export const throughs: {
  <T>(stream?: TransformStream<T, T>): TransformStream<T, T>;
  <T, R>(stream: TransformStream<T, R>): TransformStream<T, R>;
  <T, R>(fn: (s: ReadableStream<T>) => ReadableStream<R>): TransformStream<
    T, R
  >;
} = (arg: any) => {
  if (!arg) return new TransformStream();
  if (typeof arg !== "function") return throughs((s) => s.pipeThrough(arg));
  const fn = arg;
  const { writable, readable } = new TransformStream();
  return { writable, readable: fn(readable) };
};