Add models and stores for beatmap manager requirements

osu.Game/Database/RealmContextFactory.cs

@@ -2,12 +2,14 @@
 // See the LICENCE file in the repository root for full licence text.
 
 using System;
+using System.Linq;
 using System.Threading;
 using osu.Framework.Allocation;
 using osu.Framework.Development;
 using osu.Framework.Logging;
 using osu.Framework.Platform;
 using osu.Framework.Statistics;
+using osu.Game.Models;
 using Realms;
 
 #nullable enable
@@ -70,6 +72,27 @@ namespace osu.Game.Database
 
             if (!Filename.EndsWith(realm_extension, StringComparison.Ordinal))
                 Filename += realm_extension;
+
+            cleanupPendingDeletions();
+        }
+
+        private void cleanupPendingDeletions()
+        {
+            using (var realm = CreateContext())
+            using (var transaction = realm.BeginWrite())
+            {
+                var pendingDeleteSets = realm.All<RealmBeatmapSet>().Where(s => s.DeletePending);
+
+                foreach (var s in pendingDeleteSets)
+                {
+                    foreach (var b in s.Beatmaps)
+                        realm.Remove(b);
+
+                    realm.Remove(s);
+                }
+
+                transaction.Commit();
+            }
         }
 
         /// <summary>

osu.Game/Stores/ArchiveModelImporter.cs

@@ -0,0 +1,557 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+using Humanizer;
+using NuGet.Packaging;
+using osu.Framework.Extensions;
+using osu.Framework.Extensions.IEnumerableExtensions;
+using osu.Framework.Logging;
+using osu.Framework.Platform;
+using osu.Framework.Threading;
+using osu.Game.Database;
+using osu.Game.IO.Archives;
+using osu.Game.Models;
+using osu.Game.Overlays.Notifications;
+using Realms;
+
+#nullable enable
+
+namespace osu.Game.Stores
+{
+    /// <summary>
+    /// Encapsulates a model store class to give it import functionality.
+    /// Adds cross-functionality with <see cref="RealmFileStore"/> to give access to the central file store for the provided model.
+    /// </summary>
+    /// <typeparam name="TModel">The model type.</typeparam>
+    public abstract class ArchiveModelImporter<TModel> : IModelImporter<TModel>
+        where TModel : RealmObject, IHasRealmFiles, IHasGuidPrimaryKey, ISoftDelete
+    {
+        private const int import_queue_request_concurrency = 1;
+
+        /// <summary>
+        /// The size of a batch import operation before considering it a lower priority operation.
+        /// </summary>
+        private const int low_priority_import_batch_size = 1;
+
+        /// <summary>
+        /// A singleton scheduler shared by all <see cref="ArchiveModelImporter{TModel}"/>.
+        /// </summary>
+        /// <remarks>
+        /// This scheduler generally performs IO and CPU intensive work so concurrency is limited harshly.
+        /// It is mainly being used as a queue mechanism for large imports.
+        /// </remarks>
+        private static readonly ThreadedTaskScheduler import_scheduler = new ThreadedTaskScheduler(import_queue_request_concurrency, nameof(ArchiveModelImporter<TModel>));
+
+        /// <summary>
+        /// A second scheduler for lower priority imports.
+        /// For simplicity, these will just run in parallel with normal priority imports, but a future refactor would see this implemented via a custom scheduler/queue.
+        /// See https://gist.github.com/peppy/f0e118a14751fc832ca30dd48ba3876b for an incomplete version of this.
+        /// </summary>
+        private static readonly ThreadedTaskScheduler import_scheduler_low_priority = new ThreadedTaskScheduler(import_queue_request_concurrency, nameof(ArchiveModelImporter<TModel>));
+
+        public virtual IEnumerable<string> HandledExtensions => new[] { @".zip" };
+
+        protected readonly RealmFileStore Files;
+
+        protected readonly RealmContextFactory ContextFactory;
+
+        /// <summary>
+        /// Fired when the user requests to view the resulting import.
+        /// </summary>
+        public Action<IEnumerable<ILive<TModel>>>? PresentImport;
+
+        /// <summary>
+        /// Set an endpoint for notifications to be posted to.
+        /// </summary>
+        public Action<Notification>? PostNotification { protected get; set; }
+
+        protected ArchiveModelImporter(Storage storage, RealmContextFactory contextFactory)
+        {
+            ContextFactory = contextFactory;
+
+            Files = new RealmFileStore(contextFactory, storage);
+        }
+
+        /// <summary>
+        /// Import one or more <typeparamref name="TModel"/> items from filesystem <paramref name="paths"/>.
+        /// </summary>
+        /// <remarks>
+        /// This will be treated as a low priority import if more than one path is specified; use <see cref="Import(ImportTask[])"/> to always import at standard priority.
