using UnityEngine;
using UnityEngine.UI;
using UnityEngine.EventSystems;
 
/// <summary>
/// 自動吸附的滑動列表
/// </summary>
public class AutoAdsorbScrollView : MonoBehaviour, IBeginDragHandler, IEndDragHandler
{
    private ScrollRect scrollRect;//滑動框組件
    private RectTransform content;//滑動框的Content
    private GridLayoutGroup layout;//布局組件
 
    private int totalPage; //總頁數(shù)
    private int curPage; //當(dāng)前頁的下標(biāo)
    private float[] eachPageNUPos; //每頁的NormalizedPositon的值
    private float targetNUPos; //目標(biāo)頁的NormalizedPositon的值
 
    private Vector2 beginMousePos; //鼠標(biāo)開始按下的位置
    private Vector2 endMousePos; //鼠標(biāo)結(jié)束按下的位置
    private bool isDrag; //是否在拖拽
 
    [Header("是否可以滑動多頁")]
    public bool sliderMultPage;
 
    [Header("視為滑動一頁的距離")]
    [Space(25)]
    public float sliderOnePageDis;
    [Header("視為滑動多頁的距離")]
    public float sliderMultPageDis;
    [Header("緩動到目標(biāo)頁的持續(xù)時間")]
    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();//設(shè)置Content大小
 
        CalcEachPageNUPos();//計算每一頁的NormalizedPositon值
 
        SetLayout();//設(shè)置布局
    }
 
    /// <summary>
    /// 設(shè)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>
    /// 計算每一頁的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>
    /// 設(shè)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>
    /// 拖拽開始
    /// </summary>
    public void OnBeginDrag(PointerEventData eventData)
    {
        isDrag = true;
        beginMousePos = Input.mousePosition;
    }
 
    /// <summary>
    /// 拖拽結(jié)束
    /// </summary>
    /// <param name="eventData"></param>
    public void OnEndDrag(PointerEventData eventData)
    {
        isDrag = false;
        coe = 0;
 
        endMousePos = Input.mousePosition;
        Vector2 offset = endMousePos - beginMousePos;
        Debug.Log("滑動距離為：" + offset);
 
        if (sliderMultPage)
        {
            //單頁滑動
            if (Mathf.Abs(offset.x) >= sliderOnePageDis && Mathf.Abs(offset.x) < sliderMultPageDis)
            {
                float tempHorizontalNUPos = scrollRect.horizontalNormalizedPosition;
                FindNearlyPage(tempHorizontalNUPos);
            }
            //多頁滑動
            else if (Mathf.Abs(offset.x) >= sliderMultPageDis)
            {
                if (offset.x > 0)
                {
                    curPage = 0;
                }
                else if (offset.x < 0)
                {
                    curPage = totalPage - 1;
                }
            }
        }
        else
        {
            //單頁滑動
            if (Mathf.Abs(offset.x) >= sliderOnePageDis)
            {
                float tempHorizontalNUPos = scrollRect.horizontalNormalizedPosition;
                FindNearlyPage(tempHorizontalNUPos);
            }
        }
 
        targetNUPos = eachPageNUPos[curPage];
    }
 
    private float coe;//比例系數(shù)
    private void Update()
    {
        if (isDrag)
        {
            return;
        }
        coe += Time.deltaTime / duration;
        scrollRect.horizontalNormalizedPosition = Mathf.Lerp(scrollRect.horizontalNormalizedPosition, targetNUPos, coe);
    }
 
    #endregion
 
    #region Tool
 
    /// <summary>
    /// 尋找距離當(dāng)前NormalizedPositon最近的頁
    /// </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
}