not actually distributed

main.dart

import 'dart:async';

enum SagaStates { created, executing, compensating, succeeded, failed }

class Saga {
  String id;
  String label;
  SagaStates _state = SagaStates.created;
  Set<Opperation> opperations;
  List<Future> _opperations;

  Saga() {}

  set state(SagaStates s) {
    _state = s;

    // TODO: publish the change
    // TODO: commit the state to storage
  }

  get state => _state;

  execute() {
    state = SagaStates.executing;

    _opperations = opperations.map((Opperation op) => op.execute());

    Future.wait(_opperations, eagerError: true)
      .then(_onSuccess)
      .catchError(compensate);
  }

  compensate() {
    state = SagaStates.compensating;

    _opperations = opperations.map((Opperation op) => op.compensate());

    Future.wait(_opperations).whenComplete(_ensureCompensated);
  }

  _ensureCompensated() {
    _opperations = opperations
        .where((Opperation op) => op.state != SagaStates.compensating)
        .map((Opperation op) => op.compensate());

    if (_opperations.isEmpty) {
      _onFailure();
    } else {
      Future.wait(_opperations).whenComplete(_ensureCompensated);
    }
  }

  _onSuccess(List results) {
    state = SagaStates.succeeded;
  }

  _onFailure() {
    state - SagaStates.failed;
  }
}

class Opperation {
  String id;
  String label;
  SagaStates state;

  Future execute() {}
  Future compensate() {}
}