New: Restrict repack upgrades to the same release group

Closes #946

src/NzbDrone.Core/DecisionEngine/Specifications/RepackSpecification.cs

@@ -0,0 +1,43 @@
+using System;
+using System.Linq;
+using NLog;
+using NzbDrone.Core.IndexerSearch.Definitions;
+using NzbDrone.Core.Parser.Model;
+
+namespace NzbDrone.Core.DecisionEngine.Specifications
+{
+    public class RepackSpecification : IDecisionEngineSpecification
+    {
+        private readonly Logger _logger;
+
+        public RepackSpecification(Logger logger)
+        {
+            _logger = logger;
+        }
+
+        public SpecificationPriority Priority => SpecificationPriority.Database;
+        public RejectionType Type => RejectionType.Permanent;
+
+        public Decision IsSatisfiedBy(RemoteEpisode subject, SearchCriteriaBase searchCriteria)
+        {
+            if (!subject.ParsedEpisodeInfo.Quality.Revision.IsRepack)
+            {
+                return Decision.Accept();
+            }
+
+            foreach (var file in subject.Episodes.Where(c => c.EpisodeFileId != 0).Select(c => c.EpisodeFile.Value))
+            {
+                var releaseGroup = subject.ParsedEpisodeInfo.ReleaseGroup;
+                var fileReleaseGroup = file.ReleaseGroup;
+
+                if (!fileReleaseGroup.Equals(releaseGroup, StringComparison.InvariantCultureIgnoreCase))
+                {
+                    _logger.Debug("Release is a repack for a different release group. Release Group: {0}. File release group: {0}", releaseGroup, fileReleaseGroup);
+                    return Decision.Reject("Release is a repack for a different release group. Release Group: {0}. File release group: {0}", releaseGroup, fileReleaseGroup);
+                }
+            }
+
+            return Decision.Accept();
+        }
+    }
+}