设计模式：装饰者模式

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace DecoratorDemo
{
    [Flags]
    public enum BcType
    {
        None = 0,       // 0
        SdCakeType,     // 山东煎饼
        EggType,        // 蛋
        SausageType     // 肠        
    }


    public interface IBatterCake
    {
        List<BcType> Type();
        double Coast();
    }

    public class NoneBatterCake : IBatterCake
    {
        public List<BcType> Type()
        {
            return new List<BcType> {BcType.None};
        }

        public double Coast()
        {
            return 0;
        }
    }

    /// <summary>
    /// 山东煎饼
    /// </summary>
    public class SdBatterCake : IBatterCake
    {
        public List<BcType> Type()
        {
            return new List<BcType> {BcType.SdCakeType};
        }

        public double Coast()
        {
            return 3.5;
        }
    }

    /// <summary>
    /// 鸡蛋
    /// </summary>
    public class Egg : IBatterCake
    {
        private readonly IBatterCake _batterCake = new NoneBatterCake();

        public Egg(IBatterCake mMoney)
        {
            _batterCake = mMoney;
        }

        public List<BcType> Type()
        {
            List<BcType> types = _batterCake.Type();
            types.AddRange(new List<BcType>() { BcType.EggType });
            return types;
        }

        public double Coast()
        {
            return 1 + _batterCake.Coast();
        }
    }

    /// <summary>
    /// 肠
    /// </summary>
    public class Sausage : IBatterCake
    {
        private readonly IBatterCake _batterCake = new NoneBatterCake();

        public Sausage(IBatterCake mMoney)
        {
            _batterCake = mMoney;
        }

        public List<BcType> Type()
        {
            List<BcType> types = _batterCake.Type();
            types.AddRange(new List<BcType>() { BcType.SausageType });
            return types;
        }

        public double Coast()
        {            
            return 2 + _batterCake.Coast();
        }
    }

    /// <summary>
    /// 计算花费
    /// </summary>
    public class CalculateMoney : IBatterCake
    {
        private readonly IBatterCake _batterCake = new NoneBatterCake();
        public CalculateMoney(IBatterCake mMoney)
        {
            _batterCake = mMoney;
        }

        public List<BcType> Type()
        {
            return new List<BcType> {BcType.None};
        }

        public string Description()
        {
            List<BcType> types = _batterCake.Type();

            int eggs = 0, sausage = 0,battercakies = 0;
            for (int index = 0, count = types.Count(); index < count; index++)
            {
                if (types[index] == BcType.SdCakeType)
                    battercakies++;

                if (types[index] == BcType.EggType)
                    eggs++;

                if (types[index] == BcType.SausageType)
                    sausage++;
            }
            StringBuilder description = new StringBuilder();
            if (battercakies > 0)
                description.Append("煎饼").Append(battercakies).Append("个").Append("\n");

            if (eggs > 0)
                description.Append("鸡蛋").Append(eggs).Append("个").Append("\n");

            if (sausage > 0)
                description.Append("烤肠").Append(sausage).Append("个").Append("\n");

            return description.ToString();
        }

        public double Coast()
        {
            return _batterCake.Coast();
        }
    }


    public class Program
    {
        private static void Main(string[] args)
        {
            // 一个山东煎饼
            IBatterCake sdBatterCake = new SdBatterCake();
            // 一个鸡蛋
            IBatterCake egg1 = new Egg(sdBatterCake);
            // 再来个鸡蛋
            IBatterCake egg2 = new Egg(egg1);
            // 再来个肠
            IBatterCake sausage = new Sausage(egg2);

            CalculateMoney calculateMoney = new CalculateMoney(sausage);

            Console.WriteLine(calculateMoney.Description());
            Console.WriteLine("共花费 ： {0}", calculateMoney.Coast());
            Console.ReadLine();
        }
    }
}