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

public class ScrollRectHelper : MonoBehaviour, IBeginDragHandler, IEndDragHandler
{
  // 滑動速度
  public float smooting = 5;

  // 每頁顯示的項目
  [SerializeField]
  private int countPerPage = 10;

  ScrollRect srect;
  // 總頁數
  float totalPages;
  // 是否拖拽結束
  bool isDrag = false;
  // 總頁數索引比列 0-1
  List<float> listPageValue = new List<float> { 0 };
  // 滑動的目標位置
  public float targetPos = 0;
  // 當前位置索引
  float nowindex = 0;                 

  void Awake()
  {
    srect = GetComponent<ScrollRect>();
  }

  public string PageText()
  {
    return (nowindex + 1) + "/" + (totalPages + 1);
  }

  // 計算每頁比例
  public void CalcListPageValue<T>() where T : MonoBehaviour
  {
    T[] items = srect.content.GetComponentsInChildren<T>();
    srect.content.rect.Set(srect.content.rect.width / 2, srect.content.rect.y, srect.content.rect.width, srect.content.rect.height);
    totalPages = (int)(Math.Ceiling((float)items.Length / countPerPage) - 1);
    if (items.Length != 0)
    {
      for (float i = 1; i <= totalPages; i++)
      {
        //Debug.Log(i / totalPages);
        listPageValue.Add((i / totalPages));
      }
    }
  }

  void Update()
  {
    if (!isDrag)
    {
      srect.horizontalNormalizedPosition = Mathf.Lerp(srect.horizontalNormalizedPosition, targetPos,
        Time.deltaTime * smooting);
    }

    // Debug
    if (Input.GetKeyDown(KeyCode.LeftArrow)) PressLeft();
    if (Input.GetKeyDown(KeyCode.RightArrow)) PressRight();
  }

  /// <summary>
  /// 拖動開始
  /// </summary>
  /// <param name="eventData"></param>
  public void OnBeginDrag(PointerEventData eventData)
  {
    isDrag = true;
  }

  /// <summary>
  /// 拖拽結束
  /// </summary>
  /// <param name="eventData"></param>
  public void OnEndDrag(PointerEventData eventData)
  {
    isDrag = false;
    var tempPos = srect.horizontalNormalizedPosition; //獲取拖動的值
    var index = 0;
    float offset = Mathf.Abs(listPageValue[index] - tempPos);  //拖動的絕對值
    for (int i = 1; i < listPageValue.Count; i++)
    {
      float temp = Mathf.Abs(tempPos - listPageValue[i]);
      if (temp < offset)
      {
        index = i;
        offset = temp;
      }
    }
    targetPos = listPageValue[index];
    nowindex = index;
  }

  public void PressLeft()
  {
    nowindex = Mathf.Clamp(nowindex - 1, 0, totalPages);
    targetPos = listPageValue[Convert.ToInt32(nowindex)];
  }

  public void PressRight()
  {
    nowindex = Mathf.Clamp(nowindex + 1, 0, totalPages);
    targetPos = listPageValue[Convert.ToInt32(nowindex)];
  }
}