Address review comments

Emby.Server.Implementations/Library/SimilarItems/MovieSimilarItemsProvider.cs

@@ -188,7 +188,6 @@ public sealed class MovieSimilarItemsProvider : ILocalSimilarItemsProvider<Movie
         var entitiesById = _queryHelpers.ApplyNavigations(
                 context.BaseItems.AsNoTracking().Where(e => allOrderedIdsList.Contains(e.Id)),
                 filter)
-            .AsSplitQuery()
             .AsEnumerable()
             .Select(e => _queryHelpers.DeserializeBaseItem(e, filter.SkipDeserialization))
             .Where(dto => dto is not null)

Emby.Server.Implementations/Library/SimilarItems/SimilarItemsManager.cs

@@ -8,12 +8,16 @@ using System.Threading;
 using System.Threading.Tasks;
 using Jellyfin.Data.Enums;
 using Jellyfin.Database.Implementations.Entities;
+using Jellyfin.Database.Implementations.Enums;
 using Jellyfin.Extensions.Json;
+using MediaBrowser.Common.Extensions;
 using MediaBrowser.Controller;
+using MediaBrowser.Controller.Configuration;
 using MediaBrowser.Controller.Dto;
 using MediaBrowser.Controller.Entities;
 using MediaBrowser.Controller.Library;
 using MediaBrowser.Model.Configuration;
+using MediaBrowser.Model.Dto;
 using MediaBrowser.Model.Entities;
 using MediaBrowser.Model.IO;
 using MediaBrowser.Model.Querying;
@@ -30,6 +34,7 @@ public class SimilarItemsManager : ISimilarItemsManager
     private readonly IServerApplicationPaths _appPaths;
     private readonly ILibraryManager _libraryManager;
     private readonly IFileSystem _fileSystem;
+    private readonly IServerConfigurationManager _serverConfigurationManager;
     private ISimilarItemsProvider[] _similarItemsProviders = [];
 
     /// <summary>
@@ -39,16 +44,19 @@ public class SimilarItemsManager : ISimilarItemsManager
     /// <param name="appPaths">The server application paths.</param>
     /// <param name="libraryManager">The library manager.</param>
     /// <param name="fileSystem">The file system.</param>
+    /// <param name="serverConfigurationManager">The server configuration manager.</param>
     public SimilarItemsManager(
         ILogger<SimilarItemsManager> logger,
         IServerApplicationPaths appPaths,
         ILibraryManager libraryManager,
-        IFileSystem fileSystem)
+        IFileSystem fileSystem,
+        IServerConfigurationManager serverConfigurationManager)
     {
         _logger = logger;
         _appPaths = appPaths;
         _libraryManager = libraryManager;
         _fileSystem = fileSystem;
+        _serverConfigurationManager = serverConfigurationManager;
     }
 
     /// <inheritdoc/>
@@ -226,20 +234,205 @@ public class SimilarItemsManager : ISimilarItemsManager
     }
 
