From 6ffa4e05684d22f83d894fba7deda99e66596bd2 Mon Sep 17 00:00:00 2001
From: Keivan Beigi <kay.one@gmail.com>
Date: Mon, 18 Feb 2013 18:37:16 -0800
Subject: [PATCH] NzbDrone is getting on a bus! (added EventAggregator)

---
 NzbDrone.Common/Eventing/EventAggregator.cs  | 174 +++++++++++++++++++
 NzbDrone.Common/Eventing/IEventAggregator.cs |  47 +++++
 NzbDrone.Common/Eventing/IHandle.cs          |  22 +++
 NzbDrone.Common/NzbDrone.Common.csproj       |   3 +
 4 files changed, 246 insertions(+)
 create mode 100644 NzbDrone.Common/Eventing/EventAggregator.cs
 create mode 100644 NzbDrone.Common/Eventing/IEventAggregator.cs
 create mode 100644 NzbDrone.Common/Eventing/IHandle.cs

diff --git a/NzbDrone.Common/Eventing/EventAggregator.cs b/NzbDrone.Common/Eventing/EventAggregator.cs
new file mode 100644
index 000000000..bb76f8479
--- /dev/null
+++ b/NzbDrone.Common/Eventing/EventAggregator.cs
@@ -0,0 +1,174 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Reflection;
+
+//From http://caliburnmicro.codeplex.com/
+
+namespace NzbDrone.Common.Eventing
+{
+    /// <summary>
+    ///   Enables loosely-coupled publication of and subscription to events.
+    /// </summary>
+    public class EventAggregator : IEventAggregator
+    {
+        readonly List<Handler> handlers = new List<Handler>();
+
+        /// <summary>
+        ///   The default thread marshaller used for publication;
+        /// </summary>
+        public static Action<Action> DefaultPublicationThreadMarshaller = action => action();
+
+        /// <summary>
+        /// Processing of handler results on publication thread.
+        /// </summary>
+        public static Action<object, object> HandlerResultProcessing = (target, result) => { };
+
+        /// <summary>
+        ///   Initializes a new instance of the <see cref = "EventAggregator" /> class.
+        /// </summary>
+        public EventAggregator()
+        {
+            PublicationThreadMarshaller = DefaultPublicationThreadMarshaller;
+        }
+
+        /// <summary>
+        ///   Gets or sets the default publication thread marshaller.
+        /// </summary>
+        /// <value>
+        ///   The default publication thread marshaller.
+        /// </value>
+        public Action<System.Action> PublicationThreadMarshaller { get; set; }
+
+        /// <summary>
+        ///   Subscribes an instance to all events declared through implementations of <see cref = "IHandle{T}" />
+        /// </summary>
+        /// <param name = "instance">The instance to subscribe for event publication.</param>
+        public virtual void Subscribe(object instance)
+        {
+            lock (handlers)
+            {
+                if (handlers.Any(x => x.Matches(instance)))
+                {
+                    return;
+                }
+
+                handlers.Add(new Handler(instance));
+            }
+        }
+
+        /// <summary>
+        ///   Unsubscribes the instance from all events.
+        /// </summary>
+        /// <param name = "instance">The instance to unsubscribe.</param>
+        public virtual void Unsubscribe(object instance)
+        {
+            lock (handlers)
+            {
+                var found = handlers.FirstOrDefault(x => x.Matches(instance));
+
+                if (found != null)
+                {
+                    handlers.Remove(found);
+                }
+            }
+        }
+
+        /// <summary>
+        ///   Publishes a message.
+        /// </summary>
+        /// <param name = "message">The message instance.</param>
+        /// <remarks>
+        ///   Does not marshall the the publication to any special thread by default.
+        /// </remarks>
+        public virtual void Publish(object message)
+        {
+            Publish(message, PublicationThreadMarshaller);
+        }
+
+        /// <summary>
+        ///   Publishes a message.
