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using UnityEngine;

using UnityEngine.UI;

using UnityEngine.EventSystems;

/// <summary>

/// 自动吸附的滑动列表

/// </summary>

public class AutoAdsorbScrollView : MonoBehaviour, IBeginDragHandler, IEndDragHandler

{

    private ScrollRect scrollRect;//滑动框组件

    private RectTransform content;//滑动框的Content

    private GridLayoutGroup layout;//布局组件

    private int totalPage; //总页数

    private int curPage; //当前页的下标

    private float[] eachPageNUPos; //每页的NormalizedPositon的值

    private float targetNUPos; //目标页的NormalizedPositon的值

    private Vector2 beginMousePos; //鼠标开始按下的位置

    private Vector2 endMousePos; //鼠标结束按下的位置

    private bool isDrag; //是否在拖拽

    [Header("是否可以滑动多页")]

    public bool sliderMultPage;

    [Header("视为滑动一页的距离")]

    [Space(25)]

    public float sliderOnePageDis;

    [Header("视为滑动多页的距离")]

    public float sliderMultPageDis;

    [Header("缓动到目标页的持续时间")]

    public float duration;

    #region Init

    private void Awake()

    {

        scrollRect = GetComponent<ScrollRect>();

        content = scrollRect.content;

        layout = content.GetComponent<GridLayoutGroup>();

        Init();//初始化

    }

    /// <summary>

    /// 初始化

    /// </summary>

    private void Init()

    {

        totalPage = content.childCount;

        SetContentSize();//设置Content大小

        CalcEachPageNUPos();//计算每一页的NormalizedPositon值

        SetLayout();//设置布局

    }

    /// <summary>

    /// 设置Content大小

    /// </summary>

    private void SetContentSize()

    {

        content.sizeDelta = new Vector2

            (

                layout.padding.right + layout.padding.left + (totalPage - 1) * (layout.cellSize.x + layout.spacing.x) - layout.spacing.x,

                content.sizeDelta.y

            ); ;

    }

    /// <summary>

    /// 计算每一页的NormalizedPositon值

    /// </summary>

    private void CalcEachPageNUPos()

    {

        float tempNUPos = 0;

        eachPageNUPos = new float[totalPage];

        for (int i = 0; i < totalPage; i++)

        {

            eachPageNUPos[i] = tempNUPos;

            tempNUPos += 1f / (totalPage - 1);

        }

    }

    /// <summary>

    /// 设置布局

    /// </summary>

    private void SetLayout()

    {

        scrollRect.horizontal = true;

        scrollRect.vertical = false;

        layout.padding.right = layout.padding.left;

        layout.startCorner = GridLayoutGroup.Corner.UpperLeft;

        layout.childAlignment = TextAnchor.MiddleCenter;

        layout.constraintCount = 1;

    }

    #endregion

    #region Main

    /// <summary>

    /// 拖拽开始

    /// </summary>

    public void OnBeginDrag(PointerEventData eventData)

    {

        isDrag = true;

        beginMousePos = Input.mousePosition;

    }

    /// <summary>

    /// 拖拽结束

    /// </summary>

    /// <param name="eventData"></param>

    public void OnEndDrag(PointerEventData eventData)

    {

        isDrag = false;

        coe = 0;

        endMousePos = Input.mousePosition;

        Vector2 offset = endMousePos - beginMousePos;

        Debug.Log("滑动距离为：" + offset);

        if (sliderMultPage)

        {

            //单页滑动

            if (Mathf.Abs(offset.x) >= sliderOnePageDis && Mathf.Abs(offset.x) < sliderMultPageDis)

            {

                float tempHorizontalNUPos = scrollRect.horizontalNormalizedPosition;

                FindNearlyPage(tempHorizontalNUPos);

            }

            //多页滑动

            else if (Mathf.Abs(offset.x) >= sliderMultPageDis)

            {

                if (offset.x > 0)

                {

                    curPage = 0;

                }

                else if (offset.x < 0)

                {

                    curPage = totalPage - 1;

                }

            }

        }

        else

        {

            //单页滑动

            if (Mathf.Abs(offset.x) >= sliderOnePageDis)

            {

                float tempHorizontalNUPos = scrollRect.horizontalNormalizedPosition;

                FindNearlyPage(tempHorizontalNUPos);

            }

        }

        targetNUPos = eachPageNUPos[curPage];

    }

    private float coe;//比例系数

    private void Update()

    {

        if (isDrag)

        {

            return;

        }

        coe += Time.deltaTime / duration;

        scrollRect.horizontalNormalizedPosition = Mathf.Lerp(scrollRect.horizontalNormalizedPosition, targetNUPos, coe);

    }

    #endregion

    #region Tool

    /// <summary>

    /// 寻找距离当前NormalizedPositon最近的页

    /// </summary>

    private void FindNearlyPage(float tempHorizontalNUPos)

    {

        float minOffset = Mathf.Abs(eachPageNUPos[0] - tempHorizontalNUPos);

        for (int i = 0; i < totalPage; i++)

        {

            float tempHorizontalOffset = Mathf.Abs(eachPageNUPos[i] - tempHorizontalNUPos);

            if (tempHorizontalOffset <= minOffset)

            {

                minOffset = tempHorizontalOffset;

                curPage = i;

            }

        }

    }

    #endregion

}