const express = require('express');
const http = require('http');
const socketIo = require('socket.io');
const cors = require('cors');
const path = require('path');

const app = express();
const server = http.createServer(app);
const io = socketIo(server, {
    cors: {
        origin: "*",
        methods: ["GET", "POST"],
        allowedHeaders: ["Content-Type"],
        credentials: true
    },
    transports: ['websocket', 'polling']
});

// Middleware
app.use(cors());
app.use(express.json());
app.use(express.static(path.join(__dirname, 'public')));

// Store active users and rooms
const users = new Map(); // socketId -> user info
const rooms = new Map(); // roomId -> Set of socketIds
const userRooms = new Map(); // socketId -> roomId

// Default room for all users
const DEFAULT_ROOM = 'main-chat';

// Utility functions
function getUserInfo(socketId) {
    return users.get(socketId);
}

function addUserToRoom(socketId, roomId = DEFAULT_ROOM) {
    if (!rooms.has(roomId)) {
        rooms.set(roomId, new Set());
    }
    rooms.get(roomId).add(socketId);
    userRooms.set(socketId, roomId);
}

function removeUserFromRoom(socketId) {
    const roomId = userRooms.get(socketId);
    if (roomId && rooms.has(roomId)) {
        rooms.get(roomId).delete(socketId);
        if (rooms.get(roomId).size === 0) {
            rooms.delete(roomId);
        }
    }
    userRooms.delete(socketId);
}

function getRoomUsers(roomId) {
    const roomUsers = [];
    if (rooms.has(roomId)) {
        for (const socketId of rooms.get(roomId)) {
            const user = users.get(socketId);
            if (user) {
                roomUsers.push({
                    socketId,
                    nickname: user.nickname,
                    joinedAt: user.joinedAt
                });
            }
        }
    }
    return roomUsers;
}

function broadcastToRoom(roomId, event, data, exceptSocketId = null) {
    if (rooms.has(roomId)) {
        for (const socketId of rooms.get(roomId)) {
            if (socketId !== exceptSocketId) {
                io.to(socketId).emit(event, data);
            }
        }
    }
}

// Socket.IO connection handling
io.on('connection', (socket) => {
    console.log(`[${new Date().toISOString()}] User connected: ${socket.id}`);

    // Handle user joining
    socket.on('join-room', (data) => {
        try {
            const { nickname, roomId = DEFAULT_ROOM } = typeof data === 'string' 
                ? { nickname: data, roomId: DEFAULT_ROOM }
                : data;

            if (!nickname || nickname.trim().length === 0) {
                socket.emit('error', { message: 'Nickname is required' });
                return;
            }

            // Check if nickname is already taken in the room
            const roomUsers = getRoomUsers(roomId);
            const nicknameExists = roomUsers.some(user => 
                user.nickname.toLowerCase() === nickname.toLowerCase()
            );

            if (nicknameExists) {
                socket.emit('error', { 
                    message: 'Nickname already taken in this room',
                    code: 'NICKNAME_TAKEN'
                });
                return;
            }

            // Store user information
            const userInfo = {
                nickname: nickname.trim(),
                roomId,
                joinedAt: new Date().toISOString(),
                isVideoEnabled: true,
                isAudioEnabled: true
            };
            
            users.set(socket.id, userInfo);
            addUserToRoom(socket.id, roomId);

            // Join socket room
            socket.join(roomId);

            // Notify user they successfully joined
            socket.emit('joined-room', {
                roomId,
                nickname: userInfo.nickname,
                users: getRoomUsers(roomId)
            });

            // Notify others in the room
            broadcastToRoom(roomId, 'user-joined', {
                socketId: socket.id,
                nickname: userInfo.nickname,
                joinedAt: userInfo.joinedAt
            }, socket.id);

            console.log(`[${new Date().toISOString()}] ${userInfo.nickname} joined room: ${roomId}`);

        } catch (error) {
            console.error('Error in join-room:', error);
            socket.emit('error', { message: 'Failed to join room' });
        }
    });

