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

public class Asd : MonoBehaviour,IBeginDragHandler, IDragHandler,IEndDragHandler
{
  /// <summary>
  /// 可移動的最大最小X軸坐標
  /// </summary>
  private float minX, maxX;
  /// <summary>
  /// 開始觸摸時，算出偏移值，防止跳變
  /// </summary>
  private float offsetX;

  /// <summary>
  /// 靈敏度
  /// </summary>
  private float sensitivityX;
  /// <summary>
  /// 當前顯示第幾頁
  /// </summary>
  private int currentShowIndex = 1;

  private void Start()
  {
    (transform as RectTransform).pivot = new Vector2(0, 0.5f);
    Debug.Log(Screen.width + "  " + Screen.height);
    for (int i = 0; i < transform.childCount; i++)
    {
      (transform.GetChild(i) as RectTransform).sizeDelta = new Vector2(0, 0);
      //canvas的RenderMode要設置成Overlay形式
      //這里i*1080是因為canvas的UIScaleMode設置成了ScaleWithScreenSize，Resolution為x=1080,y=1920
      //如果canvas的UIScaleMode設置成ConstantPixelSize則吧這里的i*1080改成i*Screen.width
      (transform.GetChild(i) as RectTransform).anchoredPosition = new Vector2(i * 1080.0f, 0);
    }

    minX = -((transform.childCount - 1) * Screen.width);
    maxX = 0.0f;
    //如果移動超過頁面的五分之一，則切換頁面
    sensitivityX = Screen.width / 5;
  }

  public void OnBeginDrag(PointerEventData eventData)
  {
    offsetX = transform.position.x - Input.mousePosition.x;
  }

  public void OnDrag(PointerEventData eventData)
  {
    //將物體坐標限制在最大最小X軸坐標內
    transform.position = new Vector2(Input.mousePosition.x + offsetX, transform.position.y);
    if (transform.position.x <= minX)
    {
      transform.position = new Vector2(minX, transform.position.y);
    }
    else if (transform.position.x >= maxX)
    {
      transform.position = new Vector2(maxX, transform.position.y);
    }
  }

  public void OnEndDrag(PointerEventData eventData)
  {
    //判斷坐標，是否需要切換頁面
    if (transform.position.x > GetLeftX())
    {
      currentShowIndex--;
    }
    else if (transform.position.x < GetRightX())
    {
      currentShowIndex++;
    }
    transform.DOMoveX(-(currentShowIndex - 1) * Screen.width, 0.2f);
  }

  float GetLeftX() {
    return -((currentShowIndex - 1) * Screen.width - sensitivityX);
  }

  float GetRightX() {
    return -((currentShowIndex - 1) * Screen.width + sensitivityX);
  }
}