Commands are stored in memory and prevents duplicate jobs

NzbDrone.Common/Messaging/Manager/CommandManager.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using NzbDrone.Common.Cache;
+using NzbDrone.Common.Messaging.Events;
+
+namespace NzbDrone.Common.Messaging.Manager
+{
+    public interface IManageCommands
+    {
+        ICollection<CommandManagerItem> Items { get; }
+        Boolean ExistingItem(ICommand command);
+    }
+
+    public class CommandManager : IManageCommands,
+                                       IHandle<CommandStartedEvent>,
+                                       IHandle<CommandCompletedEvent>,
+                                       IHandle<CommandFailedEvent>
+    {
+        private readonly ICached<CommandManagerItem> _cache;
+
+        public CommandManager(ICacheManger cacheManger)
+        {
+            _cache = cacheManger.GetCache<CommandManagerItem>(GetType());
+        }
+
+        public void Handle(CommandStartedEvent message)
+        {
+            _cache.Set(message.Command.CommandId, new CommandManagerItem(message.Command, CommandState.Running));
+        }
+
+        public void Handle(CommandCompletedEvent message)
+        {
+            _cache.Set(message.Command.CommandId, new CommandManagerItem(message.Command, CommandState.Completed));
+        }
+
+        public void Handle(CommandFailedEvent message)
+        {
+            _cache.Set(message.Command.CommandId, new CommandManagerItem(message.Command, CommandState.Failed));
+        }
+
+        public ICollection<CommandManagerItem> Items
+        {
+            get
+            {
+                return _cache.Values;
+            }
+        }
+
+        public bool ExistingItem(ICommand command)
+        {
+            var running = Items.Where(i => i.Type == command.GetType().FullName && i.State == CommandState.Running);
+
+            var result = running.Select(r => r.Command).Contains(command, new CommandEqualityComparer());
+
+            return result;
+        }
+    }
+}