    // Handle WebRTC signaling - Offer
    socket.on('offer', (data) => {
        try {
            const user = getUserInfo(socket.id);
            if (!user) {
                socket.emit('error', { message: 'Not authenticated' });
                return;
            }

            const { targetSocketId, offer } = data;
            
            if (targetSocketId) {
                // Send to specific user
                io.to(targetSocketId).emit('offer', {
                    fromSocketId: socket.id,
                    fromNickname: user.nickname,
                    offer
                });
            } else {
                // Broadcast to room (for group calls)
                broadcastToRoom(user.roomId, 'offer', {
                    fromSocketId: socket.id,
                    fromNickname: user.nickname,
                    offer
                }, socket.id);
            }

            console.log(`[${new Date().toISOString()}] Offer from ${user.nickname} to ${targetSocketId || 'room'}`);

        } catch (error) {
            console.error('Error in offer:', error);
            socket.emit('error', { message: 'Failed to send offer' });
        }
    });

    // Handle WebRTC signaling - Answer
    socket.on('answer', (data) => {
        try {
            const user = getUserInfo(socket.id);
            if (!user) {
                socket.emit('error', { message: 'Not authenticated' });
                return;
            }

            const { targetSocketId, answer } = data;
            
            if (targetSocketId) {
                io.to(targetSocketId).emit('answer', {
                    fromSocketId: socket.id,
                    fromNickname: user.nickname,
                    answer
                });
            }

            console.log(`[${new Date().toISOString()}] Answer from ${user.nickname} to ${targetSocketId}`);

        } catch (error) {
            console.error('Error in answer:', error);
            socket.emit('error', { message: 'Failed to send answer' });
        }
    });

    // Handle WebRTC signaling - ICE Candidate
    socket.on('ice-candidate', (data) => {
        try {
            const user = getUserInfo(socket.id);
            if (!user) {
                socket.emit('error', { message: 'Not authenticated' });
                return;
            }

            const { targetSocketId, candidate } = data;
            
            if (targetSocketId) {
                io.to(targetSocketId).emit('ice-candidate', {
                    fromSocketId: socket.id,
                    fromNickname: user.nickname,
                    candidate
                });
            } else {
                // Broadcast to room
                broadcastToRoom(user.roomId, 'ice-candidate', {
                    fromSocketId: socket.id,
                    fromNickname: user.nickname,
                    candidate
                }, socket.id);
            }

        } catch (error) {
            console.error('Error in ice-candidate:', error);
            socket.emit('error', { message: 'Failed to send ICE candidate' });
        }
    });

    // Handle media state changes
    socket.on('media-state', (data) => {
        try {
            const user = getUserInfo(socket.id);
            if (!user) {
                socket.emit('error', { message: 'Not authenticated' });
                return;
            }

            const { isVideoEnabled, isAudioEnabled } = data;
            
            // Update user state
            user.isVideoEnabled = isVideoEnabled;
            user.isAudioEnabled = isAudioEnabled;

            // Broadcast to room
            broadcastToRoom(user.roomId, 'user-media-state', {
                socketId: socket.id,
                nickname: user.nickname,
                isVideoEnabled,
                isAudioEnabled
            }, socket.id);

            console.log(`[${new Date().toISOString()}] ${user.nickname} media state - Video: ${isVideoEnabled}, Audio: ${isAudioEnabled}`);

        } catch (error) {
            console.error('Error in media-state:', error);
        }
    });

    // Handle chat messages (backup for data channel failures)
    socket.on('chat-message', (data) => {
        try {
            const user = getUserInfo(socket.id);
            if (!user) {
                socket.emit('error', { message: 'Not authenticated' });
                return;
            }

            const { message } = data;
            if (!message || message.trim().length === 0) {
                return;
            }

            const messageData = {
                fromSocketId: socket.id,
                fromNickname: user.nickname,
                message: message.trim(),
                timestamp: new Date().toISOString()
            };

