Fix extras naming and version assignment

MediaBrowser.Controller/Entities/BaseItem.cs

@@ -88,7 +88,7 @@ namespace MediaBrowser.Controller.Entities
             Model.Entities.ExtraType.Short
         };
 
-        private static readonly char[] VersionDelimiters = ['-', '_', '.'];
+        private protected static readonly char[] VersionDelimiters = ['-', '_', '.'];
 
         private string _sortName;
 
@@ -1543,19 +1543,33 @@ namespace MediaBrowser.Controller.Entities
 
         private async Task<bool> RefreshExtras(BaseItem item, MetadataRefreshOptions options, IReadOnlyList<FileSystemMetadata> fileSystemChildren, CancellationToken cancellationToken)
         {
-            var extras = LibraryManager.FindExtras(item, fileSystemChildren, options.DirectoryService).ToArray();
-            var newExtraIds = Array.ConvertAll(extras, x => x.Id);
-
+            // An extra is owned by the version it is named after, so all of them are maintained together.
             var currentExtras = LibraryManager.GetItemList(new InternalItemsQuery()
             {
-                OwnerIds = [item.Id]
-            });
+                OwnerIds = item.GetOwnedVersionIds()
+            }).Where(e => e.ExtraType.HasValue).ToList();
 
             var currentExtraIds = currentExtras.Select(e => e.Id).ToArray();
 
+            // Snapshot the persisted names before resolving, as FindExtras corrects the name on the
+            // items it hands back and may well hand back these very instances.
+            var currentExtraNames = new Dictionary<Guid, string>();
+            foreach (var extra in currentExtras)
+            {
+                currentExtraNames[extra.Id] = extra.Name;
+            }
+
+            var extras = LibraryManager.FindExtras(item, fileSystemChildren, options.DirectoryService).ToArray();
+            var newExtraIds = Array.ConvertAll(extras, x => x.Id);
+
+            var renamedExtraIds = extras
+                .Where(e => currentExtraNames.TryGetValue(e.Id, out var oldName) && !string.Equals(oldName, e.Name, StringComparison.Ordinal))
+                .Select(e => e.Id)
+                .ToHashSet();
+
             var extrasChanged = !currentExtraIds.OrderBy(x => x).SequenceEqual(newExtraIds.OrderBy(x => x));
 
-            if (!extrasChanged && !options.ReplaceAllMetadata && options.MetadataRefreshMode != MetadataRefreshMode.FullRefresh)
+            if (!extrasChanged && renamedExtraIds.Count == 0 && !options.ReplaceAllMetadata && options.MetadataRefreshMode != MetadataRefreshMode.FullRefresh)
             {
                 // The owner's dates may only have become known after its extras were created, so keep
                 // them in sync even when there is nothing to refresh.
@@ -1570,12 +1584,11 @@ namespace MediaBrowser.Controller.Entities
                 return false;
             }
 
-            var ownerId = item.Id;
-
             var tasks = extras.Select(i =>
             {
+                var ownerId = item.GetOwnerIdForExtra(i);
                 var subOptions = new MetadataRefreshOptions(options);
-                if (!i.OwnerId.Equals(ownerId) || !i.ParentId.IsEmpty())
+                if (!i.OwnerId.Equals(ownerId) || !i.ParentId.IsEmpty() || renamedExtraIds.Contains(i.Id))
                 {
                     subOptions.ForceSave = true;
                 }
@@ -2920,6 +2933,25 @@ namespace MediaBrowser.Controller.Entities
             return [Id];
         }
 
+        /// <summary>
+        /// Gets the ids of this item and the versions of it whose extras it maintains.
+        /// </summary>
+        /// <returns>An array containing the version ids.</returns>
+        protected virtual Guid[] GetOwnedVersionIds()
+        {
+            return [Id];
+        }
+
+        /// <summary>
+        /// Gets the id of the version an extra belongs to.
+        /// </summary>
+        /// <param name="extra">The extra.</param>
+        /// <returns>The id of the owning version.</returns>
+        protected virtual Guid GetOwnerIdForExtra(BaseItem extra)
+        {
+            return Id;
+        }
+
         /// <summary>
         /// Get all extras associated with this item, sorted by <see cref="SortName"/>.
         /// </summary>

MediaBrowser.Controller/Entities/Video.cs

@@ -751,6 +751,80 @@ namespace MediaBrowser.Controller.Entities
                 .ToArray();
         }
 
+        /// <inheritdoc />
+        protected override Guid[] GetOwnedVersionIds()
+        {
+            // Only the versions that live beside this one in the folder this scan covers. Linked
+            // versions are items of their own and maintain their extras themselves.
+            return [Id, .. LibraryManager.GetLocalAlternateVersionIds(this)];
+        }
+
+        /// <inheritdoc />
+        protected override Guid GetOwnerIdForExtra(BaseItem extra)
+        {
+            if (string.IsNullOrEmpty(extra.Path))
+            {
+                return Id;
+            }
+
+            var extraDirectory = System.IO.Path.GetDirectoryName(extra.Path.AsSpan());
+            var extraFileName = System.IO.Path.GetFileNameWithoutExtension(extra.Path.AsSpan());
+
+            var ownerId = Id;
+            var matchedLength = MatchedVersionNameLength(Path, extraDirectory, extraFileName);
+
+            foreach (var versionId in LibraryManager.GetLocalAlternateVersionIds(this))
+            {
+                var version = LibraryManager.GetItemById(versionId);
+                if (version is null)
+                {
+                    continue;
+                }
+
+                // "Movie - [2160p]-trailer.mkv" belongs to "Movie - [2160p].mkv" rather than to the
+                // primary version, whose name it also starts with when the primary is plain "Movie.mkv"
+                var length = MatchedVersionNameLength(version.Path, extraDirectory, extraFileName);
+                if (length > matchedLength)
+                {
+                    matchedLength = length;
+                    ownerId = versionId;
+                }
+            }
+
+            return ownerId;
+        }
+
+        /// <summary>
+        /// Gets how much of an extra's file name is the name of the given version file, or 0 when the
+        /// extra is not named after it.
+        /// </summary>
+        /// <param name="versionPath">The path of the version.</param>
+        /// <param name="extraDirectory">The directory the extra lives in.</param>
+        /// <param name="extraFileName">The file name of the extra, without extension.</param>
+        /// <returns>The length of the match.</returns>
+        private static int MatchedVersionNameLength(string versionPath, ReadOnlySpan<char> extraDirectory, ReadOnlySpan<char> extraFileName)
+        {
+            if (string.IsNullOrEmpty(versionPath)
+                || !System.IO.Path.GetDirectoryName(versionPath.AsSpan()).Equals(extraDirectory, StringComparison.OrdinalIgnoreCase))
+            {
+                return 0;
+            }
+
+            var versionFileName = System.IO.Path.GetFileNameWithoutExtension(versionPath.AsSpan());
+            if (versionFileName.IsEmpty || !extraFileName.StartsWith(versionFileName, StringComparison.OrdinalIgnoreCase))
+            {
+                return 0;
+            }
+
+            // The version name has to end where the extra's own name begins, so that a version
+            // named "Movie - 4K" does not claim the extras of "Movie - 4Kish"
+            var remainder = extraFileName[versionFileName.Length..];
+
+            return !remainder.IsEmpty && (remainder[0] == ' ' || Array.IndexOf(VersionDelimiters, remainder[0]) >= 0)
+                ? versionFileName.Length
+                : 0;
+        }
+
         protected override IEnumerable<(BaseItem Item, MediaSourceType MediaSourceType)> GetAllItemsForMediaSources()
         {
             var primary = PrimaryVersionId.HasValue