Better names, more info, not using events

NzbDrone.Common/Messaging/Tracking/CommandTrackingService.cs

@@ -0,0 +1,78 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using NzbDrone.Common.Cache;
+
+namespace NzbDrone.Common.Messaging.Tracking
+{
+    public interface ITrackCommands
+    {
+        TrackedCommand TrackIfNew(ICommand command);
+        TrackedCommand Completed(TrackedCommand trackedCommand, TimeSpan runtime);
+        TrackedCommand Failed(TrackedCommand trackedCommand, Exception e);
+        ICollection<TrackedCommand> AllTracked { get; }
+        Boolean ExistingCommand(ICommand command);
+    }
+
+    public class TrackCommands : ITrackCommands
+    {
+        private readonly ICached<TrackedCommand> _cache;
+
+        public TrackCommands(ICacheManger cacheManger)
+        {
+            _cache = cacheManger.GetCache<TrackedCommand>(GetType());
+        }
+
+        public TrackedCommand TrackIfNew(ICommand command)
+        {
+            if (ExistingCommand(command))
+            {
+                return null;
+            }
+
+            var trackedCommand = new TrackedCommand(command, CommandState.Running);
+            _cache.Set(command.CommandId, trackedCommand);
+
+            return trackedCommand;
+        }
+
+        public TrackedCommand Completed(TrackedCommand trackedCommand, TimeSpan runtime)
+        {
+            trackedCommand.StateChangeTime = DateTime.UtcNow;
+            trackedCommand.State = CommandState.Completed;
+            trackedCommand.Runtime = runtime;
+
+            _cache.Set(trackedCommand.Command.CommandId, trackedCommand);
+
+            return trackedCommand;
+        }
+
+        public TrackedCommand Failed(TrackedCommand trackedCommand, Exception e)
+        {
+            trackedCommand.StateChangeTime = DateTime.UtcNow;
+            trackedCommand.State = CommandState.Failed;
+            trackedCommand.Exception = e;
+
+            _cache.Set(trackedCommand.Command.CommandId, trackedCommand);
+
+            return trackedCommand;
+        }
+
+        public ICollection<TrackedCommand> AllTracked
+        {
+            get
+            {
+                return _cache.Values;
+            }
+        }
+
+        public bool ExistingCommand(ICommand command)
+        {
+            var running = AllTracked.Where(i => i.Type == command.GetType().FullName && i.State == CommandState.Running);
+
+            var result = running.Select(r => r.Command).Contains(command, new CommandEqualityComparer());
+
+            return result;
+        }
+    }
+}