+        /// This will post notifications tracking progress.
+        /// </remarks>
+        /// <param name="paths">One or more archive locations on disk.</param>
+        public Task Import(params string[] paths)
+        {
+            var notification = new ProgressNotification { State = ProgressNotificationState.Active };
+
+            PostNotification?.Invoke(notification);
+
+            return Import(notification, paths.Select(p => new ImportTask(p)).ToArray());
+        }
+
+        public Task Import(params ImportTask[] tasks)
+        {
+            var notification = new ProgressNotification { State = ProgressNotificationState.Active };
+
+            PostNotification?.Invoke(notification);
+
+            return Import(notification, tasks);
+        }
+
+        public async Task<IEnumerable<ILive<TModel>>> Import(ProgressNotification notification, params ImportTask[] tasks)
+        {
+            if (tasks.Length == 0)
+            {
+                notification.CompletionText = $"No {HumanisedModelName}s were found to import!";
+                notification.State = ProgressNotificationState.Completed;
+                return Enumerable.Empty<RealmLive<TModel>>();
+            }
+
+            notification.Progress = 0;
+            notification.Text = $"{HumanisedModelName.Humanize(LetterCasing.Title)} import is initialising...";
+
+            int current = 0;
+
+            var imported = new List<ILive<TModel>>();
+
+            bool isLowPriorityImport = tasks.Length > low_priority_import_batch_size;
+
+            try
+            {
+                await Task.WhenAll(tasks.Select(async task =>
+                {
+                    notification.CancellationToken.ThrowIfCancellationRequested();
+
+                    try
+                    {
+                        var model = await Import(task, isLowPriorityImport, notification.CancellationToken).ConfigureAwait(false);
+
+                        lock (imported)
+                        {
+                            if (model != null)
+                                imported.Add(model);
+                            current++;
+
+                            notification.Text = $"Imported {current} of {tasks.Length} {HumanisedModelName}s";
+                            notification.Progress = (float)current / tasks.Length;
+                        }
+                    }
+                    catch (TaskCanceledException)
+                    {
+                        throw;
+                    }
+                    catch (Exception e)
+                    {
+                        Logger.Error(e, $@"Could not import ({task})", LoggingTarget.Database);
+                    }
+                })).ConfigureAwait(false);
+            }
+            catch (OperationCanceledException)
+            {
+                if (imported.Count == 0)
+                {
+                    notification.State = ProgressNotificationState.Cancelled;
+                    return imported;
+                }
+            }
+
+            if (imported.Count == 0)
+            {
+                notification.Text = $"{HumanisedModelName.Humanize(LetterCasing.Title)} import failed!";
+                notification.State = ProgressNotificationState.Cancelled;
+            }
+            else
+            {
+                notification.CompletionText = imported.Count == 1
+                    ? $"Imported {imported.First()}!"
+                    : $"Imported {imported.Count} {HumanisedModelName}s!";
+
+                if (imported.Count > 0 && PresentImport != null)
+                {
+                    notification.CompletionText += " Click to view.";
+                    notification.CompletionClickAction = () =>
+                    {
+                        PresentImport?.Invoke(imported);
+                        return true;
+                    };
+                }
+
+                notification.State = ProgressNotificationState.Completed;
+            }
+
+            return imported;
+        }
+
+        /// <summary>
+        /// Import one <typeparamref name="TModel"/> from the filesystem and delete the file on success.
+        /// Note that this bypasses the UI flow and should only be used for special cases or testing.
+        /// </summary>
+        /// <param name="task">The <see cref="ImportTask"/> containing data about the <typeparamref name="TModel"/> to import.</param>
+        /// <param name="lowPriority">Whether this is a low priority import.</param>
+        /// <param name="cancellationToken">An optional cancellation token.</param>
+        /// <returns>The imported model, if successful.</returns>
+        public async Task<ILive<TModel>?> Import(ImportTask task, bool lowPriority = false, CancellationToken cancellationToken = default)
+        {
+            cancellationToken.ThrowIfCancellationRequested();
+
+            ILive<TModel>? import;
+            using (ArchiveReader reader = task.GetReader())
+                import = await Import(reader, lowPriority, cancellationToken).ConfigureAwait(false);
+
+            // We may or may not want to delete the file depending on where it is stored.
+            //  e.g. reconstructing/repairing database with items from default storage.
+            // Also, not always a single file, i.e. for LegacyFilesystemReader
+            // TODO: Add a check to prevent files from storage to be deleted.
+            try
+            {
+                if (import != null && File.Exists(task.Path) && ShouldDeleteArchive(task.Path))
+                    File.Delete(task.Path);
+            }
+            catch (Exception e)
+            {
+                Logger.Error(e, $@"Could not delete original file after import ({task})");
+            }
+
+            return import;
+        }
+
+        /// <summary>
+        /// Silently import an item from an <see cref="ArchiveReader"/>.
