some preliminary work to move decision engine to use the visitor pattern.

NzbDrone.Core/DecisionEngine/Specifications/NotInQueueSpecification.cs

@@ -0,0 +1,32 @@
+using NLog;
+using NzbDrone.Core.Download;
+using NzbDrone.Core.Model;
+
+namespace NzbDrone.Core.DecisionEngine.Specifications
+{
+    public class NotInQueueSpecification : IFetchableSpecification
+    {
+        private readonly DownloadProvider _downloadProvider;
+
+
+        public NotInQueueSpecification(DownloadProvider downloadProvider)
+        {
+            _downloadProvider = downloadProvider;
+
+        }
+
+        public string RejectionReason
+        {
+            get
+            {
+                return "Already in download queue.";
+            }
+        }
+
+        public virtual bool IsSatisfiedBy(EpisodeParseResult subject)
+        {
+            return !_downloadProvider.GetActiveDownloadClient().IsInQueue(subject);
+        }
+
+    }
+}