public interface IUser

{

    bool HasVoucher{get;}

    Guid UserId { get; }

    Voucher Voucher {get;}

    string CountryCode {get;}

}

​

public class StockCounter

{

    public static Dictionary<Product, int> stock = new Dictionary<Product, int>();

​

    public static void Initialize()

{

        // stock gets initialized 

// and loaded here

    }

​

    public int CheckStock(Product product)

{

        if(stock.ContainsKey(product))

{

            return stock[product];

        }

​

        return -1;

    }

​

    public void UpdateStock(Product product, int qty)

{

        stock[product] -= qty;

    }

​

}

​

public class ShoppingCart

{

    private IUser _user

    private ILog _log;

​

    public ShoppingCart(IUser user) 

{

        _user = user

    }   

​

public ShoppingCart(ILog log)

{

        _log = log;

    }

​

public ShoppingCart(IUser user, ILog log)

    :this(user)

{

        products = new List<Product>();

quantities = new List<int>();

}       

​

    public List<Product> products;

    public List<int> quantities;

    public List<float> price;

​

    public string Add(Product product, int qty)

{

        var q = qty;

​

        try

{

​

            var stockCounter = new StockCounter();

            var stockCount = stockCounter.CheckStock(product, qty);

​

            if(stockCount > 0){

                stockCounter.UpdateStock(product, stockCount - qty);

            }else{

                Log.Error("no stock")

                return "no stock";

            }

​

            products.Add(product);

            quantities.Add(quantity);

​

            var price = product.Price;

​

            log.Info("Adding product to cart")

            // add tax

            switch(_user.CountryCode){

                case "IE":

                    price *= 0.21

                    break;

                case "UK":

                    price *= 0.12

                    break;

                case "EN"

                    price *= 0.21

                    break;

            }

​

            if(_user.HasVoucher){

                var voucherProcessor = new VoucherProcessor();

                voucherProcessor.ApplyVoucher(price, _user.Voucher);

            }

​

            price.Add(price);

​

        }

        catch(Exception ex){

            return ex.Message;

        }

​

        return "";

    }

}

​

​