import { Request, Response, NextFunction, RequestHandler } from 'express';

// Express 4 does not forward a rejected promise from an async handler to the
// error middleware. An async route that throws therefore never responds at all
// — the request hangs until the client gives up, which reads to a user as "the
// page is empty" rather than "the server failed". Wrapping the handler routes
// the rejection into next(), so the error middleware can answer with a 500.
//
// Express 5 does this natively; drop this helper if the project ever upgrades.
export function asyncRoute(
  handler: (req: Request, res: Response, next: NextFunction) => unknown
): RequestHandler {
  // Returning a promise where Express expects void is the entire point of this
  // wrapper, and the promise cannot reject — `.catch(next)` is the last link in
  // the chain. Express ignores the return value; the unit tests await it to
  // observe that next() was called.
  // eslint-disable-next-line @typescript-eslint/no-misused-promises
  return (req, res, next) => {
    // Promise.resolve also captures a synchronous throw, so both failure modes
    // reach the same place.
    return Promise.resolve()
      .then(() => handler(req, res, next))
      .catch(next);
  };
}