I have a small solution to the following hypothetical problem:
Basic sales tax is applicable at a rate of 10% on all goods, except books, food, and medical products that are exempt. Import duty is an additional sales tax applicable on all imported goods at a rate of 5%, with no exemptions.
When I purchase items I receive a receipt which lists the name of all the items and their price (including tax), finishing with the total cost of the items, and the total amounts of sales taxes paid. The rounding rules for sales tax are that for a tax rate of n%, a shelf price of p contains (np/100 rounded up to the nearest 0.05) amount of sales tax. Write an application that prints out the receipt details for these shopping baskets.
INPUT:
- Input 1: 1 book at 12.49 1 music CD at 14.99 1 chocolate bar at 0.85
- Input 2: 1 imported box of chocolates at 10.00 1 imported bottle of perfume at 47.50
- Input 3: 1 imported bottle of perfume at 27.99 1 bottle of perfume at 18.99 1 packet of headache pills at 9.75 1 box of imported chocolates at 11.25
OUTPUT
- Output 1: 1 book : 12.49 1 music CD: 16.49 1 chocolate bar: 0.85 Sales Taxes: 1.50 Total: 29.83
- Output 2: 1 imported box of chocolates: 10.50 1 imported bottle of perfume: 54.65 Sales Taxes: 7.65 Total: 65.15
- Output 3: 1 imported bottle of perfume: 32.19 1 bottle of perfume: 20.89 1 packet of headache pills: 9.75 1 imported box of chocolates: 11.85 Sales Taxes: 6.70 Total: 74.68
I'm interested in feedback on my use of design patterns, whether there are any extensibility issues, how SOLID the code is and the style/structure of the unit tests. I'd really appreciate hearing constructive criticisms.
Full solution is available here
This is part of the main solution:
public class SalesItem : ISalesItem
{
private string _name;
private decimal _price;
public SalesItem(string name, decimal price)
{
#region Parameter Checking
if (String.IsNullOrWhiteSpace(name))
throw new ArgumentException("name");
if(price < 0)
throw new ArgumentException("price");
#endregion
this._name = name;
this._price = price;
}
#region ISalesItem Members
public string Name
{
get { return this._name; }
}
public decimal GetPrice()
{
return this._price;
}
public decimal GetSalesTax()
{
return 0.0M;
}
public decimal GetTotal()
{
return this.GetPrice() + this.GetSalesTax();
}
#endregion
}
public class SalesItemTaxDecorator: ISalesItem
{
protected ISalesItem _decoratedSalesItem;
protected ITax _salesTax;
public SalesItemTaxDecorator(ISalesItem salesItem, ITax salesTax)
{
this._decoratedSalesItem = salesItem;
this._salesTax = salesTax;
}
#region ISalesItem Members
public string Name
{
get { return _decoratedSalesItem.Name; }
}
public virtual decimal GetSalesTax()
{
return this._decoratedSalesItem.GetSalesTax() + _salesTax.CalculateTax(this._decoratedSalesItem.GetPrice());
}
public virtual decimal GetPrice()
{
return this._decoratedSalesItem.GetPrice();
}
public virtual decimal GetTotal()
{
return this.GetPrice() + this.GetSalesTax();
}
#endregion
}
public class Tax : ITax
{
private decimal _rate;
private IRounding _rounding;
public Tax(decimal rate, IRounding rounding)
{
this._rate = rate;
this._rounding = rounding;
}
#region ISalesTax Members
public decimal Rate
{
get { return this._rate; }
}
public IRounding Rounding
{
get { return this._rounding; }
}
public virtual decimal CalculateTax(decimal itemPrice)
{
decimal tempTax = itemPrice * this.Rate;
decimal roundedTax = Rounding.Round(tempTax);
return roundedTax;
}
#endregion
}
public static class SalesItemFactory
{
private static readonly Rounding ROUNDING = new Rounding(0.05M);
private static readonly ITax BASICTAX = new Tax(0.1M, ROUNDING);
private static readonly ITax IMPORTTAX = new Tax(0.05M, ROUNDING);
private static readonly Dictionary<ItemType, ITax> itemTaxLookup = new Dictionary<ItemType, ITax>()
{
{ ItemType.Basic, BASICTAX },
{ ItemType.Import, IMPORTTAX }
};
public static ISalesItem GetSalesItem(string name, decimal price, ItemType itemType)
{
ISalesItem item = new SalesItem(name, price);
foreach (int flag in Enum.GetValues(typeof(ItemType)))
{
if ((flag & (int)itemType) == flag)
{
item = (ISalesItem)Activator.CreateInstance(typeof(SalesItemTaxDecorator), new object[] { item, itemTaxLookup[(ItemType)flag] });
}
}
return item;
}
public static ISalesItem GetSalesItem(string name, decimal price)
{
return new SalesItem(name, price);
}
}
