refactor(events): replace MediatR with custom event handlers

- Removed MediatR dependency and introduced custom interfaces for handling watcher events and closures.
- Updated relevant classes to use the new event handler system, promoting better separation of concerns and reducing unnecessary coupling.
- Ensured backward compatibility by adapting the configuration in the service registration.

Author: winromulus

src/ES.Kubernetes.Reflector/ES.Kubernetes.Reflector.csproj

@@ -15,7 +15,6 @@
 		<PackageReference Include="ES.FX.Ignite.KubernetesClient" />
 		<PackageReference Include="ES.FX.Microsoft.AspNetCore.JsonPatch" />
 		<PackageReference Include="ES.FX.Newtonsoft.Json" />
-		<PackageReference Include="MediatR" />
 		<PackageReference Include="Microsoft.VisualStudio.Azure.Containers.Tools.Targets" />
 	</ItemGroup>
 

src/ES.Kubernetes.Reflector/Mirroring/Core/ResourceMirror.cs

@@ -7,15 +7,13 @@
 using k8s;
 using k8s.Autorest;
 using k8s.Models;
-using MediatR;
 using Microsoft.AspNetCore.JsonPatch;
 using Newtonsoft.Json;
 
 namespace ES.Kubernetes.Reflector.Mirroring.Core;
 
 public abstract class ResourceMirror<TResource>(ILogger logger, IKubernetes kubernetes) :
-    INotificationHandler<WatcherEvent>,
-    INotificationHandler<WatcherClosed>
+    IWatcherEventHandler, IWatcherClosedHandler
     where TResource : class, IKubernetesObject<V1ObjectMeta>
 {
     private readonly ConcurrentDictionary<NamespacedName, HashSet<NamespacedName>> _autoReflectionCache = new();

src/ES.Kubernetes.Reflector/Program.cs

@@ -10,7 +10,6 @@
 using ES.Kubernetes.Reflector.Watchers;
 using ES.Kubernetes.Reflector.Watchers.Core.Events;
 using k8s.Models;
-using MediatR;
 
 return await ProgramEntry.CreateBuilder(args).UseSerilog().Build().RunAsync(async _ =>
 {
@@ -24,8 +23,6 @@
         config.Destructure.ByTransforming<V1ObjectReference>(v => v.NamespacedName()));
     builder.IgniteSeqOpenTelemetryExporter();
     builder.IgniteKubernetesClient();
-    builder.Services.AddMediatR(config =>
-        config.RegisterServicesFromAssembly(typeof(void).Assembly));
 
     builder.Services.Configure<ReflectorOptions>(builder.Configuration.GetSection(nameof(ES.Kubernetes.Reflector)));
 
@@ -36,11 +33,11 @@
     builder.Services.AddSingleton<SecretMirror>();
     builder.Services.AddSingleton<ConfigMapMirror>();
 
-    builder.Services.AddSingleton<INotificationHandler<WatcherEvent>>(sp => sp.GetRequiredService<SecretMirror>());
-    builder.Services.AddSingleton<INotificationHandler<WatcherClosed>>(sp => sp.GetRequiredService<SecretMirror>());
+    builder.Services.AddSingleton<IWatcherEventHandler>(sp => sp.GetRequiredService<SecretMirror>());
+    builder.Services.AddSingleton<IWatcherClosedHandler>(sp => sp.GetRequiredService<SecretMirror>());
 
-    builder.Services.AddSingleton<INotificationHandler<WatcherEvent>>(sp => sp.GetRequiredService<ConfigMapMirror>());
-    builder.Services.AddSingleton<INotificationHandler<WatcherClosed>>(sp => sp.GetRequiredService<ConfigMapMirror>());
+    builder.Services.AddSingleton<IWatcherEventHandler>(sp => sp.GetRequiredService<ConfigMapMirror>());
+    builder.Services.AddSingleton<IWatcherClosedHandler>(sp => sp.GetRequiredService<ConfigMapMirror>());
 
     var app = builder.Build();
     app.Ignite();

src/ES.Kubernetes.Reflector/Watchers/ConfigMapWatcher.cs

@@ -1,19 +1,21 @@
 using ES.Kubernetes.Reflector.Configuration;
 using ES.Kubernetes.Reflector.Watchers.Core;
+using ES.Kubernetes.Reflector.Watchers.Core.Events;
 using k8s;
 using k8s.Autorest;
 using k8s.Models;
-using MediatR;
 using Microsoft.Extensions.Options;
 
 namespace ES.Kubernetes.Reflector.Watchers;
 
 public class ConfigMapWatcher(
     ILogger<ConfigMapWatcher> logger,
-    IMediator mediator,
     IKubernetes kubernetes,
-    IOptionsMonitor<ReflectorOptions> options)
-    : WatcherBackgroundService<V1ConfigMap, V1ConfigMapList>(logger, mediator, options)
+    IOptionsMonitor<ReflectorOptions> options,
+    IEnumerable<IWatcherEventHandler> watcherEventHandlers,
+    IEnumerable<IWatcherClosedHandler> watcherClosedHandlers)
+    : WatcherBackgroundService<V1ConfigMap, V1ConfigMapList>(
+        logger, options, watcherEventHandlers, watcherClosedHandlers)
 {
     protected override Task<HttpOperationResponse<V1ConfigMapList>> OnGetWatcher(CancellationToken cancellationToken) =>
         kubernetes.CoreV1.ListConfigMapForAllNamespacesWithHttpMessagesAsync(watch: true,

