public IActionResult Post([FromRoute] Guid cartId, [FromBody] IEnumerable <Product> lineItems)
        {
            var cart = shoppingCartRepository.Find(cartId);

            if (cart == null)
            {
                return(NotFound());
            }

            var service = new ShoppingService();

            foreach (var item in lineItems)
            {
                service.AddProductToCart(cart, item);
            }
            shoppingCartRepository.Save(cart);
            return(Ok());
        }
        public IActionResult Put(Guid id, [FromBody] ShoppingCart cart)
        {
            var existingCart = shoppingCartRepository.Find(id);

            if (existingCart == null)
            {
                return(NotFound());
            }

            if (cart.State != State.Confirmed)
            {
                return(BadRequest("Cart can only be confirmed."));
            }

            var service = new ShoppingService();

            service.ConfirmCart(cart);

            shoppingCartRepository.Save(cart);

            return(Ok());
        }