     /// <inheritdoc/>
-    public Task<Dictionary<Guid, IReadOnlyList<BaseItem>>> GetBatchSimilarItemsAsync(
-        IReadOnlyList<BaseItem> sourceItems,
+    public async Task<IReadOnlyList<SimilarItemsRecommendation>> GetMovieRecommendationsAsync(
+        User? user,
+        Guid parentId,
+        int categoryLimit,
+        int itemLimit,
+        DtoOptions dtoOptions,
+        CancellationToken cancellationToken)
+    {
+        ArgumentNullException.ThrowIfNull(dtoOptions);
+
+        var recentlyPlayedMovies = _libraryManager.GetItemList(new InternalItemsQuery(user)
+        {
+            IncludeItemTypes = [BaseItemKind.Movie],
+            OrderBy = [(ItemSortBy.DatePlayed, SortOrder.Descending), (ItemSortBy.Random, SortOrder.Descending)],
+            Limit = 7,
+            ParentId = parentId,
+            Recursive = true,
+            IsPlayed = true,
+            EnableGroupByMetadataKey = true,
+            DtoOptions = dtoOptions
+        });
+
+        var itemTypes = new List<BaseItemKind> { BaseItemKind.Movie };
+        if (_serverConfigurationManager.Configuration.EnableExternalContentInSuggestions)
+        {
+            itemTypes.Add(BaseItemKind.Trailer);
+            itemTypes.Add(BaseItemKind.LiveTvProgram);
+        }
+
+        var likedMovies = _libraryManager.GetItemList(new InternalItemsQuery(user)
+        {
+            IncludeItemTypes = itemTypes.ToArray(),
+            IsMovie = true,
+            OrderBy = [(ItemSortBy.Random, SortOrder.Descending)],
+            Limit = 10,
+            IsFavoriteOrLiked = true,
+            ExcludeItemIds = recentlyPlayedMovies.Select(i => i.Id).ToArray(),
+            EnableGroupByMetadataKey = true,
+            ParentId = parentId,
+            Recursive = true,
+            DtoOptions = dtoOptions
+        });
+
+        var mostRecentMovies = recentlyPlayedMovies.Take(Math.Min(recentlyPlayedMovies.Count, 6)).ToList();
+        var recentDirectors = GetPeopleNames(mostRecentMovies, [PersonType.Director]);
+        var recentActors = GetPeopleNames(mostRecentMovies, [PersonType.Actor, PersonType.GuestStar]);
+
+        // Cap baseline items to categoryLimit - the round-robin can't use more categories than that.
+        var recentlyPlayedBaseline = recentlyPlayedMovies.Count > categoryLimit
+            ? recentlyPlayedMovies.Take(categoryLimit).ToList()
+            : recentlyPlayedMovies;
+        var likedBaseline = likedMovies.Count > categoryLimit
+            ? likedMovies.Take(categoryLimit).ToList()
+            : likedMovies;
+
+        var batchQuery = new SimilarItemsQuery
+        {
+            User = user,
+            Limit = itemLimit,
+            DtoOptions = dtoOptions
+        };
+
+        var similarToRecentlyPlayed = await GetSimilarItemsRecommendationsAsync(
+            recentlyPlayedBaseline,
+            RecommendationType.SimilarToRecentlyPlayed,
+            batchQuery).ConfigureAwait(false);
+
+        var similarToLiked = await GetSimilarItemsRecommendationsAsync(
+            likedBaseline,
+            RecommendationType.SimilarToLikedItem,
+            batchQuery).ConfigureAwait(false);
+
+        var hasDirectorFromRecentlyPlayed = GetPersonRecommendations(user, recentDirectors, itemLimit, dtoOptions, RecommendationType.HasDirectorFromRecentlyPlayed, itemTypes);
+        var hasActorFromRecentlyPlayed = GetPersonRecommendations(user, recentActors, itemLimit, dtoOptions, RecommendationType.HasActorFromRecentlyPlayed, itemTypes);
+
+        // Use a single enumerator per list, listed twice so MoveNext advances it
+        // twice per round-robin pass (giving these categories double weight).
+        // IMPORTANT: Declare as IEnumerator<T> to box the List<T>.Enumerator struct once;
+        // using var would box separately per list insertion, creating independent copies.
+        IEnumerator<SimilarItemsRecommendation> similarToRecentlyPlayedEnum = similarToRecentlyPlayed.GetEnumerator();
+        IEnumerator<SimilarItemsRecommendation> similarToLikedEnum = similarToLiked.GetEnumerator();
+
+        var categoryTypes = new List<IEnumerator<SimilarItemsRecommendation>>
+        {
+            similarToRecentlyPlayedEnum,
+            similarToRecentlyPlayedEnum,
+            similarToLikedEnum,
+            similarToLikedEnum,
+            hasDirectorFromRecentlyPlayed.GetEnumerator(),
+            hasActorFromRecentlyPlayed.GetEnumerator()
+        };
+
+        var categories = new List<SimilarItemsRecommendation>();
+        while (categories.Count < categoryLimit)
+        {
+            var allEmpty = true;
+            foreach (var category in categoryTypes)
+            {
+                if (category.MoveNext())
+                {
+                    categories.Add(category.Current);
+                    allEmpty = false;
+
+                    if (categories.Count >= categoryLimit)
+                    {
+                        break;
+                    }
+                }
+            }
+
+            if (allEmpty)
+            {
+                break;
+            }
+        }
+
+        return [.. categories.OrderBy(i => i.RecommendationType)];
+    }
+
+    private async Task<IReadOnlyList<SimilarItemsRecommendation>> GetSimilarItemsRecommendationsAsync(
+        IReadOnlyList<BaseItem> baselineItems,
+        RecommendationType recommendationType,
         SimilarItemsQuery query)
     {
         var batchProvider = _similarItemsProviders
             .OfType<IBatchLocalSimilarItemsProvider>()
             .FirstOrDefault();
 
