Move GetDifficultyRating helper method to StarDifficulty

osu.Game/Beatmaps/StarDifficulty.cs

@@ -4,6 +4,7 @@
 #nullable disable
 
 using JetBrains.Annotations;
+using osu.Framework.Utils;
 using osu.Game.Rulesets.Difficulty;
 
 namespace osu.Game.Beatmaps
@@ -50,6 +51,34 @@ namespace osu.Game.Beatmaps
             Attributes = null;
         }
 
-        public DifficultyRating DifficultyRating => BeatmapDifficultyCache.GetDifficultyRating(Stars);
+        public DifficultyRating DifficultyRating => GetDifficultyRating(Stars);
+
+        /// <summary>
+        /// Retrieves the <see cref="DifficultyRating"/> that describes a star rating.
+        /// </summary>
+        /// <remarks>
+        /// For more information, see: https://osu.ppy.sh/help/wiki/Difficulties
+        /// </remarks>
+        /// <param name="starRating">The star rating.</param>
+        /// <returns>The <see cref="DifficultyRating"/> that best describes <paramref name="starRating"/>.</returns>
+        public static DifficultyRating GetDifficultyRating(double starRating)
+        {
+            if (Precision.AlmostBigger(starRating, 6.5, 0.005))
+                return DifficultyRating.ExpertPlus;
+
+            if (Precision.AlmostBigger(starRating, 5.3, 0.005))
+                return DifficultyRating.Expert;
+
+            if (Precision.AlmostBigger(starRating, 4.0, 0.005))
+                return DifficultyRating.Insane;
+
+            if (Precision.AlmostBigger(starRating, 2.7, 0.005))
+                return DifficultyRating.Hard;
+
+            if (Precision.AlmostBigger(starRating, 2.0, 0.005))
+                return DifficultyRating.Normal;
+
+            return DifficultyRating.Easy;
+        }
     }
 }