src/middleware/errorHandler.js

// Centralized error handling middleware
const errorHandler = (err, req, res, next) => {
  console.error('Error occurred:', err);

  // Default error
  let statusCode = err.statusCode || 500;
  let message = err.message || 'Internal Server Error';

  // Handle specific error types
  if (err.code === 'ER_DUP_ENTRY') {
    statusCode = 409;
    message = 'Duplicate entry: This record already exists';
  }

  if (err.code === 'ER_NO_REFERENCED_ROW_2') {
    statusCode = 400;
    message = 'Invalid reference: Related record does not exist';
  }

  if (err.code === 'ECONNREFUSED') {
    statusCode = 503;
    message = 'Database connection failed';
  }

  res.status(statusCode).json({
    success: false,
    error: message,
    ...(process.env.NODE_ENV === 'development' && { stack: err.stack })
  });
};

module.exports = errorHandler;