bridgeopenbook.cs

using System;
using System.Collections.Generic;
 
  // Bridge Pattern Example                           Judith Bishop Dec 2006, Aug 2007
  // Extending SpaceBook with a second implementation via a Portal
 
  // Abstraction  
  class Portal  {
    Bridge bridge;
    public Portal (Bridge aSpaceBook) {
      bridge = aSpaceBook;
    }
    public void Add(string message)
       {bridge.Add(message);}
    public void Add(string friend, string message)
       {bridge.Add(friend,message);}
    public void Poke(string who)
       {bridge.Poke(who);}
  }
 
  //Bridge
  interface Bridge {
    void Add(string message);
    void Add(string friend, string message);
    void Poke(string who);
  }
 
  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 string Add(string s) {
        pages += gap+s;
        return gap+"======== "+name+"'s SpaceBook ========="+
                  pages+"\n"+
                gap+"================================";
      }
    
      internal string Add(string friend, string message) {
         return community[friend].Add(message);
        }
      
      internal void Poke (string who, string friend) {
        community[who].pages += gap + friend + " poked you";
      }
    }

 
    // The Proxy (CANNOT CHANGE)
    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)
          Console.WriteLine(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();
        }
      }
    }
 
    // A Proxy with little to do
    // Illustrates an alternative implementation in the Bridge pattern
    public class MyOpenBook : Bridge {
      // Combination of a virtual and authentication proxy
      SpaceBook myOpenBook;
      string name;
      static int users;
      
      public MyOpenBook (string n) {
        name = n;
        users++;
        myOpenBook = new SpaceBook(name+"-"+users);
      }
      
      public void Add(string message) {
         Console.WriteLine(myOpenBook.Add(message));
      }
      
      public void Add(string friend, string message) {
        Console.WriteLine(myOpenBook.Add(friend, name + " : "+message));
      }
      
      public void Poke(string who) {
        myOpenBook.Poke(who,name);
      }
    }
  } // end class SpaceBookSystem

  static class OpenBookExtensions {
    public static void SuperPoke (this Portal me, string who, string what) {
      me.Add(who, what+" you");
    }
  }
 
  // The Client
  class BridgePattern : SpaceBookSystem {
    static void Main () {
       Portal me = new Portal(new MyOpenBook("Judith"));
       me.Add("Hello world");
       me.Add("Today I worked 18 hours");
      
       Portal tom = new Portal(new MyOpenBook("Tom"));
       tom.Poke("Judith-1");
       tom.SuperPoke("Judith-1","hugged");
       tom.Add("Judith-1","Poor you");
       tom.Add("Hey, I'm on OpenBook - it was so easy!");
    }
  }
/* Output
Let's register you for SpaceBook
All SpaceBook names must be unique
Type in a user name: Judith
Type in a password: yey
Thanks for registering with SpaceBook
Welcome Judith. Please type in your password: yey
Logged into SpaceBook

        ======== Judith's SpaceBook =========
        Hello world
        Today I worked 18 hours
        Tom poked you
        Tom : hugged you

        ================================

        ======== Judith's SpaceBook =========
        Hello world
        Today I worked 18 hours
        Tom poked you
        Tom : hugged you
        Tom : Poor you

        ================================

        ======== Tom-1's SpaceBook =========
        Hey, I'm on OpenBook - it was so easy!

        ================================
*/