Coalesce alternate-version progress onto primary in resume filter

3 files changed, 156 insertions, 5 deletions

diff --git a/Emby.Server.Implementations/Dto/DtoService.cs b/Emby.Server.Implementations/Dto/DtoService.cs
index c9c31ebee4..2bf478953e 100644
--- a/Emby.Server.Implementations/Dto/DtoService.cs
+++ b/Emby.Server.Implementations/Dto/DtoService.cs
@@ -167,9 +167,13 @@ namespace Emby.Server.Implementations.Dto
 
             // Batch-fetch user data for all items
             Dictionary<Guid, UserItemData>? userDataBatch = null;
+            IReadOnlyDictionary<Guid, VersionResumeData>? resumeDataBatch = null;
             if (user is not null && options.EnableUserData)
             {
                 userDataBatch = _userDataRepository.GetUserDataBatch(accessibleItems, user);
+
+                // For items with alternate versions, the most recently played version drives resume.
+                resumeDataBatch = _userDataRepository.GetResumeUserDataBatch(accessibleItems, user);
             }
 
             // Pre-compute collection folders once to avoid N+1 queries in CanDelete
@@ -248,7 +252,8 @@ namespace Emby.Server.Implementations.Dto
                     allCollectionFolders,
                     childCountBatch,
                     playedCountBatch,
-                    artistsBatch);
+                    artistsBatch,
+                    resumeDataBatch?.GetValueOrDefault(item.Id));
 
                 if (item is LiveTvChannel tvChannel)
                 {
@@ -309,7 +314,8 @@ namespace Emby.Server.Implementations.Dto
             List<Folder>? allCollectionFolders = null,
             Dictionary<Guid, int>? childCountBatch = null,
             Dictionary<Guid, (int Played, int Total)>? playedCountBatch = null,
-            IReadOnlyDictionary<string, MusicArtist[]>? artistsBatch = null)
+            IReadOnlyDictionary<string, MusicArtist[]>? artistsBatch = null,
+            VersionResumeData? resumeData = null)
         {
             var dto = new BaseItemDto
             {
@@ -353,7 +359,8 @@ namespace Emby.Server.Implementations.Dto
                     options,
                     userData,
                     childCountBatch,
-                    playedCountBatch);
+                    playedCountBatch,
+                    resumeData);
             }
 
             if (item is IHasMediaSources
@@ -538,7 +545,8 @@ namespace Emby.Server.Implementations.Dto
             DtoOptions options,
             UserItemData? userData = null,
             Dictionary<Guid, int>? childCountBatch = null,
-            Dictionary<Guid, (int Played, int Total)>? playedCountBatch = null)
+            Dictionary<Guid, (int Played, int Total)>? playedCountBatch = null,
+            VersionResumeData? resumeData = null)
         {
             if (item.IsFolder)
             {
@@ -600,6 +608,9 @@ namespace Emby.Server.Implementations.Dto
                         // Use pre-fetched user data
                         dto.UserData = GetUserItemDataDto(userData, item.Id);
                         item.FillUserDataDtoValues(dto.UserData, userData, dto, user, options);
+
+                        // For items with alternate versions, the most recently played version drives resume.
+                        resumeData?.ApplyTo(dto.UserData);
                     }
                     else
                     {
diff --git a/Emby.Server.Implementations/Library/MediaSourceManager.cs b/Emby.Server.Implementations/Library/MediaSourceManager.cs
index 9ccfefa86e..4a520cad0d 100644
--- a/Emby.Server.Implementations/Library/MediaSourceManager.cs
+++ b/Emby.Server.Implementations/Library/MediaSourceManager.cs
@@ -229,7 +229,11 @@ namespace Emby.Server.Implementations.Library
                 list.Add(source);
             }
 
-            return SortMediaSources(list).ToArray();
+            var preferredId = mediaSources.Count > 0 && Guid.TryParse(mediaSources[0].Id, out var topSourceId)
+                ? topSourceId
+                : item.Id;
+
+            return SortMediaSources(list, preferredId).ToArray();
         }
 
