Initial commit of cart service using .net core 2.0. Working prototype without cache implementation (yet)

src/cartservice/CartServiceImpl.cs

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+using System.Collections.Concurrent;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using Grpc.Core;
+using Hipstershop;
+using static Hipstershop.CartService;
+
+namespace cartservice
+{
+    // Cart wrapper to deal with grpc communication
+    internal class CartServiceImpl : CartServiceBase
+    {
+        private CartStore cartStore;
+
+        public CartServiceImpl(CartStore cartStore)
+        {
+            this.cartStore = cartStore;
+        }
+
+        public override Task<Empty> AddItem(AddItemRequest request, Grpc.Core.ServerCallContext context)
+        {
+            cartStore.AddItem(request.UserId, request.Item.ProductId, request.Item.Quantity);
+            return Task.FromResult(new Empty());
+        }
+
+        public override Task<Empty> EmptyCart(EmptyCartRequest request, ServerCallContext context)
+        {
+            cartStore.EmptyCart(request.UserId);
+            return Task.FromResult(new Empty());
+        }
+
+        public override Task<Hipstershop.Cart> GetCart(GetCartRequest request, ServerCallContext context)
+        {
+            var cart = cartStore.GetCart(request.UserId);
+            return Task.FromResult(cart.ToHipsterCart());
+        }
+    }
+
+    internal class CartStore
+    {
+        // Maps between user and their cart
+        private ConcurrentDictionary<string, Cart> userCartItems = new ConcurrentDictionary<string, Cart>();
+
+        public void AddItem(string userId, string productId, int quantity)
+        {
+            Cart cart;
+            if (!userCartItems.TryGetValue(userId, out cart))
+            {
+                cart = new Cart(userId);
+            }
+            else
+            {
+                cart = userCartItems[userId];
+            }
+            cart.AddItem(productId, quantity);
+        }
+
+        public void EmptyCart(string userId)
+        {
+            Cart cart;
+            if (userCartItems.TryGetValue(userId, out cart))
+            {
+                cart.EmptyCart();
+            }
+        }
+
+        public Cart GetCart(string userId)
+        {
+            Cart cart = null;
+            userCartItems.TryGetValue(userId, out cart);
+            return cart;
+        }
+    }
+
+    internal static class CartUtils
+    {
+        public static Hipstershop.Cart ToHipsterCart(this Cart cart)
+        {
+            var hipsterCart = new Hipstershop.Cart
+            {
+                UserId = cart.UserId,
+                Items = { cart.Items.Select(i => new CartItem { ProductId = i.Key, Quantity = i.Value }) }
+            };
+            return hipsterCart;
+        }
+    }
+
+    // Actual implementation of the cart
+    internal class Cart
+    {
+        // Maps between productId and its quantity
+        private Dictionary<string, int> cart = new Dictionary<string, int>();
+
+        public Cart(string userId)
+        {
+            UserId = userId;
+        }
+
+        public string UserId { get; set; }
+
+        public void AddItem(string productId, int quantity)
+        {
+            cart.Add(productId, quantity);
+        }
+
+        public void EmptyCart()
+        {
+            cart.Clear();
+        }
+
+        public IReadOnlyDictionary<string, int> Items
+        {
+            get
+            {
+                return cart;
+            }
+        }
+    }
+}