using UnityEngine;
using System.Collections;
using UnityEngine.UI;
using System.Collections.Generic;
using UnityEngine.EventSystems;
using System;
 
public class PageView : MonoBehaviour, IBeginDragHandler, IEndDragHandler {
  ScrollRect rect;      //滑動組件 
 //public ScrollRect rect2;      //滑動組件2 
 
 private float targethorizontal = 0;    //滑動的起始坐標 
 private bool isDrag = false;     //是否拖拽結(jié)束 
 private List<float> posList = new List<float> ();//求出每頁的臨界角，頁索引從0開始 
 private int currentPageIndex = -1;
 public Action<int> OnPageChanged;
 
 private bool stopMove = true;
 public float smooting = 4;  //滑動速度 
 public float sensitivity = 0;
 private float startTime;
 
 private float startDragHorizontal; 
 
 
 void Awake () {
  // rect = rect2;
  rect = transform.GetComponent<ScrollRect> ();
  // rect2 = transform.GetComponent<ScrollRect>();
  float horizontalLength = rect.content.rect.width - GetComponent<RectTransform> ().rect.width;
  //float horizontalLength2 = rect2.content.rect.width - GetComponent<RectTransform>().rect.width;
  posList.Add (0);
  for(int i = 1; i < rect.content.transform.childCount - 1; i++) {
   posList.Add (GetComponent<RectTransform> ().rect.width * i / horizontalLength);
  }
  posList.Add (1);
 }
 
 void Update () {
  if(!isDrag && !stopMove) {
   startTime += Time.deltaTime;
   float t = startTime * smooting;
   rect.horizontalNormalizedPosition = Mathf.Lerp (rect.horizontalNormalizedPosition , targethorizontal , t);
   // rect2.horizontalNormalizedPosition = Mathf.Lerp(rect2.horizontalNormalizedPosition, targethorizontal, t);
   if (t >= 1)
    stopMove = true;
  }
 }
 
 public void pageTo (int index) {
  if(index >= 0 && index < posList.Count) {
   rect.horizontalNormalizedPosition = posList[index];
   SetPageIndex(index);
  } else {
   Debug.LogWarning ("頁碼不存在");
  }
 }
 private void SetPageIndex (int index) {
  if(currentPageIndex != index) {
   currentPageIndex = index;
   if(OnPageChanged != null)
    OnPageChanged (index);
  }
 }
 
 public void OnBeginDrag (PointerEventData eventData) {
  isDrag = true;
  startDragHorizontal = rect.horizontalNormalizedPosition;
  // startDragHorizontal = rect2.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;
   }
  }
  SetPageIndex (index);
 
  targethorizontal = posList[index]; //設置當前坐標，更新函數(shù)進行插值 
  isDrag = false;
  startTime = 0;
  stopMove = false;
 } 
}