src/exception/globalExceptionHandler.js

import { AppError } from './errors.js';

// Lets controllers be plain async functions: a thrown error or rejected promise reaches errorHandler
export const asyncHandler = (fn) => (req, res, next) => Promise.resolve(fn(req, res, next)).catch(next);

// Registered last in index.js
export function errorHandler(err, req, res, next) {
    if (res.headersSent) return next(err);

    if (err instanceof AppError) {
        return res.status(err.status).json({ error: err.code, message: err.message });
    }

    // express.json() payload problems (too large, malformed JSON) carry their own 4xx status
    if (err.status >= 400 && err.status < 500) {
        return res.status(err.status).json({ error: 'BAD_REQUEST', message: err.message });
    }

    console.error('[Unhandled Error]', err);
    res.status(500).json({ error: 'INTERNAL_ERROR', message: 'Something went wrong on the server.' });
}