public decimal GetAllDiscounts(IList <string> scannedItems, IItemCatalogue itemCatalogue)
        {
            var discounts = 0m;

            foreach (var offer in _currentOffers)
            {
                var discountAndProportion = offer.DiscountItemAndProportion();
                var timesApplicable       = offer.TimesApplicable(scannedItems);

                var itemPrice       = itemCatalogue.LookupPrice(discountAndProportion.Item);
                var priceProportion = discountAndProportion.Proportion;

                discounts += itemPrice * priceProportion * timesApplicable;
            }

            return(-discounts);
        }
        private decimal CalculateItem(string item)
        {
            var itemPrice = _itemCatalogue.LookupPrice(item);

            return(itemPrice);
        }