// Decorator pattern demo 

// based on head first design pattern book

​

​

using System;

public class Program

{

    // Main method

    public static void Main()

    {

      Beverage obj = new DarkRoast(Size.Medium);

      Console.WriteLine(obj.GetDescription() + " Cost: $" + obj.Cost());

      Beverage obj1 = new DarkRoast(Size.Large);

      obj1 = new Cream(obj1);

      obj1 = new Mocha(obj1);

      Console.WriteLine(obj1.GetDescription() + " Cost: $" + obj1.Cost());

    }

}

​

//Abstract Beverage class

public abstract class Beverage

{

   public string description = "Unknown Beverage" ;

   public Size size  = Size.Regular;

   public Size GetSize()

   {

     return this.size;

   }

   public virtual string GetDescription()

   {

     return description;

   }

   // all child to implement this method

   public abstract double Cost();

}

​

// Beverage child class

​

public class DarkRoast : Beverage

{

   public DarkRoast(Size size)

   { 

     this.size = size;

     description = "Dark roast";

   }

   public override double Cost()

   {

    return 100;

   }

}

​

​

public class Mocha :Beverage

{

  Beverage beverage;

  public Mocha(Beverage beverage)

  {

   this.beverage = beverage;

  }

  public override string GetDescription()

  {

    return beverage.GetDescription()  + ", Mocha";

  }

  public override double Cost()

  {

     Size size = beverage.size;

     if (size == Size.Regular )

     {

      return beverage.Cost() + 20;

     }

     else if (size == Size.Medium)

     {

      return beverage.Cost() + 40;

     }

     else

     {

       return beverage.Cost() + 60;

     }

  }

}

​

public class Soya :Beverage

{

  Beverage beverage;

  public Soya(Beverage beverage)

  {

   this.beverage = beverage;

  }

  public override string GetDescription()

  {

    return beverage.GetDescription()  + ", Soya";

  }

  public override double Cost()

  {

     Size size = beverage.size;

     if (size == Size.Regular )

     {

      return beverage.Cost() + 25;

     }

     else if (size == Size.Medium)

     {

      return beverage.Cost() + 50;

     }

     else

     {

       return beverage.Cost() + 75;

     }

  }

}

​

public class Cream :Beverage

{

  Beverage beverage;

  public Cream(Beverage beverage)

  {

   this.beverage = beverage;

  }

  public override string GetDescription()

  {

    return beverage.GetDescription()  + ", Cream";

  }

  public override double Cost()

  {

     Size size = beverage.size;

     if (size == Size.Regular )

     {

      return beverage.Cost() + 100;

     }

     else if (size == Size.Medium)

     {

      return beverage.Cost() + 120;

     }

     else

     {

       return beverage.Cost() + 160;

     }

  }

}

​

​

​

public enum Size

{

   Regular,

   Medium,

   Large

}

​

​

​