using UnityEngine;
using System.Collections;
using UnityEngine.UI;
using System.Collections.Generic;
using UnityEngine.EventSystems;
using System;

public class PageView : MonoBehaviour, IBeginDragHandler, IEndDragHandler
{
    public int PageCount;
    public float SlideSpeed = 4;  //滑动速度 
    public float sensitivity = 0.3f;

    public Action<int> OnPageChanged;

    ScrollRect rect;      //滑动组件
    private float targethorizontal = 0;    //滑动的起始坐标 
    private bool isDrag = false;     //是否拖拽结束 
    List<float> posList = new List<float>();//求出每页的临界角，页索引从0开始 
    private int currentPageIndex = -1;

    private bool stopMove = true;
    private float startTime;

    private float startDragHorizontal;


    void Awake()
    {
        rect = transform.GetComponent<ScrollRect>();

        int tSplitCount = Mathf.Max(1, PageCount);
        float tDelta = tSplitCount > 1 ? (1f / (tSplitCount - 1)) : 1;

        for (int i = 0; i < tSplitCount; i++)
        {
            posList.Add(tDelta * i);
        }
    }

    void Update()
    {
        if (!isDrag && !stopMove)
        {
            startTime += Time.deltaTime;
            float t = startTime * SlideSpeed;
            rect.horizontalNormalizedPosition = Mathf.Lerp(rect.horizontalNormalizedPosition, targethorizontal, t);
            if (t >= 1)
                stopMove = true;
        }
    }

    public void PageFix(int index)
    {
        PageTo(index, false);
    }

    public void PageScroll(int index)
    {
        PageTo(index);
    }

    public void PageTo(int index, bool pWithScroll = true)
    {
        if (index >= 0 && index < posList.Count)
        {
            if (currentPageIndex != index)
            {
                currentPageIndex = index;

                if (OnPageChanged != null)
                    OnPageChanged(index);
            }

            if (pWithScroll)
            {
                targethorizontal = posList[currentPageIndex]; //设置当前坐标，更新函数进行插值 
                isDrag = false;
                startTime = 0;
                stopMove = false;
            }
            else
            {
                rect.horizontalNormalizedPosition = posList[index];
            }
        }
        else
        {
            Debug.LogError("页码不存在");
        }
    }

    public void OnBeginDrag(PointerEventData eventData)
    {
        isDrag = true;
        startDragHorizontal = rect.horizontalNormalizedPosition;
    }

    public void OnEndDrag(PointerEventData eventData)
    {
        float posX = rect.horizontalNormalizedPosition;
        posX += ((posX - startDragHorizontal) * sensitivity);
        posX = posX < 1 ? posX : 1;
        posX = posX > 0 ? posX : 0;
        int index = 0;
        float offset = Mathf.Abs(posList[index] - posX);
        for (int i = 1; i < posList.Count; i++)
        {
            float temp = Mathf.Abs(posList[i] - posX);
            if (temp < offset)
            {
                index = i;
                offset = temp;
            }
        }
        PageTo(index);
    }
}