+        /// </summary>
+        /// <param name = "message">The message instance.</param>
+        /// <param name = "marshal">Allows the publisher to provide a custom thread marshaller for the message publication.</param>
+        public virtual void Publish(object message, Action<System.Action> marshal)
+        {
+            Handler[] toNotify;
+            lock (handlers)
+            {
+                toNotify = handlers.ToArray();
+            }
+
+            marshal(() =>
+            {
+                var messageType = message.GetType();
+
+                var dead = toNotify
+                    .Where(handler => !handler.Handle(messageType, message))
+                    .ToList();
+
+                if (dead.Any())
+                {
+                    lock (handlers)
+                    {
+                        foreach (var item in dead)
+                        {
+                            handlers.Remove(item);
+                        }
+                    }
+                }
+            });
+        }
+
+
+        class Handler
+        {
+            readonly WeakReference reference;
+            readonly Dictionary<Type, MethodInfo> supportedHandlers = new Dictionary<Type, MethodInfo>();
+
+            public Handler(object handler)
+            {
+                reference = new WeakReference(handler);
+
+                var interfaces = handler.GetType().GetInterfaces()
+                    .Where(x => typeof(IHandle).IsAssignableFrom(x) && x.IsGenericType);
+
+                foreach (var @interface in interfaces)
+                {
+                    var type = @interface.GetGenericArguments()[0];
+                    var method = @interface.GetMethod("Handle");
+                    supportedHandlers[type] = method;
+                }
+            }
+
+            public bool Matches(object instance)
+            {
+                return reference.Target == instance;
+            }
+
+            public bool Handle(Type messageType, object message)
+            {
+                var target = reference.Target;
+                if (target == null)
+                {
+                    return false;
+                }
+
+                foreach (var pair in supportedHandlers)
+                {
+                    if (pair.Key.IsAssignableFrom(messageType))
+                    {
+                        var result = pair.Value.Invoke(target, new[] { message });
+                        if (result != null)
+                        {
+                            HandlerResultProcessing(target, result);
+                        }
+                        return true;
+                    }
+                }
+
+                return true;
+            }
+        }
+    }
+}
\ No newline at end of file
diff --git a/NzbDrone.Common/Eventing/IEventAggregator.cs b/NzbDrone.Common/Eventing/IEventAggregator.cs
new file mode 100644
index 000000000..369b8a8f1
--- /dev/null
+++ b/NzbDrone.Common/Eventing/IEventAggregator.cs
@@ -0,0 +1,47 @@
+using System;
+using System.Linq;
+
+namespace NzbDrone.Common.Eventing
+{
+    /// <summary>
+    ///   Enables loosely-coupled publication of and subscription to events.
+    /// </summary>
+    public interface IEventAggregator
+    {
+        /// <summary>
+        ///   Gets or sets the default publication thread marshaller.
+        /// </summary>
+        /// <value>
+        ///   The default publication thread marshaller.
+        /// </value>
+        Action<Action> PublicationThreadMarshaller { get; set; }
+
+        /// <summary>
+        ///   Subscribes an instance to all events declared through implementations of <see cref = "IHandle{T}" />
+        /// </summary>
+        /// <param name = "instance">The instance to subscribe for event publication.</param>
+        void Subscribe(object instance);
+
+        /// <summary>
+        ///   Unsubscribes the instance from all events.
+        /// </summary>
+        /// <param name = "instance">The instance to unsubscribe.</param>
+        void Unsubscribe(object instance);
+
+        /// <summary>
+        ///   Publishes a message.
+        /// </summary>
+        /// <param name = "message">The message instance.</param>
+        /// <remarks>
+        ///   Uses the default thread marshaller during publication.
+        /// </remarks>
+        void Publish(object message);
+
+        /// <summary>
+        ///   Publishes a message.
+        /// </summary>
+        /// <param name = "message">The message instance.</param>
+        /// <param name = "marshal">Allows the publisher to provide a custom thread marshaller for the message publication.</param>
+        void Publish(object message, Action<System.Action> marshal);
+    }
+}
\ No newline at end of file
diff --git a/NzbDrone.Common/Eventing/IHandle.cs b/NzbDrone.Common/Eventing/IHandle.cs
new file mode 100644
index 000000000..afbf70fae
--- /dev/null
+++ b/NzbDrone.Common/Eventing/IHandle.cs
@@ -0,0 +1,22 @@
+using System.Linq;
+
+namespace NzbDrone.Common.Eventing
+{
+    /// <summary>
+    ///   Denotes a class which can handle a particular type of message.
+    /// </summary>
+    /// <typeparam name = "TMessage">The type of message to handle.</typeparam>
+    public interface IHandle<TMessage> : IHandle
+    {
+        /// <summary>
+        ///   Handles the message.
+        /// </summary>
+        /// <param name = "message">The message.</param>
+        void Handle(TMessage message);
+    }
+
+    /// <summary>
+    ///   A marker interface for classes that subscribe to messages.
+    /// </summary>
+    public interface IHandle { }
+}
\ No newline at end of file
diff --git a/NzbDrone.Common/NzbDrone.Common.csproj b/NzbDrone.Common/NzbDrone.Common.csproj
index db9143e3c..2f450d59c 100644
--- a/NzbDrone.Common/NzbDrone.Common.csproj
+++ b/NzbDrone.Common/NzbDrone.Common.csproj
@@ -110,6 +110,9 @@
     <Compile Include="EnsureThat\Resources\ExceptionMessages.Designer.cs" />
     <Compile Include="EnsureThat\StringExtensions.cs" />
     <Compile Include="EnsureThat\TypeParam.cs" />
+    <Compile Include="Eventing\EventAggregator.cs" />
+    <Compile Include="Eventing\IEventAggregator.cs" />
+    <Compile Include="Eventing\IHandle.cs" />
     <Compile Include="HostController.cs" />
     <Compile Include="StringExtention.cs" />
     <Compile Include="HttpProvider.cs" />