import type { FlowSource } from "./FlowSource";
import { toStream } from "./froms";
import { parallels } from "./parallels";
/**
 * return a transform stream that merges streams from sources
 * don't get confused with mergeStreamw
 * merges     : returns a TransformStream, which also merges upstream
 * mergeStream: returns a ReadableStream, which doesnt have upstream
 */
export const merges: <T>(...streams: FlowSource<T>[]) => TransformStream<T, T> =
  (...srcs: FlowSource<any>[]) => {
    if (!srcs.length) return new TransformStream();
    const upstream = new TransformStream();
    return {
      writable: upstream.writable,
      readable: parallels(upstream.readable, ...srcs.map(toStream)),
    } as TransformStream;
  };