using UnityEngine;
using UnityEngine.Events;
using UnityEngine.EventSystems;

public class DraggablePolygonPoint : MonoBehaviour, IBeginDragHandler, IDragHandler, IEndDragHandler
{
    //操作对应的下标
    [SerializeField]
    int index = 0;
    [SerializeField]
    RectTransform parent;

    private bool dragging = false;
    private bool useCenterDrag = false;

    public UnityEvent<int,Vector3> OnBeginDragEvent;
    public UnityEvent<int,Vector3> OnEndDragEvent;
    public UnityEvent<int, Vector3> OnDragEvent;

    Vector2 pointerOffset;
    RectTransform rect;

    void Awake() {
        rect = parent != null ? parent : (RectTransform)(transform);
    }

    public void SetUseCenterDrag(bool value)
    {
        useCenterDrag = value;
    }

    Vector2 GetDragAnchorWorldPosition()
    {
        if (!useCenterDrag)
            return rect.position;
        return rect.TransformPoint(rect.rect.center);
    }

    void MoveToDragAnchor(Vector2 targetWorldPosition)
    {
        if (!useCenterDrag)
        {
            rect.position = targetWorldPosition;
            return;
        }

        Vector2 delta = targetWorldPosition - (Vector2)rect.TransformPoint(rect.rect.center);
        rect.position += (Vector3)delta;
    }

    public void OnBeginDrag(PointerEventData eventData)
    {
        dragging = true;
        pointerOffset = eventData.position - GetDragAnchorWorldPosition();

        OnBeginDragEvent.Invoke(index, rect.localPosition);
    }

    public void OnDrag(PointerEventData eventData)
    {
        if (dragging)
        {
            MoveToDragAnchor(eventData.position - pointerOffset);

            OnDragEvent.Invoke(index, rect.localPosition);
        }
    }

    public void OnEndDrag(PointerEventData eventData)
    {
        dragging = false;
        // 更新多边形的顶点等操作...
        pointerOffset = Vector2.zero;
        OnEndDragEvent.Invoke(index, rect.localPosition);
    }
}