From 442e68ac1a496529869e7cbb75ad40bc4881aef4 Mon Sep 17 00:00:00 2001
From: Natelytle <nathenbr@gmail.com>
Date: Tue, 25 Oct 2022 17:41:20 -0400
Subject: [PATCH] Implement taiko deviation estimation

---
 .../Difficulty/TaikoPerformanceAttributes.cs  |  3 +++
 .../Difficulty/TaikoPerformanceCalculator.cs  | 27 +++++++++++++++----
 .../osu.Game.Rulesets.Taiko.csproj            |  4 +++
 3 files changed, 29 insertions(+), 5 deletions(-)

diff --git a/osu.Game.Rulesets.Taiko/Difficulty/TaikoPerformanceAttributes.cs b/osu.Game.Rulesets.Taiko/Difficulty/TaikoPerformanceAttributes.cs
index b61c13a2df..fa8c3fd27a 100644
--- a/osu.Game.Rulesets.Taiko/Difficulty/TaikoPerformanceAttributes.cs
+++ b/osu.Game.Rulesets.Taiko/Difficulty/TaikoPerformanceAttributes.cs
@@ -19,6 +19,9 @@ namespace osu.Game.Rulesets.Taiko.Difficulty
 
         [JsonProperty("effective_miss_count")]
         public double EffectiveMissCount { get; set; }
+        
+        [JsonProperty("estimated_ur")]
+        public double EstimatedUR { get; set; }
 
         public override IEnumerable<PerformanceDisplayAttribute> GetAttributesForDisplay()
         {
diff --git a/osu.Game.Rulesets.Taiko/Difficulty/TaikoPerformanceCalculator.cs b/osu.Game.Rulesets.Taiko/Difficulty/TaikoPerformanceCalculator.cs
index dc7bad2f75..7d5cf3accd 100644
--- a/osu.Game.Rulesets.Taiko/Difficulty/TaikoPerformanceCalculator.cs
+++ b/osu.Game.Rulesets.Taiko/Difficulty/TaikoPerformanceCalculator.cs
@@ -11,6 +11,7 @@ using osu.Game.Rulesets.Mods;
 using osu.Game.Rulesets.Scoring;
 using osu.Game.Rulesets.Taiko.Objects;
 using osu.Game.Scoring;
+using MathNet.Numerics;
 
 namespace osu.Game.Rulesets.Taiko.Difficulty
 {
@@ -21,6 +22,7 @@ namespace osu.Game.Rulesets.Taiko.Difficulty
         private int countMeh;
         private int countMiss;
         private double accuracy;
+        private double estimatedUR;
 
         private double effectiveMissCount;
 
@@ -37,7 +39,7 @@ namespace osu.Game.Rulesets.Taiko.Difficulty
             countOk = score.Statistics.GetValueOrDefault(HitResult.Ok);
             countMeh = score.Statistics.GetValueOrDefault(HitResult.Meh);
             countMiss = score.Statistics.GetValueOrDefault(HitResult.Miss);
-            accuracy = customAccuracy;
+            estimatedUR = 10 * computeEstimatedUR(score, taikoAttributes);
 
             // The effectiveMissCount is calculated by gaining a ratio for totalSuccessfulHits and increasing the miss penalty for shorter object counts lower than 1000.
             if (totalSuccessfulHits > 0)
@@ -64,6 +66,7 @@ namespace osu.Game.Rulesets.Taiko.Difficulty
                 Difficulty = difficultyValue,
                 Accuracy = accuracyValue,
                 EffectiveMissCount = effectiveMissCount,
+                EstimatedUR = 10 * estimatedUR,
                 Total = totalValue
             };
         }
@@ -97,10 +100,9 @@ namespace osu.Game.Rulesets.Taiko.Difficulty
             if (attributes.GreatHitWindow <= 0)
                 return 0;
 
-            double accuracyValue = Math.Pow(60.0 / attributes.GreatHitWindow, 1.1) * Math.Pow(accuracy, 8.0) * Math.Pow(attributes.StarRating, 0.4) * 27.0;
+            double accuracyValue = Math.Pow(75 / estimatedUR, 1.1) * Math.Pow(attributes.StarRating, 0.4) * 70.0;
 
             double lengthBonus = Math.Min(1.15, Math.Pow(totalHits / 1500.0, 0.3));
-            accuracyValue *= lengthBonus;
 
             // Slight HDFL Bonus for accuracy. A clamp is used to prevent against negative values
             if (score.Mods.Any(m => m is ModFlashlight<TaikoHitObject>) && score.Mods.Any(m => m is ModHidden))
@@ -109,10 +111,25 @@ namespace osu.Game.Rulesets.Taiko.Difficulty
             return accuracyValue;
         }
 
+        private double computeEstimatedUR(ScoreInfo score, TaikoDifficultyAttributes attributes)
+        {
+            if (totalHits == 0)
+                return double.PositiveInfinity;
+            
+            double greatProbability = 1 - (countOk + countMiss + 1.0) / (totalHits + 1.0);
+
+            if (greatProbability <= 0)
+            {
+                return double.PositiveInfinity;
+            }
+
+            double deviation = attributes.GreatHitWindow / (Math.Sqrt(2) * SpecialFunctions.ErfInv(greatProbability));
+
+            return deviation;
+        }
+
         private int totalHits => countGreat + countOk + countMeh + countMiss;
 
         private int totalSuccessfulHits => countGreat + countOk + countMeh;
-
-        private double customAccuracy => totalHits > 0 ? (countGreat * 300 + countOk * 150) / (totalHits * 300.0) : 0;
     }
 }
diff --git a/osu.Game.Rulesets.Taiko/osu.Game.Rulesets.Taiko.csproj b/osu.Game.Rulesets.Taiko/osu.Game.Rulesets.Taiko.csproj
index b752c13d18..b2953106d8 100644
--- a/osu.Game.Rulesets.Taiko/osu.Game.Rulesets.Taiko.csproj
+++ b/osu.Game.Rulesets.Taiko/osu.Game.Rulesets.Taiko.csproj
@@ -15,4 +15,8 @@
   <ItemGroup Label="Project References">
     <ProjectReference Include="..\osu.Game\osu.Game.csproj" />
   </ItemGroup>
+
+  <ItemGroup>
+    <PackageReference Include="MathNet.Numerics" Version="5.0.0" />
+  </ItemGroup>
 </Project>