+        /// </summary>
+        /// <param name="archive">The archive to be imported.</param>
+        /// <param name="lowPriority">Whether this is a low priority import.</param>
+        /// <param name="cancellationToken">An optional cancellation token.</param>
+        public async Task<ILive<TModel>?> Import(ArchiveReader archive, bool lowPriority = false, CancellationToken cancellationToken = default)
+        {
+            cancellationToken.ThrowIfCancellationRequested();
+
+            TModel? model = null;
+
+            try
+            {
+                model = CreateModel(archive);
+
+                if (model == null)
+                    return null;
+            }
+            catch (TaskCanceledException)
+            {
+                throw;
+            }
+            catch (Exception e)
+            {
+                LogForModel(model, @$"Model creation of {archive.Name} failed.", e);
+                return null;
+            }
+
+            var scheduledImport = Task.Factory.StartNew(async () => await Import(model, archive, lowPriority, cancellationToken).ConfigureAwait(false),
+                cancellationToken, TaskCreationOptions.HideScheduler, lowPriority ? import_scheduler_low_priority : import_scheduler).Unwrap();
+
+            return await scheduledImport.ConfigureAwait(true);
+        }
+
+        /// <summary>
+        /// Any file extensions which should be included in hash creation.
+        /// Generally should include all file types which determine the file's uniqueness.
+        /// Large files should be avoided if possible.
+        /// </summary>
+        /// <remarks>
+        /// This is only used by the default hash implementation. If <see cref="ComputeHash"/> is overridden, it will not be used.
+        /// </remarks>
+        protected abstract string[] HashableFileTypes { get; }
+
+        internal static void LogForModel(TModel? model, string message, Exception? e = null)
+        {
+            string trimmedHash;
+            if (model == null || !model.IsValid || string.IsNullOrEmpty(model.Hash))
+                trimmedHash = "?????";
+            else
+                trimmedHash = model.Hash.Substring(0, 5);
+
+            string prefix = $"[{trimmedHash}]";
+
+            if (e != null)
+                Logger.Error(e, $"{prefix} {message}", LoggingTarget.Database);
+            else
+                Logger.Log($"{prefix} {message}", LoggingTarget.Database);
+        }
+
+        /// <summary>
+        /// Whether the implementation overrides <see cref="ComputeHash"/> with a custom implementation.
+        /// Custom hash implementations must bypass the early exit in the import flow (see <see cref="computeHashFast"/> usage).
+        /// </summary>
+        protected virtual bool HasCustomHashFunction => false;
+
+        /// <summary>
+        /// Create a SHA-2 hash from the provided archive based on file content of all files matching <see cref="HashableFileTypes"/>.
+        /// </summary>
+        /// <remarks>
+        ///  In the case of no matching files, a hash will be generated from the passed archive's <see cref="ArchiveReader.Name"/>.
+        /// </remarks>
+        protected virtual string ComputeHash(TModel item, ArchiveReader? reader = null)
+        {
+            if (reader != null)
+                // fast hashing for cases where the item's files may not be populated.
+                return computeHashFast(reader);
+
+            // for now, concatenate all hashable files in the set to create a unique hash.
+            MemoryStream hashable = new MemoryStream();
+
+            foreach (RealmNamedFileUsage file in item.Files.Where(f => HashableFileTypes.Any(ext => f.Filename.EndsWith(ext, StringComparison.OrdinalIgnoreCase))).OrderBy(f => f.Filename))
+            {
+                using (Stream s = Files.Store.GetStream(file.File.StoragePath))
+                    s.CopyTo(hashable);
+            }
+
+            if (hashable.Length > 0)
+                return hashable.ComputeSHA2Hash();
+
+            return item.Hash;
+        }
+
+        /// <summary>
+        /// Silently import an item from a <typeparamref name="TModel"/>.
+        /// </summary>
+        /// <param name="item">The model to be imported.</param>
+        /// <param name="archive">An optional archive to use for model population.</param>
+        /// <param name="lowPriority">Whether this is a low priority import.</param>
+        /// <param name="cancellationToken">An optional cancellation token.</param>
+        public virtual async Task<ILive<TModel>?> Import(TModel item, ArchiveReader? archive = null, bool lowPriority = false, CancellationToken cancellationToken = default)
+        {
+            using (var realm = ContextFactory.CreateContext())
+            {
+                cancellationToken.ThrowIfCancellationRequested();
+
+                bool checkedExisting = false;
+                TModel? existing = null;
+
+                if (archive != null && !HasCustomHashFunction)
+                {
+                    // this is a fast bail condition to improve large import performance.
