url)
      VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
    `, [
      event_uid,
      title,
      description || null,
      start_time,
      end_time,
      room_uid || null,
      targetUser.id,
      '#6366f1',
      from_user,
      join_url || null,
    ]);

    res.json({ success: true });
  } catch (err) {
    log.server.error(`Calendar federation receive error: ${err.message}`);
    res.status(500).json({ error: 'Failed to process calendar event' });
  }
});

// ── Helper: Generate ICS content ────────────────────────────────────────────
function generateICS(event, location, prodIdDomain) {
  const formatDate = (dateStr) => {
    const d = new Date(dateStr);
    return d.toISOString().replace(/[-:]/g, '').replace(/\.\d{3}/, '');
  };

  const escapeICS = (str) => {
    if (!str) return '';
    return str.replace(/\\/g, '\\\\').replace(/;/g, '\\;').replace(/,/g, '\\,').replace(/\n/g, '\\n');
  };

  const now = formatDate(new Date().toISOString());
  const dtStart = formatDate(event.start_time);
  const dtEnd = formatDate(event.end_time);

  let ics = [
    'BEGIN:VCALENDAR',
    'VERSION:2.0',
    `PRODID:-//${prodIdDomain}//Redlight Calendar//EN`,
    'CALSCALE:GREGORIAN',
    'METHOD:PUBLISH',
    'BEGIN:VEVENT',
    `UID:${event.uid}@${prodIdDomain}`,
    `DTSTAMP:${now}`,
    `DTSTART:${dtStart}`,
    `DTEND:${dtEnd}`,
    `SUMMARY:${escapeICS(event.title)}`,
  ];

  if (event.description) {
    ics.push(`DESCRIPTION:${escapeICS(event.description)}`);
  }
  if (location) {
    ics.push(`LOCATION:${escapeICS(location)}`);
    ics.push(`URL:${location}`);
  }
  if (event.organizer_name && event.organizer_email) {
    ics.push(`ORGANIZER;CN=${escapeICS(event.organizer_name)}:mailto:${event.organizer_email}`);
  }

  ics.push('END:VEVENT', 'END:VCALENDAR');
  return ics.join('\r\n');
}

export default router;