iterable_future_all_settled.dart

import 'dart:async';
import 'dart:collection';

Future<void> main() async {
  final list = await [
    Future.delayed(const Duration(milliseconds: 1500), () => 1),
    Future.delayed(const Duration(milliseconds: 5000), () => throw '2'),
    Future.delayed(const Duration(milliseconds: 1200), () => 3),
    Future.delayed(const Duration(milliseconds: 8000), () => throw '4'),
    Future.delayed(const Duration(milliseconds: 4300), () => 5),
    Future.delayed(const Duration(milliseconds: 3000), () => 6),
    Future.delayed(const Duration(milliseconds: 7000), () => 6),
    Future.delayed(const Duration(milliseconds: 3000), () => 7),
    Future.delayed(const Duration(milliseconds: 4000), () => 8),
    Future.delayed(const Duration(milliseconds: 3000), () => 9),
    Future.delayed(const Duration(milliseconds: 6000), () => 10),
  ].allSettled(
    parallel: 2,
    onSuccess: (index, value) {
      print('index: $index, value: $value');
    },
    onError: (index, e, s) {
      print('index: $index, error: $e');
    },
  );
  print(list);
}

extension IterableFuture<T> on Iterable<Future<T>> {
  Future<List<FutureResult<T>>> allSettled({
    int parallel = 0,
    void Function(int index, T value)? onSuccess,
    void Function(int index, Object error, StackTrace stackTrace)? onError,
    void Function(
      int index,
      FutureResultStatus status,
      T? value,
      Object? error,
      StackTrace? stackTrace,
    )?
        onComplete,
  }) {
    final len = length;
    if (len == 0) {
      return Future.value(<FutureResult<T>>[]);
    }
    final completer = Completer<List<FutureResult<T>>>();
    int remaining = len;
    final list = List<FutureResult<T>?>.filled(len, null);
    if (parallel <= 0) {
      void handleFuture(int index, Future<T> future) {
        future.then((value) {
          list[index] = FutureResult.success(value);
          onSuccess?.call(index, value);
          onComplete?.call(
              index, FutureResultStatus.success, value, null, null);
        }).catchError((e, s) {
          list[index] = FutureResult.error(e, s);
          onError?.call(index, e, s);
          onComplete?.call(index, FutureResultStatus.error, null, e, s);
        }).whenComplete(() {
          if (--remaining == 0) {
            completer.complete(List.unmodifiable(list.cast()));
          }
        });
      }

      for (int i = 0; i < len; i++) {
        handleFuture(i, elementAt(i));
      }
    } else {
      int running = 0;
      int index = 0;
      final queue = Queue<Future<T>>.from(this);
      void exec() {
        void handleFuture(int index, Future<T> future) {
          future.then((value) {
            list[index] = FutureResult.success(value);
            onSuccess?.call(index, value);
            onComplete?.call(
              index,
              FutureResultStatus.success,
              value,
              null,
              null,
            );
          }).catchError((e, s) {
            list[index] = FutureResult.error(e, s);
            onError?.call(index, e, s);
            onComplete?.call(index, FutureResultStatus.error, null, e, s);
          }).whenComplete(() {
            if (--remaining == 0) {
              completer.complete(List.unmodifiable(list.cast()));
            }
            running--;
            exec();
          });
        }

        while (queue.isNotEmpty && running < parallel) {
          running++;
          final future = queue.removeFirst();
          handleFuture(index++, future);
        }
      }

      exec();
    }
    return completer.future;
  }
}

enum FutureResultStatus {
  success,
  error,
  ;
}

class FutureResult<T> {
  factory FutureResult.success(T value) {
    return FutureResult._success(FutureResultStatus.success, value);
  }

  factory FutureResult.error(Object error, StackTrace stackTrace) {
    return FutureResult._error(FutureResultStatus.error, error, stackTrace);
  }

  FutureResult._success(this.status, this._value);

  FutureResult._error(this.status, this._error, this._stackTrace);

  final FutureResultStatus status;
  late final T _value;
  late final Object _error;
  late final StackTrace _stackTrace;

  FutureOr<R?> when<R>({
    FutureOr<R> Function(T value)? success,
    FutureOr<R?> Function(Object error, StackTrace stackTrace)? error,
  }) {
    switch (status) {
      case FutureResultStatus.success:
        return success?.call(_value);
      case FutureResultStatus.error:
        return error?.call(_error, _stackTrace);
    }
  }

  @override
  String toString() {
    return 'FutureResult(status: $status, ${when(success: (value) => 'value: $_value', error: (e, s) => 'error: $_error, stackTrace: $_stackTrace')})';
  }
}