            // Broadcast to room
            broadcastToRoom(user.roomId, 'chat-message', messageData, socket.id);

            console.log(`[${new Date().toISOString()}] Message from ${user.nickname}: ${message}`);

        } catch (error) {
            console.error('Error in chat-message:', error);
        }
    });

    // Handle room list request
    socket.on('get-rooms', () => {
        try {
            const roomList = [];
            for (const [roomId, userSet] of rooms.entries()) {
                roomList.push({
                    roomId,
                    userCount: userSet.size,
                    users: getRoomUsers(roomId).map(u => ({
                        nickname: u.nickname,
                        joinedAt: u.joinedAt
                    }))
                });
            }
            socket.emit('rooms-list', roomList);
        } catch (error) {
            console.error('Error getting rooms:', error);
            socket.emit('error', { message: 'Failed to get rooms' });
        }
    });

    // Handle user list request for current room
    socket.on('get-room-users', () => {
        try {
            const user = getUserInfo(socket.id);
            if (user) {
                const roomUsers = getRoomUsers(user.roomId);
                socket.emit('room-users', {
                    roomId: user.roomId,
                    users: roomUsers
                });
            }
        } catch (error) {
            console.error('Error getting room users:', error);
        }
    });

    // Handle ping for connection monitoring
    socket.on('ping', () => {
        socket.emit('pong', { timestamp: Date.now() });
    });

    // Handle disconnection
    socket.on('disconnect', (reason) => {
        try {
            const user = getUserInfo(socket.id);
            if (user) {
                // Notify others in the room
                broadcastToRoom(user.roomId, 'user-left', {
                    socketId: socket.id,
                    nickname: user.nickname,
                    reason
                });

                console.log(`[${new Date().toISOString()}] ${user.nickname} left room: ${user.roomId} (${reason})`);
                
                // Clean up
                removeUserFromRoom(socket.id);
                users.delete(socket.id);
            } else {
                console.log(`[${new Date().toISOString()}] Unknown user disconnected: ${socket.id} (${reason})`);
            }
        } catch (error) {
            console.error('Error handling disconnect:', error);
        }
    });

    // Handle errors
    socket.on('error', (error) => {
        console.error(`[${new Date().toISOString()}] Socket error for ${socket.id}:`, error);
    });
});

// REST API endpoints
app.get('/api/status', (req, res) => {
    res.json({
        status: 'running',
        timestamp: new Date().toISOString(),
        connectedUsers: users.size,
        activeRooms: rooms.size,
        uptime: process.uptime()
    });
});

app.get('/api/rooms', (req, res) => {
    const roomList = [];
    for (const [roomId, userSet] of rooms.entries()) {
        roomList.push({
            roomId,
            userCount: userSet.size,
            users: getRoomUsers(roomId).map(u => ({
                nickname: u.nickname,
                joinedAt: u.joinedAt
            }))
        });
    }
    res.json(roomList);
});

app.get('/api/rooms/:roomId', (req, res) => {
    const { roomId } = req.params;
    if (rooms.has(roomId)) {
        res.json({
            roomId,
            userCount: rooms.get(roomId).size,
            users: getRoomUsers(roomId)
        });
    } else {
        res.status(404).json({ error: 'Room not found' });
    }
});

// Health check endpoint
app.get('/health', (req, res) => {
    res.status(200).json({ 
        status: 'healthy',
        timestamp: new Date().toISOString()
    });
});