+                    item.Hash = computeHashFast(archive);
+
+                    checkedExisting = true;
+                    existing = CheckForExisting(item, realm);
+
+                    if (existing != null)
+                    {
+                        // bare minimum comparisons
+                        //
+                        // note that this should really be checking filesizes on disk (of existing files) for some degree of sanity.
+                        // or alternatively doing a faster hash check. either of these require database changes and reprocessing of existing files.
+                        if (CanSkipImport(existing, item) &&
+                            getFilenames(existing.Files).SequenceEqual(getShortenedFilenames(archive).Select(p => p.shortened).OrderBy(f => f)))
+                        {
+                            LogForModel(item, @$"Found existing (optimised) {HumanisedModelName} for {item} (ID {existing.ID}) – skipping import.");
+
+                            using (var transaction = realm.BeginWrite())
+                            {
+                                existing.DeletePending = false;
+                                transaction.Commit();
+                            }
+
+                            return existing.ToLive();
+                        }
+
+                        LogForModel(item, @"Found existing (optimised) but failed pre-check.");
+                    }
+                }
+
+                try
+                {
+                    LogForModel(item, @"Beginning import...");
+
+                    // TODO: do we want to make the transaction this local? not 100% sure, will need further investigation.
+                    using (var transaction = realm.BeginWrite())
+                    {
+                        if (archive != null)
+                            // TODO: look into rollback of file additions (or delayed commit).
+                            item.Files.AddRange(createFileInfos(archive, Files, realm));
+
+                        item.Hash = ComputeHash(item, archive);
+
+                        // TODO: we may want to run this outside of the transaction.
+                        await Populate(item, archive, realm, cancellationToken).ConfigureAwait(false);
+
+                        if (!checkedExisting)
+                            existing = CheckForExisting(item, realm);
+
+                        if (existing != null)
+                        {
+                            if (CanReuseExisting(existing, item))
+                            {
+                                LogForModel(item, @$"Found existing {HumanisedModelName} for {item} (ID {existing.ID}) – skipping import.");
+                                existing.DeletePending = false;
+
+                                return existing.ToLive();
+                            }
+
+                            LogForModel(item, @"Found existing but failed re-use check.");
+
+                            existing.DeletePending = true;
+
+                            // todo: actually delete? i don't think this is required...
+                            // ModelStore.PurgeDeletable(s => s.ID == existing.ID);
+                        }
+
+                        PreImport(item, realm);
+
+                        // import to store
+                        realm.Add(item);
+
+                        transaction.Commit();
+                    }
+
+                    LogForModel(item, @"Import successfully completed!");
+                }
+                catch (Exception e)
+                {
+                    if (!(e is TaskCanceledException))
+                        LogForModel(item, @"Database import or population failed and has been rolled back.", e);
+
+                    throw;
+                }
+
+                return item.ToLive();
+            }
+        }
+
+        private string computeHashFast(ArchiveReader reader)
+        {
+            MemoryStream hashable = new MemoryStream();
+
+            foreach (var file in reader.Filenames.Where(f => HashableFileTypes.Any(ext => f.EndsWith(ext, StringComparison.OrdinalIgnoreCase))).OrderBy(f => f))
+            {
+                using (Stream s = reader.GetStream(file))
+                    s.CopyTo(hashable);
+            }
+
+            if (hashable.Length > 0)
+                return hashable.ComputeSHA2Hash();
+
+            return reader.Name.ComputeSHA2Hash();
+        }
+
+        /// <summary>
+        /// Create all required <see cref="File"/>s for the provided archive, adding them to the global file store.
+        /// </summary>
+        private List<RealmNamedFileUsage> createFileInfos(ArchiveReader reader, RealmFileStore files, Realm realm)
+        {
+            var fileInfos = new List<RealmNamedFileUsage>();
+
+            // import files to manager
+            foreach (var filenames in getShortenedFilenames(reader))
+            {
+                using (Stream s = reader.GetStream(filenames.original))
+                {
+                    var item = new RealmNamedFileUsage(files.Add(s, realm), filenames.shortened);
+                    fileInfos.Add(item);
+                }
+            }
+
+            return fileInfos;
+        }
+
+        private IEnumerable<(string original, string shortened)> getShortenedFilenames(ArchiveReader reader)
+        {
+            string prefix = reader.Filenames.GetCommonPrefix();
+            if (!(prefix.EndsWith('/') || prefix.EndsWith('\\')))
+                prefix = string.Empty;
+
+            // import files to manager
+            foreach (string file in reader.Filenames)
+                yield return (file, file.Substring(prefix.Length).ToStandardisedPath());
+        }
+
+        /// <summary>
+        /// Create a barebones model from the provided archive.
+        /// Actual expensive population should be done in <see cref="Populate"/>; this should just prepare for duplicate checking.
