Angular interceptor for switching requests

Question

I want to create an interceptor (or any other solution that will affect all the services), that will hold the POST requests for ~300ms and in case there are new POST requests in that time gap, will perform switchMap on them.

Something like that:

@Injectable()
export class DebounceInterceptorService implements HttpInterceptor {
  intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
    if (req.method != HttpMethod.Post) {
      return next.handle(req);
    } else {
      return of().pipe(switchMap(() => next.handle(req)));
    }
  }
}

This doesn't work, but the agenda is to handle all requests in case the user double click a save button or any other case that shouldn't happen.

Edit:

That should work but the intercept() function must have a returned value. Any thoughts on that would solve it

  test: Subject<any>;
  constructor() {
    this.test.pipe(
      debounceTime(5000),
      switchMap(({ req, next }: { req: HttpRequest<any>; next: HttpHandler }) => next.handle(req))
    );
  }

  intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
    if (req.method != HttpMethod.Post) {
      return next.handle(req);
    } else {
      this.test.next({ req, next });
    }
  }