Mediator

// Mediator pattern -- Real World example

using System;
using System.Collections;

namespace DoFactory.GangOfFour.Mediator.RealWorld
{
  
  // MainApp test application

  class MainApp
  {
    static void Main()
    {
      // Create chatroom
      Chatroom chatroom = new Chatroom();

      // Create participants and register them
      Participant George = new Beatle("George");
      Participant Paul = new Beatle("Paul");
      Participant Ringo = new Beatle("Ringo");
      Participant John = new Beatle("John") ;
      Participant Yoko = new NonBeatle("Yoko");

      chatroom.Register(George);
      chatroom.Register(Paul);
      chatroom.Register(Ringo);
      chatroom.Register(John);
      chatroom.Register(Yoko);

      // Chatting participants
      Yoko.Send ("John", "Hi John!");
      Paul.Send ("Ringo", "All you need is love");
      Ringo.Send("George", "My sweet Lord");
      Paul.Send ("John", "Can't buy me love");
      John.Send ("Yoko", "My sweet love") ;

      // Wait for user
      Console.Read();
    }
  }

  // "Mediator"

  abstract class AbstractChatroom
  {
    public abstract void Register(Participant participant);
    public abstract void Send(
      string from, string to, string message);
  }

  // "ConcreteMediator"

  class Chatroom : AbstractChatroom
  {
    private Hashtable participants = new Hashtable();

    public override void Register(Participant participant)
    {
      if (participants[participant.Name] == null)
      {
        participants[participant.Name] = participant;
      }

      participant.Chatroom = this;
    }

    public override void Send(
      string from, string to, string message)
    {
      Participant pto = (Participant)participants[to];
      if (pto != null)
      {
        pto.Receive(from, message);
      }
    }
  }

  // "AbstractColleague"

  class Participant
  {
    private Chatroom chatroom;
    private string name;

    // Constructor
    public Participant(string name)
    {
      this.name = name;
    }

    // Properties
    public string Name
    {
      get{ return name; }
    }

    public Chatroom Chatroom
    {
      set{ chatroom = value; }
      get{ return chatroom; }
    }

    public void Send(string to, string message)
    {
      chatroom.Send(name, to, message);
    }

    public virtual void Receive(
      string from, string message)
    {
      Console.WriteLine("{0} to {1}: '{2}'",
        from, Name, message);
    }
  }

  //" ConcreteColleague1"

  class Beatle : Participant
  {
    // Constructor
    public Beatle(string name) : base(name)
    {
    }

    public override void Receive(string from, string message)
    {
      Console.Write("To a Beatle: ");
      base.Receive(from, message);
    }
  }

  //" ConcreteColleague2"

  class NonBeatle : Participant
  {
    // Constructor
    public NonBeatle(string name) : base(name)
    {
    }

    public override void Receive(string from, string message)
    {
      Console.Write("To a non-Beatle: ");
      base.Receive(from, message);
    }
  }
}