backend/src/middleware/errorHandler.js

import { ZodError } from 'zod';
import logger from '../utils/logger.js';

/**
 * Centralized error handling middleware
 * Must be registered LAST in the Express middleware chain
 */
export const errorHandler = (err, req, res, _next) => {
  // Log the error
  logger.error('Unhandled error', {
    message: err.message,
    stack: process.env.NODE_ENV === 'development' ? err.stack : undefined,
    method: req.method,
    url: req.url,
    ip: req.ip,
  });

  // Handle Zod validation errors
  if (err instanceof ZodError) {
    return res.status(400).json({
      success: false,
      error: 'Validation failed',
      details: err.errors.map((e) => ({
        field: e.path.join('.'),
        message: e.message,
      })),
    });
  }

  // Prisma known errors
  if (err.code === 'P2002') {
    return res.status(409).json({
      success: false,
      error: 'A record with this information already exists.',
      field: err.meta?.target?.[0],
    });
  }

  if (err.code === 'P2025') {
    return res.status(404).json({
      success: false,
      error: 'Record not found.',
    });
  }

  if (err.code === 'P2003') {
    return res.status(400).json({
      success: false,
      error: 'Invalid reference. The related record does not exist.',
    });
  }

  // Generic HTTP errors
  const statusCode = err.statusCode || err.status || 500;
  const message =
    statusCode < 500 || process.env.NODE_ENV === 'development'
      ? err.message
      : 'An internal server error occurred. Please try again later.';

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

/**
 * 404 Not Found handler
 */
export const notFoundHandler = (req, res) => {
  res.status(404).json({
    success: false,
    error: `Route not found: ${req.method} ${req.path}`,
  });
};

/**
 * Create a custom HTTP error
 */
export class AppError extends Error {
  constructor(message, statusCode = 500) {
    super(message);
    this.statusCode = statusCode;
    this.name = 'AppError';
    Error.captureStackTrace(this, this.constructor);
  }
}