FSM (Finite State Machine)

A super simple finite state machine pattern implementation. If you are not sure what this is, a finite state machine is a state manager that ensures a system is only in a single state out of a predefined, finite number of states at one time, and has a set of predefined paths that it can take.

Example

In this example, this traffic light loops between each state forever. Because we defined the possible transitions in the transitions variable, we know that the machine can ONLY go in the sequence we defined.

If the ORANGE_OFF event is fired when the light is GREEN, the event is just ignored since there is no transition defined for such a scenario, this way we can ensure our system always follows a predictable and predefined pattern.

enum State {
	GREEN,
	ORANGE,
    RED,
}

enum Event {
	GREEN_OFF,
	ORANGE_OFF,
	RED_OFF,
}

const transitions: Transition<State, Event>[] = [
    // When the GREEN_OFF event fires, and we're in the GREEN state, switch to ORANGE
	{ event: Event.GREEN_OFF, from: State.GREEN, to: State.ORANGE },

    // When the ORANGE_OFF event fires, and we're in the ORANGE state, switch to RED
	{ event: Event.ORANGE_OFF, from: State.ORANGE, to: State.RED },

    // When the RED_OFF event fires, and we're in the RED state, switch back to GREEN
	{ event: Event.RED_OFF, from: State.RED, to: State.GREEN },

    // Create more states, events, transitions... get as complex as you want
];

const trafficLight = new FiniteStateMachine(State.GREEN, ...transitions);

trafficLight.onState(State.GREEN, () => {
	print('THE LIGHT IS GREEN');
	task.delay(2.5, () => trafficLight.processEvent(Event.GREEN_OFF));
});

trafficLight.onState(State.ORANGE, () => {
	print('THE LIGHT IS ORANGE');
	task.delay(1, () => trafficLight.processEvent(Event.ORANGE_OFF));
});

trafficLight.onState(State.RED, () => {
	print('THE LIGHT IS RED');
	task.delay(2.5, () => trafficLight.processEvent(Event.RED_OFF));
});

// Since the initial state was defined GREEN, the system is currently
// in the GREEN state, so the only event that will do anything is GREEN_OFF
trafficLight.processEvent(Event.GREEN_OFF);