_startScrollingIfNecessary()

in src/cdk/drag-drop/drop-list-ref.ts [583:648]

• 55 lines of code
• 17 McCabe index (conditional complexity)

  _startScrollingIfNecessary(pointerX: number, pointerY: number) {
    if (this.autoScrollDisabled) {
      return;
    }

    let scrollNode: HTMLElement | Window | undefined;
    let verticalScrollDirection = AutoScrollVerticalDirection.NONE;
    let horizontalScrollDirection = AutoScrollHorizontalDirection.NONE;

    // Check whether we should start scrolling any of the parent containers.
    this._parentPositions.positions.forEach((position, element) => {
      // We have special handling for the `document` below. Also this would be
      // nicer with a  for...of loop, but it requires changing a compiler flag.
      if (element === this._document || !position.clientRect || scrollNode) {
        return;
      }

      if (
        isPointerNearClientRect(position.clientRect, DROP_PROXIMITY_THRESHOLD, pointerX, pointerY)
      ) {
        [verticalScrollDirection, horizontalScrollDirection] = getElementScrollDirections(
          element as HTMLElement,
          position.clientRect,
          pointerX,
          pointerY,
        );

        if (verticalScrollDirection || horizontalScrollDirection) {
          scrollNode = element as HTMLElement;
        }
      }
    });

    // Otherwise check if we can start scrolling the viewport.
    if (!verticalScrollDirection && !horizontalScrollDirection) {
      const {width, height} = this._viewportRuler.getViewportSize();
      const clientRect = {
        width,
        height,
        top: 0,
        right: width,
        bottom: height,
        left: 0,
      } as ClientRect;
      verticalScrollDirection = getVerticalScrollDirection(clientRect, pointerY);
      horizontalScrollDirection = getHorizontalScrollDirection(clientRect, pointerX);
      scrollNode = window;
    }

    if (
      scrollNode &&
      (verticalScrollDirection !== this._verticalScrollDirection ||
        horizontalScrollDirection !== this._horizontalScrollDirection ||
        scrollNode !== this._scrollNode)
    ) {
      this._verticalScrollDirection = verticalScrollDirection;
      this._horizontalScrollDirection = horizontalScrollDirection;
      this._scrollNode = scrollNode;

      if ((verticalScrollDirection || horizontalScrollDirection) && scrollNode) {
        this._ngZone.runOutsideAngular(this._startScrollInterval);
      } else {
        this._stopScrolling();
      }
    }
  }