interface IState
 {
  string Name { get; set; }
  //后件處理
  IList<IState> Nexts { get; set; }
  Func<IState /*this*/, IState /*next*/> Selector { get; set; }
  
 }
 class State : IState
 {
  public string Name { get; set; } = "State";

  IList<IState> IState.Nexts { get; set; } = new List<IState>();
  public Func<IState, IState> Selector { get; set; }
 }

delegate bool HandleType<T>(IState current, IState previous,ref T value);
 interface IContext<T> : IEnumerator<T>, IEnumerable<T>
 {
  //data
  T Value { get; set; }
  //前件處理
  IDictionary<Tuple<IState/*this*/, IState/*previous*/>, HandleType<T>> Handles { get; set; }
  IState CurrentState { get; set; }
  bool transition(IState next);
 }

class Context<T> : IContext<T>
 {
  T data;
  T IContext<T>.Value { get=>data ; set=>data = value; }
  IDictionary<Tuple<IState, IState>, HandleType<T>> IContext<T>.Handles { get; set; } 
   = new Dictionary<Tuple<IState, IState>, HandleType<T>>();
  public IState CurrentState { get; set;}
  T IEnumerator<T>.Current => (this as IContext<T>).Value ;
  object IEnumerator.Current => (this as IContext<T>).Value;
  bool IContext<T>.transition(IState next)
  {
   IContext<T> context= this as IContext<T>;
   if (context.CurrentState == null || context.CurrentState.Nexts.Contains(next))
   {
    //前件處理
    var key = Tuple.Create(next, context.CurrentState);
    if (context.Handles.ContainsKey(key) && context.Handles[key] !=null)
     if (!context.Handles[key](next, context.CurrentState,ref this.data))
      return false;

    context.CurrentState = next;
    return true;
   }
   return false;
  }
  bool IEnumerator.MoveNext()
  {
   //后件處理
   IContext<T> context = this as IContext<T>;
   IState current = context.CurrentState; 
   if (current == null)
    throw new Exception("必須設(shè)置初始狀態(tài)");
   if (context.CurrentState.Selector != null)
   {
    IState next= context.CurrentState.Selector(context.CurrentState);
    return context.transition(next);
   }
   return false;
  }
  void IEnumerator.Reset()
  {
   throw new NotImplementedException();
  }
  #region IDisposable Support
  private bool disposedValue = false; // 要檢測(cè)冗余調(diào)用
  protected virtual void Dispose(bool disposing)
  {
   if (!disposedValue)
   {
    if (disposing)
    {
     // TODO: 釋放托管狀態(tài)(托管對(duì)象)。
    }
    // TODO: 釋放未托管的資源(未托管的對(duì)象)并在以下內(nèi)容中替代終結(jié)器。
    // TODO: 將大型字段設(shè)置為 null。
    disposedValue = true;
   }
  }
  // TODO: 僅當(dāng)以上 Dispose(bool disposing) 擁有用于釋放未托管資源的代碼時(shí)才替代終結(jié)器。
  // ~Context() {
  // // 請(qǐng)勿更改此代碼。將清理代碼放入以上 Dispose(bool disposing) 中。
  // Dispose(false);
  // }
  // 添加此代碼以正確實(shí)現(xiàn)可處置模式。
  void IDisposable.Dispose()
  {
   // 請(qǐng)勿更改此代碼。將清理代碼放入以上 Dispose(bool disposing) 中。
   Dispose(true);
   // TODO: 如果在以上內(nèi)容中替代了終結(jié)器，則取消注釋以下行。
   // GC.SuppressFinalize(this);
  }
  IEnumerator<T> IEnumerable<T>.GetEnumerator()
  {
   return this;
  }
  IEnumerator IEnumerable.GetEnumerator()
  {
   return this;
  }
  #endregion
 }

bool IContext<T>.transition(IState next)
  {
   IContext<T> context= this as IContext<T>;
   if (context.CurrentState == null || context.CurrentState.Nexts.Contains(next))
   {
    //前件處理
    var key = Tuple.Create(next, context.CurrentState);
    if (context.Handles.ContainsKey(key) && context.Handles[key] !=null)
     if (!context.Handles[key](next, context.CurrentState,ref this.data))
      return false;
    context.CurrentState = next;
    return true;
   }
   return false;
  }

bool IEnumerator.MoveNext()
  {
   //后件處理
   IContext<T> context = this as IContext<T>;
   IState current = context.CurrentState; 
   if (current == null)
    throw new Exception("必須設(shè)置初始狀態(tài)");
   if (context.CurrentState.Selector != null)
   {
    IState next= context.CurrentState.Selector(context.CurrentState);
    return context.transition(next);
   }
   return false;
  }

//測(cè)試代碼
//---------創(chuàng)建部分---------
string mess = "";//3   
IState s3 = new State() { Name = "s3" };
//2   
IState s2 = new State() { Name = "s2" };
//1   
IState s1 = new State() { Name = "s1" };
//---------組合起來(lái)---------   
s1.Nexts = new List<IState> { s2, s3 };   
s2.Nexts = new List<IState> { s1, s3 };   
s3.Nexts = new List<IState> { }; //注意end寫(xiě)法
//---------上下文---------    
//transition   
IContext<int> cont = new Context<int> { CurrentState=s1};//begin   
cont.Value = 0;
//---------狀態(tài)處理器--------- 
HandleType<int> funcLaji = (IState current, IState previous, ref int v) => { mess += $"{current.Name}:垃圾{previous.Name}\n"; v++; return true; };
//1   
cont.Handles.Add(Tuple.Create(s1 , default(IState)), funcLaji);   
cont.Handles.Add(Tuple.Create(s1, s2), funcLaji);
//2   
cont.Handles.Add(Tuple.Create(s2, s1), funcLaji);
//3   
cont.Handles.Add(Tuple.Create(s3, s1), funcLaji); 
cont.Handles.Add(Tuple.Create(s3, s2), funcLaji);
//---------狀態(tài)選擇器---------    
var rval = new Random();   
Func<int,int> round = x => rval.Next(x);   
s1.Selector = st => round(2)==0? s2:s3;   
s2.Selector = st => round(2)==0? s1:s3;

//選擇器跳轉(zhuǎn)   
mess += "選擇器跳轉(zhuǎn)：\n------------------------\n";
foreach (var stor in cont)
    mess+=$"狀態(tài)轉(zhuǎn)變次數(shù)：{stor}\n";
//直接控制跳轉(zhuǎn)
mess += "\n直接控制狀態(tài)跳轉(zhuǎn)：\n------------------------\n";
cont.transition(s1);
cont.transition(s2);
cont.transition(s3);