FactorialCalculator implementation improved to handle large factorials

src/HitF5.Factorial.Tests/HitF5.Factorial.Tests.csproj

@@ -0,0 +1,19 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net6.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.3.2" />
+    <PackageReference Include="NUnit" Version="3.13.3" />
+    <PackageReference Include="Shouldly" Version="4.1.0" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\HitF5.Factorial\HitF5.Factorial.csproj" />
+  </ItemGroup>
+
+</Project>

src/HitF5.Factorial.Tests/when_calculating_factorial.cs

@@ -0,0 +1,41 @@
+using System.Numerics;
+using NUnit.Framework;
+using Shouldly;
+
+namespace HitF5.Factorial.Tests
+{
+    [TestFixture]
+    public class when_calculating_factorial
+    {
+        protected static IEnumerable<TestCaseData> FactorialIsCalculatedCorrectlyTestCases()
+        {
+            yield return new TestCaseData(0, new BigInteger(1))
+                .SetName("0");
+            yield return new TestCaseData(1, new BigInteger(1))
+                .SetName("1");
+            yield return new TestCaseData(2, new BigInteger(2))
+                .SetName("2");
+            yield return new TestCaseData(3, new BigInteger(6))
+                .SetName("3");
+            yield return new TestCaseData(4, new BigInteger(24))
+                .SetName("4");
+            yield return new TestCaseData(50, BigInteger.Parse("30414093201713378043612608166064768844377641568960512000000000000"))
+                .SetName("50");
+        }
+        [TestCaseSource(nameof(FactorialIsCalculatedCorrectlyTestCases))]
+        public void factorial_is_calculated_correctly(int value, BigInteger expectedFactorialValue)
+        {
+            var factorial = new FactorialCalculator().Calculate(value);
+
+            factorial.ShouldBe(expectedFactorialValue);
+        }
+
+        [Test]
+        public void exception_is_thrown_for_negative_value()
+        {
+            var ex = Should.Throw<ArgumentOutOfRangeException>(() => new FactorialCalculator().Calculate(-1));
+
+            ex.Message.ShouldBe("Value has to be non-negative. (Parameter 'value')");
+        }
+    }
+}

src/HitF5.Factorial/FactorialCalculator.cs

@@ -1,34 +1,22 @@
 using System;
-using System.Collections.Generic;
-using System.Diagnostics;
+using System.Numerics;
 
 namespace HitF5.Factorial
 {
-    [DebuggerDisplay("FactorialCalculator s minimem {minimum}.")]
     public class FactorialCalculator : IFactorialCalculator
     {
-        private static readonly int minimum = 1;
-
-        public int Calculate(int value)
+        public BigInteger Calculate(int value)
         {
-            if (value <= minimum)
-            {
-                return minimum;
-            }
-            else
+            if (value < 0) throw new ArgumentOutOfRangeException(nameof(value), "Value has to be non-negative.");
+
+            var bi = new BigInteger(1);
+            var factorial = value;
+            for (var i = 1; i <= factorial; i++)
             {
-                return value * this.Calculate(this.GetNext(value));
+                bi *= i;
             }
-        }
 
-        private int GetNext(int value)
-        {
-            return value - 1;
-        }
-
-        public override string ToString()
-        {
-            return "ToString";
+            return bi;
         }
     }
 }

src/HitF5.Factorial/IFactorialCalculator.cs

@@ -1,7 +1,9 @@
-namespace HitF5.Factorial
+using System.Numerics;
+
+namespace HitF5.Factorial
 {
     public interface IFactorialCalculator
     {
-        int Calculate(int value);
+        BigInteger Calculate(int value);
     }
 }

src/HitF5.sln

@@ -1,17 +1,21 @@
 
 Microsoft Visual Studio Solution File, Format Version 12.00
-# Visual Studio Version 16
-VisualStudioVersion = 16.0.29020.237
+# Visual Studio Version 17
+VisualStudioVersion = 17.3.32922.545
 MinimumVisualStudioVersion = 10.0.40219.1
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "HitF5.Random", "HitF5.Random\HitF5.Random.csproj", "{F45D20CB-4922-4255-BA12-DD34D2049BCE}"
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "HitF5.Custom", "HitF5.Custom\HitF5.Custom.csproj", "{A41E9F29-CEED-4DAA-A63F-14227B5A20D4}"
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "HitF5.Factorial", "HitF5.Factorial\HitF5.Factorial.csproj", "{338903E4-54D9-4443-A5C8-B27130BAD0FF}"
 EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "HitF5.Api", "HitF5.Api\HitF5.Api.csproj", "{0750FB3B-BFFD-451E-BA6C-954044A735D0}"
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "HitF5.Api", "HitF5.Api\HitF5.Api.csproj", "{0750FB3B-BFFD-451E-BA6C-954044A735D0}"
 EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "HitF5.Api.Client", "HitF5.Api.Client\HitF5.Api.Client.csproj", "{4D6833CC-F7E9-4791-A371-FA40B32B0C37}"
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "HitF5.Api.Client", "HitF5.Api.Client\HitF5.Api.Client.csproj", "{4D6833CC-F7E9-4791-A371-FA40B32B0C37}"
+EndProject
+Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Tests", "Tests", "{516F625A-3EDB-4B85-96F0-F20B3010815E}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "HitF5.Factorial.Tests", "HitF5.Factorial.Tests\HitF5.Factorial.Tests.csproj", "{5D2DDF72-EEC2-48B0-BDB0-33DCBDC5BA27}"
 EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
@@ -39,10 +43,17 @@ Global
 		{4D6833CC-F7E9-4791-A371-FA40B32B0C37}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{4D6833CC-F7E9-4791-A371-FA40B32B0C37}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{4D6833CC-F7E9-4791-A371-FA40B32B0C37}.Release|Any CPU.Build.0 = Release|Any CPU
+		{5D2DDF72-EEC2-48B0-BDB0-33DCBDC5BA27}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{5D2DDF72-EEC2-48B0-BDB0-33DCBDC5BA27}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{5D2DDF72-EEC2-48B0-BDB0-33DCBDC5BA27}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{5D2DDF72-EEC2-48B0-BDB0-33DCBDC5BA27}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
 	EndGlobalSection
+	GlobalSection(NestedProjects) = preSolution
+		{5D2DDF72-EEC2-48B0-BDB0-33DCBDC5BA27} = {516F625A-3EDB-4B85-96F0-F20B3010815E}
+	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {51A73852-7393-4087-87E4-17E1AB8490A3}
 	EndGlobalSection