From 5ed3cd205f068d572caddc0ae01aa7ab8a580a6a Mon Sep 17 00:00:00 2001
From: Dean Herbert <pe@ppy.sh>
Date: Wed, 3 Jun 2020 22:35:01 +0900
Subject: [PATCH] Simplify reuse check using FileInfo IDs

---
 .../Beatmaps/IO/ImportBeatmapTest.cs          |  9 +++++----
 osu.Game/Database/ArchiveModelManager.cs      | 20 +++++++++----------
 2 files changed, 15 insertions(+), 14 deletions(-)

diff --git a/osu.Game.Tests/Beatmaps/IO/ImportBeatmapTest.cs b/osu.Game.Tests/Beatmaps/IO/ImportBeatmapTest.cs
index 12f06059f7..9b34eece5f 100644
--- a/osu.Game.Tests/Beatmaps/IO/ImportBeatmapTest.cs
+++ b/osu.Game.Tests/Beatmaps/IO/ImportBeatmapTest.cs
@@ -154,9 +154,9 @@ namespace osu.Game.Tests.Beatmaps.IO
         }
 
         [Test]
-        public async Task TestImportThenImportWithNewerTimestamp()
+        public async Task TestImportThenImportWithChangedFile()
         {
-            using (HeadlessGameHost host = new CleanRunHeadlessGameHost(nameof(TestImportThenImportWithNewerTimestamp)))
+            using (HeadlessGameHost host = new CleanRunHeadlessGameHost(nameof(TestImportThenImportWithChangedFile)))
             {
                 try
                 {
@@ -174,8 +174,9 @@ namespace osu.Game.Tests.Beatmaps.IO
                         using (var zip = ZipArchive.Open(temp))
                             zip.WriteToDirectory(extractedFolder);
 
-                        // change timestamp
-                        new FileInfo(Directory.GetFiles(extractedFolder).First()).LastWriteTime = DateTime.Now;
+                        // arbitrary write to non-hashed file
+                        using (var sw = new FileInfo(Directory.GetFiles(extractedFolder, "*.mp3").First()).AppendText())
+                            sw.WriteLine("text");
 
                         using (var zip = ZipArchive.Create())
                         {
diff --git a/osu.Game/Database/ArchiveModelManager.cs b/osu.Game/Database/ArchiveModelManager.cs
index 5ca9423de2..0fe8dd1268 100644
--- a/osu.Game/Database/ArchiveModelManager.cs
+++ b/osu.Game/Database/ArchiveModelManager.cs
@@ -667,10 +667,16 @@ namespace osu.Game.Database
         /// <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) =>
-            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));
+            // 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 FileInfo IDs.
+            getIDs(existing.Files).SequenceEqual(getIDs(import.Files)) &&
+            getFilenames(existing.Files).SequenceEqual(getFilenames(import.Files));
+
+        private IEnumerable<long> getIDs(List<TFileModel> files)
+        {
+            foreach (var f in files.OrderBy(f => f.Filename))
+                yield return f.FileInfo.ID;
+        }
 
         private IEnumerable<string> getFilenames(List<TFileModel> files)
         {
@@ -678,12 +684,6 @@ namespace osu.Game.Database
                 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>();
 
         protected virtual string HumanisedModelName => $"{typeof(TModel).Name.Replace("Info", "").ToLower()}";