abstract class State {}
class Open extends State {}
class Closed extends State {}


abstract class Event {}
class OnOpening extends Event {}
class OnClosing extends Event {}


abstract class SideEffect {
  void call(State state, Event event);
}

class MakeSomeNoise extends SideEffect {
  @override
  void call(State state, Event event) => print("Ka-chunk-creeeeeeak-squeekie-squeekie");
}

final RxStateMachine<State, Event, SideEffect> _stateMachine =
    RxStateMachine<State, Event, SideEffect>.create((g) => g
      ..initialState(Open())
      ..state<Open>((b) => b
        ..on<OnClosing>((state, event) {
          return b.transitionTo(Closed(), MakeSomeNoise());
        }))
      ..state<Closed>((b) => b
        ..on<OnOpening>((state, event) {
          return b.transitionTo(Open(), MakeSomeNoise());
        }))
      ..onTransition((transition) {
        if (transition is Valid) {
          final item = transition as Valid;
          print("Valid transition: from [${item.fromState}] to [${item.toState}] by [${item.event}]");
          if(item.sideEffect is SideEffect) {
            item.sideEffect(item.toState, item.event);
          }
        } else if (transition is Invalid) {
          final item = transition as Invalid;
          print("Invalid transition: from [${item.fromState}] by [${item.event}]");
        }
      })
);

_stateMachine.states.listen((state) {
    if(state is Open && !_security.authenticated()) {
      _security.alarm();
    }
  });

  _stateMachine.transition(new OnClosing());
  //...
  _stateMachine.transition(new OnOpening());