using System;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.EventSystems;
using UnityEngine.UI;
[RequireComponent(typeof(ScrollRect))]
public class UIScrollFocusHelper: MonoBehaviour, IBeginDragHandler, IDragHandler, IEndDragHandler
{
    public GameObject itemTemplate;
    public Transform focusItemTrans;
    
    private ScrollRect _scrollRect;
    private GameObject _content;
    private bool _isVertical;
    private List<GameObject> _itemList;

    private Delegate _focusItemFunc;
    private Delegate _unFocusItemFunc;

    #region DragHandler

    public void OnBeginDrag(PointerEventData eventData)
    {
        
    }
    
    public void OnDrag(PointerEventData eventData)
    {
        if (_itemList == null)
        {
            return;
        }
        
        for (int i = 0; i < _itemList.Count; i++)
        {
            var item = _itemList[i];
            var posX = item.GetComponent<RectTransform>().position.x;
            var distance = Mathf.Abs(posX - focusItemTrans.GetComponent<RectTransform>().position.x);
            if (distance < _GetLimitDistance())
            {
                if (_focusItemFunc != null)
                {
                    if (_focusItemFunc is Action<GameObject> action)
                    {
                        action.Invoke(item);
                    }
                }
            }
            else
            {
                if (_unFocusItemFunc != null)
                {
                    if (_unFocusItemFunc is Action<GameObject> unFocusAction)
                    {
                        unFocusAction.Invoke(item);
                    }
                }
            }
        }
    }

    public void OnEndDrag(PointerEventData eventData)
    {
        
    }

    #endregion

    

    #region UnityEvent Function

    private void Awake()
    {
        _scrollRect = gameObject.GetComponent<ScrollRect>();
        if (!_scrollRect)
        {
            DebugUtil.LogError("UIScrollFocusHelper Error!!! 请检查节点是否绑定ScrollRect组件!!! ");
            return;
        }

        _content = _scrollRect.transform.Find("Viewport/Content").gameObject;
        
        bool isVertical = true;
        if (_scrollRect.horizontal)
        {
            if (_scrollRect.vertical)
            {
                DebugUtil.LogError("UIScrollFocusHelper Error!!! 仅支持ScrollRect单方向拖动!!! ");
                return;
            }
            isVertical = false;
        }

        _isVertical = isVertical;

        var layoutGroup = _GetContentLayoutGroup();
        if (layoutGroup)
        {
            if (_isVertical)
            {
                layoutGroup = (VerticalLayoutGroup)layoutGroup;
            }
            else
            {
                layoutGroup = (HorizontalLayoutGroup)layoutGroup;
            }
        }
    }

    #endregion

    private LayoutGroup _GetContentLayoutGroup()
    {
        if (!_content)
        {
            DebugUtil.LogError("UIScrollFocusHelper Error!!! 请检查ScrollRect的Content节点!!! ");
        }

        var layoutGroup = _content.GetComponent<LayoutGroup>();
        return layoutGroup;
    }

    private float _GetLimitDistance()
    {
        var rect = itemTemplate.GetComponent<RectTransform>().rect;
        return rect.width * 0.5f;
    }

    #region API

    public void SetData(List<GameObject> list)
    {
        _itemList = list;
    }

    public void SetFocusItemFunc(Action<GameObject> action)
    {
        _focusItemFunc = action;
    }

    public void SetUnFocusItemFunc(Action<GameObject> action)
    {
        _unFocusItemFunc = action;
    }

    #endregion
}