From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Fri, 15 Jun 2018 00:30:32 -0400
Subject: [PATCH] Configurable Alternative LootPool Luck Formula

Rewrites the Vanilla luck application formula so that luck can be
applied to items that do not have any quality defined.

See: https://luckformula.emc.gs for data and details
-----------

The rough summary is:
My goal was that in a pool, when luck was applied, the pool
rebalances so the percentages for bigger items is
lowered and smaller items is boosted.

Do this by boosting and then reducing the weight value,
so that larger numbers are penalized more than smaller numbers.
resulting in a larger reduction of entries for more common
items than the reduction on small weights,
giving smaller weights more of a chance

-----------

This work kind of obsoletes quality, but quality would be useful
for 2 items with same weight that you want luck to impact
in varying directions.

Fishing still falls into that as the weights are closer, so luck
will invalidate junk more.

This change will result in some major changes to fishing formulas.

-----------

I would love to see this change in Vanilla, so Mojang please pull :)

diff --git a/src/main/java/com/destroystokyo/paper/PaperConfig.java b/src/main/java/com/destroystokyo/paper/PaperConfig.java
index 05a5abb951abe37f30a719cb75376d2d43c0d252..77a03abd59db4a43f6f2d59d4c7ef176e782f205 100644
--- a/src/main/java/com/destroystokyo/paper/PaperConfig.java
+++ b/src/main/java/com/destroystokyo/paper/PaperConfig.java
@@ -288,4 +288,12 @@ public class PaperConfig {
             SpigotConfig.save();
         }
     }
+
+    public static boolean useAlternativeLuckFormula = false;
+    private static void useAlternativeLuckFormula() {
+        useAlternativeLuckFormula = getBoolean("settings.use-alternative-luck-formula", false);
+        if (useAlternativeLuckFormula) {
+            Bukkit.getLogger().log(Level.INFO, "Using Aikar's Alternative Luck Formula to apply Luck attribute to all loot pool calculations. See https://luckformula.emc.gs");
+        }
+    }
 }
diff --git a/src/main/java/net/minecraft/world/level/storage/loot/entries/LootPoolSingletonContainer.java b/src/main/java/net/minecraft/world/level/storage/loot/entries/LootPoolSingletonContainer.java
index ceb5e5405ed20c8de954847bbb269109107a43fc..d99bc0b8a1e9c4749b176a823b879ced9efdd7d6 100644
--- a/src/main/java/net/minecraft/world/level/storage/loot/entries/LootPoolSingletonContainer.java
+++ b/src/main/java/net/minecraft/world/level/storage/loot/entries/LootPoolSingletonContainer.java
@@ -8,7 +8,6 @@ import java.util.List;
 import java.util.function.BiFunction;
 import java.util.function.Consumer;
 import net.minecraft.util.GsonHelper;
-import net.minecraft.util.Mth;
 import net.minecraft.world.item.ItemStack;
 import net.minecraft.world.level.storage.loot.LootContext;
 import net.minecraft.world.level.storage.loot.ValidationContext;
@@ -20,8 +19,8 @@ import org.apache.commons.lang3.ArrayUtils;
 
 public abstract class LootPoolSingletonContainer extends LootPoolEntryContainer {
 
-    protected final int weight;
-    protected final int quality;
+    protected final int weight; public int getWeight() { return weight; } // Paper - OBFHELPER
+    protected final int quality; public int getQuality() { return quality; } // Paper - OBFHELPER
     protected final LootItemFunction[] functions;
     private final BiFunction<ItemStack, LootContext, ItemStack> compositeFunction;
     private final LootPoolEntry entry = new LootPoolSingletonContainer.EntryBase() {
@@ -152,11 +151,38 @@ public abstract class LootPoolSingletonContainer extends LootPoolEntryContainer
 
     public abstract class EntryBase implements LootPoolEntry {
 
-        protected EntryBase() {}
+        protected EntryBase() {
+        }
 
         @Override
         public int getWeight(float luck) {
-            return Math.max(Mth.floor((float) LootPoolSingletonContainer.this.weight + (float) LootPoolSingletonContainer.this.quality * luck), 0);
+            // Paper start - Offer an alternative loot formula to refactor how luck bonus applies
+            // SEE: https://luckformula.emc.gs for details and data
+            if (lastLuck != null && lastLuck == luck) {
+                return lastWeight;
+            }
+            // This is vanilla
+            float qualityModifer = (float) getQuality() * luck;
+            double baseWeight = (getWeight() + qualityModifer);
+            if (com.destroystokyo.paper.PaperConfig.useAlternativeLuckFormula) {
+                // Random boost to avoid losing precision in the final int cast on return
+                final int weightBoost = 100;
+                baseWeight *= weightBoost;
+                // If we have vanilla 1, bump that down to 0 so nothing is is impacted
+                // vanilla 3 = 300, 200 basis = impact 2%
+                // =($B2*(($B2-100)/100/100))
+                double impacted = baseWeight * ((baseWeight - weightBoost) / weightBoost / 100);
+                // =($B$7/100)
+                float luckModifier = Math.min(100, luck * 10) / 100;
+                // =B2 - (C2 *($B$7/100))
+                baseWeight = Math.ceil(baseWeight - (impacted * luckModifier));
+            }
+            lastLuck = luck;
+            lastWeight = (int) Math.max(0, Math.floor(baseWeight));
+            return lastWeight;
         }
     }
+    private Float lastLuck = null;
+    private int lastWeight = 0;
+    // Paper end
 }