using UnityEngine;
using UnityEngine.UIElements;

namespace DanieleMarotta.RiversongCodeShowcase
{
    public class DraggableManipulator : PointerManipulator
    {
        private const string DraggedUssClassName = "dragged";

        private Vector2 _startMousePosition;

        private Vector2 _startElementPosition;

        private VisualElement _draggedElement;

        public DraggableManipulator(VisualElement draggedElement)
        {
            _draggedElement = draggedElement;
        }

        protected override void RegisterCallbacksOnTarget()
        {
            target.RegisterCallback<PointerDownEvent>(OnPointerDown);
            target.RegisterCallback<PointerMoveEvent>(OnPointerMove);
            target.RegisterCallback<PointerUpEvent>(OnPointerUp);
        }

        protected override void UnregisterCallbacksFromTarget()
        {
            target.UnregisterCallback<PointerDownEvent>(OnPointerDown);
            target.UnregisterCallback<PointerMoveEvent>(OnPointerMove);
            target.UnregisterCallback<PointerUpEvent>(OnPointerUp);
        }

        private void OnPointerDown(PointerDownEvent evt)
        {
            if (evt.button != 0) return;

            target.CapturePointer(evt.pointerId);
            evt.StopPropagation();

            _startMousePosition = evt.position;
            _startElementPosition = new Vector2(_draggedElement.resolvedStyle.left, _draggedElement.resolvedStyle.top);

            _draggedElement.AddToClassList(DraggedUssClassName);
        }

        private void OnPointerMove(PointerMoveEvent evt)
        {
            if (!target.HasPointerCapture(evt.pointerId)) return;

            var delta = (Vector2)evt.position - _startMousePosition;
            _draggedElement.style.left = _startElementPosition.x + delta.x;
            _draggedElement.style.top = _startElementPosition.y + delta.y;
        }

        private void OnPointerUp(PointerUpEvent evt)
        {
            if (!target.HasPointerCapture(evt.pointerId)) return;

            target.ReleasePointer(evt.pointerId);

            _draggedElement.RemoveFromClassList(DraggedUssClassName);
        }
    }
}