Typescript State Machine

traffic-light.ts

interface TrafficLightOperations {
    onButtonPressed(): void;
    onWaitedToTurnGreen(): void;
    waitToTurnRed(): void;
    onWaitedToTurnRed(): void;
}

interface TrafficLightContext {
    activeLight?: "red" | "green";
}

abstract class TrafficLightState implements TrafficLightOperations {

    protected instance: TrafficLight;

    constructor(instance: TrafficLight) {
        this.instance = instance;
    }

    public abstract get name(): string;

    public abstract handle(): void;

    public onButtonPressed(): TrafficLightState {
        throw new Error("Method not implemented.");
    }

    public onWaitedToTurnGreen(): TrafficLightState {
        throw new Error("Method not implemented.");
    }

    public waitToTurnRed(): TrafficLightState {
        throw new Error("Method not implemented.");
    }

    public onWaitedToTurnRed(): TrafficLightState {
        throw new Error("Method not implemented.");
    }

}

class TrafficLightRedState extends TrafficLightState {

    public get name(): string { return "Red"; }

    public handle(): void {
        this.instance.activeLight = "red";
    }

    public onButtonPressed(): TrafficLightWaitingToTurnGreenState {
        return new TrafficLightWaitingToTurnGreenState(this.instance);
    }

}

class TrafficLightWaitingToTurnGreenState extends TrafficLightState {

    public get name(): string { return "WaitingToTurnGreen"; }

    public handle(): void {
        setTimeout(() => this.instance.onWaitedToTurnGreen(), 1000);
    }

    public onWaitedToTurnGreen(): TrafficLightGreenState {
        return new TrafficLightGreenState(this.instance);
    }

}

class TrafficLightGreenState extends TrafficLightState {

    public get name(): string { return "Green"; }

    public handle(): void {
        this.instance.activeLight = "green";
        setTimeout(() => this.instance.waitToTurnRed());
    }

    public waitToTurnRed(): TrafficLightWaitingToTurnRedState {
        return new TrafficLightWaitingToTurnRedState(this.instance);
    }

}

class TrafficLightWaitingToTurnRedState extends TrafficLightState {

    public get name(): string { return "WaitingToTurnRed"; }

    public handle(): void {
        setTimeout(() => this.instance.onWaitedToTurnRed(), 1000);
    }

    public onWaitedToTurnRed(): TrafficLightRedState {
        return new TrafficLightRedState(this.instance);
    }

}

class TrafficLight implements TrafficLightOperations {

    private _context: TrafficLightContext;
    private _state: TrafficLightState;

    constructor() {
        this._context = {};
        this._state = new TrafficLightRedState(this);
    }

    set activeLight(activeLight: "red" | "green" | undefined) {
        this._context.activeLight = activeLight;
        console.log(`traffic light changed to ${activeLight}`);
    }

    get activeLight() {
        return this._context.activeLight;
    }

    onButtonPressed(): void {
        this._state = this._state.onButtonPressed();
        console.log(`state transitioned to ${this._state.name}`);
        this._state.handle();
    }

    onWaitedToTurnGreen(): void {
        this._state = this._state.onWaitedToTurnGreen();
        console.log(`state transitioned to ${this._state.name}`);
        this._state.handle();
    }

    waitToTurnRed(): void {
        this._state = this._state.waitToTurnRed();
        console.log(`state transitioned to ${this._state.name}`);
        this._state.handle();
    }

    onWaitedToTurnRed(): void {
        this._state = this._state.onWaitedToTurnRed();
        console.log(`state transitioned to ${this._state.name}`);
        this._state.handle();
    }

}

const trafficLight = new TrafficLight();
setTimeout(() => trafficLight.onButtonPressed(), 1000);