using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;
using System.Linq;
 
/// <summary>
/// 無限滑動列表
/// </summary>
public class InfiniteScrollView : MonoBehaviour
{
    private ScrollRect scrollRect;//滑動框組件
    private RectTransform content;//滑動框的Content
    private GridLayoutGroup layout;//布局組件
 
    [Header("滑動類型")]
    public ScrollType scrollType;
    [Header("固定的Item數(shù)量")]
    public int fixedCount;
    [Header("Item的預(yù)制體")]
    public GameObject itemPrefab;
 
    private int totalCount;//總的數(shù)據(jù)數(shù)量
    private List<RectTransform> dataList = new List<RectTransform>();//數(shù)據(jù)實(shí)體列表
    private int headIndex;//頭下標(biāo)
    private int tailIndex;//尾下標(biāo)
    private Vector2 firstItemAnchoredPos;//第一個(gè)Item的錨點(diǎn)坐標(biāo)
 
    #region Init
 
    /// <summary>
    /// 實(shí)例化Item
    /// </summary>
    private void InitItem()
    {
        for (int i = 0; i < fixedCount; i++)
        {
            GameObject tempItem = Instantiate(itemPrefab, content);
            dataList.Add(tempItem.GetComponent<RectTransform>());
            SetShow(tempItem.GetComponent<RectTransform>(), i);
        }
    }
 
    /// <summary>
    /// 設(shè)置Content大小
    /// </summary>
    private void SetContentSize()
    {
        content.sizeDelta = new Vector2
            (
                layout.padding.left + layout.padding.right + totalCount * (layout.cellSize.x + layout.spacing.x) - layout.spacing.x - content.rect.width,
                layout.padding.top + layout.padding.bottom + totalCount * (layout.cellSize.y + layout.spacing.y) - layout.spacing.y
            );
    }
 
    /// <summary>
    /// 設(shè)置布局
    /// </summary>
    private void SetLayout()
    {
        layout.startCorner = GridLayoutGroup.Corner.UpperLeft;
        layout.startAxis = GridLayoutGroup.Axis.Horizontal;
        layout.childAlignment = TextAnchor.UpperLeft;
        layout.constraintCount = 1;
        if (scrollType == ScrollType.Horizontal)
        {
            scrollRect.horizontal = true;
            scrollRect.vertical = false;
            layout.constraint = GridLayoutGroup.Constraint.FixedRowCount;
        }
        else if (scrollType == ScrollType.Vertical)
        {
            scrollRect.horizontal = false;
            scrollRect.vertical = true;
            layout.constraint = GridLayoutGroup.Constraint.FixedColumnCount;
        }
    }
 
    /// <summary>
    /// 得到第一個(gè)數(shù)據(jù)的錨點(diǎn)位置
    /// </summary>
    private void GetFirstItemAnchoredPos()
    {
        firstItemAnchoredPos = new Vector2
            (
                layout.padding.left + layout.cellSize.x / 2,
                -layout.padding.top - layout.cellSize.y / 2
            );
    }
 
    #endregion
 
    #region Main
 
    /// <summary>
    /// 滑動中
    /// </summary>
    private void OnScroll(Vector2 v)
    {
        if (dataList.Count == 0)
        {
            Debug.LogWarning("先調(diào)用SetTotalCount方法設(shè)置數(shù)據(jù)總數(shù)量再調(diào)用Init方法進(jìn)行初始化");
            return;
        }
 
        if (scrollType == ScrollType.Vertical)
        {
            //向上滑
            while (content.anchoredPosition.y >= layout.padding.top + (headIndex + 1) * (layout.cellSize.y + layout.spacing.y)
            && tailIndex != totalCount - 1)
            {
                //將數(shù)據(jù)列表中的第一個(gè)元素移動到最后一個(gè)
                RectTransform item = dataList[0];
                dataList.Remove(item);
                dataList.Add(item);
 
                //設(shè)置位置
                SetPos(item, tailIndex + 1);
                //設(shè)置顯示
                SetShow(item, tailIndex + 1);
 
                headIndex++;
                tailIndex++;
            }
            //向下滑
            while (content.anchoredPosition.y <= layout.padding.top + headIndex * (layout.cellSize.y + layout.spacing.y)
                && headIndex != 0)
            {
                //將數(shù)據(jù)列表中的最后一個(gè)元素移動到第一個(gè)
                RectTransform item = dataList.Last();
                dataList.Remove(item);
                dataList.Insert(0, item);
 
