Select recommended difficulty

osu.Game/Screens/Select/BeatmapCarousel.cs

@@ -23,6 +23,8 @@ using osu.Game.Graphics.Containers;
 using osu.Game.Graphics.Cursor;
 using osu.Game.Input.Bindings;
 using osu.Game.Screens.Select.Carousel;
+using osu.Game.Online.API;
+using osu.Game.Users;
 
 namespace osu.Game.Screens.Select
 {
@@ -31,6 +33,8 @@ namespace osu.Game.Screens.Select
         private const float bleed_top = FilterControl.HEIGHT;
         private const float bleed_bottom = Footer.HEIGHT;
 
+        private readonly Bindable<User> localUser = new Bindable<User>();
+
         /// <summary>
         /// Triggered when the <see cref="BeatmapSets"/> loaded change and are completely loaded.
         /// </summary>
@@ -140,7 +144,7 @@ namespace osu.Game.Screens.Select
         private BeatmapManager beatmaps { get; set; }
 
         [BackgroundDependencyLoader(permitNulls: true)]
-        private void load(OsuConfigManager config)
+        private void load(OsuConfigManager config, IAPIProvider api)
         {
             config.BindWith(OsuSetting.RandomSelectAlgorithm, RandomAlgorithm);
             config.BindWith(OsuSetting.SongSelectRightMouseScroll, RightClickScrollingEnabled);
@@ -154,6 +158,8 @@ namespace osu.Game.Screens.Select
             beatmaps.BeatmapRestored += beatmapRestored;
 
             loadBeatmapSets(GetLoadableBeatmaps());
+
+            localUser.BindTo(api.LocalUser);
         }
 
         protected virtual IEnumerable<BeatmapSetInfo> GetLoadableBeatmaps() => beatmaps.GetAllUsableBeatmapSetsEnumerable();
@@ -588,7 +594,7 @@ namespace osu.Game.Screens.Select
                     b.Metadata = beatmapSet.Metadata;
             }
 
-            var set = new CarouselBeatmapSet(beatmapSet);
+            var set = new CarouselBeatmapSet(beatmapSet, localUser);
 
             foreach (var c in set.Beatmaps)
             {

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

@@ -4,19 +4,23 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using osu.Framework.Bindables;
 using osu.Framework.Extensions.IEnumerableExtensions;
 using osu.Game.Beatmaps;
 using osu.Game.Screens.Select.Filter;
+using osu.Game.Users;
 
 namespace osu.Game.Screens.Select.Carousel
 {
     public class CarouselBeatmapSet : CarouselGroupEagerSelect
     {
+        private readonly Bindable<User> localUser;
+
         public IEnumerable<CarouselBeatmap> Beatmaps => InternalChildren.OfType<CarouselBeatmap>();
 
         public BeatmapSetInfo BeatmapSet;
 
-        public CarouselBeatmapSet(BeatmapSetInfo beatmapSet)
+        public CarouselBeatmapSet(BeatmapSetInfo beatmapSet, Bindable<User> localUser)
         {
             BeatmapSet = beatmapSet ?? throw new ArgumentNullException(nameof(beatmapSet));
 
@@ -24,10 +28,32 @@ namespace osu.Game.Screens.Select.Carousel
                       .Where(b => !b.Hidden)
                       .Select(b => new CarouselBeatmap(b))
                       .ForEach(AddChild);
+
+            this.localUser = localUser;
         }
 
         protected override DrawableCarouselItem CreateDrawableRepresentation() => new DrawableCarouselBeatmapSet(this);
 
+        protected override CarouselItem GetNextToSelect()
+        {
+            if (LastSelected == null)
+            {
+                decimal? pp = localUser.Value?.Statistics?.PP ?? 60; // TODO: This needs to get ruleset specific statistics
+
+                var recommendedDifficulty = Math.Pow((double)pp, 0.4) * 0.195;
+                return Children.OfType<CarouselBeatmap>()
+                               .Where(b => !b.Filtered.Value)
+                               .OrderBy(b =>
+                               {
+                                   var difference = b.Beatmap.StarDifficulty - recommendedDifficulty;
+                                   return difference >= 0 ? difference * 2 : difference * -1; // prefer easier over harder
+                               })
+                               .FirstOrDefault();
+            }
+
+            return base.GetNextToSelect();
+        }
+
         public override int CompareTo(FilterCriteria criteria, CarouselItem other)
         {
             if (!(other is CarouselBeatmapSet otherSet))

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

@@ -90,11 +90,15 @@ namespace osu.Game.Screens.Select.Carousel
             PerformSelection();
         }
 
+        protected virtual CarouselItem GetNextToSelect()
+        {
+            return Children.Skip(lastSelectedIndex).FirstOrDefault(i => !i.Filtered.Value) ??
+                   Children.Reverse().Skip(InternalChildren.Count - lastSelectedIndex).FirstOrDefault(i => !i.Filtered.Value);
+        }
+
         protected virtual void PerformSelection()
         {
-            CarouselItem nextToSelect =
+            CarouselItem nextToSelect = GetNextToSelect();
-                Children.Skip(lastSelectedIndex).FirstOrDefault(i => !i.Filtered.Value) ??
-                Children.Reverse().Skip(InternalChildren.Count - lastSelectedIndex).FirstOrDefault(i => !i.Filtered.Value);
 
             if (nextToSelect != null)
                 nextToSelect.State.Value = CarouselItemState.Selected;