/*!
 * Copyright (c) 2020 Ville de Montreal. All rights reserved.
 * Licensed under the MIT license.
 * See LICENSE file in the project root for full license information.
 */

/**
 * A watch that can measure elapsed time using high-resolution real time
 */
export class Stopwatch {
  private hrstart?: bigint;

  private hrend?: bigint;

  /**
   * creates a new watch and start it
   */
  public static startNew() {
    const watch = new Stopwatch();
    watch.start();
    return watch;
  }

  /** tells if the watch is started */
  public isStarted() {
    return !!this.hrstart;
  }

  /** tells if the watch is stopped */
  public isStopped() {
    return !!this.hrend;
  }

  /**
   * Starts the watch.
   * @throws Error if the watch is already started
   */
  public start() {
    if (this.isStarted()) {
      // tslint:disable-next-line: quotemark
      throw new Error("You can't start an already started watch!");
    }
    this.hrstart = process.hrtime.bigint();
    this.hrend = undefined;
  }

  /**
   * Stops the watch.
   * @throws Error if the watch has not been started
   */
  public stop() {
    if (!this.isStarted()) {
      throw new Error('You must start the watch before calling this method');
    }
    this.hrend = process.hrtime.bigint();
  }

  /** resets the watch */
  public reset() {
    this.hrstart = undefined;
    this.hrend = undefined;
  }

  /** resets the watch and start it again */
  public restart() {
    this.reset();
    this.start();
  }

  /**
   * gets the elapsed time in nano seconds since the start
   * @throws Error if the watch has not been started
   */
  public elapsedTimeInNanos() {
    if (this.hrstart) {
      let { hrend } = this;
      if (!hrend) {
        hrend = process.hrtime.bigint();
      }
      return hrend - this.hrstart;
    }
    throw new Error('You must start the watch to obtain elapsed time');
  }

  /**
   * gets the elapsed time in milli seconds since the start
   * @throws Error if the watch has not been started
   */
  public elapsedTimeInMS() {
    return Number(this.elapsedTimeInNanos() / BigInt(1000000));
  }

  /** gets a string representation of the watch's state */
  public toString() {
    if (this.isStopped()) {
      return `Watch stopped after ${this.elapsedTimeInMS()} ms`;
    }
    if (this.isStarted()) {
      return `Watch still running after ${this.elapsedTimeInMS()} ms`;
    }
    return 'Watch is empty';
  }
}