/**
 * Production Backend Server for India Driver Tracking
 * GitHub: socketio/socket.io (60k stars), expressjs/express (65k stars)
 */

const express = require('express');
const { createServer } = require('http');
const { Server } = require('socket.io');
const Redis = require('ioredis');
const cors = require('cors');
const helmet = require('helmet');
const compression = require('compression');
const rateLimit = require('express-rate-limit');

const app = express();
const httpServer = createServer(app);
const io = new Server(httpServer, {
  cors: {
    origin: "*", // Configure for your domain in production
    methods: ["GET", "POST"]
  },
  transports: ['websocket', 'polling'] // Fallback for Indian mobile networks
});

// Redis for real-time location storage (65k stars: redis/redis)
const redis = new Redis({
  host: process.env.REDIS_HOST || 'localhost',
  port: process.env.REDIS_PORT || 6379,
  retryDelayOnFailover: 100
});

// Security middleware
app.use(helmet());
app.use(compression());
app.use(cors());
app.use(express.json({ limit: '10mb' }));

// Rate limiting for India mobile networks
const limiter = rateLimit({
  windowMs: 1 * 60 * 1000, // 1 minute
  max: 100, // limit each IP to 100 requests per windowMs
  message: 'Too many requests from this IP'
});
app.use('/api/', limiter);

// Active drivers storage (in-memory + Redis)
const activeDrivers = new Map();

// Socket.IO connection handling
io.on('connection', (socket) => {
  console.log('Client connected:', socket.id);
  
  // Driver authentication middleware
  socket.on('driver:auth', async (data) => {
    const { driverId, vehicleId, authToken } = data;
    // Verify token here in production
    socket.driverId = driverId;
    socket.vehicleId = vehicleId;
    socket.isDriver = true;
    
    // Store socket mapping
    await redis.hset(`driver:${driverId}`, 'socketId', socket.id, 'status', 'online');
    socket.join(`driver:${driverId}`);
    socket.join('all-drivers');
    
    console.log(`Driver ${driverId} authenticated`);
    socket.emit('auth:success', { message: 'Connected to tracking server' });
  });

  // Admin dashboard authentication
  socket.on('admin:auth', (data) => {
    socket.isAdmin = true;
    socket.join('admins');
    // Send current active drivers list
    const driversList = Array.from(activeDrivers.values());
    socket.emit('drivers:list', driversList);
  });

  // Real-time GPS update from driver app
  socket.on('location:update', async (data) => {
    if (!socket.isDriver) return;
    
    const { lat, lng, accuracy, speed, heading, timestamp } = data;
    const driverId = socket.driverId;
    
    // Validate coordinates (India boundaries roughly)
    if (lat < 6 || lat > 37 || lng < 68 || lng > 97) {
      return socket.emit('error', { message: 'Invalid coordinates for India' });
    }

    const locationData = {
      driverId,
      vehicleId: socket.vehicleId,
      lat,
      lng,
      accuracy: accuracy || 0,
      speed: speed || 0,
      heading: heading || 0,
      timestamp: timestamp || Date.now(),
      lastUpdate: Date.now()
    };

    // Update Redis (expires in 5 minutes if no update)
    await redis.setex(`loc:${driverId}`, 300, JSON.stringify(locationData));
    await redis.geoadd('drivers:geo', lng, lat, driverId);
    
    // Update memory
    activeDrivers.set(driverId, locationData);
    
    // Broadcast to admins with throttling (every 2 seconds per driver)
    socket.to('admins').emit('driver:moved', locationData);
  });

  // Handle driver status changes
  socket.on('status:update', async (data) => {
    if (!socket.isDriver) return;
    const { status } = data; // 'available', 'busy', 'offline'
    
    await redis.hset(`driver:${socket.driverId}`, 'status', status);
    io.to('admins').emit('driver:status', {
      driverId: socket.driverId,
      status,
      timestamp: Date.now()
    });
  });

  // Admin requesting specific driver history
  socket.on('admin:track-driver', async (driverId) => {
    if (!socket.isAdmin) return;
    socket.join(`track:${driverId}`);
    
    const lastLoc = await redis.get(`loc:${driverId}`);
    if (lastLoc) {
      socket.emit('driver:location', JSON.parse(lastLoc));
    }
  });

  // Handle disconnect
  socket.on('disconnect', async () => {
    if (socket.isDriver && socket.driverId) {
      await redis.hset(`driver:${socket.driverId}`, 'status', 'offline');
      await redis.expire(`driver:${socket.driverId}`, 3600); // Keep for 1 hour
      activeDrivers.delete(socket.driverId);
      io.to('admins').emit('driver:offline', { driverId: socket.driverId });
    }
    console.log('Client disconnected:', socket.id);
  });
});

// REST API endpoints for historical data
app.get('/api/drivers/active', async (req, res) => {
  try {
    const drivers = [];
    const keys = await redis.keys('loc:*');
    
    for (const key of keys) {
      const data = await redis.get(key);
      if (data) drivers.push(JSON.parse(data));
    }
    
    res.json({ count: drivers.length, drivers });
  } catch (err) {
    res.status(500).json({ error: err.message });
  }
});

// Get drivers in specific radius (for India city operations)
app.get('/api/drivers/nearby', async (req, res) => {
  const { lat, lng, radius = 10 } = req.query; // radius in km
  
  try {
    const nearby = await redis.georadius(
      'drivers:geo', 
      parseFloat(lng), 
      parseFloat(lat), 
      parseFloat(radius), 
      'km',
      'WITHCOORD',
      'WITHDIST'
    );
    res.json({ nearby });
  } catch (err) {
    res.status(500).json({ error: err.message });
  }
});

// Health check
app.get('/health', (req, res) => {
  res.json({ 
    status: 'ok', 
    uptime: process.uptime(),
    timestamp: new Date().toISOString(),
    region: 'India'
  });
});

const PORT = process.env.PORT || 3000;
httpServer.listen(PORT, () => {
  console.log(`🚀 Production Tracking Server running on port ${PORT}`);
  console.log(`📍 Optimized for India GPS tracking`);
});