+        /// </summary>
+        /// <param name="archive">The archive to create the model for.</param>
+        /// <returns>A model populated with minimal information. Returning a null will abort importing silently.</returns>
+        protected abstract TModel? CreateModel(ArchiveReader archive);
+
+        /// <summary>
+        /// Populate the provided model completely from the given archive.
+        /// After this method, the model should be in a state ready to commit to a store.
+        /// </summary>
+        /// <param name="model">The model to populate.</param>
+        /// <param name="archive">The archive to use as a reference for population. May be null.</param>
+        /// <param name="realm">The current realm context.</param>
+        /// <param name="cancellationToken">An optional cancellation token.</param>
+        protected abstract Task Populate(TModel model, ArchiveReader? archive, Realm realm, CancellationToken cancellationToken = default);
+
+        /// <summary>
+        /// Perform any final actions before the import to database executes.
+        /// </summary>
+        /// <param name="model">The model prepared for import.</param>
+        /// <param name="realm">The current realm context.</param>
+        protected virtual void PreImport(TModel model, Realm realm)
+        {
+        }
+
+        /// <summary>
+        /// Check whether an existing model already exists for a new import item.
+        /// </summary>
+        /// <param name="model">The new model proposed for import.</param>
+        /// <param name="realm">The current realm context.</param>
+        /// <returns>An existing model which matches the criteria to skip importing, else null.</returns>
+        protected TModel? CheckForExisting(TModel model, Realm realm) => string.IsNullOrEmpty(model.Hash) ? null : realm.All<TModel>().FirstOrDefault(b => b.Hash == model.Hash);
+
+        /// <summary>
+        /// Whether import can be skipped after finding an existing import early in the process.
+        /// Only valid when <see cref="ComputeHash"/> is not overridden.
+        /// </summary>
+        /// <param name="existing">The existing model.</param>
+        /// <param name="import">The newly imported model.</param>
+        /// <returns>Whether to skip this import completely.</returns>
+        protected virtual bool CanSkipImport(TModel existing, TModel import) => true;
+
+        /// <summary>
+        /// After an existing <typeparamref name="TModel"/> is found during an import process, the default behaviour is to use/restore the existing
+        /// item and skip the import. This method allows changing that behaviour.
+        /// </summary>
+        /// <param name="existing">The existing model.</param>
+        /// <param name="import">The newly imported model.</param>
+        /// <returns>Whether the existing model should be restored and used. Returning false will delete the existing and force a re-import.</returns>
+        protected virtual bool CanReuseExisting(TModel existing, TModel import) =>
+            // for the best or worst, we copy and import files of a new import before checking whether
+            // it is a duplicate. so to check if anything has changed, we can just compare all File IDs.
+            getIDs(existing.Files).SequenceEqual(getIDs(import.Files)) &&
+            getFilenames(existing.Files).SequenceEqual(getFilenames(import.Files));
+
+        /// <summary>
+        /// Whether this specified path should be removed after successful import.
+        /// </summary>
+        /// <param name="path">The path for consideration. May be a file or a directory.</param>
+        /// <returns>Whether to perform deletion.</returns>
+        protected virtual bool ShouldDeleteArchive(string path) => false;
+
+        private IEnumerable<string> getIDs(IEnumerable<INamedFile> files)
+        {
+            foreach (var f in files.OrderBy(f => f.Filename))
+                yield return f.File.Hash;
+        }
+
+        private IEnumerable<string> getFilenames(IEnumerable<INamedFile> files)
+        {
+            foreach (var f in files.OrderBy(f => f.Filename))
+                yield return f.Filename;
+        }
+
+        public virtual string HumanisedModelName => $"{typeof(TModel).Name.Replace(@"Info", "").ToLower()}";
+
+        private string getValidFilename(string filename)
+        {
+            foreach (char c in Path.GetInvalidFileNameChars())
+                filename = filename.Replace(c, '_');
+            return filename;
+        }
+    }
+}

osu.Game/Stores/BeatmapImporter.cs

@@ -0,0 +1,336 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+using NuGet.Packaging;
+using osu.Framework.Audio.Track;
+using osu.Framework.Extensions;
+using osu.Framework.Extensions.IEnumerableExtensions;
+using osu.Framework.Graphics.Textures;
+using osu.Framework.Logging;
+using osu.Framework.Platform;
+using osu.Framework.Testing;
+using osu.Game.Beatmaps;
+using osu.Game.Beatmaps.Formats;
+using osu.Game.Database;
+using osu.Game.IO;
+using osu.Game.IO.Archives;
+using osu.Game.Models;
+using osu.Game.Rulesets;
+using osu.Game.Rulesets.Objects;
+using osu.Game.Skinning;
+using Realms;
+
+#nullable enable
+
+namespace osu.Game.Stores
+{
+    /// <summary>
+    /// Handles the storage and retrieval of Beatmaps/WorkingBeatmaps.
