/// <summary>
/// Adds the specified product to the cart
/// </summary>
/// <param name="productId">The product id</param>
/// <param name="quantity">The product's quantity to be added to the cart</param>
/// <exception cref="ProductIsNotForSaleException">Thrown if the product is not for sale</exception>
public void AddProductToCart(int productId, int quantity)
{
var product = ActiveContext.Products
.Where(p => p.Id == productId)
.SingleOrDefault();
if (product == null || product.IsDiscontinued)
{
throw new ProductIsNotForSaleException();
}
CurrentCart.AddProduct(product.Id, quantity, product.UnitPrice.Value);
}