using UnityEngine;
using UnityEngine.EventSystems;
using UnityEngine.UI;

/// <summary>
/// 可拖动的悬浮按钮
/// 点击打开调试工具，可以在屏幕上自由拖动
/// </summary>
public class DraggableFloatingButton : MonoBehaviour, IBeginDragHandler, IDragHandler, IEndDragHandler
{
    [Header("设置")]
    [Tooltip("是否限制在屏幕范围内")]
    public bool clampToScreen = true;
    
    [Tooltip("与屏幕边缘的最小距离")]
    public float edgePadding = 20f;
    
    [Header("自动吸附")]
    [Tooltip("是否自动吸附到屏幕边缘")]
    public bool snapToEdge = true;
    
    [Tooltip("吸附动画时间")]
    public float snapDuration = 0.3f;
    
    private RectTransform rectTransform;
    private Canvas canvas;
    private Vector2 dragOffset;
    private bool isDragging = false;
    private Vector2 targetPosition;
    private bool isSnapping = false;
    
    // 用于区分点击和拖动
    private Vector2 dragStartPosition;
    private const float clickThreshold = 5f; // 小于这个距离算点击
    private bool wasDragging = false; // 标记刚才是否拖动过
    
    private void Awake()
    {
        rectTransform = GetComponent<RectTransform>();
        canvas = GetComponentInParent<Canvas>();
        
        if (canvas == null)
        {
            Debug.LogError("DraggableFloatingButton 必须在Canvas下！");
        }
        
        targetPosition = rectTransform.anchoredPosition;
    }
    
    private void Update()
    {
        // 平滑移动到目标位置（吸附动画）
        if (isSnapping && !isDragging)
        {
            rectTransform.anchoredPosition = Vector2.Lerp(
                rectTransform.anchoredPosition, 
                targetPosition, 
                Time.deltaTime / snapDuration
            );
            
            if (Vector2.Distance(rectTransform.anchoredPosition, targetPosition) < 0.5f)
            {
                rectTransform.anchoredPosition = targetPosition;
                isSnapping = false;
            }
        }
    }
    
    public void OnBeginDrag(PointerEventData eventData)
    {
        isDragging = true;
        isSnapping = false;
        
        // 记录起始位置，用于判断是点击还是拖动
        dragStartPosition = eventData.position;
        
        // 计算拖动偏移
        RectTransformUtility.ScreenPointToLocalPointInRectangle(
            canvas.transform as RectTransform,
            eventData.position,
            eventData.pressEventCamera,
            out Vector2 localPoint
        );
        
        dragOffset = rectTransform.anchoredPosition - localPoint;
    }
    
    public void OnDrag(PointerEventData eventData)
    {
        if (!isDragging) return;
        
        // 转换屏幕坐标到Canvas局部坐标
        RectTransformUtility.ScreenPointToLocalPointInRectangle(
            canvas.transform as RectTransform,
            eventData.position,
            eventData.pressEventCamera,
            out Vector2 localPoint
        );
        
        // 应用拖动偏移
        Vector2 newPosition = localPoint + dragOffset;
        
        // 限制在屏幕范围内
        if (clampToScreen)
        {
            newPosition = ClampToScreen(newPosition);
        }
        
        rectTransform.anchoredPosition = newPosition;
    }
    
    public void OnEndDrag(PointerEventData eventData)
    {
        isDragging = false;
        
        // 计算拖动距离
        float dragDistance = Vector2.Distance(dragStartPosition, eventData.position);
        
        // 如果拖动距离超过阈值，说明是拖动而不是点击
        if (dragDistance > clickThreshold)
        {
            wasDragging = true;
            // 在下一帧重置标记
            StartCoroutine(ResetDragFlag());
        }
        
        // 自动吸附到最近的边缘
        if (snapToEdge)
        {
            SnapToNearestEdge();
        }
    }
    
    private System.Collections.IEnumerator ResetDragFlag()
    {
        yield return null; // 等待一帧
        wasDragging = false;
    }
    
    /// <summary>
    /// 检查是否刚拖动过（用于Button点击事件判断）
    /// </summary>
    public bool GetWasDragging()
    {
        return wasDragging;
    }
    
    private Vector2 ClampToScreen(Vector2 position)
    {
        RectTransform canvasRect = canvas.transform as RectTransform;
        Vector2 canvasSize = canvasRect.sizeDelta;
        Vector2 buttonSize = rectTransform.sizeDelta;
        
        // 计算可移动范围
        float minX = -canvasSize.x / 2 + buttonSize.x / 2 + edgePadding;
        float maxX = canvasSize.x / 2 - buttonSize.x / 2 - edgePadding;
        float minY = -canvasSize.y / 2 + buttonSize.y / 2 + edgePadding;
        float maxY = canvasSize.y / 2 - buttonSize.y / 2 - edgePadding;
        
        position.x = Mathf.Clamp(position.x, minX, maxX);
        position.y = Mathf.Clamp(position.y, minY, maxY);
        
        return position;
    }
    
    private void SnapToNearestEdge()
    {
        RectTransform canvasRect = canvas.transform as RectTransform;
        Vector2 canvasSize = canvasRect.sizeDelta;
        Vector2 currentPos = rectTransform.anchoredPosition;
        
        // 计算到各个边缘的距离
        float distToLeft = Mathf.Abs(currentPos.x + canvasSize.x / 2);
        float distToRight = Mathf.Abs(currentPos.x - canvasSize.x / 2);
        float distToTop = Mathf.Abs(currentPos.y - canvasSize.y / 2);
        float distToBottom = Mathf.Abs(currentPos.y + canvasSize.y / 2);
        
        // 找到最近的边
        float minDist = Mathf.Min(distToLeft, distToRight, distToTop, distToBottom);
        
        Vector2 snapPosition = currentPos;
        Vector2 buttonSize = rectTransform.sizeDelta;
        
        if (minDist == distToLeft)
        {
            // 吸附到左边
            snapPosition.x = -canvasSize.x / 2 + buttonSize.x / 2 + edgePadding;
        }
        else if (minDist == distToRight)
        {
            // 吸附到右边
            snapPosition.x = canvasSize.x / 2 - buttonSize.x / 2 - edgePadding;
        }
        else if (minDist == distToTop)
        {
            // 吸附到顶部
            snapPosition.y = canvasSize.y / 2 - buttonSize.y / 2 - edgePadding;
        }
        else if (minDist == distToBottom)
        {
            // 吸附到底部
            snapPosition.y = -canvasSize.y / 2 + buttonSize.y / 2 + edgePadding;
        }
        
        // 确保在屏幕范围内
        snapPosition = ClampToScreen(snapPosition);
        
        targetPosition = snapPosition;
        isSnapping = true;
    }
    
    /// <summary>
    /// 设置悬浮按钮位置
    /// </summary>
    public void SetPosition(Vector2 position)
    {
        if (clampToScreen)
        {
            position = ClampToScreen(position);
        }
        rectTransform.anchoredPosition = position;
        targetPosition = position;
    }
    
    /// <summary>
    /// 获取当前位置
    /// </summary>
    public Vector2 GetPosition()
    {
        return rectTransform.anchoredPosition;
    }
}