+    /// </summary>
+    [ExcludeFromDynamicCompile]
+    public class BeatmapImporter : ArchiveModelImporter<RealmBeatmapSet>, IDisposable
+    {
+        public override IEnumerable<string> HandledExtensions => new[] { ".osz" };
+
+        protected override string[] HashableFileTypes => new[] { ".osu" };
+
+        // protected override string ImportFromStablePath => ".";
+        //
+        // protected override Storage PrepareStableStorage(StableStorage stableStorage) => stableStorage.GetSongStorage();
+        //
+        // protected override bool ShouldDeleteArchive(string path) => Path.GetExtension(path)?.ToLowerInvariant() == ".osz";
+        //
+        // protected override bool CheckLocalAvailability(RealmBeatmapSet model, System.Linq.IQueryable<RealmBeatmapSet> items)
+        //     => base.CheckLocalAvailability(model, items) || (model.OnlineID != null && items.Any(b => b.OnlineID == model.OnlineID));
+
+        private readonly dynamic? onlineLookupQueue = null; // todo: BeatmapOnlineLookupQueue is private
+
+        public BeatmapImporter(RealmContextFactory contextFactory, Storage storage, bool performOnlineLookups = false)
+            : base(storage, contextFactory)
+        {
+            if (performOnlineLookups)
+            {
+                // onlineLookupQueue = new BeatmapOnlineLookupQueue(api, storage);
+            }
+        }
+
+        protected override bool ShouldDeleteArchive(string path) => Path.GetExtension(path).ToLowerInvariant() == ".osz";
+
+        protected override async Task Populate(RealmBeatmapSet beatmapSet, ArchiveReader? archive, Realm realm, CancellationToken cancellationToken = default)
+        {
+            if (archive != null)
+                beatmapSet.Beatmaps.AddRange(createBeatmapDifficulties(beatmapSet.Files, realm));
+
+            foreach (RealmBeatmap b in beatmapSet.Beatmaps)
+                b.BeatmapSet = beatmapSet;
+
+            validateOnlineIds(beatmapSet, realm);
+
+            bool hadOnlineBeatmapIDs = beatmapSet.Beatmaps.Any(b => b.OnlineID > 0);
+
+            if (onlineLookupQueue != null)
+                await onlineLookupQueue.UpdateAsync(beatmapSet, cancellationToken).ConfigureAwait(false);
+
+            // ensure at least one beatmap was able to retrieve or keep an online ID, else drop the set ID.
+            if (hadOnlineBeatmapIDs && !beatmapSet.Beatmaps.Any(b => b.OnlineID > 0))
+            {
+                if (beatmapSet.OnlineID != null)
+                {
+                    beatmapSet.OnlineID = null;
+                    LogForModel(beatmapSet, "Disassociating beatmap set ID due to loss of all beatmap IDs");
+                }
+            }
+        }
+
+        protected override void PreImport(RealmBeatmapSet beatmapSet, Realm realm)
+        {
+            // if (beatmapSet.Beatmaps.Any(b => b.Difficulty == null))
+            //     throw new InvalidOperationException($"Cannot import {nameof(IBeatmapInfo)} with null {nameof(IBeatmapInfo.Difficulty)}.");
+
+            // check if a set already exists with the same online id, delete if it does.
+            if (beatmapSet.OnlineID != null)
+            {
+                var existingOnlineId = realm.All<RealmBeatmapSet>().FirstOrDefault(b => b.OnlineID == beatmapSet.OnlineID);
+
+                if (existingOnlineId != null)
+                {
+                    existingOnlineId.DeletePending = true;
+
+                    // in order to avoid a unique key constraint, immediately remove the online ID from the previous set.
+                    existingOnlineId.OnlineID = null;
+                    foreach (var b in existingOnlineId.Beatmaps)
+                        b.OnlineID = null;
+
+                    LogForModel(beatmapSet, $"Found existing beatmap set with same OnlineID ({beatmapSet.OnlineID}). It has been deleted.");
+                }
+            }
+        }
+
+        private void validateOnlineIds(RealmBeatmapSet beatmapSet, Realm realm)
+        {
+            var beatmapIds = beatmapSet.Beatmaps.Where(b => b.OnlineID.HasValue).Select(b => b.OnlineID).ToList();
+
+            // ensure all IDs are unique
+            if (beatmapIds.GroupBy(b => b).Any(g => g.Count() > 1))
+            {
+                LogForModel(beatmapSet, "Found non-unique IDs, resetting...");
+                resetIds();
+                return;
+            }
+
+            // find any existing beatmaps in the database that have matching online ids
+            List<RealmBeatmap> existingBeatmaps = new List<RealmBeatmap>();
+
+            foreach (var id in beatmapIds)
+                existingBeatmaps.AddRange(realm.All<RealmBeatmap>().Where(b => b.OnlineID == id));
+
+            if (existingBeatmaps.Any())
+            {
+                // reset the import ids (to force a re-fetch) *unless* they match the candidate CheckForExisting set.
