From c155ab83399a51bdab44a48d5805463c8520318a Mon Sep 17 00:00:00 2001
From: Dean Herbert <pe@ppy.sh>
Date: Wed, 3 Jun 2020 18:03:10 +0900
Subject: [PATCH] Check filenames and timestamps before reusing an already
 imported model

---
 osu.Game/Beatmaps/BeatmapManager.cs      |  4 ++--
 osu.Game/Database/ArchiveModelManager.cs | 22 +++++++++++++++++++---
 2 files changed, 21 insertions(+), 5 deletions(-)

diff --git a/osu.Game/Beatmaps/BeatmapManager.cs b/osu.Game/Beatmaps/BeatmapManager.cs
index f626b45e42..e7cef13c68 100644
--- a/osu.Game/Beatmaps/BeatmapManager.cs
+++ b/osu.Game/Beatmaps/BeatmapManager.cs
@@ -258,9 +258,9 @@ namespace osu.Game.Beatmaps
         /// <returns>The first result for the provided query, or null if no results were found.</returns>
         public BeatmapSetInfo QueryBeatmapSet(Expression<Func<BeatmapSetInfo, bool>> query) => beatmaps.ConsumableItems.AsNoTracking().FirstOrDefault(query);
 
-        protected override bool CanUndelete(BeatmapSetInfo existing, BeatmapSetInfo import)
+        protected override bool CanReuseExisting(BeatmapSetInfo existing, BeatmapSetInfo import)
         {
-            if (!base.CanUndelete(existing, import))
+            if (!base.CanReuseExisting(existing, import))
                 return false;
 
             var existingIds = existing.Beatmaps.Select(b => b.OnlineBeatmapID).OrderBy(i => i);
diff --git a/osu.Game/Database/ArchiveModelManager.cs b/osu.Game/Database/ArchiveModelManager.cs
index ae55a7b14a..4d7d3e96e6 100644
--- a/osu.Game/Database/ArchiveModelManager.cs
+++ b/osu.Game/Database/ArchiveModelManager.cs
@@ -332,7 +332,7 @@ namespace osu.Game.Database
 
                         if (existing != null)
                         {
-                            if (CanUndelete(existing, item))
+                            if (CanReuseExisting(existing, item))
                             {
                                 Undelete(existing);
                                 LogForModel(item, $"Found existing {HumanisedModelName} for {item} (ID {existing.ID}) – skipping import.");
@@ -660,13 +660,29 @@ namespace osu.Game.Database
         protected TModel CheckForExisting(TModel model) => model.Hash == null ? null : ModelStore.ConsumableItems.FirstOrDefault(b => b.Hash == model.Hash);
 
         /// <summary>
-        /// After an existing <typeparamref name="TModel"/> is found during an import process, the default behaviour is to restore the existing
+        /// 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 CanUndelete(TModel existing, TModel import) => true;
+        protected virtual bool CanReuseExisting(TModel existing, TModel import) =>
+            getFilenames(existing.Files).SequenceEqual(getFilenames(import.Files)) &&
+            // poor-man's (cheap) equality comparison, avoiding hashing unnecessarily.
+            // can switch to full hash checks on a per-case basis (or for all) if we decide this is not a performance issue.
+            getTimestamps(existing.Files).SequenceEqual(getTimestamps(import.Files));
+
+        private IEnumerable<string> getFilenames(List<TFileModel> files)
+        {
+            foreach (var f in files.OrderBy(f => f.Filename))
+                yield return f.Filename;
+        }
+
+        private IEnumerable<long> getTimestamps(List<TFileModel> files)
+        {
+            foreach (var f in files.OrderBy(f => f.Filename))
+                yield return File.GetLastWriteTimeUtc(Files.Storage.GetFullPath(f.FileInfo.StoragePath)).ToFileTime();
+        }
 
         private DbSet<TModel> queryModel() => ContextFactory.Get().Set<TModel>();