Introduce HostBuilder Feature (#13)

* Introduce HostBuilder Feature

* Clean up

src/Featurize.AspNetCore/IHostFeature.cs

@@ -0,0 +1,16 @@
+using Microsoft.Extensions.Hosting;
+
+namespace Featurize.AspNetCore;
+
+/// <summary>
+/// Describes a HostBuilder feature.
+/// </summary>
+/// <seealso cref="Featurize.IFeature" />
+public interface IHostFeature : IFeature
+{
+    /// <summary>
+    /// Allow the feature to configure the Host specific properties.
+    /// </summary>
+    /// <param name="hostBuilder">The Host builder.</param>
+    void Configure(IHostBuilder hostBuilder);
+}

src/Featurize.AspNetCore/WebApplicationBuilderExtensions.cs

@@ -27,11 +27,18 @@ public static WebApplication BuildWithFeatures(this WebApplicationBuilder builde
     {
         var features = builder.Features();
 
+        foreach (var feature in features.GetHostFeatures())
+        {
+            feature.Configure(builder.Host);
+        }
+
         foreach (var feature in features.GetServiceCollectionFeatures())
         {
             feature.Configure(builder.Services);
         }
+
         var application = builder.Build();
+
         foreach (var feature in features.GetUseFeatures())
         {
             feature.Use(application);
@@ -44,6 +51,16 @@ public static WebApplication BuildWithFeatures(this WebApplicationBuilder builde
     /// </summary>
     /// <param name="features">The <see cref="IFeatureCollection"/>.</param>
     /// <returns>List of <see cref="IUseFeature"/>.</returns>
+    [Pure]
     public static IEnumerable<IUseFeature> GetUseFeatures(this IFeatureCollection features)
         => features.OfType<IUseFeature>();
+
+    /// <summary>
+    /// Gets all features implmenting <see cref="IHostFeature"/>.
+    /// </summary>
+    /// <param name="features">The <see cref="IFeatureCollection"/>.</param>
+    /// <returns>List of <see cref="IHostFeature"/>.</returns>
+    [Pure]
+    public static IEnumerable<IHostFeature> GetHostFeatures(this IFeatureCollection features)
+        => features.OfType<IHostFeature>();
 }

src/Featurize/DependencyFeatures/DependencyResolver.cs

@@ -21,7 +21,7 @@ internal static IEnumerable<T> GetDependencies<T>(T item, HashSet<T> source)
         foreach (var dep in dependencies)
         {
             var depType = dep.GetGenericArguments()[0];
-            var d = source.FirstOrDefault(x=> x.GetType() == depType);
+            var d = source.FirstOrDefault(x => x?.GetType() == depType);
 
             if (d is null)
                 throw new InvalidOperationException($"Dependenvy '{dep.Name}' required for '{item.GetType().Name}' has not been registered.");

src/Featurize/DependencyFeatures/IDependsOn.cs

@@ -1,12 +1,9 @@
-using System;
-using System.Collections.Generic;
-using System.Diagnostics.CodeAnalysis;
-using System.Linq;
-using System.Reflection.Metadata.Ecma335;
-using System.Text;
-using System.Threading.Tasks;
+namespace Featurize.SortFeatures;
 
-namespace Featurize.SortFeatures;
+/// <summary>
+/// Marks a feature that it depends on <typeparamref name="TFeature"/>.
+/// </summary>
+/// <typeparam name="TFeature">The feature that it depends on.</typeparam>
 public interface IDependsOn<TFeature>
     where TFeature : IFeature
 {

test/Featurize.AspNetCore/HostBuilder_Features.cs

@@ -0,0 +1,41 @@
+using Microsoft.Extensions.Hosting;
+
+namespace Featurize.AspNetCore.Tests;
+public class HostBuilder_Features
+{
+    [Test]
+    public void should_be_used()
+    {
+        var feature = new SimpleHostFeature();
+        var builder = WebApplication.CreateBuilder();
+        builder.Features()
+            .Add(feature);
+
+        var app = builder.BuildWithFeatures();
+
+        feature.IsUsed.Should().BeTrue();
+
+        var act = () => app.Services.GetRequiredService<SimpleHostRegistration>();
+
+        act.Should().NotThrow<InvalidOperationException>();
+
+    }
+}
+
+internal class SimpleHostFeature : IHostFeature
+{
+    public bool IsUsed { get; set; }
+
+    public void Configure(IHostBuilder hostBuilder)
+    {
+        IsUsed = true;
+
+        hostBuilder.ConfigureServices(s =>
+        {
+            s.AddTransient<SimpleHostRegistration>();
+        });
+
+    }
+}
+
+public class SimpleHostRegistration { }

test/Featurize.Tests/ConfigurableFeature.cs

@@ -17,7 +17,7 @@ public void Configure_Should_Be_Called()
         features.Add(configureFeature);
         features.Add(optionsFeature);
 
-        var c = features.Get<ConfigurableFeature>();
+        var c = features.Get<ConfigurableFeature>()!;
         c.ConfigCalled.Should().BeTrue();
     }
 }