+                // we can ignore the case where the new ids are contained by the CheckForExisting set as it will either be used (import skipped) or deleted.
+
+                var existing = CheckForExisting(beatmapSet, realm);
+
+                if (existing == null || existingBeatmaps.Any(b => !existing.Beatmaps.Contains(b)))
+                {
+                    LogForModel(beatmapSet, "Found existing import with online IDs already, resetting...");
+                    resetIds();
+                }
+            }
+
+            void resetIds() => beatmapSet.Beatmaps.ForEach(b => b.OnlineID = null);
+        }
+
+        protected override bool CanSkipImport(RealmBeatmapSet existing, RealmBeatmapSet import)
+        {
+            if (!base.CanSkipImport(existing, import))
+                return false;
+
+            return existing.Beatmaps.Any(b => b.OnlineID != null);
+        }
+
+        protected override bool CanReuseExisting(RealmBeatmapSet existing, RealmBeatmapSet import)
+        {
+            if (!base.CanReuseExisting(existing, import))
+                return false;
+
+            var existingIds = existing.Beatmaps.Select(b => b.OnlineID).OrderBy(i => i);
+            var importIds = import.Beatmaps.Select(b => b.OnlineID).OrderBy(i => i);
+
+            // force re-import if we are not in a sane state.
+            return existing.OnlineID == import.OnlineID && existingIds.SequenceEqual(importIds);
+        }
+
+        public override string HumanisedModelName => "beatmap";
+
+        protected override RealmBeatmapSet? CreateModel(ArchiveReader reader)
+        {
+            // let's make sure there are actually .osu files to import.
+            string? mapName = reader.Filenames.FirstOrDefault(f => f.EndsWith(".osu", StringComparison.OrdinalIgnoreCase));
+
+            if (string.IsNullOrEmpty(mapName))
+            {
+                Logger.Log($"No beatmap files found in the beatmap archive ({reader.Name}).", LoggingTarget.Database);
+                return null;
+            }
+
+            Beatmap beatmap;
+            using (var stream = new LineBufferedReader(reader.GetStream(mapName)))
+                beatmap = Decoder.GetDecoder<Beatmap>(stream).Decode(stream);
+
+            return new RealmBeatmapSet
+            {
+                OnlineID = beatmap.BeatmapInfo.BeatmapSet?.OnlineBeatmapSetID,
+                // Metadata = beatmap.Metadata,
+                DateAdded = DateTimeOffset.UtcNow
+            };
+        }
+
+        /// <summary>
+        /// Create all required <see cref="RealmBeatmap"/>s for the provided archive.
+        /// </summary>
+        private List<RealmBeatmap> createBeatmapDifficulties(IList<RealmNamedFileUsage> files, Realm realm)
+        {
+            var beatmaps = new List<RealmBeatmap>();
+
+            foreach (var file in files.Where(f => f.Filename.EndsWith(".osu", StringComparison.OrdinalIgnoreCase)))
+            {
+                using (var raw = Files.Store.GetStream(file.File.StoragePath))
+                using (var ms = new MemoryStream()) // we need a memory stream so we can seek
+                using (var sr = new LineBufferedReader(ms))
+                {
+                    raw.CopyTo(ms);
+                    ms.Position = 0;
+
+                    var decoder = Decoder.GetDecoder<Beatmap>(sr);
+                    IBeatmap beatmap = decoder.Decode(sr);
+
+                    string hash = ms.ComputeSHA2Hash();
+
+                    if (beatmaps.Any(b => b.Hash == hash))
+                        continue;
+
+                    var beatmapInfo = beatmap.BeatmapInfo;
+
+                    var ruleset = realm.All<RealmRuleset>().FirstOrDefault(r => r.OnlineID == beatmapInfo.RulesetID);
+                    var rulesetInstance = (ruleset as IRulesetInfo)?.CreateInstance();
+
+                    if (ruleset == null || rulesetInstance == null)
+                    {
+                        Logger.Log($"Skipping import due to missing local ruleset {beatmapInfo.RulesetID}.", LoggingTarget.Database);
+                        continue;
+                    }
+
+                    beatmapInfo.Path = file.Filename;
+                    beatmapInfo.Hash = hash;
+                    beatmapInfo.MD5Hash = ms.ComputeMD5Hash();
+
+                    // TODO: this should be done in a better place once we actually need to dynamically update it.
