added redis integration and command line arguments handling to cart service. Didn't test in the cloud yet

src/cartservice/cartstore/LocalCartStore.cs

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+using System.Collections.Concurrent;
+using cartservice.interfaces;
+
+namespace cartservice.cartstore
+{
+    internal class LocalCartStore 
+    {
+        // 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;
+        }
+    }
+}

src/cartservice/cartstore/RedisCartStore.cs

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+using System;
+using System.IO;
+using System.Threading.Tasks;
+using cartservice.interfaces;
+using Google.Protobuf;
+using Hipstershop;
+using StackExchange.Redis;
+
+namespace cartservice.cartstore
+{
+    public class RedisCartStore : ICartStore
+    {
+        private const string CART_FIELD_NAME = "cart";
+
+        private readonly ConnectionMultiplexer redis;
+
+        private readonly byte[] emptyCartBytes;
+
+        public RedisCartStore(string redisAddress)
+        {
+            // Serialize empty cart into byte array.
+            var cart = new Hipstershop.Cart();
+            emptyCartBytes = cart.ToByteArray();
+
+            string connectionString = $"{redisAddress},ssl=false,allowAdmin=true";
+            Console.WriteLine("Connecting to Redis: " + connectionString);
+            redis = ConnectionMultiplexer.Connect(connectionString);
+        }
+
+        public async Task AddItemAsync(string userId, string productId, int quantity)
+        {
+            var db = redis.GetDatabase();
+            
+            // Access the cart from the cache
+            var value = await db.HashGetAsync(userId, CART_FIELD_NAME);
+
+            Hipstershop.Cart cart;
+            if (value.IsNull)
+            {
+                cart = new Hipstershop.Cart();
+            }
+            else
+            {
+                cart = Hipstershop.Cart.Parser.ParseFrom(value);
+            }
+
+            cart.Items.Add(new Hipstershop.CartItem { ProductId = productId, Quantity = quantity });
+        }
+
+        public async Task EmptyCartAsync(string userId)
+        {
+            var db = redis.GetDatabase();
+
+            // Update the cache with empty cart for given user
+            await db.HashSetAsync(userId, new[] { new HashEntry(CART_FIELD_NAME, emptyCartBytes) });
+        }
+
+        public async Task<Hipstershop.Cart> GetCartAsync(string userId)
+        {
+            var db = redis.GetDatabase();
+
+            // Access the cart from the cache
+            var value = await db.HashGetAsync(userId, CART_FIELD_NAME);
+
+            Hipstershop.Cart cart = null;
+            if (!value.IsNull)
+            {
+                cart = Hipstershop.Cart.Parser.ParseFrom(value);
+            }
+
+            return cart;
+        }
+    }
+}

src/cartservice/interfaces/ICartStore.cs

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+using System.Threading.Tasks;
+
+namespace cartservice.interfaces
+{
+    internal interface ICartStore
+    {
+        Task AddItemAsync(string userId, string productId, int quantity);
+        Task EmptyCartAsync(string userId);
+
+        Task<Hipstershop.Cart> GetCartAsync(string userId);
+    }
+}

src/cartservice/run_redis_emulator_windows.bat

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+@echo off
+rem install redis on windows using choco
+rem choco install redis-64
+
+rem run redis
+redis-server --daemonize yes
+
+rem testing locally
+rem redis-cli
+rem SET foo bar
+rem GET foo