using UnityEngine;
using System.Collections.Generic;

/// <summary>
/// UI拖动组管理器，用于限制同时只能拖动一个UI元素
/// </summary>
public class UIDragGroup : MonoBehaviour
{
    private static UIDragGroup instance;
    private HashSet<UIDragHandler> dragHandlers = new HashSet<UIDragHandler>();
    private UIDragHandler activeDragHandler = null;

    private void Awake()
    {
        if (instance == null)
        {
            instance = this;
            DontDestroyOnLoad(gameObject);
        }
        else
        {
            Destroy(gameObject);
        }
    }

    /// <summary>
    /// 注册拖动处理器
    /// </summary>
    public static void RegisterDragHandler(UIDragHandler handler)
    {
        if (instance != null)
        {
            instance.dragHandlers.Add(handler);
        }
    }

    /// <summary>
    /// 取消注册拖动处理器
    /// </summary>
    public static void UnregisterDragHandler(UIDragHandler handler)
    {
        if (instance != null)
        {
            instance.dragHandlers.Remove(handler);
            if (instance.activeDragHandler == handler)
            {
                instance.activeDragHandler = null;
            }
        }
    }

    /// <summary>
    /// 开始拖动处理
    /// </summary>
    public static bool BeginDrag(UIDragHandler handler)
    {
        if (instance == null) return true;
        
        // 如果已有活动的拖动处理器且不是当前处理器，则拒绝拖动
        if (instance.activeDragHandler != null && instance.activeDragHandler != handler)
        {
            return false;
        }
        
        instance.activeDragHandler = handler;
        return true;
    }

    /// <summary>
    /// 结束拖动处理
    /// </summary>
    public static void EndDrag(UIDragHandler handler)
    {
        if (instance != null && instance.activeDragHandler == handler)
        {
            instance.activeDragHandler = null;
        }
    }

    private void OnDestroy()
    {
        if (instance == this)
        {
            instance = null;
        }
    }
}