From 453ecd21b32b552947ee1141f793e26d88774113 Mon Sep 17 00:00:00 2001
From: Dean Herbert <pe@ppy.sh>
Date: Tue, 14 Dec 2021 19:11:56 +0900
Subject: [PATCH] Fix `OnlinePlayBeatmapAvailabilityTracker` potentially in
 incorrect state

Adter an import of a modified version of a beatmap (that was already
present in the local database), it's feasible that one of these trackers
would not see the state change due to the nuances of the import process.
---
 .../OnlinePlayBeatmapAvailabilityTracker.cs   | 45 +++++++++++++++++--
 1 file changed, 42 insertions(+), 3 deletions(-)

diff --git a/osu.Game/Online/Rooms/OnlinePlayBeatmapAvailabilityTracker.cs b/osu.Game/Online/Rooms/OnlinePlayBeatmapAvailabilityTracker.cs
index aa0e37363b..a32f069470 100644
--- a/osu.Game/Online/Rooms/OnlinePlayBeatmapAvailabilityTracker.cs
+++ b/osu.Game/Online/Rooms/OnlinePlayBeatmapAvailabilityTracker.cs
@@ -40,6 +40,11 @@ public sealed class OnlinePlayBeatmapAvailabilityTracker : CompositeDrawable
 
         private BeatmapDownloadTracker downloadTracker;
 
+        /// <summary>
+        /// The beatmap matching the required hash (and providing a final <see cref="BeatmapAvailability.LocallyAvailable"/> state).
+        /// </summary>
+        private BeatmapInfo matchingHash;
+
         protected override void LoadComplete()
         {
             base.LoadComplete();
@@ -71,13 +76,34 @@ protected override void LoadComplete()
                         progressUpdate = Scheduler.AddDelayed(updateAvailability, progressUpdate == null ? 0 : 500);
                 }, true);
             }, true);
+
+            // These events are needed for a fringe case where a modified/altered beatmap is imported with matching OnlineIDs.
+            // During the import process this will cause the existing beatmap set to be silently deleted and replaced with the new one.
+            // This is not exposed to us via `BeatmapDownloadTracker` so we have to take it into our own hands (as we care about the hash matching).
+            beatmapManager.ItemUpdated += itemUpdated;
+            beatmapManager.ItemRemoved += itemRemoved;
         }
 
+        private void itemUpdated(BeatmapSetInfo item) => Schedule(() =>
+        {
+            if (matchingHash?.BeatmapSet.ID == item.ID || SelectedItem.Value?.Beatmap.Value.BeatmapSet?.OnlineID == item.OnlineID)
+                updateAvailability();
+        });
+
+        private void itemRemoved(BeatmapSetInfo item) => Schedule(() =>
+        {
+            if (matchingHash?.BeatmapSet.ID == item.ID)
+                updateAvailability();
+        });
+
         private void updateAvailability()
         {
             if (downloadTracker == null)
                 return;
 
+            // will be repopulated below if still valid.
+            matchingHash = null;
+
             switch (downloadTracker.State.Value)
             {
                 case DownloadState.NotDownloaded:
@@ -93,7 +119,9 @@ private void updateAvailability()
                     break;
 
                 case DownloadState.LocallyAvailable:
-                    bool hashMatches = checkHashValidity();
+                    matchingHash = findMatchingHash();
+
+                    bool hashMatches = matchingHash != null;
 
                     availability.Value = hashMatches ? BeatmapAvailability.LocallyAvailable() : BeatmapAvailability.NotDownloaded();
 
@@ -108,12 +136,23 @@ private void updateAvailability()
             }
         }
 
-        private bool checkHashValidity()
+        private BeatmapInfo findMatchingHash()
         {
             int onlineId = SelectedItem.Value.Beatmap.Value.OnlineID;
             string checksum = SelectedItem.Value.Beatmap.Value.MD5Hash;
 
-            return beatmapManager.QueryBeatmap(b => b.OnlineID == onlineId && b.MD5Hash == checksum && !b.BeatmapSet.DeletePending) != null;
+            return beatmapManager.QueryBeatmap(b => b.OnlineID == onlineId && b.MD5Hash == checksum && !b.BeatmapSet.DeletePending);
+        }
+
+        protected override void Dispose(bool isDisposing)
+        {
+            base.Dispose(isDisposing);
+
+            if (beatmapManager != null)
+            {
+                beatmapManager.ItemUpdated -= itemUpdated;
+                beatmapManager.ItemRemoved -= itemRemoved;
+            }
         }
     }
 }