export class SwipeHandlerService {
  private xDown: number = null;
  private yDown: number = null;

  public init(): void {
    document.addEventListener('touchstart', this.handleTouchStart, false);
    document.addEventListener('touchmove', this.handleTouchMove, false);
  }

  public destroy(): void {
    document.removeEventListener('touchstart', this.handleTouchStart, false);
    document.removeEventListener('touchmove', this.handleTouchMove, false);
  }

  private handleTouchStart(event: any): void {
    const firstTouch = event.touches[0];
    this.xDown = firstTouch.clientX;
    this.yDown = firstTouch.clientY;
  }

  private handleTouchMove(event: any): void {
    if (!this.xDown || !this.yDown) {
      return;
    }

    const xUp = event.touches[0].clientX;
    const yUp = event.touches[0].clientY;

    const xDiff = this.xDown - xUp;
    const yDiff = this.yDown - yUp;

    if (Math.abs(xDiff) > Math.abs(yDiff)) {
      if (xDiff > 0) {
        // swipe left
      } else {
        // swipe right
      }
    } else {
      if (yDiff > 0) {
        // swipe up
      } else {
        // swipe down
      }
    }

    /* reset values */
    this.xDown = null;
    this.yDown = null;
  }
}