ajinkya-mhetre-mern/backend/src/app.js

A MERN starter with frontend and backend folders

// ===== src/app.js =====
const express = require('express');
const cors = require('cors');
const helmet = require('helmet');
const rateLimit = require('express-rate-limit');
const path = require('path');

// Import routes
const authRoutes = require('./routes/auth');
const adminRoutes = require('./routes/admin');
const farmerRoutes = require('./routes/farmer');
const customerRoutes = require('./routes/customer');

const app = express();

// Security middleware
app.use(helmet());
app.use(cors({
  origin: process.env.CLIENT_URL || "http://localhost:3000",
  credentials: true
}));

// Rate limiting
const limiter = rateLimit({
  windowMs: 5 * 60 * 1000, // 5 minutes
  max: 10000 // limit each IP to 10000 requests per windowMs
});
app.use('/api/', limiter);

// Body parsing middleware
app.use(express.json({ limit: '10mb' }));
app.use(express.urlencoded({ extended: true, limit: '10mb' }));

// Static files
app.use('/uploads', express.static(path.join(__dirname, '../uploads')));

// API routes
app.use('/api/auth', authRoutes);
app.use('/api/admin', adminRoutes);
app.use('/api/farmer', farmerRoutes);
app.use('/api/customer', customerRoutes);

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

// 404 handler
app.use('*', (req, res) => {
  res.status(404).json({
    message: 'Route not found'
  });
});

// Global error handler
app.use((error, req, res, next) => {
  console.error('Error:', error);
  
  if (error.name === 'ValidationError') {
    const errors = Object.values(error.errors).map(err => err.message);
    return res.status(400).json({
      message: 'Validation Error',
      errors
    });
  }
  
  if (error.code === 11000) {
    const field = Object.keys(error.keyValue)[0];
    return res.status(400).json({
      message: `${field} already exists`
    });
  }
  
  res.status(500).json({
    message: process.env.NODE_ENV === 'production' 
      ? 'Internal server error' 
      : error.message
  });
});

module.exports = app;