function expressErrorHandler(err, req, res, next) {
  if (res.headersSent) return next(err);

  const requestedStatus = Number(err?.statusCode || err?.status);
  const status = Number.isInteger(requestedStatus) && requestedStatus >= 400 && requestedStatus <= 599
    ? requestedStatus
    : 500;

  console.error(`[未处理错误] ${req.method} ${req.originalUrl}`, {
    message: err?.message,
    stack: err?.stack
  });

  return res.status(status).json({
    success: false,
    message: status >= 500 ? '服务器内部错误' : (err?.message || '请求处理失败')
  });
}

module.exports = { expressErrorHandler };