index.js

const express = require('express');
const cors = require('cors');
const morgan = require('morgan');

const app = express();
const PORT = process.env.PORT || 3000;

// Middleware
app.use(cors());
app.use(morgan('combined'));
app.use(express.json());
app.use(express.urlencoded({ extended: true }));

// In-memory data store for demo purposes
let users = [
  { id: 1, name: 'John Doe', email: 'john@example.com', age: 30 },
  { id: 2, name: 'Jane Smith', email: 'jane@example.com', age: 25 },
  { id: 3, name: 'Bob Johnson', email: 'bob@example.com', age: 35 }
];

let posts = [
  { id: 1, title: 'First Post', content: 'This is the first post', userId: 1, createdAt: new Date() },
  { id: 2, title: 'Second Post', content: 'This is the second post', userId: 2, createdAt: new Date() }
];

let nextUserId = 4;
let nextPostId = 3;

// Helper function to find user by ID
const findUserById = (id) => users.find(user => user.id === parseInt(id));

// Helper function to find post by ID
const findPostById = (id) => posts.find(post => post.id === parseInt(id));

// Routes

// Root endpoint - API documentation
app.get('/', (req, res) => {
  res.json({
    name: 'Simple Express.js API',
    version: '1.0.0',
    description: 'A simple REST API built with Express.js',
    endpoints: {
      'GET /': 'API documentation',
      'GET /health': 'Health check',
      'GET /users': 'Get all users',
      'GET /users/:id': 'Get user by ID',
      'POST /users': 'Create new user',
      'PUT /users/:id': 'Update user by ID',
      'DELETE /users/:id': 'Delete user by ID',
      'GET /posts': 'Get all posts',
      'GET /posts/:id': 'Get post by ID',
      'POST /posts': 'Create new post',
      'PUT /posts/:id': 'Update post by ID',
      'DELETE /posts/:id': 'Delete post by ID',
      'GET /users/:id/posts': 'Get posts by user ID',
      'GET /stats': 'Get API statistics'
    },
    timestamp: new Date().toISOString()
  });
});

// Health check endpoint
app.get('/health', (req, res) => {
  res.json({
    status: 'healthy',
    timestamp: new Date().toISOString(),
    uptime: process.uptime(),
    environment: process.env.NODE_ENV || 'development'
  });
});

// Error handling middleware
app.use((error, req, res, next) => {
  console.error('Error:', error);
  
  res.status(500).json({
    error: 'Internal Server Error',
    message: 'Something went wrong on the server',
    timestamp: new Date().toISOString()
  });
});

// Start server
app.listen(PORT, () => {
  console.log(`🚀 Server running on port ${PORT}`);
  console.log(`📖 API Documentation: http://localhost:${PORT}/`);
  console.log(`❤️  Health Check: http://localhost:${PORT}/health`);
});

module.exports = app;