using UnityEngine;
using UnityEngine.EventSystems;

/// <summary>
/// UI元素拖动处理组件
/// </summary>
[RequireComponent(typeof(RectTransform))]
public class UIDragHandler : MonoBehaviour, IDragHandler, IBeginDragHandler, IEndDragHandler
{
    [Header("拖动设置")]
    [SerializeField] private bool restrictToParent = true;
    [SerializeField] private bool enableSmoothDrag = true;
    [SerializeField] private float smoothSpeed = 0.2f;
    
    [Header("事件回调")]
    public UnityEngine.Events.UnityEvent onDragBegin;
    public UnityEngine.Events.UnityEvent onDrag;
    public UnityEngine.Events.UnityEvent onDragEnd;
    
    private RectTransform rectTransform;
    private RectTransform parentRectTransform;
    private Canvas canvas;
    private Vector2 offset = Vector2.zero;
    private Vector3 targetPosition;
    private bool isDragging = false;

    private void Awake()
    {
        rectTransform = GetComponent<RectTransform>();
        canvas = GetComponentInParent<Canvas>();
        parentRectTransform = rectTransform.parent as RectTransform;
    }

    public void OnBeginDrag(PointerEventData eventData)
    {
        // 计算鼠标与UI元素的偏移量
        RectTransformUtility.ScreenPointToLocalPointInRectangle(
            rectTransform, eventData.position, canvas.worldCamera, out offset);
        
        isDragging = true;
        onDragBegin?.Invoke();
    }

    public void OnDrag(PointerEventData eventData)
    {
        if (canvas == null) return;
        
        // 将鼠标屏幕坐标转换为Canvas中的局部坐标
        if (RectTransformUtility.ScreenPointToLocalPointInRectangle(
            parentRectTransform, eventData.position, canvas.worldCamera, out Vector2 localPoint))
        {
            // 应用偏移量并设置位置
            targetPosition = parentRectTransform.TransformPoint(localPoint - offset);
            
            // 边界限制
            if (restrictToParent && parentRectTransform != null)
            {
                targetPosition = RestrictPositionToParent(targetPosition);
            }
            
            // 平滑拖动或直接设置位置
            if (enableSmoothDrag)
            {
                rectTransform.position = Vector3.Lerp(rectTransform.position, targetPosition, smoothSpeed);
            }
            else
            {
                rectTransform.position = targetPosition;
            }
        }
        
        onDrag?.Invoke();
    }

    public void OnEndDrag(PointerEventData eventData)
    {
        isDragging = false;
        onDragEnd?.Invoke();
    }

    private Vector3 RestrictPositionToParent(Vector3 position)
    {
        Vector3 clampedPosition = position;
        
        if (parentRectTransform != null)
        {
            // 获取父容器的边界
            Vector2 parentSize = parentRectTransform.sizeDelta;
            Vector2 min = -parentSize * parentRectTransform.pivot;
            Vector2 max = parentSize * (Vector2.one - parentRectTransform.pivot);
            
            // 获取当前UI元素的边界
            Vector2 size = rectTransform.sizeDelta;
            Vector2 halfSize = size * 0.5f;
            
            // 计算限制后的位置
            clampedPosition.x = Mathf.Clamp(clampedPosition.x, min.x + halfSize.x, max.x - halfSize.x);
            clampedPosition.y = Mathf.Clamp(clampedPosition.y, min.y + halfSize.y, max.y - halfSize.y);
        }
        
        return clampedPosition;
    }
}