Allow the Mediator to be subscribed to and therefore handled

Toolkit.Foundation/HandlerProvider.cs

@@ -4,7 +4,7 @@ public class HandlerProvider(SubscriptionCollection subscriptions) :
     IHandlerProvider
 {
     public IEnumerable<object?> Get(Type type,
-        object key)
+        object? key = null)
     {
         string subscriptionKey = $"{(key is not null ? $"{key}:" : "")}{type}";
         if (subscriptions.TryGetValue(subscriptionKey, out List<WeakReference>? subscribers))

Toolkit.Foundation/IHandlerProvider.cs

@@ -3,6 +3,7 @@ namespace Toolkit.Foundation
 {
     public interface IHandlerProvider
     {
-        IEnumerable<object?> Get(Type type, object key);
+        IEnumerable<object?> Get(Type type, 
+            object? key = null);
     }
 }

Toolkit.Foundation/IMediator.cs

@@ -3,7 +3,11 @@ namespace Toolkit.Foundation
 {
     public interface IMediator
     {
-        Task<object?> Handle(object message, CancellationToken cancellationToken = default);
-        Task<TResponse?> Handle<TRequest, TResponse>(TRequest request, CancellationToken cancellationToken = default) where TRequest : notnull;
+        Task<object?> Handle(object message, 
+            CancellationToken cancellationToken = default);
+
+        Task<TResponse?> Handle<TMessage, TResponse>(TMessage message, 
+            CancellationToken cancellationToken = default) 
+            where TMessage : notnull;
     }
 }

Toolkit.Foundation/Mediator.cs

@@ -1,27 +1,62 @@
-using System.Reflection;
+using Microsoft.Extensions.DependencyInjection;
+using System.Reflection;
 
 namespace Toolkit.Foundation;
 
-public class Mediator(IServiceProvider provider) :
+public class Mediator(IHandlerProvider handlerProvider,
+    IServiceProvider provider) :
     IMediator
 {
-    public Task<TResponse?> Handle<TRequest, TResponse>(TRequest request,
+    public async Task<TResponse?> Handle<TMessage, TResponse>(TMessage message,
         CancellationToken cancellationToken = default)
-        where TRequest : notnull
+        where TMessage : notnull
     {
-        Type handlerType = typeof(HandlerWrapper<,>).MakeGenericType(request.GetType(),
-            typeof(TResponse));
+        Type messageType = message.GetType();
+        Type handlerWrapperType = typeof(HandlerWrapper<,>).MakeGenericType(messageType, typeof(TResponse));
 
-        if (provider.GetService(handlerType)
-            is object handler)
+        Dictionary<Type, List<object?>> handlers = [];
+
+        foreach (object? service in provider.GetServices(handlerWrapperType))
         {
-            if (handlerType.GetMethod("Handle") is MethodInfo handleMethod)
+            if (service?.GetType() is Type serviceType)
             {
-                return (Task<TResponse?>)handleMethod.Invoke(handler, new object[] { request, cancellationToken })!;
+                if (!handlers.TryGetValue(serviceType, out List<object?>? handlerList))
+                {
+                    handlerList = [];
+                    handlers.Add(serviceType, handlerList);
+                }
+
+                handlerList.Add(service);
             }
         }
 
-        return Task.FromResult<TResponse?>(default);
+        foreach (object? handler in handlerProvider.Get(messageType))
+        {
+            if (handler is not null)
+            {
+                Type handlerType = handler.GetType();
+                if (!handlers.TryGetValue(handlerType, out List<object?>? handlerList))
+                {
+                    handlerList = [];
+                    handlers.Add(handlerType, handlerList);
+                }
+                handlerList.Add(handler);
+            }
+        }
+
+        foreach (KeyValuePair<Type, List<object?>> handlerEntry in handlers)
+        {
+            foreach (object? handler in handlerEntry.Value)
+            {
+                if (handler?.GetType().GetMethod("Handle") is MethodInfo handleMethod)
+                {
+                    return await (Task<TResponse?>)handleMethod.Invoke(handler, 
+                        new object[] { message, cancellationToken })!;
+                }
+            }
+        }
+
+        return default;
     }
 
     public Task<object?> Handle(object message,

Toolkit.Foundation/Publisher.cs

@@ -25,12 +25,11 @@ public class Publisher(IHandlerProvider handlerProvider,
         object? key = null)
     {
         Type notificationType = message.GetType();
+        Type handlerType = typeof(NotificationHandlerWrapper<>)
+            .MakeGenericType(notificationType);
 
-        List<object?> handlers = provider.GetServices(typeof(NotificationHandlerWrapper<>)
-            .MakeGenericType(notificationType)).ToList();
-
-        foreach (object? handler in handlerProvider
-            .Get(notificationType, key!))
+        List<object?> handlers = provider.GetServices(handlerType).ToList();
+        foreach (object? handler in handlerProvider.Get(notificationType, key))
         {
             handlers.Add(handler);
         }
@@ -39,8 +38,7 @@ public class Publisher(IHandlerProvider handlerProvider,
         {
             if (handler is not null)
             {
-                Type? handlerType = handler.GetType();
-                MethodInfo? handleMethod = handlerType.GetMethod("Handle",
+                MethodInfo? handleMethod = handler.GetType().GetMethod("Handle",
                     [notificationType]);
 
                 if (handleMethod is not null)

Toolkit.Foundation/Subscription.cs

@@ -76,6 +76,11 @@ public class Subscription(SubscriptionCollection subscriptions,
             ? handler.GetPropertyValue(() => attribute.Key) is { } value ? value : attribute.Key : null;
 
     private IEnumerable<Type> GetHandlerInterfaces(Type handlerType) =>
-        handlerType.GetInterfaces().Where(interfaceType => interfaceType.IsGenericType &&
-            interfaceType.GetGenericTypeDefinition() == typeof(INotificationHandler<>));
+        handlerType.GetInterfaces().Where(interfaceType =>
+        {
+            Type? definition = interfaceType.IsGenericType ? interfaceType.GetGenericTypeDefinition() : null;
+            return definition == typeof(INotificationHandler<>) ||
+                   definition == typeof(IHandler<>) ||
+                   definition == typeof(IHandler<,>);
+        });
 }