/// 主要關注屬性、事件及函數：
///  public int CurrentIndex;
///  public Action<int> OnIndexChange;
///  public virtual void MoveToIndex(int ind);
///  public virtual void AddChild(RectTransform t);
/// by yangxun
using UnityEngine;
using System.Collections;
using System.Collections.Generic;
using UnityEngine.UI;
using UnityEngine.EventSystems;
using System;
/// <summary>
/// 輪播圖組件
/// </summary>
[RequireComponent(typeof(RectTransform)), ExecuteInEditMode]
public class Carousel : UIBehaviour, IEventSystemHandler, IBeginDragHandler, IInitializePotentialDragHandler, IDragHandler, IEndDragHandler, ICanvasElement {
 
 /// <summary>
 /// 子物體size
 /// </summary>
 public Vector2 CellSize;
 /// <summary>
 /// 子物體間隔
 /// </summary>
 public Vector2 Spacing;
 /// <summary>
 /// 方向
 /// </summary>
 public Axis MoveAxis;
 /// <summary>
 /// Tween時的步數
 /// </summary>
 public int TweenStepCount = 10;
 /// <summary>
 /// 自動輪播
 /// </summary>
 public bool AutoLoop = false;
 /// <summary>
 /// 輪播間隔
 /// </summary>
 public float LoopSpace = 1;
 /// <summary>
 /// 輪播方向--1為向左移動，-1為向右移動
 /// </summary>
 public int LoopDir = 1;
 /// <summary>
 /// 可否拖動
 /// </summary>
 public bool Drag = true;
 /// <summary>
 /// 位于正中的子元素變化的事件,參數為index
 /// </summary>
 public Action<int> OnIndexChange;
 /// <summary>
 /// 當前處于正中的元素
 /// </summary>
 public int CurrentIndex {
  get {
   return m_index;
  }
 }
 
 private bool m_Dragging = false;
 private bool m_IsNormalizing = false;
 private Vector2 m_CurrentPos;
 private int m_currentStep = 0;
 private RectTransform viewRectTran;
 private Vector2 m_PrePos;
 private int m_index = 0,m_preIndex = 0;
 private RectTransform header;
 private bool contentCheckCache = true;
 
 private float currTimeDelta = 0;
 private float viewRectXMin {
  get{
   Vector3[] v = new Vector3[4];
   viewRectTran.GetWorldCorners(v);
   return v[0].x;
  }
 }
 private float viewRectXMax {
  get {
   Vector3[] v = new Vector3[4];
   viewRectTran.GetWorldCorners(v);
   return v[3].x;
  }
 }
 private float viewRectYMin {
  get {
   Vector3[] v = new Vector3[4];
   viewRectTran.GetWorldCorners(v);
   return v[0].y;
  }
 }
 private float viewRectYMax {
  get {
   Vector3[] v = new Vector3[4];
   viewRectTran.GetWorldCorners(v);
   return v[2].y;
  }
 }
 
