server/src/middleware/errorHandler.ts

import { Request, Response, NextFunction } from 'express';
import { logger } from '../utils/logger';

export const errorHandler = (
    err: Error,
    _req: Request,
    res: Response,
    _next: NextFunction
): void => {
    logger.error(err.message, { stack: err.stack });

    if (err.name === 'ValidationError') {
        res.status(400).json({ error: err.message });
        return;
    }

    if (err.name === 'CastError') {
        res.status(400).json({ error: 'Invalid ID format.' });
        return;
    }

    if ((err as any).code === 11000) {
        res.status(409).json({ error: 'Duplicate entry. Resource already exists.' });
        return;
    }

    res.status(500).json({ error: 'Internal server error.' });
};