// Define the Mediator Object.

//Define the Mediator class (object) which is responsible for managing messages that are exchanged between colleagues.
//Callback methods are used to invoke the Receive() method on the relevant Colleagues classes (objects).
public class Mediator
{
public delegate void Callback(string message, string from);

private Callback _respond;

public void SignOn(Callback method)
{
_respond += method;
}

public void Block(Callback method)
{
_respond -= method;
}

public void Unblock(Callback method)
{
_respond += method;
}

public void Send(string message, string from)
{
_respond(message, from);
Console.WriteLine();
}
}