import { TimerAlreadyRunning, TimerNotStarted } from './exceptions';

import { TimerResponse } from './response';

export class Timer {

private startTime: number | null = null;

/**

* start the timer.

*/

start(): Timer {

if (this.startTime) throw new TimerAlreadyRunning();

this.startTime = Date.now();

return this;

}

/**

* stop the timer and return timer results.

*/

stop(): TimerResponse {

if (!this.startTime) throw new TimerNotStarted();

const endTime = Date.now();

return new TimerResponse(this.calculateElapsed(this.startTime, endTime));

}

private calculateElapsed(startTime: number, endTime: number) {

return endTime - startTime;

}

/**

* create a new timer instance.

*/

static create() {

return new Timer();

}

}