import 'dart:async';

/// Example app showing how exceptions are not caught if they have not been awaited
/// by the time they complete.
///
/// Outputs: """
///   caught Exception: Top level error
///   Uncaught Error: Exception: rpc error
/// """
Future<void> main() async {
  try {
    final transaction = SimplifiedTransaction();
    final futures = <Future<int>>[];
    futures.add(transaction.createRpc().send().first);

    // The exception from this RPC leaks because the future has not been awaited
    // by the time it completes.
    futures.add(transaction.createRpc(error: 'rpc error').send().first);

    await transaction.commit();
    final results = await Future.wait(futures);
    print('got results: $results');
  } on Exception catch(e) {
    print('caught $e');
  }
}

class SimplifiedTransaction {
  final _rpcs = <FakeRpc>[];

  FakeRpc createRpc({String error}) {
    _rpcs.add(FakeRpc()..error = error);
    return _rpcs.last;
  }

  Future<void> commit() {
    for (final rpc in _rpcs) rpc.complete();
    if (_rpcs.any((rpc) => rpc.error != null)) {
      return Future.error(Exception('Top level error'));
    }
    return Future.value();
  }
}

class FakeRpc {
  String error;
  final _sc = StreamController<int>.broadcast();

  Stream<int> send() => _sc.stream;

  void complete() {
    Future.delayed(Duration(milliseconds: 50)).then((_) {
      if (error != null) _sc.addError(Exception(error));
      else _sc.add(200);
      _sc.close();
    });
  }
}