                //設(shè)置位置
                SetPos(item, headIndex - 1);
                //設(shè)置顯示
                SetShow(item, headIndex - 1);
 
                headIndex--;
                tailIndex--;
            }
        }
        else if (scrollType == ScrollType.Horizontal)
        {
            //向左滑
            while (content.anchoredPosition.x <= -layout.padding.left - (headIndex + 1) * (layout.cellSize.x + layout.spacing.x)
            && tailIndex != totalCount - 1)
            {
                //將數(shù)據(jù)列表中的第一個(gè)元素移動到最后一個(gè)
                RectTransform item = dataList[0];
                dataList.Remove(item);
                dataList.Add(item);
 
                //設(shè)置位置
                SetPos(item, tailIndex + 1);
                //設(shè)置顯示
                SetShow(item, tailIndex + 1);
 
                headIndex++;
                tailIndex++;
            }
            //向右滑
            while (content.anchoredPosition.x >= -layout.padding.left - headIndex * (layout.cellSize.x + layout.spacing.x)
            && headIndex != 0)
            {
                //將數(shù)據(jù)列表中的最后一個(gè)元素移動到第一個(gè)
                RectTransform item = dataList.Last();
                dataList.Remove(item);
                dataList.Insert(0, item);
 
                //設(shè)置位置
                SetPos(item, headIndex - 1);
                //設(shè)置顯示
                SetShow(item, headIndex - 1);
 
                headIndex--;
                tailIndex--;
            }
        }
    }
 
    #endregion
 
    #region Tool
 
    /// <summary>
    /// 設(shè)置位置
    /// </summary>
    private void SetPos(RectTransform trans, int index)
    {
        if (scrollType == ScrollType.Horizontal)
        {
            trans.anchoredPosition = new Vector2
            (
                index == 0 ? layout.padding.left + firstItemAnchoredPos.x :
                layout.padding.left + firstItemAnchoredPos.x + index * (layout.cellSize.x + layout.spacing.x),
                firstItemAnchoredPos.y
            );
        }
        else if (scrollType == ScrollType.Vertical)
        {
            trans.anchoredPosition = new Vector2
            (
                firstItemAnchoredPos.x,
                index == 0 ? -layout.padding.top + firstItemAnchoredPos.y :
                -layout.padding.top + firstItemAnchoredPos.y - index * (layout.cellSize.y + layout.spacing.y)
            );
        }
    }
 
    #endregion
 
    #region 外部調(diào)用
 
    /// <summary>
    /// 初始化
    /// </summary>
    public void Init()
    {
        scrollRect = GetComponent<ScrollRect>();
        content = scrollRect.content;
        layout = content.GetComponent<GridLayoutGroup>();
        scrollRect.onValueChanged.AddListener((Vector2 v) => OnScroll(v));
 
        //設(shè)置布局
        SetLayout();
 
        //設(shè)置頭下標(biāo)和尾下標(biāo)
        headIndex = 0;
        tailIndex = fixedCount - 1;
 
        //設(shè)置Content大小
        SetContentSize();
 
        //實(shí)例化Item
        InitItem();
 
        //得到第一個(gè)Item的錨點(diǎn)位置
        GetFirstItemAnchoredPos();
    }
 
    /// <summary>
    /// 設(shè)置顯示
    /// </summary>
    public void SetShow(RectTransform trans, int index)
    {
        //=====根據(jù)需求進(jìn)行編寫
        trans.GetComponentInChildren<Text>().text = index.ToString();
        trans.name = index.ToString();
    }
 
    /// <summary>
    /// 設(shè)置總的數(shù)據(jù)數(shù)量
    /// </summary>
    public void SetTotalCount(int count)
    {
        totalCount = count;
    }
 
    /// <summary>
    /// 銷毀所有的元素
    /// </summary>
    public void DestoryAll()
    {
        for (int i = dataList.Count - 1; i >= 0; i--)
        {
            DestroyImmediate(dataList[i].gameObject);
        }
        dataList.Clear();
    }
 
    #endregion
}
 
/// <summary>
/// 滑動類型
/// </summary>
public enum ScrollType
{
    Horizontal,//豎直滑動
    Vertical,//水平滑動
}