app.ts

/**
 * Express.js Backend for MongoDB Sample MFlix Application
 * 
 * This application demonstrates MongoDB operations using the Node.js driver
 * with TypeScript. The code prioritizes readability and educational value
 * over performance optimization.
 */

import express from 'express';
import cors from 'cors';
import dotenv from 'dotenv';
import { connectToDatabase, verifyRequirements } from './config/database';
import { errorHandler } from './utils/errorHandler';
import moviesRouter from './routes/movies';

// Load environment variables from .env file
// This must be called before any other imports that use environment variables
dotenv.config();

const app = express();
const PORT = process.env.PORT || 3001;

/**
 * CORS Configuration
 * Allows the frontend to communicate with this Express backend
 * In production, this should be configured to only allow specific origins
 */
app.use(cors({
  origin: process.env.CORS_ORIGIN || 'http://localhost:3000',
  credentials: true
}));

/**
 * Middleware Configuration
 * Express.json() parses incoming JSON requests and puts the parsed data in req.body
 * The limit is set to handle potentially large movie documents
 */
app.use(express.json({ limit: '10mb' }));
app.use(express.urlencoded({ extended: true, limit: '10mb' }));

/**
 * API Routes
 * All movie-related CRUD operations are handled by the movies router
 */
app.use('/api/movies', moviesRouter);

/**
 * Root Endpoint
 * Provides basic information about the API
 */
app.get('/', (req, res) => {
  res.json({
    name: 'MongoDB Sample MFlix API',
    version: '1.0.0',
    description: 'Express.js backend demonstrating MongoDB operations with the sample_mflix dataset',
    endpoints: {
      movies: '/api/movies'
    }
  });
});

/**
 * Global Error Handler
 * This middleware catches any unhandled errors and returns a consistent error response
 * It should be the last middleware in the chain
 */
app.use(errorHandler);

/**
 * Application Startup Function
 * Handles database connection, requirement verification, and server startup
 */
async function startServer() {
  try {
    console.log('Starting MongoDB Sample MFlix API...');
    
    // Connect to MongoDB database
    console.log('Connecting to MongoDB...');
    await connectToDatabase();
    console.log('Connected to MongoDB successfully');
    
    // Verify that all required indexes and sample data exist
    console.log('Verifying requirements (indexes and sample data)...');
    await verifyRequirements();
    console.log('All requirements verified successfully');
    
    // Start the Express server
    app.listen(PORT, () => {
      console.log(`Server running on port ${PORT}`);
      console.log(`API documentation available at http://localhost:${PORT}`);
    });
    
  } catch (error) {
    console.error('Failed to start server:', error);
    
    // Exit the process if we can't start properly
    // This ensures the application doesn't run in a broken state
    process.exit(1);
  }
}

/**
 * Graceful Shutdown Handler
 * Ensures the application shuts down cleanly when terminated
 */
process.on('SIGINT', () => {
  console.log('\nReceived SIGINT. Shutting down...');
  process.exit(0);
});

process.on('SIGTERM', () => {
  console.log('\nReceived SIGTERM. Shutting down...');
  process.exit(0);
});

// Start the server
startServer();