Stream followedBy()

in lib/src/concatenate.dart [24:80]
49 lines of code
10 McCabe index (conditional complexity)

  Stream<T> followedBy(Stream<T> next) {
    var controller = isBroadcast
        ? StreamController<T>.broadcast(sync: true)
        : StreamController<T>(sync: true);

    next = isBroadcast && !next.isBroadcast ? next.asBroadcastStream() : next;

    StreamSubscription<T>? subscription;
    var currentStream = this;
    var thisDone = false;
    var secondDone = false;

    late void Function() currentDoneHandler;

    void listen() {
      subscription = currentStream.listen(controller.add,
          onError: controller.addError, onDone: () => currentDoneHandler());
    }

    void onSecondDone() {
      secondDone = true;
      controller.close();
    }

    void onThisDone() {
      thisDone = true;
      currentStream = next;
      currentDoneHandler = onSecondDone;
      listen();
    }

    currentDoneHandler = onThisDone;

    controller.onListen = () {
      assert(subscription == null);
      listen();
      if (!isBroadcast) {
        controller
          ..onPause = () {
            if (!thisDone || !next.isBroadcast) return subscription!.pause();
            subscription!.cancel();
            subscription = null;
          }
          ..onResume = () {
            if (!thisDone || !next.isBroadcast) return subscription!.resume();
            listen();
          };
      }
      controller.onCancel = () {
        if (secondDone) return null;
        var toCancel = subscription!;
        subscription = null;
        return toCancel.cancel();
      };
    };
    return controller.stream;
  }