         /// <inheritdoc />>
@@ -400,6 +404,72 @@ namespace Emby.Server.Implementations.Library
                         source.SupportsDirectStream = user.HasPermission(PermissionKind.EnablePlaybackRemuxing);
                     }
                 }
+
+                sources = SetAlternateVersionResumeStates(item, sources, user);
+            }
+
+            return sources;
+        }
+
+        /// <summary>
+        /// Populates each source's own playback position for the user and, when the queried item is a
+        /// primary, moves the most recently played version to the front so that resuming without an
+        /// explicit source selection plays the version that was last watched. A directly queried
+        /// alternate version keeps its own source first.
+        /// </summary>
+        /// <param name="item">The queried item.</param>
+        /// <param name="sources">The item's media sources.</param>
+        /// <param name="user">The user.</param>
+        /// <returns>The media sources, reordered when a version drives resume.</returns>
+        private IReadOnlyList<MediaSourceInfo> SetAlternateVersionResumeStates(BaseItem item, IReadOnlyList<MediaSourceInfo> sources, User user)
+        {
+            // For a video, multiple sources means alternate versions.
+            if (item is not Video video || sources.Count < 2)
+            {
+                return sources;
+            }
+
+            var versions = video.GetAllVersions();
+            if (versions.Count < 2)
+            {
+                return sources;
+            }
+
+            var userDataByVersion = _userDataManager.GetUserDataBatch(versions, user);
+            var dataBySourceId = new Dictionary<string, UserItemData>(versions.Count, StringComparer.OrdinalIgnoreCase);
+            foreach (var version in versions)
+            {
+                if (userDataByVersion.TryGetValue(version.Id, out var data))
+                {
+                    dataBySourceId[version.Id.ToString("N", CultureInfo.InvariantCulture)] = data;
+                }
+            }
+
+            MediaSourceInfo resumeSource = null;
+            UserItemData resumeData = null;
+            foreach (var source in sources)
+            {
+                if (source.Id is null
+                    || !dataBySourceId.TryGetValue(source.Id, out var data)
+                    || data.PlaybackPositionTicks <= 0)
+                {
+                    continue;
+                }
+
+                source.PlaybackPositionTicks = data.PlaybackPositionTicks;
+
+                if (resumeData is null || (data.LastPlayedDate ?? DateTime.MinValue) > (resumeData.LastPlayedDate ?? DateTime.MinValue))
+                {
+                    resumeSource = source;
+                    resumeData = data;
+                }
+            }
+
+            if (resumeSource is not null && !video.PrimaryVersionId.HasValue && !ReferenceEquals(sources[0], resumeSource))
+            {
+                var reordered = new List<MediaSourceInfo>(sources.Count) { resumeSource };
+                reordered.AddRange(sources.Where(s => !ReferenceEquals(s, resumeSource)));
+                return reordered;
             }
 
             return sources;
diff --git a/Emby.Server.Implementations/Library/UserDataManager.cs b/Emby.Server.Implementations/Library/UserDataManager.cs
index 962dd6fda8..4fda853bb1 100644
--- a/Emby.Server.Implementations/Library/UserDataManager.cs
+++ b/Emby.Server.Implementations/Library/UserDataManager.cs
@@ -247,6 +247,72 @@ namespace Emby.Server.Implementations.Library
             return result;
         }
 
+        /// <inheritdoc />
+        public VersionResumeData? GetResumeUserData(User user, BaseItem item)
+        {
+            return GetResumeUserDataBatch([item], user).GetValueOrDefault(item.Id);
+        }
+
+        /// <inheritdoc />
+        public IReadOnlyDictionary<Guid, VersionResumeData> GetResumeUserDataBatch(IReadOnlyList<BaseItem> items, User user)
+        {
+            ArgumentNullException.ThrowIfNull(user);
+
+            var result = new Dictionary<Guid, VersionResumeData>();
+            List<(Guid PrimaryId, IReadOnlyList<Video> Versions)>? versionGroups = null;
+            List<BaseItem>? allVersions = null;
+
+            foreach (var item in items)
+            {
+                // Only primary items aggregate over their versions; a directly queried version keeps its own data.
+                if (item is not Video video
+                    || video.PrimaryVersionId.HasValue
+                    || (video.LinkedAlternateVersions.Length == 0 && !video.HasLocalAlternateVersions))
+                {
+                    continue;
+                }
+
+                var versions = video.GetAllVersions();
+                if (versions.Count < 2)
+                {
+                    continue;
+                }
+
+                (versionGroups ??= []).Add((item.Id, versions));
+                (allVersions ??= []).AddRange(versions);
+            }
+
+            if (versionGroups is null)
+            {
+                return result;
+            }
+
+            var userDataByVersion = GetUserDataBatch(allVersions!.DistinctBy(i => i.Id).ToList(), user);
+
+            foreach (var (primaryId, versions) in versionGroups)
+            {
+                Video? resumeVersion = null;
+                UserItemData? resumeData = null;
+                foreach (var version in versions)
+                {
+                    if (userDataByVersion.TryGetValue(version.Id, out var data)
+                        && data.PlaybackPositionTicks > 0
+                        && (resumeData is null || (data.LastPlayedDate ?? DateTime.MinValue) > (resumeData.LastPlayedDate ?? DateTime.MinValue)))
+                    {
+                        resumeVersion = version;
+                        resumeData = data;
+                    }
+                }
+
+                if (resumeData is not null)
+                {
+                    result[primaryId] = new VersionResumeData(resumeData, resumeVersion!.RunTimeTicks);
+                }
+            }
+
+            return result;
+        }
+
         /// <summary>
         /// Gets the internal key.
         /// </summary>
@@ -281,6 +347,10 @@ namespace Emby.Server.Implementations.Library
             var dto = GetUserItemDataDto(userData, item.Id);
 
             item.FillUserDataDtoValues(dto, userData, itemDto, user, options);
+
+            // For an item with alternate versions, surface the most recently played version's resume point.
+            GetResumeUserData(user, item)?.ApplyTo(dto);
+
             return dto;
         }