using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

public class Program

{

    public static void Main()

    {

        var register = new Register();

        register.Feed(new Book("Robinson Crusoe",4.56M));

        register.Feed(new Book("Robinson Crusoe",4.56M));

        register.Feed(new Food("Imported dog food",6.52M,TaxModificationPercent.Import));

        register.Feed(new Other("Perfume",6.23M));

        register.Print();

    }

}

​

public enum TaxModificationPercent

{

    Import  = 5

}

​

public class Register

{

    private List<Product> products = new List<Product>();

    public void Feed(Product product)

    {

        this.products.Add(product);

    }

    public void Print()

    {

        decimal total = 0;

        foreach(var nameGroup in this.products.GroupBy( p => p.Name ))

        {

            decimal item = nameGroup.Sum( p => p.Price );

            total += item;

            StringBuilder lineItem = new StringBuilder();

            lineItem

                .Append(nameGroup.Key)

                .Append(": " )

                .Append(string.Format("{0:C}",item));

            if( nameGroup.Count() > 1 ) 

                lineItem.Append(" (")

                    .Append(nameGroup.Count())

                    .Append(" @ ")

                    .Append(string.Format("{0:C}",nameGroup.First().Price))

                    .Append(")");

            Console.WriteLine(lineItem.ToString());

        }

        decimal tax = this.products.Sum( p => p.Price*p.Tax );

        Console.WriteLine("Sales Taxes: " + string.Format("{0:C}",tax));

        Console.WriteLine("Total: " + string.Format("{0:C}",total));

    }

}

​

public class Book : Product

{

    public Book(string Name, decimal Price) : base(Name, Price){}

    public Book(string Name, decimal Price,TaxModificationPercent taxMod) 

        : base (Name, Price, taxMod){}

}

​

public class Food : Product

{

    public Food(string Name, decimal Price) : base(Name, Price){}

    public Food(string Name, decimal Price,TaxModificationPercent taxMod) 

        : base (Name, Price, taxMod){}

}

​

public class Medical : Product

{

    public Medical(string Name, decimal Price) : base(Name, Price){}

    public Medical(string Name, decimal Price,TaxModificationPercent taxMod) 

        : base (Name, Price, taxMod){}

}

​

public class Other : Product

{

    private decimal _tax = 0.1M;

    public override decimal Tax 

    { 

        get { return _tax; } 

        protected set { _tax = value; }

    }

    public Other(string Name, decimal Price) : base(Name, Price){}

    public Other(string Name, decimal Price,TaxModificationPercent taxMod) 

        : base (Name, Price, taxMod){}

}

​

public abstract class Product

{

    public decimal Price { get; protected set; }

    public string Name { get; protected set; }

    protected decimal _Tax = 0;

    public virtual decimal Tax 

    { 

        get { return _Tax; } 

        protected set { _Tax = value; }

    }

    public Product(string Name, decimal Price)

    {

        this.Name = Name;

        this.Price = Price;

    }

    public Product(string Name, decimal Price, TaxModificationPercent taxMod) : this(Name,Price)

    {

        this.Tax += (decimal)taxMod/100;

    }

}