-        if (batchProvider is null)
+        if (batchProvider is null || baselineItems.Count == 0)
         {
-            return Task.FromResult(new Dictionary<Guid, IReadOnlyList<BaseItem>>());
+            return [];
         }
 
-        return batchProvider.GetBatchSimilarItemsAsync(sourceItems, query);
+        var batchResults = await batchProvider.GetBatchSimilarItemsAsync(baselineItems, query).ConfigureAwait(false);
+
+        var recommendations = new List<SimilarItemsRecommendation>(baselineItems.Count);
+        foreach (var baseline in baselineItems)
+        {
+            if (batchResults.TryGetValue(baseline.Id, out var similar) && similar.Count > 0)
+            {
+                recommendations.Add(new SimilarItemsRecommendation
+                {
+                    BaselineItemName = baseline.Name,
+                    CategoryId = baseline.Id,
+                    RecommendationType = recommendationType,
+                    Items = similar
+                });
+            }
+        }
+
+        return recommendations;
+    }
+
+    private IEnumerable<SimilarItemsRecommendation> GetPersonRecommendations(
+        User? user,
+        IReadOnlyList<string> names,
+        int itemLimit,
+        DtoOptions dtoOptions,
+        RecommendationType type,
+        IReadOnlyList<BaseItemKind> itemTypes)
+    {
+        var personTypes = type == RecommendationType.HasDirectorFromRecentlyPlayed
+            ? [PersonType.Director]
+            : Array.Empty<string>();
+
+        foreach (var name in names)
+        {
+            var items = _libraryManager.GetItemList(new InternalItemsQuery(user)
+            {
+                Person = name,
+                Limit = itemLimit + 2,
+                PersonTypes = personTypes,
+                IncludeItemTypes = itemTypes.ToArray(),
+                IsMovie = true,
+                IsPlayed = false,
+                EnableGroupByMetadataKey = true,
+                DtoOptions = dtoOptions
+            })
+                .DistinctBy(i => i.GetProviderId(MetadataProvider.Imdb) ?? Guid.NewGuid().ToString("N", CultureInfo.InvariantCulture))
+                .Take(itemLimit)
+                .ToList();
+
+            if (items.Count > 0)
+            {
+                yield return new SimilarItemsRecommendation
+                {
+                    BaselineItemName = name,
+                    CategoryId = name.GetMD5(),
+                    RecommendationType = type,
+                    Items = items
+                };
+            }
+        }
+    }
+
+    private IReadOnlyList<string> GetPeopleNames(IReadOnlyList<BaseItem> items, IReadOnlyList<string> personTypes)
+    {
+        var itemIds = items.Select(i => i.Id).ToArray();
+        return _libraryManager.GetPeopleNamesByItems(itemIds, personTypes, limit: 0);
     }
 
     private List<(BaseItem Item, float Score)> ResolveRemoteReferences(