src/ES.Kubernetes.Reflector/Watchers/Core/Events/IWatcherClosedHandler.cs

@@ -0,0 +1,6 @@
+namespace ES.Kubernetes.Reflector.Watchers.Core.Events;
+
+public interface IWatcherClosedHandler
+{
+    public Task Handle(WatcherClosed e, CancellationToken cancellationToken);
+}

src/ES.Kubernetes.Reflector/Watchers/Core/Events/IWatcherEventHandler.cs

@@ -0,0 +1,6 @@
+namespace ES.Kubernetes.Reflector.Watchers.Core.Events;
+
+public interface IWatcherEventHandler
+{
+    public Task Handle(WatcherEvent e, CancellationToken cancellationToken);
+}

src/ES.Kubernetes.Reflector/Watchers/Core/Events/WatcherClosed.cs

@@ -1,8 +1,6 @@
-using MediatR;
+namespace ES.Kubernetes.Reflector.Watchers.Core.Events;
 
-namespace ES.Kubernetes.Reflector.Watchers.Core.Events;
-
-public class WatcherClosed : INotification
+public class WatcherClosed
 {
     public required Type ResourceType { get; set; }
     public bool Faulted { get; set; }

src/ES.Kubernetes.Reflector/Watchers/Core/Events/WatcherEvent.cs

@@ -1,10 +1,9 @@
 using k8s;
 using k8s.Models;
-using MediatR;
 
 namespace ES.Kubernetes.Reflector.Watchers.Core.Events;
 
-public class WatcherEvent : INotification
+public class WatcherEvent
 {
     public WatchEventType EventType { get; set; }
     public IKubernetesObject<V1ObjectMeta>? Item { get; set; }

src/ES.Kubernetes.Reflector/Watchers/Core/WatcherBackgroundService.cs

@@ -5,15 +5,15 @@
 using k8s;
 using k8s.Autorest;
 using k8s.Models;
-using MediatR;
 using Microsoft.Extensions.Options;
 
 namespace ES.Kubernetes.Reflector.Watchers.Core;
 
 public abstract class WatcherBackgroundService<TResource, TResourceList>(
     ILogger logger,
-    IMediator mediator,
-    IOptionsMonitor<ReflectorOptions> options)
+    IOptionsMonitor<ReflectorOptions> options,
+    IEnumerable<IWatcherEventHandler> watcherEventHandlers,
+    IEnumerable<IWatcherClosedHandler> watcherClosedHandlers)
     : BackgroundService
     where TResource : IKubernetesObject<V1ObjectMeta>
 {
@@ -48,11 +48,12 @@ protected override async Task ExecuteAsync(CancellationToken stoppingToken)
                     {
                         var watcherEvent = await eventChannel.Reader.ReadAsync(cancellationToken)
                             .ConfigureAwait(false);
-                        await mediator.Publish(new WatcherEvent
-                        {
-                            Item = watcherEvent.Item,
-                            EventType = watcherEvent.EventType
-                        }, cancellationToken).ConfigureAwait(false);
+                        foreach (var watcherEventHandler in watcherEventHandlers)
+                            await watcherEventHandler.Handle(new WatcherEvent
+                            {
+                                Item = watcherEvent.Item,
+                                EventType = watcherEvent.EventType
+                            }, cancellationToken);
                     }
                 }, cancellationToken);
 
@@ -95,11 +96,12 @@ await eventChannel.Writer.WriteAsync(new WatcherEvent
                 logger.LogInformation("Session closed. Duration: {duration}. Faulted: {faulted}.", sessionElapsed,
                     sessionFaulted);
 
-                await mediator.Publish(new WatcherClosed
-                {
-                    ResourceType = typeof(TResource),
-                    Faulted = sessionFaulted
-                }, stoppingToken).ConfigureAwait(false);
+                foreach (var handler in watcherClosedHandlers)
+                    await handler.Handle(new WatcherClosed
+                    {
+                        ResourceType = typeof(TResource),
+                        Faulted = sessionFaulted
+                    }, stoppingToken);
             }
         }
     }

src/ES.Kubernetes.Reflector/Watchers/NamespaceWatcher.cs

@@ -1,19 +1,21 @@
 using ES.Kubernetes.Reflector.Configuration;
 using ES.Kubernetes.Reflector.Watchers.Core;
+using ES.Kubernetes.Reflector.Watchers.Core.Events;
 using k8s;
 using k8s.Autorest;
 using k8s.Models;
-using MediatR;
 using Microsoft.Extensions.Options;
 
 namespace ES.Kubernetes.Reflector.Watchers;
 
 public class NamespaceWatcher(
     ILogger<NamespaceWatcher> logger,
-    IMediator mediator,
     IKubernetes kubernetes,
-    IOptionsMonitor<ReflectorOptions> options)
-    : WatcherBackgroundService<V1Namespace, V1NamespaceList>(logger, mediator, options)
+    IOptionsMonitor<ReflectorOptions> options,
+    IEnumerable<IWatcherEventHandler> watcherEventHandlers,
+    IEnumerable<IWatcherClosedHandler> watcherClosedHandlers)
+    : WatcherBackgroundService<V1Namespace, V1NamespaceList>(
+        logger, options, watcherEventHandlers, watcherClosedHandlers)
 {
     protected override Task<HttpOperationResponse<V1NamespaceList>> OnGetWatcher(CancellationToken cancellationToken) =>
         kubernetes.CoreV1.ListNamespaceWithHttpMessagesAsync(watch: true, timeoutSeconds: WatcherTimeout,