Fixed: Computing most common author now we have multiple authors

src/NzbDrone.Core/MediaFiles/BookImport/Identification/CandidateService.cs

@@ -285,7 +285,13 @@ namespace NzbDrone.Core.MediaFiles.BookImport.Identification
             }
             else
             {
-                authorTags.AddRange(localEdition.LocalBooks.MostCommon(x => x.FileTrackInfo.Authors));
+                // the most common list of authors reported by a file
+                var authors = localEdition.LocalBooks.Select(x => x.FileTrackInfo.Authors.Where(a => a.IsNotNullOrWhiteSpace()).ToList())
+                    .GroupBy(x => x.ConcatToString())
+                    .OrderByDescending(x => x.Count())
+                    .First()
+                    .First();
+                authorTags.AddRange(authors);
             }
 
             var bookTag = localEdition.LocalBooks.MostCommon(x => x.FileTrackInfo.BookTitle) ?? "";

src/NzbDrone.Core/MediaFiles/BookImport/Identification/DistanceCalculator.cs

@@ -23,12 +23,14 @@ namespace NzbDrone.Core.MediaFiles.BookImport.Identification
         {
             var dist = new Distance();
 
-            var authors = new List<string>();
+            // the most common list of authors reported by a file
+            var fileAuthors = localTracks.Select(x => x.FileTrackInfo.Authors.Where(a => a.IsNotNullOrWhiteSpace()).ToList())
+                .GroupBy(x => x.ConcatToString())
+                .OrderByDescending(x => x.Count())
+                .First()
+                .First();
 
-            var fileAuthors = localTracks.MostCommon(x => x.FileTrackInfo.Authors);
-            if (fileAuthors?.Any() ?? false)
-            {
-                authors.AddRange(fileAuthors);
+            var authors = new List<string>(fileAuthors);
 
             foreach (var author in fileAuthors)
             {
@@ -37,7 +39,6 @@ namespace NzbDrone.Core.MediaFiles.BookImport.Identification
                     authors.Add(authors[0].Split(',', 2).Select(x => x.Trim()).Reverse().ConcatToString(" "));
                 }
             }
-            }
 
             dist.AddString("author", authors, edition.Book.Value.AuthorMetadata.Value.Name);
             Logger.Trace("author: '{0}' vs '{1}'; {2}", authors.ConcatToString("' or '"), edition.Book.Value.AuthorMetadata.Value.Name, dist.NormalizedDistance());