 public int CellCount {
  get {
   return transform.childCount;
  }
 }
 protected override void Awake() {
  base.Awake();
  viewRectTran = GetComponent<RectTransform>();
  header = GetChild(viewRectTran, 0);
 }
 public void resizeChildren() {
  //init child size and pos
  Vector2 delta;
  if (MoveAxis == Axis.Horizontal) {
   delta = new Vector2(CellSize.x + Spacing.x, 0);
  }
  else {
   delta = new Vector2(0, CellSize.y + Spacing.y);
  }
  for (int i = 0; i < CellCount; i++) {
   var t = GetChild(viewRectTran, i);
   if (t) {
    t.localPosition = delta * i;
    t.sizeDelta = CellSize;
   }
  }
  m_IsNormalizing = false;
  m_CurrentPos = Vector2.zero;
  m_currentStep = 0;
 }
 /// <summary>
 /// 加子物體到當前列表的最后面
 /// </summary>
 /// <param name="t"></param>
 public virtual void AddChild(RectTransform t) {
  if (t!=null) {
   t.SetParent(viewRectTran, false);
   t.SetAsLastSibling();
   Vector2 delta;
   if (MoveAxis == Axis.Horizontal) {
    delta = new Vector2(CellSize.x + Spacing.x, 0);
   }
   else {
    delta = new Vector2(0, CellSize.y + Spacing.y);
   }
   if (CellCount == 0) {
    t.localPosition = Vector3.zero;
    header = t;
   }
   else {
    t.localPosition = delta + (Vector2)GetChild(viewRectTran,CellCount-1).localPosition;
   }
  }
 }
 protected override void OnEnable() {
  base.OnEnable();
  resizeChildren();
  return;
  if (Application.isPlaying) {
   if (ContentIsLongerThanRect()) {
    int s;
    do {
     s = GetBoundaryState();
     LoopCell(s);
    } while (s != 0);
   }
  }
 }
 protected virtual void Update() {
  if (ContentIsLongerThanRect()) {
   //實現在必要時loop子元素
   if (Application.isPlaying) {
    int s = GetBoundaryState();
    LoopCell(s);
   }
   //緩動回指定位置
   if (m_IsNormalizing && EnsureListCanAdjust()) {
    if (m_currentStep == TweenStepCount) {
     m_IsNormalizing = false;
     m_currentStep = 0;
     m_CurrentPos = Vector2.zero;
     return;
    }
    Vector2 delta = m_CurrentPos/TweenStepCount;
    m_currentStep++;
    TweenToCorrect(-delta);
   }
   //自動loop
   if (AutoLoop && !m_IsNormalizing && EnsureListCanAdjust()) {
    currTimeDelta += Time.deltaTime;
    if (currTimeDelta>LoopSpace) {
     currTimeDelta = 0;
     MoveToIndex(m_index + LoopDir);
    }
   }
   //檢測index是否變化
   if (MoveAxis == Axis.Horizontal) {
    m_index = (int)(header.localPosition.x / (CellSize.x + Spacing.x-1));
   }
   else {
    m_index = (int)(header.localPosition.y / (CellSize.y + Spacing.y-1));
   }
   if (m_index<=0) {
    m_index = Mathf.Abs(m_index);
   }
   else {
    m_index = CellCount - m_index;
   }
   if (m_index != m_preIndex) {
    if (OnIndexChange != null) {
     OnIndexChange(m_index);
    }
   }
   m_preIndex = m_index;
  }
 }
 public virtual void OnBeginDrag(PointerEventData eventData) {
  if (!Drag || !contentCheckCache) {
   return;
  }
  Vector2 vector;
  if (((eventData.button == PointerEventData.InputButton.Left) && this.IsActive()) && RectTransformUtility.ScreenPointToLocalPointInRectangle(this.viewRectTran, eventData.position, eventData.pressEventCamera, out vector)) {
   this.m_Dragging = true;
   m_PrePos = vector;
  }
 }
 
 public virtual void OnInitializePotentialDrag(PointerEventData eventData) {
  if (!Drag) {
   return;
  }
  return;
 }
 
 public virtual void OnDrag(PointerEventData eventData) {
  if (!Drag || !contentCheckCache) {
   return;
  }
  Vector2 vector;
  if (((eventData.button == PointerEventData.InputButton.Left) && this.IsActive()) && RectTransformUtility.ScreenPointToLocalPointInRectangle(this.viewRectTran, eventData.position, eventData.pressEventCamera, out vector)) {
   m_IsNormalizing = false;
   m_CurrentPos = Vector2.zero;
   m_currentStep = 0;
   Vector2 vector2 = vector - this.m_PrePos;
   Vector2 vec = CalculateOffset(vector2);
   this.SetContentPosition(vec);
   m_PrePos = vector;
  }
 }
 /// <summary>
 /// 移動到指定索引
 /// </summary>
 /// <param name="ind"></param>
 public virtual void MoveToIndex(int ind) {
  if (m_IsNormalizing) {
   return;
  }
  //Debug.LogFormat("{0}->{1}",m_index,ind);
  if (ind == m_index) {
   return;
  }
  this.m_IsNormalizing = true;
  Vector2 offset;
  if (MoveAxis == Axis.Horizontal) {
   offset = new Vector2(CellSize.x + Spacing.x, 0);
  }
  else {
   offset = new Vector2(0, CellSize.y + Spacing.y);
  }
  var delta = CalcCorrectDeltaPos();
  int vindex = m_index;
  m_CurrentPos = delta + offset * (ind - vindex);
  //m_CurrentPos = -(Vector2)header.localPosition + offset * (ind - m_index);
  m_currentStep = 0;
 }
 private Vector2 CalculateOffset(Vector2 delta) {
  if (MoveAxis == Axis.Horizontal) {
   delta.y = 0;
  }
  else {
   delta.x = 0;
  }
  return delta;
 }
 private void SetContentPosition(Vector2 position) {
  foreach (RectTransform i in viewRectTran) {
   i.localPosition += (Vector3)position;
  }
  return;
 }
 
