type AnyFunc = (...args: unknown) => unknown;
type Gateway = (req: Request, res: Response, next: AnyFunc) => Promise<void>;

interface GatewayOptions {
  redirect_url: string;
  use_stored_sessions?: boolean;
}

class GatewayClass {
  private _options: GatewayOptions;

  public constructor (options: GatewayOptions) {
    this._options = options;
  }

  private redirect (res): void {
    res.statusCode = 302;
    res.setHeader ('Location', this._options.redirect_url);
    res.end ();
  }

  private async authenticate (req: Request): Promise<boolean> {
    await Promise.resolve (req.body);
    return false;
  }

  public async process_request (
    req: Request,
    res: Response,
    next: AnyFunc
  ): Promise<void> {
    if (await this.authenticate (req))
      return next ();
    return this.redirect (res);
  }
}

export default function create_gateway (options: GatewayOptions): Gateway {
  const g = new GatewayClass (options);
  return g.process_request;
}