Utility timer class

timer.ts

import EventEmitter from 'events';

export interface TimerEvents {
    'tick': (time: number) => void;
    'complete': () => void;
}

export interface Timer {
    addListener<U extends keyof TimerEvents>(event: U, listener: TimerEvents[U]): this;
    prependListener<U extends keyof TimerEvents>(event: U, listener: TimerEvents[U]): this;
    prependOnceListener<U extends keyof TimerEvents>(event: U, listener: TimerEvents[U]): this;
    removeListener<U extends keyof TimerEvents>(event: U, listener: TimerEvents[U]): this;
    removeAllListeners(event?: keyof TimerEvents): this;
    once<U extends keyof TimerEvents>(event: U, listener: TimerEvents[U]): this;
    on<U extends keyof TimerEvents>(event: U, listener: TimerEvents[U]): this;
    off<U extends keyof TimerEvents>(event: U, listener: TimerEvents[U]): this;
    emit<U extends keyof TimerEvents>(event: U, ...args: Parameters<TimerEvents[U]>): boolean;
    eventNames<U extends keyof TimerEvents>(): U[];
    listenerCount(type: keyof TimerEvents): number;
    listeners<U extends keyof TimerEvents>(type: U): TimerEvents[U][];
    rawListeners<U extends keyof TimerEvents>(type: U): TimerEvents[U][];
}

const A_SECOND_IN_MILLISECONDS = 1000;
const A_MINUTE_IN_SECONDS = 60;

export class Timer extends EventEmitter {
    private start: number;
    private _running: boolean;

    public get running(): boolean { return this._running; }

    private remaining: number = A_SECOND_IN_MILLISECONDS;
    private delay: number = A_SECOND_IN_MILLISECONDS;

    private time: number = A_MINUTE_IN_SECONDS;
    private currentTime: number = A_MINUTE_IN_SECONDS;

    private timerId: NodeJS.Timeout;

    public constructor() { super(); }

    public setTime(timeInSeconds: number): void {
        this.time = timeInSeconds;
        this.currentTime = timeInSeconds;

        this.pause();
        this.reset();
    }

    public getTime(): number { return this.currentTime; }

    public setPace(timeInMilliseconds: number): void {
        this.remaining = timeInMilliseconds;
        this.delay = timeInMilliseconds;

        this.pause();
        this.reset();
    }

    public getPace(): number { return this.delay; }

    public pause(): void {
        clearTimeout(this.timerId);
        this.remaining -= Date.now() - this.start;

        this._running = false;
    }

    public resume(): void {
        this._running = true;
        this.start = Date.now();

        this.timerId = setTimeout(() => {
            this.remaining = this.delay;
            this.currentTime = this.currentTime - 1;
            this.emit('tick', this.currentTime);

            this.loop();
        }, this.remaining);
    }

    public reset(): void {
        this.remaining = this.delay;
        this.currentTime = this.time;

        this._running = false;
    }

    private loop(): void {
        if (this.currentTime)
            return this.resume();

        this._running = false;
        this.emit('complete');
    }
}