 public virtual void OnEndDrag(PointerEventData eventData) {
  if (!Drag || !contentCheckCache) {
   return;
  }
  this.m_Dragging = false;
  this.m_IsNormalizing = true;
  m_CurrentPos = CalcCorrectDeltaPos();
  m_currentStep = 0;
 }
 
 public virtual void Rebuild(CanvasUpdate executing) {
  return;
 }
 /// <summary>
 /// List是否處于可自由調整狀態
 /// </summary>
 /// <returns></returns>
 public virtual bool EnsureListCanAdjust() {
  return !m_Dragging && ContentIsLongerThanRect();
 }
 /// <summary>
 /// 內容是否比顯示范圍大
 /// </summary>
 /// <returns></returns>
 public virtual bool ContentIsLongerThanRect() {
  float contentLen;
  float rectLen;
  if (MoveAxis == Axis.Horizontal) {
   contentLen = CellCount*(CellSize.x + Spacing.x) - Spacing.x;
   rectLen = viewRectTran.rect.xMax - viewRectTran.rect.xMin;
  }
  else {
   contentLen = CellCount * (CellSize.y + Spacing.y) - Spacing.y;
   rectLen = viewRectTran.rect.yMax - viewRectTran.rect.yMin;
  }
  contentCheckCache = contentLen > rectLen;
  return contentCheckCache;
 }
 /// <summary>
 /// 檢測邊界情況，分為0未觸界，-1左(下)觸界，1右(上)觸界
 /// </summary>
 /// <returns></returns>
 public virtual int GetBoundaryState() {
  RectTransform left;
  RectTransform right;
  left = GetChild(viewRectTran, 0);
  right = GetChild(viewRectTran, CellCount - 1);
  Vector3[] l = new Vector3[4];
  left.GetWorldCorners(l);
  Vector3[] r = new Vector3[4];
  right.GetWorldCorners(r);
  if (MoveAxis == Axis.Horizontal) {
   if (l[0].x>=viewRectXMin) {
    return -1;
   }
   else if (r[3].x < viewRectXMax) {
    return 1;
   }
  }
  else {
   if (l[0].y >= viewRectYMin) {
    return -1;
   }
   else if (r[1].y < viewRectYMax) {
    return 1;
   }
  }
  return 0;
 }
 /// <summary>
 /// Loop列表，分為-1把最右(上)邊一個移到最左(下)邊，1把最左(下)邊一個移到最右(上)邊
 /// </summary>
 /// <param name="dir"></param>
 protected virtual void LoopCell(int dir) {
  if (dir == 0) {
   return;
  }
  RectTransform MoveCell;
  RectTransform Tarborder;
  Vector2 TarPos;
  if (dir == 1) {
   MoveCell = GetChild(viewRectTran, 0);
   Tarborder = GetChild(viewRectTran, CellCount - 1);
   MoveCell.SetSiblingIndex(CellCount-1);
  }
  else {
   Tarborder = GetChild(viewRectTran, 0);
   MoveCell = GetChild(viewRectTran, CellCount - 1);
   MoveCell.SetSiblingIndex(0);
  }
  if (MoveAxis == Axis.Horizontal) {
   TarPos = Tarborder.localPosition + new Vector3((CellSize.x + Spacing.x) * dir, 0,0);
  }
  else {
   TarPos = (Vector2)Tarborder.localPosition + new Vector2(0, (CellSize.y + Spacing.y) * dir);
  }
  MoveCell.localPosition = TarPos;
 }
 /// <summary>
 /// 計算一個最近的正確位置
 /// </summary>
 /// <returns></returns>
 public virtual Vector2 CalcCorrectDeltaPos() {
  Vector2 delta = Vector2.zero;
  float distance = float.MaxValue;
  foreach (RectTransform i in viewRectTran) {
   var td = Mathf.Abs(i.localPosition.x) + Mathf.Abs(i.localPosition.y);
   if (td<=distance) {
    distance = td;
    delta = i.localPosition;
   }
   else {
    break;
   }
  }
  return delta;
 }
 /// <summary>
 /// 移動指定增量
 /// </summary>
 protected virtual void TweenToCorrect(Vector2 delta) {
  foreach (RectTransform i in viewRectTran) {
   i.localPosition += (Vector3)delta;
  }
 }
 public enum Axis {
  Horizontal,
  Vertical
 }
 private static RectTransform GetChild(RectTransform parent, int index) {
  if (parent == null||index>=parent.childCount) {
   return null;
  }
  return parent.GetChild(index) as RectTransform;
 }
}