public void PostNewPrice(PriceClass price)
 {
     throw new NotImplementedException();
 }
        public void PostNewPrice(PriceClass price)
        {
            if (price.Id == 0)
            {
                var newId = Prices.Select(@class => @class.Id).Max() + 1;
                price.Id = newId;
                Prices.Add(price);

                var newPriceChange = new PriceChangeClass
                {
                    Action = "New",
                    Id = price.Id,
                    ItemName = price.ItemName,
                    Price = price.Price,
                    priceWas = 0
                };
                PriceChanges.Add(newPriceChange);
            }

            else
            {
                var oldPrice = Prices.FirstOrDefault(@class => @class.Id == price.Id);
                Prices.Remove(oldPrice);
                Prices.Add(price);

                var newPriceChange = new PriceChangeClass
                {
                    Action = "Edit",
                    Id = price.Id,
                    ItemName = price.ItemName,
                    Price = price.Price,
                    priceWas = oldPrice.Price
                };
                PriceChanges.Add(newPriceChange);
            }
            Utils.SaveToFile();
        }