// Serve a simple test page
app.get('/', (req, res) => {
    res.send(`
        <!DOCTYPE html>
        <html>
        <head>
            <title>ChatRTC Signaling Server</title>
            <meta charset="utf-8">
            <meta name="viewport" content="width=device-width, initial-scale=1">
            <style>
                body { font-family: Arial, sans-serif; margin: 40px; background: #f5f5f5; }
                .container { max-width: 800px; margin: 0 auto; background: white; padding: 30px; border-radius: 10px; box-shadow: 0 2px 10px rgba(0,0,0,0.1); }
                h1 { color: #2196F3; }
                .status { background: #e8f5e8; padding: 15px; border-radius: 5px; margin: 20px 0; }
                .endpoint { background: #f8f9fa; padding: 10px; margin: 10px 0; border-left: 4px solid #2196F3; }
                code { background: #f0f0f0; padding: 2px 5px; border-radius: 3px; }
            </style>
        </head>
        <body>
            <div class="container">
                <h1>🚀 ChatRTC Signaling Server</h1>
                <div class="status">
                    <strong>✅ Server is running successfully!</strong><br>
                    Connected Users: <span id="users">${users.size}</span><br>
                    Active Rooms: <span id="rooms">${rooms.size}</span><br>
                    Uptime: <span id="uptime">${Math.floor(process.uptime())}s</span>
                </div>
                
                <h2>📡 API Endpoints</h2>
                <div class="endpoint">
                    <strong>GET /api/status</strong> - Server status and statistics
                </div>
                <div class="endpoint">
                    <strong>GET /api/rooms</strong> - List all active rooms
                </div>
                <div class="endpoint">
                    <strong>GET /api/rooms/:roomId</strong> - Get specific room info
                </div>
                <div class="endpoint">
                    <strong>GET /health</strong> - Health check endpoint
                </div>
                
                <h2>🔧 Socket.IO Events</h2>
                <p>The server handles the following Socket.IO events for WebRTC signaling:</p>
                <ul>
                    <li><code>join-room</code> - Join a chat room</li>
                    <li><code>offer</code> - WebRTC offer signaling</li>
                    <li><code>answer</code> - WebRTC answer signaling</li>
                    <li><code>ice-candidate</code> - ICE candidate exchange</li>
                    <li><code>media-state</code> - Video/audio state updates</li>
                    <li><code>chat-message</code> - Text message fallback</li>
                </ul>
                
                <h2>📱 Android App Connection</h2>
                <p>Update your Android app's WebRTCManager.java with this server URL:</p>
                <div class="endpoint">
                    <code>private static final String SIGNALING_SERVER_URL = "http://YOUR_SERVER_IP:${process.env.PORT || 3000}";</code>
                </div>
                
                <p><em>Server started at: ${new Date().toISOString()}</em></p>
            </div>
            
            <script>
                // Auto-refresh stats every 5 seconds
                setInterval(async () => {
                    try {
                        const response = await fetch('/api/status');
                        const data = await response.json();
                        document.getElementById('users').textContent = data.connectedUsers;
                        document.getElementById('rooms').textContent = data.activeRooms;
                        document.getElementById('uptime').textContent = Math.floor(data.uptime) + 's';
                    } catch (error) {
                        console.error('Failed to update stats:', error);
                    }
                }, 5000);
            </script>
        </body>
        </html>
    `);
});

// Error handling
app.use((err, req, res, next) => {
    console.error('Express error:', err);
    res.status(500).json({ error: 'Internal server error' });
});

// Graceful shutdown
process.on('SIGTERM', () => {
    console.log('SIGTERM received, shutting down gracefully');
    server.close(() => {
        console.log('Server closed');
        process.exit(0);
    });
});

process.on('SIGINT', () => {
    console.log('SIGINT received, shutting down gracefully');
    server.close(() => {
        console.log('Server closed');
        process.exit(0);
    });
});

// Start server
const PORT = process.env.PORT || 3000;
const HOST = process.env.HOST || '0.0.0.0';

server.listen(PORT, HOST, () => {
    console.log('🚀 ChatRTC Signaling Server Started');
    console.log(`📡 Server running on http://${HOST}:${PORT}`);
    console.log(`🌐 Socket.IO enabled with CORS`);
    console.log(`📱 Ready for Android app connections`);
    console.log(`⏰ Started at: ${new Date().toISOString()}`);
});

module.exports = { app, server, io };