Add automatic downloading support when spectating a multiplayer room

osu.Game/Screens/OnlinePlay/Multiplayer/Match/MultiplayerSpectateButton.cs

@@ -1,27 +1,32 @@
 // 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.
 
-#nullable disable
-
+using System.Linq;
+using System.Threading;
 using osu.Framework.Allocation;
 using osu.Framework.Bindables;
+using osu.Framework.Extensions;
 using osu.Framework.Graphics;
+using osu.Game.Beatmaps;
+using osu.Game.Configuration;
+using osu.Game.Database;
 using osu.Game.Graphics;
 using osu.Game.Graphics.UserInterfaceV2;
 using osu.Game.Online.Multiplayer;
+using osu.Game.Online.Rooms;
 using osuTK;
 
 namespace osu.Game.Screens.OnlinePlay.Multiplayer.Match
 {
     public partial class MultiplayerSpectateButton : MultiplayerRoomComposite
     {
         [Resolved]
-        private OngoingOperationTracker ongoingOperationTracker { get; set; }
+        private OngoingOperationTracker ongoingOperationTracker { get; set; } = null!;
 
         [Resolved]
-        private OsuColour colours { get; set; }
+        private OsuColour colours { get; set; } = null!;
 
-        private IBindable<bool> operationInProgress;
+        private IBindable<bool> operationInProgress = null!;
 
         private readonly RoundedButton button;
 
@@ -46,10 +51,11 @@ private void onClick()
         }
 
         [BackgroundDependencyLoader]
-        private void load()
+        private void load(OsuConfigManager config)
         {
             operationInProgress = ongoingOperationTracker.InProgress.GetBoundCopy();
             operationInProgress.BindValueChanged(_ => updateState());
+            automaticallyDownload = config.GetBindable<bool>(OsuSetting.AutomaticallyDownloadMissingBeatmaps);
         }
 
         protected override void OnRoomUpdated()
@@ -77,6 +83,70 @@ private void updateState()
             button.Enabled.Value = Client.Room != null
                                    && Client.Room.State != MultiplayerRoomState.Closed
                                    && !operationInProgress.Value;
+
+            Scheduler.AddOnce(checkForAutomaticDownload);
+        }
+
+        #region Automatic download handling
+
+        [Resolved]
+        private BeatmapLookupCache beatmapLookupCache { get; set; } = null!;
+
+        [Resolved]
+        private BeatmapModelDownloader beatmapDownloader { get; set; } = null!;
+
+        [Resolved]
+        private BeatmapManager beatmaps { get; set; } = null!;
+
+        private Bindable<bool> automaticallyDownload = null!;
+
+        private CancellationTokenSource? downloadCheckCancellation;
+
+        protected override void PlaylistItemChanged(MultiplayerPlaylistItem item)
+        {
+            base.PlaylistItemChanged(item);
+            Scheduler.AddOnce(checkForAutomaticDownload);
         }
+
+        private void checkForAutomaticDownload()
+        {
+            MultiplayerPlaylistItem? item = Client.Room?.Playlist.FirstOrDefault(i => !i.Expired);
+
+            downloadCheckCancellation?.Cancel();
+
+            if (item == null)
+                return;
+
+            if (!automaticallyDownload.Value)
+                return;
+
+            // While we can support automatic downloads when not spectating, there are some usability concerns.
+            // - In host rotate mode, this could potentially be unwanted by some users (even though they want automatic downloads everywhere else).
+            // - When first joining a room, the expectation should be that the user is checking out the room, and they may not immediately want to download the selected beatmap.
+            //
+            // Rather than over-complicating this flow, let's only auto-download when spectating for the time being.
+            // A potential path forward would be to have a local auto-download checkbox above the playlist item list area.
+            if (Client.LocalUser?.State != MultiplayerUserState.Spectating)
+                return;
+
+            // In a perfect world we'd use BeatmapAvailability, but there's no event-driven flow for when a selection changes.
+            // ie. if selection changes from "not downloaded" to another "not downloaded" we wouldn't get a value changed raised.
+            beatmapLookupCache
+                .GetBeatmapAsync(item.BeatmapID, (downloadCheckCancellation = new CancellationTokenSource()).Token)
+                .ContinueWith(resolved => Schedule(() =>
+                {
+                    var beatmapSet = resolved.GetResultSafely()?.BeatmapSet;
+
+                    if (beatmapSet == null)
+                        return;
+
+                    if (beatmaps.IsAvailableLocally(new BeatmapSetInfo { OnlineID = beatmapSet.OnlineID }))
+                        return;
+
+                    beatmapDownloader.Download(beatmapSet);
+                }));
+        }
+
+        #endregion
     }
 }