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

public class PageTurning : MonoBehaviour, IPointerClickHandler,IPointerEnterHandler,IPointerExitHandler
{
    public Scrollbar slider;
    //检测鼠标是否在此UI上的布尔值
    public bool Isin;
    // Start is called before the first frame update
    void Start()
    {

    }

    // Update is called once per frame
    void Update()
    {
        ChangePage();
        MouseWheel();
        if (this.transform.childCount == 0)
        {
            slider.size = 1;
        }
        else 
        {
            ChangeScollbarLong();
        }
    }

    //让此页面的滚动跟随右侧的滑动条
    void ChangePage()
    {
        if (this.transform.childCount != 0)
        {
            float all=0;
            for (int n = 0; n < this.transform.childCount; n++)
            {
                if (n != 0)
                {
                    all += this.GetComponent<VerticalLayoutGroup>().spacing;
                }
                all += this.transform.GetChild(n).GetComponent<RectTransform>().sizeDelta.y;
            }
            //Debug.Log(all);
            if (all < this.transform.GetComponent<RectTransform>().sizeDelta.y)
            {
                return;
            }
            this.GetComponent<VerticalLayoutGroup>().padding.top = Convert.ToInt32(Math.Floor(-slider.value * (all - this.transform.GetComponent<RectTransform>().sizeDelta.y)));
            LayoutRebuilder.ForceRebuildLayoutImmediate(this.GetComponent<RectTransform>());
        }
    }

    public void OnPointerClick(PointerEventData pointerEventData)
    {
        
    }

    public void OnPointerEnter(PointerEventData pointerEventData)
    {
        Isin = true;
    }

    public void OnPointerExit(PointerEventData pointerEventData)
    {
        Isin = false;
    }

    void MouseWheel() 
    {
        if (Isin) 
        {
            slider.value += Input.GetAxis("Mouse ScrollWheel")*0.06f;
        }
        if (slider.value > 1) 
        {
            slider.value = 1;
        }
        if (slider.value < 0) 
        {
            slider.value = 0;
        }
    }

    void ChangeScollbarLong()
    {
        float all = 0;
        for (int n = 0; n < this.transform.childCount; n++)
        {
            all += this.transform.GetChild(n).GetComponent<RectTransform>().sizeDelta.y;
        }
        if (all < this.transform.GetComponent<RectTransform>().sizeDelta.y)
        {
            slider.size = 1;
        }
        else
        {
            slider.size = this.transform.GetComponent<RectTransform>().sizeDelta.y/all;
        }
    }
}