class DragTargetView extends View {
	/**
	 * Called by the dragged movable object.
	 * Checks all drag target views if they're underneath the object at position x, y. If so, their onDragOver() function is called.
	 * You must speficy the draggableType (a string) of the draggedObject.
	 * The sourceView is the view where the object was taken from.
	 */
	static dragObject(draggedObject, draggableType, sourceView, x, y) {
		if (!DragTargetView.dragTargetViews) {
			return;
		}

		DragTargetView.sourceView = sourceView;

		var dragTarget = null;
		var validTarget = false;

		for (var i = 0; i < DragTargetView.dragTargetViews.length; i++) {
			var dragTargetView = DragTargetView.dragTargetViews[i];

			var rect = dragTargetView.element.getBoundingClientRect();
			if (x >= rect.x && x <= rect.x + rect.width && y >= rect.y && y <= rect.y + rect.height) {
				validTarget = dragTargetView.acceptsType(draggableType);

				dragTargetView.onDragOver(draggedObject, validTarget, sourceView, x, y);
				
				if (validTarget) {
					dragTarget = dragTargetView;
					break;
				}
			}
		}

		if (DragTargetView.currentDragTarget != dragTarget) {
			if (DragTargetView.currentDragTarget) {
				DragTargetView.currentDragTarget.onDragExit(sourceView);
			}
			if (dragTarget) {
				dragTarget.onDragEnter(draggedObject, validTarget, sourceView);
			}
		}

		DragTargetView.currentDragTarget = dragTarget;
	}

	/**
	 * Called by the movable object when it's released.
	 * Checks if there is a droppable target. If there is one, the onDrop function of the target is called.
	 * Returns true if the object was dropped somewhere. False if not.
	 */
	static dropObject(droppedObject, x, y) {
		if (!DragTargetView.currentDragTarget) {
			return false;
		}

		DragTargetView.currentDragTarget.onDrop(droppedObject, DragTargetView.sourceView, x, y);
		DragTargetView.currentDragTarget.onDragEnd();

		DragTargetView.sourceView = null;
		DragTargetView.currentDragTarget = null;

		return true;
	}

	constructor(element) {
		super(element);

		if (!DragTargetView.dragTargetViews) {
			DragTargetView.dragTargetViews = [ ];
		}
		DragTargetView.dragTargetViews.push(this);
	}

	onDragOver(draggedObject, validType, sourceView, x, y) { }
	onDragEnter(draggedObject, validType, sourceView) { }
	onDragExit() { }
	onDragEnd() { }
	onDrop(droppedObject, sourceView) { }

	/**
	 * Override this in your drag target view to specify which draggable object types it accepts.
	 * Return true or false depending on whether you want to accept the given draggableType or not.
	 */
	acceptsType(draggableType) {
		return true;
	}
}