Prevent negative item orders (#392)

* Pulling changes over from previous branch

* Adding exception and guard clause

src/ApplicationCore/Entities/BasketAggregate/BasketItem.cs

@@ -1,4 +1,7 @@
-namespace Microsoft.eShopWeb.ApplicationCore.Entities.BasketAggregate
+using Ardalis.GuardClauses;
+using System;
+
+namespace Microsoft.eShopWeb.ApplicationCore.Entities.BasketAggregate
 {
     public class BasketItem : BaseEntity
     {
@@ -11,17 +14,21 @@
         public BasketItem(int catalogItemId, int quantity, decimal unitPrice)
         {
             CatalogItemId = catalogItemId;
-            Quantity = quantity;
             UnitPrice = unitPrice;
+            SetQuantity(quantity);
         }
 
         public void AddQuantity(int quantity)
         {
+            Guard.Against.OutOfRange(quantity, nameof(quantity), 0, int.MaxValue);
+
             Quantity += quantity;
         }
 
-        public void SetNewQuantity(int quantity)
+        public void SetQuantity(int quantity)
         {
+            Guard.Against.OutOfRange(quantity, nameof(quantity), 0, int.MaxValue);
+
             Quantity = quantity;
         }
     }

src/ApplicationCore/Exceptions/EmptyBasketOnCheckoutException.cs

@@ -0,0 +1,24 @@
+using System;
+
+namespace Microsoft.eShopWeb.ApplicationCore.Exceptions
+{
+    public class EmptyBasketOnCheckoutException : Exception
+    {
+        public EmptyBasketOnCheckoutException()
+            : base($"Basket cannot have 0 items on checkout")
+        {
+        }
+
+        protected EmptyBasketOnCheckoutException(System.Runtime.Serialization.SerializationInfo info, System.Runtime.Serialization.StreamingContext context) : base(info, context)
+        {
+        }
+
+        public EmptyBasketOnCheckoutException(string message) : base(message)
+        {
+        }
+
+        public EmptyBasketOnCheckoutException(string message, Exception innerException) : base(message, innerException)
+        {
+        }
+    }
+}

src/ApplicationCore/Exceptions/GuardExtensions.cs

@@ -1,5 +1,7 @@
 using Microsoft.eShopWeb.ApplicationCore.Exceptions;
 using Microsoft.eShopWeb.ApplicationCore.Entities.BasketAggregate;
+using System.Collections.Generic;
+using System.Linq;
 
 namespace Ardalis.GuardClauses
 {
@@ -10,5 +12,11 @@ namespace Ardalis.GuardClauses
             if (basket == null)
                 throw new BasketNotFoundException(basketId);
         }
+
+        public static void EmptyBasketOnCheckout(this IGuardClause guardClause, IReadOnlyCollection<BasketItem> basketItems)
+        {
+            if (!basketItems.Any())
+                throw new EmptyBasketOnCheckoutException();
+        }
     }
 }

src/ApplicationCore/Services/BasketService.cs

@@ -55,12 +55,13 @@ namespace Microsoft.eShopWeb.ApplicationCore.Services
             Guard.Against.Null(quantities, nameof(quantities));
             var basket = await _basketRepository.GetByIdAsync(basketId);
             Guard.Against.NullBasket(basketId, basket);
+
             foreach (var item in basket.Items)
             {
                 if (quantities.TryGetValue(item.Id.ToString(), out var quantity))
                 {
                     if (_logger != null) _logger.LogInformation($"Updating quantity of item ID:{item.Id} to {quantity}.");
-                    item.SetNewQuantity(quantity);
+                    item.SetQuantity(quantity);
                 }
             }
             basket.RemoveEmptyItems();

src/ApplicationCore/Services/OrderService.cs

@@ -33,6 +33,7 @@ namespace Microsoft.eShopWeb.ApplicationCore.Services
             var basket = await _basketRepository.FirstOrDefaultAsync(basketSpec);
 
             Guard.Against.NullBasket(basketId, basket);
+            Guard.Against.EmptyBasketOnCheckout(basket.Items);
 
             var catalogItemsSpecification = new CatalogItemsSpecification(basket.Items.Select(item => item.CatalogItemId).ToArray());
             var catalogItems = await _itemRepository.ListAsync(catalogItemsSpecification);