Use DI for DieController

src/DiceApi.Core/Die.cs

@@ -2,30 +2,17 @@
 
 namespace DiceApi.Core
 {
-    public class Die
+    public class Die : IRollable
     {
         /// <summary>
         /// Initializes a new instance of <see cref="Die" /> with a 
         /// specified number of sides.
         /// </summary>
-        /// <param name="sides">Number of sides on the die.</param>
-        public Die(int sides)
+        public Die()
         {
-            if (sides < 1) {
-                throw new ArgumentOutOfRangeException(nameof(sides));
-            }
-
-            this.Sides = sides;
-
             this.RandomNumberGenerator = new Random();
         }
 
-        /// <summary>
-        /// Gets the number of sides on the die.
-        /// </summary>
-        /// <returns></returns>
-        public int Sides { get; }
-
         /// <summary>
         /// Gets an instance of Random that we instantiate with the Die 
         /// constructor. This is used by Roll() to create a random value 
@@ -36,11 +23,16 @@ public Die(int sides)
         /// <summary>
         /// Rolls the die, returning its value.
         /// </summary>
+        /// <param name="sides">Number of sides on the die.</param>
         /// <returns>Result of die roll.</returns>
-        public int Roll() 
+        public int Roll(int sides) 
         {
+            if (sides < 1) {
+                throw new ArgumentOutOfRangeException(nameof(sides));
+            }
+
             // Range for Next() is inclusive on the minimum, exclusive on the maximum
-            return this.RandomNumberGenerator.Next(1, this.Sides + 1);
+            return this.RandomNumberGenerator.Next(1, sides + 1);
         }
     }
 }

src/DiceApi.Core/IRollable.cs

@@ -0,0 +1,7 @@
+namespace DiceApi.Core
+{
+    public interface IRollable
+    {
+        int Roll(int sides);
+    }
+}

src/DiceApi.WebApi/Controllers/DieController.cs

@@ -5,7 +5,14 @@ namespace DiceApi.WebApi.Controllers
 {
     [Route("api/[controller]")]
     public class DieController : Controller
-    {        
+    {   
+        private IRollable Die { get; }
+
+        public DieController(IRollable die) 
+        {
+            this.Die = die;
+        }
+
         // GET api/die
         [HttpGet]
         public IActionResult Get([FromQuery] int sides)
@@ -21,10 +28,8 @@ public IActionResult Get([FromQuery] int sides)
             {
                 return this.BadRequest();
             }
-
-            var die = new Die(sides);
 
-            return this.Ok(die.Roll());
+            return this.Ok(this.Die.Roll(sides));
         }
     }
 }

src/DiceApi.WebApi/Startup.cs

@@ -2,6 +2,8 @@
 using System.Collections.Generic;
 using System.Linq;
 using System.Threading.Tasks;
+
+using DiceApi.Core;
 using Microsoft.AspNetCore.Builder;
 using Microsoft.AspNetCore.Hosting;
 using Microsoft.Extensions.Configuration;
@@ -29,6 +31,11 @@ public void ConfigureServices(IServiceCollection services)
         {
             // Add framework services.
             services.AddMvc();
+
+            // Register Die class as IRollable with DI container, doing this as singleton
+            // since we want to have the same Random instance performing all our random 
+            // number generation.
+            services.AddSingleton<IRollable, Die>();
         }
 
         // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.

test/DiceApi.Core.Tests/DieTest.cs

@@ -15,9 +15,10 @@ public class DieTest
         /// an invalid number of sides.
         /// </summary>
         [Fact]
-        public void Constructor_GivenZeroSides_ThrowsException()
+        public void Roll_GivenZeroSides_ThrowsException()
         {
-            var exception = Record.Exception(() => new Die(0));
+            var die = new Die();
+            var exception = Record.Exception(() => die.Roll(0));
 
             Assert.NotNull(exception);
             Assert.IsType<ArgumentOutOfRangeException>(exception);
@@ -31,13 +32,13 @@ public void Constructor_GivenZeroSides_ThrowsException()
         public void Roll_GivenValidSides_ReturnsValueWithinRange()
         {
             int sides = 6;
-            var die = new Die(sides);
+            var die = new Die();
 
             // Naive brute force verification that we always get a correct value
             // within range.
             for (int i = 0; i < 100; i++) 
             {
-                var result = die.Roll();
+                var result = die.Roll(sides);
 
                 Assert.True(this.WithinRange(sides, result));
             }

test/DiceApi.WebApi.Tests/DieControllerTest.cs

@@ -1,6 +1,7 @@
 using Microsoft.AspNetCore.Mvc;
 using Xunit;
 
+using DiceApi.Core;
 using DiceApi.WebApi.Controllers;
 
 namespace DiceApi.WebApi.Tests
@@ -18,7 +19,7 @@ public class DieControllerTest
         [Fact]
         public void Get_GivenSidesLessThanZero_ReturnsBadRequestResult()
         {
-            var sut = new DieController();
+            var sut = new DieController(new Die());
 
             var result = sut.Get(-1);
 
@@ -32,7 +33,7 @@ public void Get_GivenSidesLessThanZero_ReturnsBadRequestResult()
         [Fact]
         public void Get_GivenValidSizeValue_ReturnsOkResult()
         {
-            var sut = new DieController();
+            var sut = new DieController(new Die());
 
             var result = sut.Get(6);
 

test/DiceApi.WebApi.Tests/project.json

@@ -7,7 +7,11 @@
          "DiceApi.WebApi": {
             "version":"1.0.0",
             "target":"project"
-        }       
+        },
+        "DiceApi.Core": {
+            "version":"1.0.0",
+            "target":"project"
+        }
     },
     "frameworks": {
         "netcoreapp1.0": {