using System;

  using System.Collections.Generic;

  // Proxy Pattern Example              Judith Bishop  Aug 2007

  // Sets up a SpaceBook page with registration and authentication

  class SpaceBookSystem {    

    // The Subject

    private class SpaceBook {

      static SortedList <string,SpaceBook> community =

            new SortedList <string,SpaceBook> (100);

      string pages;

      string name;

      string gap = "\n\t\t\t\t";

      static public bool IsUnique (string name) {

         return community.ContainsKey(name);

      }

      internal SpaceBook (string n) {

         name = n;

         community [n] = this;

      }

      internal void Add(string s) {

         pages += gap+s;

         Console.Write(gap+"======== "+name+"'s SpaceBook =========");

         Console.Write(pages);

         Console.WriteLine(gap+"===================================");

      }

      internal void Add(string friend, string message) {

         community[friend].Add(message);

      }

      internal void Poke (string who, string friend) {

         community[who].pages += gap + friend + " poked you";

      }

    }

    // The Proxy

    public class MySpaceBook {

      // Combination of a virtual and authentication proxy

      SpaceBook mySpaceBook;

      string password;

      string name;

      bool loggedIn = false;

      void Register () {

         Console.WriteLine("Let's register you for SpaceBook");

         do {

            Console.WriteLine("All SpaceBook names must be unique");

            Console.Write("Type in a user name: ");

            name = Console.ReadLine();

         } while (SpaceBook.IsUnique(name));

         Console.Write("Type in a password: ");

         password = Console.ReadLine();

         Console.WriteLine("Thanks for registering with SpaceBook");

      }

      bool Authenticate () {

         Console.Write("Welcome "+name+". Please type in your password: ");

         string supplied = Console.ReadLine();

         if (supplied==password) {

            loggedIn = true;

            Console.WriteLine("Logged into SpaceBook");

            if (mySpaceBook == null)

              mySpaceBook = new SpaceBook(name);

            return true;

         }

         Console.WriteLine("Incorrect password");

         return false;

      }

      public void Add(string message) {

         Check();

         if (loggedIn) mySpaceBook.Add(message);

      }

      public void Add(string friend, string message) {

         Check();

         if (loggedIn)

            mySpaceBook.Add(friend, name + " said: "+message);

      }

      public void Poke(string who) {

         Check();

         if (loggedIn)

              mySpaceBook.Poke(who,name);

      }

      void Check() {

        if (!loggedIn)

          if (password==null)

            Register();

          if (mySpaceBook == null)

            Authenticate();

        }

      }

    }

  // The Client

  class ProxyPattern : SpaceBookSystem {

    static void Main () {

      MySpaceBook me = new MySpaceBook();

      me.Add("Hello world");

      me.Add("Today I worked 18 hours");

      MySpaceBook tom = new MySpaceBook();

      tom.Poke("Judith");

      tom.Add("Judith","Poor you");

      tom.Add("Off to see the Lion King tonight");

    }

  }