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

NzbDrone.Core/DecisionEngine/Specifications/RetentionSpecification.cs

@@ -0,0 +1,39 @@
+using NLog;
+using NzbDrone.Core.Configuration;
+using NzbDrone.Core.Model;
+
+namespace NzbDrone.Core.DecisionEngine.Specifications
+{
+    public class RetentionSpecification : IFetchableSpecification
+    {
+        private readonly IConfigService _configService;
+        private readonly Logger _logger;
+
+        public RetentionSpecification(IConfigService configService, Logger logger)
+        {
+            _configService = configService;
+            _logger = logger;
+        }
+
+
+        public string RejectionReason
+        {
+            get
+            {
+                return "Report past retention limit.";
+            }
+        }
+
+        public virtual bool IsSatisfiedBy(EpisodeParseResult subject)
+        {
+            _logger.Trace("Checking if report meets retention requirements. {0}", subject.Age);
+            if (_configService.Retention > 0 && subject.Age > _configService.Retention)
+            {
+                _logger.Trace("Report age: {0} rejected by user's retention limit", subject.Age);
+                return false;
+            }
+
+            return true;
+        }
+    }
+}