From c9124cd25e78527e2fa34714c5a4d3d54f39dbc0 Mon Sep 17 00:00:00 2001
From: Maksym Pavlenko <pavlenko.maksym@gmail.com>
Date: Thu, 5 Jan 2017 17:25:17 -0800
Subject: [PATCH] Detect RSS builders automatically via reflection

---
 .../Services/Builder/CompositeRssBuilder.cs   | 24 +++++----
 src/Podsync/Services/Builder/IRssBuilder.cs   |  6 +++
 src/Shared/ServiceProviderExtensions.cs       | 50 +++++++++++++++++++
 3 files changed, 69 insertions(+), 11 deletions(-)

diff --git a/src/Podsync/Services/Builder/CompositeRssBuilder.cs b/src/Podsync/Services/Builder/CompositeRssBuilder.cs
index 592d5d9..fea6c53 100644
--- a/src/Podsync/Services/Builder/CompositeRssBuilder.cs
+++ b/src/Podsync/Services/Builder/CompositeRssBuilder.cs
@@ -1,4 +1,8 @@
 using System;
+using System.Collections.Generic;
+using System.Collections.ObjectModel;
+using System.Linq;
+using System.Reflection;
 using System.Threading.Tasks;
 using Podsync.Services.Feed;
 using Podsync.Services.Links;
@@ -10,13 +14,15 @@ namespace Podsync.Services.Builder
     // ReSharper disable once ClassNeverInstantiated.Global
     public class CompositeRssBuilder : RssBuilderBase
     {
-        private readonly YouTubeRssBuilder _youTubeBuilder;
-        private readonly VimeoRssBuilder _vimeoBuilder;
+        private readonly IDictionary<Provider, IRssBuilder> _builders;
 
         public CompositeRssBuilder(IServiceProvider serviceProvider, IStorageService storageService) : base(storageService)
         {
-            _youTubeBuilder = serviceProvider.CreateInstance<YouTubeRssBuilder>();
-            _vimeoBuilder = serviceProvider.CreateInstance<VimeoRssBuilder>();
+            // Find all RSS builders (all implementations of IRssBuilder), create instances and make dictionary for fast search by Provider type
+            var buildTypes = serviceProvider.FindAllImplementationsOf<IRssBuilder>(Assembly.GetEntryAssembly()).Where(x => x != typeof(CompositeRssBuilder));
+            var builders = buildTypes.Select(builderType => (IRssBuilder)serviceProvider.CreateInstance(builderType)).ToDictionary(builder => builder.Provider);
+
+            _builders = new ReadOnlyDictionary<Provider, IRssBuilder>(builders);
         }
 
         public override Provider Provider
@@ -26,14 +32,10 @@ namespace Podsync.Services.Builder
 
         public override Task<Rss> Query(Uri baseUrl, string feedId, FeedMetadata feed)
         {
-            if (feed.Provider == Provider.YouTube)
+            IRssBuilder builder;
+            if (_builders.TryGetValue(feed.Provider, out builder))
             {
-                return _youTubeBuilder.Query(baseUrl, feedId, feed);
-            }
-
-            if (feed.Provider == Provider.Vimeo)
-            {
-                return _vimeoBuilder.Query(baseUrl, feedId, feed);
+                return builder.Query(baseUrl, feedId, feed);
             }
 
             throw new NotSupportedException("Not supported provider");
diff --git a/src/Podsync/Services/Builder/IRssBuilder.cs b/src/Podsync/Services/Builder/IRssBuilder.cs
index deb6004..e6f2586 100644
--- a/src/Podsync/Services/Builder/IRssBuilder.cs
+++ b/src/Podsync/Services/Builder/IRssBuilder.cs
@@ -1,11 +1,17 @@
 using System;
 using System.Threading.Tasks;
 using Podsync.Services.Feed;
+using Podsync.Services.Links;
+using Podsync.Services.Storage;
 
 namespace Podsync.Services.Builder
 {
     public interface IRssBuilder
     {
+        Provider Provider { get; }
+
         Task<Rss> Query(Uri baseUrl, string feedId);
+
+        Task<Rss> Query(Uri baseUrl, string feedId, FeedMetadata metadata);
     }
 }
\ No newline at end of file
diff --git a/src/Shared/ServiceProviderExtensions.cs b/src/Shared/ServiceProviderExtensions.cs
index 5eae046..82a9182 100644
--- a/src/Shared/ServiceProviderExtensions.cs
+++ b/src/Shared/ServiceProviderExtensions.cs
@@ -1,4 +1,7 @@
 using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Reflection;
 using Microsoft.Extensions.DependencyInjection;
 
 namespace Shared
@@ -19,5 +22,52 @@ namespace Shared
         {
             return ActivatorUtilities.CreateInstance(serviceProvider, type);
         }
+
+        public static IEnumerable<Type> FindAllImplementationsOf(this IServiceProvider serviceProvider, Type interfaceType, Assembly assembly)
+        {
+            if (!interfaceType.GetTypeInfo().IsInterface)
+            {
+                throw new ArgumentException("T should be an interface");
+            }
+
+            return GetLoadableTypes(assembly).Where(type => IsAssignableFrom(interfaceType, type));
+        }
+
+        public static IEnumerable<Type> FindAllImplementationsOf<T>(this IServiceProvider serviceProvider, Assembly assembly)
+        {
+            return serviceProvider.FindAllImplementationsOf(typeof(T), assembly);
+        }
+
+        private static bool IsAssignableFrom(Type interfaceType, Type serviceType)
+        {
+            var serviceTypeInfo = serviceType.GetTypeInfo();
+            if (serviceTypeInfo.IsInterface || serviceTypeInfo.IsAbstract)
+            {
+                return false;
+            }
+
+            var interfaceTypeInfo = interfaceType.GetTypeInfo();
+            if (!interfaceTypeInfo.IsGenericType)
+            {
+                return interfaceType.IsAssignableFrom(serviceType);
+            }
+
+            return serviceType
+                .GetInterfaces()
+                .Where(type => type.GetTypeInfo().IsGenericType)
+                .Any(type => type.GetGenericTypeDefinition() == interfaceType);
+        }
+
+        private static IEnumerable<Type> GetLoadableTypes(Assembly assembly)
+        {
+            try
+            {
+                return assembly.GetTypes();
+            }
+            catch (ReflectionTypeLoadException e)
+            {
+                return e.Types.Where(x => x != null);
+            }
+        }
     }
 }
\ No newline at end of file