// API Gateway example for microservices
const express = require('express');
const { createProxyMiddleware } = require('http-proxy-middleware');
const rateLimit = require('express-rate-limit');
const helmet = require('helmet');
const cors = require('cors');

const app = express();
const PORT = 8080;

// Add security headers
app.use(helmet());

// Enable CORS
app.use(cors());

// Basic request logging middleware
app.use((req, res, next) => {
  console.log(`[${new Date().toISOString()}] ${req.method} ${req.url}`);
  const start = Date.now();
  res.on('finish', () => {
    const duration = Date.now() - start;
    console.log(`[${new Date().toISOString()}] ${req.method} ${req.url} ${res.statusCode} - ${duration}ms`);
  });
  next();
});

// Apply rate limiting
const apiLimiter = rateLimit({
  windowMs: 15 * 60 * 1000, // 15 minutes
  max: 100, // limit each IP to 100 requests per windowMs
  message: 'Too many requests from this IP, please try again later'
});
app.use('/api/', apiLimiter);

// Authentication middleware
function authenticate(req, res, next) {
  const authHeader = req.headers.authorization;
  
  if (!authHeader || !authHeader.startsWith('Bearer ')) {
    return res.status(401).json({ error: 'Unauthorized: Missing or invalid token' });
  }
  
  const token = authHeader.split(' ')[1];
  
  // In a real app, verify the token (e.g., with JWT)
  if (token === 'valid-token') {
    // Add user info to request for downstream services
    req.user = { id: 123, role: 'user' };
    next();
  } else {
    res.status(401).json({ error: 'Unauthorized: Invalid token' });
  }
}

// Service discovery (hardcoded for simplicity)
const serviceRegistry = {
  userService: 'http://localhost:3001',
  productService: 'http://localhost:3002',
  orderService: 'http://localhost:3003'
};

// Proxy configurations
const userServiceProxy = createProxyMiddleware({
  target: serviceRegistry.userService,
  changeOrigin: true,
  pathRewrite: { '^/api/users': '/users' }
});

const productServiceProxy = createProxyMiddleware({
  target: serviceRegistry.productService,
  changeOrigin: true,
  pathRewrite: { '^/api/products': '/products' }
});

const orderServiceProxy = createProxyMiddleware({
  target: serviceRegistry.orderService,
  changeOrigin: true,
  pathRewrite: { '^/api/orders': '/orders' }
});

// Route requests to appropriate services
app.use('/api/users', authenticate, userServiceProxy);
app.use('/api/products', productServiceProxy);
app.use('/api/orders', authenticate, orderServiceProxy);

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

// Error handling
app.use((err, req, res, next) => {
  console.error(`[ERROR] ${err.stack}`);
  res.status(500).json({ error: 'Internal Server Error' });
});

// Start the server
app.listen(PORT, () => {
  console.log(`API Gateway running on port ${PORT}`);
});