+                    beatmap.BeatmapInfo.Ruleset = rulesetInstance.RulesetInfo;
+                    beatmap.BeatmapInfo.StarDifficulty = rulesetInstance.CreateDifficultyCalculator(new DummyConversionBeatmap(beatmap)).Calculate().StarRating;
+                    beatmap.BeatmapInfo.Length = calculateLength(beatmap);
+                    beatmap.BeatmapInfo.BPM = 60000 / beatmap.GetMostCommonBeatLength();
+
+                    var difficulty = new RealmBeatmapDifficulty
+                    {
+                        DrainRate = beatmapInfo.BaseDifficulty.DrainRate,
+                        CircleSize = beatmapInfo.BaseDifficulty.CircleSize,
+                        OverallDifficulty = beatmapInfo.BaseDifficulty.OverallDifficulty,
+                        ApproachRate = beatmapInfo.BaseDifficulty.ApproachRate,
+                        SliderMultiplier = beatmapInfo.BaseDifficulty.SliderMultiplier,
+                        SliderTickRate = beatmapInfo.BaseDifficulty.SliderTickRate,
+                    };
+
+                    var metadata = new RealmBeatmapMetadata
+                    {
+                        Title = beatmap.Metadata.Title,
+                        TitleUnicode = beatmap.Metadata.TitleUnicode,
+                        Artist = beatmap.Metadata.Artist,
+                        ArtistUnicode = beatmap.Metadata.ArtistUnicode,
+                        Author = beatmap.Metadata.AuthorString,
+                        Source = beatmap.Metadata.Source,
+                        Tags = beatmap.Metadata.Tags,
+                        PreviewTime = beatmap.Metadata.PreviewTime,
+                        AudioFile = beatmap.Metadata.AudioFile,
+                        BackgroundFile = beatmap.Metadata.BackgroundFile,
+                    };
+
+                    var realmBeatmap = new RealmBeatmap(ruleset, difficulty, metadata)
+                    {
+                        DifficultyName = beatmapInfo.Version,
+                        OnlineID = beatmapInfo.OnlineBeatmapID,
+                        Length = beatmapInfo.Length,
+                        BPM = beatmapInfo.BPM,
+                        Hash = beatmapInfo.Hash,
+                        StarRating = beatmapInfo.StarDifficulty,
+                        MD5Hash = beatmapInfo.MD5Hash,
+                        Hidden = beatmapInfo.Hidden,
+                        AudioLeadIn = beatmapInfo.AudioLeadIn,
+                        StackLeniency = beatmapInfo.StackLeniency,
+                        SpecialStyle = beatmapInfo.SpecialStyle,
+                        LetterboxInBreaks = beatmapInfo.LetterboxInBreaks,
+                        WidescreenStoryboard = beatmapInfo.WidescreenStoryboard,
+                        EpilepsyWarning = beatmapInfo.EpilepsyWarning,
+                        SamplesMatchPlaybackRate = beatmapInfo.SamplesMatchPlaybackRate,
+                        DistanceSpacing = beatmapInfo.DistanceSpacing,
+                        BeatDivisor = beatmapInfo.BeatDivisor,
+                        GridSize = beatmapInfo.GridSize,
+                        TimelineZoom = beatmapInfo.TimelineZoom,
+                    };
+
+                    // TODO: IBeatmap.BeatmapInfo needs to be updated to the new interface.
+                    // beatmaps.Add(beatmap.BeatmapInfo);
+
+                    beatmaps.Add(realmBeatmap);
+                }
+            }
+
+            return beatmaps;
+        }
+
+        public void Dispose()
+        {
+            onlineLookupQueue?.Dispose();
+        }
+
+        private double calculateLength(IBeatmap b)
+        {
+            if (!b.HitObjects.Any())
+                return 0;
+
+            var lastObject = b.HitObjects.Last();
+
+            //TODO: this isn't always correct (consider mania where a non-last object may last for longer than the last in the list).
+            double endTime = lastObject.GetEndTime();
+            double startTime = b.HitObjects.First().StartTime;
+
+            return endTime - startTime;
+        }
+
+        /// <summary>
+        /// A dummy WorkingBeatmap for the purpose of retrieving a beatmap for star difficulty calculation.
+        /// </summary>
+        private class DummyConversionBeatmap : WorkingBeatmap
+        {
+            private readonly IBeatmap beatmap;
+
+            public DummyConversionBeatmap(IBeatmap beatmap)
+                : base(beatmap.BeatmapInfo, null)
+            {
+                this.beatmap = beatmap;
+            }
+
+            protected override IBeatmap GetBeatmap() => beatmap;
+            protected override Texture? GetBackground() => null;
+            protected override Track? GetBeatmapTrack() => null;
+            protected internal override ISkin? GetSkin() => null;
+            public override Stream? GetStream(string storagePath) => null;
+        }
+    }
+}