Tidy up function passing, naming, ordering etc.

osu.Game/Screens/Select/BeatmapCarousel.cs

@@ -49,6 +49,11 @@ namespace osu.Game.Screens.Select
         /// </summary>
         public BeatmapSetInfo SelectedBeatmapSet => selectedBeatmapSet?.BeatmapSet;
 
+        /// <summary>
+        /// A function to optionally decide on a recommended difficulty from a beatmap set.
+        /// </summary>
+        public Func<IEnumerable<BeatmapInfo>, BeatmapInfo> GetRecommendedBeatmap;
+
         private CarouselBeatmapSet selectedBeatmapSet;
 
         /// <summary>
@@ -120,8 +125,6 @@ namespace osu.Game.Screens.Select
 
         private CarouselRoot root;
 
-        public DifficultyRecommender DifficultyRecommender;
-
         public BeatmapCarousel()
         {
             root = new CarouselRoot(this);
@@ -586,12 +589,10 @@ namespace osu.Game.Screens.Select
                     b.Metadata = beatmapSet.Metadata;
             }
 
-            BeatmapInfo recommender(IEnumerable<BeatmapInfo> beatmaps)
+            var set = new CarouselBeatmapSet(beatmapSet)
             {
-                return DifficultyRecommender?.GetRecommendedBeatmap(beatmaps);
+                GetRecommendedBeatmap = beatmaps => GetRecommendedBeatmap?.Invoke(beatmaps)
-            }
+            };
-
-            var set = new CarouselBeatmapSet(beatmapSet, recommender);
 
             foreach (var c in set.Beatmaps)
             {

osu.Game/Screens/Select/Carousel/CarouselBeatmapSet.cs

@@ -12,13 +12,13 @@ namespace osu.Game.Screens.Select.Carousel
 {
     public class CarouselBeatmapSet : CarouselGroupEagerSelect
     {
-        private readonly Func<IEnumerable<BeatmapInfo>, BeatmapInfo> getRecommendedBeatmap;
-
         public IEnumerable<CarouselBeatmap> Beatmaps => InternalChildren.OfType<CarouselBeatmap>();
 
         public BeatmapSetInfo BeatmapSet;
 
-        public CarouselBeatmapSet(BeatmapSetInfo beatmapSet, Func<IEnumerable<BeatmapInfo>, BeatmapInfo> getRecommendedBeatmap)
+        public Func<IEnumerable<BeatmapInfo>, BeatmapInfo> GetRecommendedBeatmap;
+
+        public CarouselBeatmapSet(BeatmapSetInfo beatmapSet)
         {
             BeatmapSet = beatmapSet ?? throw new ArgumentNullException(nameof(beatmapSet));
 
@@ -26,8 +26,6 @@ namespace osu.Game.Screens.Select.Carousel
                       .Where(b => !b.Hidden)
                       .Select(b => new CarouselBeatmap(b))
                       .ForEach(AddChild);
-
-            this.getRecommendedBeatmap = getRecommendedBeatmap;
         }
 
         protected override DrawableCarouselItem CreateDrawableRepresentation() => new DrawableCarouselBeatmapSet(this);
@@ -36,9 +34,8 @@ namespace osu.Game.Screens.Select.Carousel
         {
             if (LastSelected == null)
             {
-                var recommendedBeatmapInfo = getRecommendedBeatmap(Children.OfType<CarouselBeatmap>().Where(b => !b.Filtered.Value).Select(b => b.Beatmap));
+                if (GetRecommendedBeatmap?.Invoke(Children.OfType<CarouselBeatmap>().Where(b => !b.Filtered.Value).Select(b => b.Beatmap)) is BeatmapInfo recommended)
-                if (recommendedBeatmapInfo != null)
+                    return Children.OfType<CarouselBeatmap>().First(b => b.Beatmap == recommended);
-                    return Children.OfType<CarouselBeatmap>().First(b => b.Beatmap == recommendedBeatmapInfo);
             }
 
             return base.GetNextToSelect();

osu.Game/Screens/Select/DifficultyRecommender.cs

@@ -33,10 +33,33 @@ namespace osu.Game.Screens.Select
         [BackgroundDependencyLoader]
         private void load()
         {
-            updateRecommended();
+            calculateRecommendedDifficulties();
         }
 
-        private void updateRecommended()
+        /// <summary>
+        /// Find the recommended difficulty from a selection of available difficulties for the current local user.
+        /// </summary>
+        /// <remarks>
+        /// This requires the user to be online for now.
+        /// </remarks>
+        /// <param name="beatmaps">A collection of beatmaps to select a difficulty from.</param>
+        /// <returns>The recommended difficulty, or null if a recommendation could not be provided.</returns>
+        public BeatmapInfo GetRecommendedBeatmap(IEnumerable<BeatmapInfo> beatmaps)
+        {
+            if (!recommendedStarDifficulty.ContainsKey(ruleset.Value))
+            {
+                calculateRecommendedDifficulties();
+                return null;
+            }
+
+            return beatmaps.OrderBy(b =>
+            {
+                var difference = b.StarDifficulty - recommendedStarDifficulty[ruleset.Value];
+                return difference >= 0 ? difference * 2 : difference * -1; // prefer easier over harder
+            }).FirstOrDefault();
+        }
+
+        private void calculateRecommendedDifficulties()
         {
             if (pendingAPIRequests > 0)
                 return;
@@ -60,20 +83,5 @@ namespace osu.Game.Screens.Select
                 api.Queue(req);
             });
         }
-
-        public BeatmapInfo GetRecommendedBeatmap(IEnumerable<BeatmapInfo> beatmaps)
-        {
-            if (!recommendedStarDifficulty.ContainsKey(ruleset.Value))
-            {
-                updateRecommended();
-                return null;
-            }
-
-            return beatmaps.OrderBy(b =>
-            {
-                var difference = b.StarDifficulty - recommendedStarDifficulty[ruleset.Value];
-                return difference >= 0 ? difference * 2 : difference * -1; // prefer easier over harder
-            }).FirstOrDefault();
-        }
     }
 }

osu.Game/Screens/Select/SongSelect.cs

@@ -80,7 +80,8 @@ namespace osu.Game.Screens.Select
         protected override BackgroundScreen CreateBackground() => new BackgroundScreenBeatmap(Beatmap.Value);
 
         protected BeatmapCarousel Carousel { get; private set; }
-        private DifficultyRecommender difficultyRecommender;
+
+        private DifficultyRecommender recommender;
 
         private BeatmapInfoWedge beatmapInfoWedge;
         private DialogOverlay dialogOverlay;
@@ -108,10 +109,9 @@ namespace osu.Game.Screens.Select
             // initial value transfer is required for FilterControl (it uses our re-cached bindables in its async load for the initial filter).
             transferRulesetValue();
 
-            AddInternal(difficultyRecommender = new DifficultyRecommender());
-
             AddRangeInternal(new Drawable[]
             {
+                recommender = new DifficultyRecommender(),
                 new ResetScrollContainer(() => Carousel.ScrollToSelected())
                 {
                     RelativeSizeAxes = Axes.Y,
@@ -159,7 +159,7 @@ namespace osu.Game.Screens.Select
                                             RelativeSizeAxes = Axes.Both,
                                             SelectionChanged = updateSelectedBeatmap,
                                             BeatmapSetsChanged = carouselBeatmapsLoaded,
-                                            DifficultyRecommender = difficultyRecommender,
+                                            GetRecommendedBeatmap = recommender.GetRecommendedBeatmap,
                                         },
                                     }
                                 },