import type { ErrorHandlerService } from "@batch-cooking/error-tools";
import type { NextFunction, Request, Response } from "express";

/** Express error-handling middleware signature (the 4-arg form Express detects as an error handler). */
type ExpressErrorMiddleware = (
  err: unknown,
  req: Request,
  res: Response,
  next: NextFunction,
) => void;

/**
 * Builds the final Express error-handling middleware for an app: every
 * thrown/`next(err)`-ed error ends up here, gets mapped by the given
 * {@link ErrorHandlerService}, and sent as the response. Keeps the actual
 * "what does this error mean" logic in the service, testable on its own —
 * this factory is just the thin Express adapter.
 *
 * @example
 * app.use(createErrorMiddleware(errorHandlerService));
 */
export function createErrorMiddleware(errorHandler: ErrorHandlerService): ExpressErrorMiddleware {
  return (err, _req, res, _next) => {
    const { status, body } = errorHandler.handle(err);
    res.status(status).json(body);
  };
}