market-data-service/middleware/errorHandler.js

const { logger } = require('../utils/logger');

// Custom Error class
class AppError extends Error {
  constructor(message, statusCode, isOperational = true) {
    super(message);
    this.statusCode = statusCode;
    this.isOperational = isOperational;
    this.status = `${statusCode}`.startsWith('4') ? 'fail' : 'error';

    Error.captureStackTrace(this, this.constructor);
  }
}

// Global error handler middleware
const errorHandler = (err, req, res, next) => {
  let error = { ...err };
  error.message = err.message;

  // Log error
  logger.error('Error occurred:', {
    message: err.message,
    stack: err.stack,
    url: req.originalUrl,
    method: req.method,
    ip: req.ip,
    userAgent: req.get('User-Agent')
  });

  // Mongoose bad ObjectId
  if (err.name === 'CastError') {
    const message = 'Resource not found';
    error = new AppError(message, 404);
  }

  // Mongoose duplicate key
  if (err.code === 11000) {
    const message = 'Duplicate field value entered';
    error = new AppError(message, 400);
  }

  // Mongoose validation error
  if (err.name === 'ValidationError') {
    const message = Object.values(err.errors).map(val => val.message).join(', ');
    error = new AppError(message, 400);
  }

  // JWT errors
  if (err.name === 'JsonWebTokenError') {
    const message = 'Invalid token';
    error = new AppError(message, 401);
  }

  if (err.name === 'TokenExpiredError') {
    const message = 'Token expired';
    error = new AppError(message, 401);
  }

  // Database connection errors
  if (err.code === 'ECONNREFUSED' || err.code === 'ENOTFOUND') {
    const message = 'Database connection failed';
    error = new AppError(message, 503);
  }

  // Send error response
  const statusCode = error.statusCode || 500;
  const status = error.status || 'error';
  const message = error.message || 'Something went wrong';

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

// 404 handler
const notFound = (req, res, next) => {
  const error = new AppError(`Not found - ${req.originalUrl}`, 404);
  next(error);
};

// Async error wrapper
const catchAsync = (fn) => {
  return (req, res, next) => {
    fn(req, res, next).catch(next);
  };
};

// Development error sender (for debugging)
const sendErrorDev = (err, res) => {
  res.status(err.statusCode || 500).json({
    status: err.status,
    error: err,
    message: err.message,
    stack: err.stack
  });
};

// Production error sender (security-conscious)
const sendErrorProd = (err, res) => {
  // Operational, trusted error: send message to client
  if (err.isOperational) {
    res.status(err.statusCode).json({
      status: err.status,
      message: err.message
    });
  } else {
    // Programming or other unknown error: don't leak error details
    logger.error('ERROR 💥', err);

    res.status(500).json({
      status: 'error',
      message: 'Something went wrong!'
    });
  }
};

module.exports = {
  AppError,
  errorHandler,
  notFound,
  catchAsync,
  sendErrorDev,
  sendErrorProd
};