using System;
using System.Collections.Generic;
using Cysharp.Threading.Tasks;
using UnityEngine;
using UnityEngine.EventSystems;
using UnityEngine.UI;
using DG.Tweening;

[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;

    private int _curIndex;
    private List<float> _childPosXList;
    private float _centerPosX;
    private float _spacing;

    private Vector2 _lastFrameContentPos;
    private RectTransform _contentRectTrans;

    private int _maxIndex;
    private int _minIndex;

    private bool _isPlayingMove;
    public int CurIndex => _curIndex;

    #region DragHandler

    public void OnBeginDrag(PointerEventData eventData)
    {
        
    }
    
    public void OnDrag(PointerEventData eventData)
    {
        if (_itemList == null || _itemList.Count <= 0)
        {
            return;
        }
        
        _SetCurIndexFocus();
    }

    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;

        _contentRectTrans = _content.GetComponent<RectTransform>();

        var layoutGroup = _GetContentLayoutGroup();
        if (layoutGroup)
        {
            if (_isVertical)
            {
                //layoutGroup = (VerticalLayoutGroup)layoutGroup;
                var lay = layoutGroup as VerticalLayoutGroup;
                if (lay)
                {
                    _spacing = lay.spacing;
                }
                _centerPosX = _scrollRect.GetComponent<RectTransform>().rect.height * 0.5f;
            }
            else
            {
                //layoutGroup = (HorizontalLayoutGroup)layoutGroup;
                var lay = layoutGroup as HorizontalLayoutGroup;
                if (lay)
                {
                    _spacing = lay.spacing;
                }
                _centerPosX = _scrollRect.GetComponent<RectTransform>().rect.width * 0.5f;
            }
        }

        _scrollRect.onValueChanged.AddListener(_RefreshCurIndex);
        _isPlayingMove = false;
    }
    #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 void _RefreshCurIndex(Vector2 pos)
    {
        if (_itemList == null || _itemList.Count <= 0)
        {
            return;
        }
        _SetCurIndexFocus();
    }

    private void _SetCurIndexFocus()
    {
        var curIdx = FindClosestIndex();
        if (_curIndex != curIdx)
        {
            _curIndex = curIdx;
            var item = _itemList[curIdx];
            if (_focusItemFunc != null)
            {
                if (_focusItemFunc is Action<GameObject> action)
                {
                    action.Invoke(item);
                }
            }
            if (_unFocusItemFunc != null)
            {
                for (int i = 0; i < _itemList.Count; i++)
                {
                    if (i != curIdx)
                    {
                        if (_unFocusItemFunc is Action<GameObject> unFocusAction)
                        {
                            unFocusAction.Invoke(_itemList[i]);
                        } 
                    }
                }
            }
        }
    }

    private void _SetCachePosData()
    {
        if (_itemList == null || _itemList.Count <= 0)
        {
            return;
        }

        if (_childPosXList == null)
        {
            _childPosXList = new List<float>();
        }
        else
        {
            _childPosXList.Clear();
        }

        var childPosX = itemTemplate.GetComponent<RectTransform>().rect.width * 0.5f;
        _childPosXList.Add(childPosX);
        for (int i = 1; i < _itemList.Count; i++)
        {
            childPosX = childPosX + itemTemplate.GetComponent<RectTransform>().rect.width + _spacing;
            _childPosXList.Add(childPosX);
        }
    }

    private int FindClosestIndex()
    {
        int retIndex = 0;
        var contentPosX = _contentRectTrans.localPosition.x;
        var curCenterPosX = _centerPosX - contentPosX;
        
        var minDis = itemTemplate.GetComponent<RectTransform>().rect.width;
        for(int i = 0; i < _childPosXList.Count; i++)
        {
            var distance = Mathf.Abs(curCenterPosX - _childPosXList[i]);
            if (distance < minDis)
            {
                minDis = distance;
                retIndex = i;
            }
        }

        return retIndex;
    }

    private async void _DoMoveContent(bool isRight)
    {
        if (isRight)
        {
            _isPlayingMove = true;
            var curIndex = _curIndex + 1;
            if (curIndex < _maxIndex)
            {
                //计算相邻两个item之间的距离
                var oldPosX = _childPosXList[_curIndex];
                _curIndex++;
                var newPosX = _childPosXList[_curIndex];
                var distance = Mathf.Abs(oldPosX - newPosX);
                
                //播放移动动画
                var curPos = _contentRectTrans.localPosition;
                var childPosX = curPos.x - distance;
                var newPos = new Vector3(childPosX, curPos.y, curPos.z);
                _contentRectTrans.DOLocalMove(newPos, 0.75f);
                UniTask.Delay(750);
                _isPlayingMove = false;
            }
        }
        else
        {
            var curIndex = _curIndex - 1;
            if (curIndex > _minIndex)
            {
                //计算相邻两个item之间的距离
                var oldPosX = _childPosXList[_curIndex];
                _curIndex--;
                var newPosX = _childPosXList[_curIndex];
                var distance = Mathf.Abs(oldPosX - newPosX);
                
                //播放移动动画
                var curPos = _contentRectTrans.localPosition;
                var childPosX = curPos.x + distance;
                var newPos = new Vector3(childPosX, curPos.y, curPos.z);
                _contentRectTrans.DOLocalMove(newPos, 0.75f);
                UniTask.Delay(750);
                _isPlayingMove = false;
            }
        }
    }

    #region API

    public void Init()
    {
        _SetCachePosData();
        _SetCurIndexFocus();
    }
    public void SetData(List<GameObject> list, int maxIndex, int minIndex = 0)
    {
        _itemList = list;
        _maxIndex = maxIndex;
        _minIndex = minIndex;
    }

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

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

    public void ChangeIndex(bool isAdd)
    {
        if (_isPlayingMove)
        {
            return;
        }
        _DoMoveContent(isAdd);
    }

    #endregion
}