/**
 * Class to record duration of interactions
 */
export class Stopwatch {
  private _slices: Slice[] = [];

  start = (): void => {
    const now = Date.now();
    this._slices.push({
      start: now,
    });
  };

  /**
   * stops the time and reset
   */
  stop = (): void => {
    this._slices.length = 0;
  };

  /**
   * pauses the time call start to resume
   */
  pause = (): void => {
    const latestSlice = this._slices[this._slices.length - 1];
    if (!latestSlice) {
      return;
    }

    latestSlice.stop = Date.now();
  };

  /**
   * get the total elapsed time
   */
  getElapsedMilliseconds = (): number =>
    this._slices.reduce((accumulator, currentValue) => accumulator + ((currentValue.stop || Date.now()) - currentValue.start), 0);
}

type Slice = {
  start: number;
  stop?: number;
};