From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Wed, 20 Dec 2017 17:36:49 -0500
Subject: [PATCH] Ability to apply mending to XP API

This allows plugins that give players the ability to apply the experience
points to the Item Mending formula, which will repair an item instead
of giving the player experience points.

Both an API To standalone mend, and apply mending logic to .giveExp has been added.

== AT ==
public net.minecraft.world.entity.ExperienceOrb durabilityToXp(I)I
public net.minecraft.world.entity.ExperienceOrb xpToDurability(I)I

diff --git a/src/main/java/org/bukkit/craftbukkit/entity/CraftPlayer.java b/src/main/java/org/bukkit/craftbukkit/entity/CraftPlayer.java
index f53504221e660bfe86220a8cc1ae28750794f0cf..93550342c6f181b7622f5d649cd3e5075a464e55 100644
--- a/src/main/java/org/bukkit/craftbukkit/entity/CraftPlayer.java
+++ b/src/main/java/org/bukkit/craftbukkit/entity/CraftPlayer.java
@@ -1638,7 +1638,41 @@ public class CraftPlayer extends CraftHumanEntity implements Player {
     }
 
     @Override
-    public void giveExp(int exp) {
+    // Paper start
+    public int applyMending(int amount) {
+        ServerPlayer handle = this.getHandle();
+        // Logic copied from EntityExperienceOrb and remapped to unobfuscated methods/properties
+
+        final Optional<net.minecraft.world.item.enchantment.EnchantedItemInUse> stackEntry = net.minecraft.world.item.enchantment.EnchantmentHelper
+            .getRandomItemWith(net.minecraft.world.item.enchantment.EnchantmentEffectComponents.REPAIR_WITH_XP, handle, net.minecraft.world.item.ItemStack::isDamaged);
+        final net.minecraft.world.item.ItemStack itemstack = stackEntry.map(net.minecraft.world.item.enchantment.EnchantedItemInUse::itemStack).orElse(net.minecraft.world.item.ItemStack.EMPTY);
+        if (!itemstack.isEmpty() && itemstack.getItem().components().has(net.minecraft.core.component.DataComponents.MAX_DAMAGE)) {
+            net.minecraft.world.entity.ExperienceOrb orb = net.minecraft.world.entity.EntityType.EXPERIENCE_ORB.create(handle.level());
+            orb.value = amount;
+            orb.spawnReason = org.bukkit.entity.ExperienceOrb.SpawnReason.CUSTOM;
+            orb.setPosRaw(handle.getX(), handle.getY(), handle.getZ());
+
+            final int possibleDurabilityFromXp = net.minecraft.world.item.enchantment.EnchantmentHelper.modifyDurabilityToRepairFromXp(
+                handle.serverLevel(), itemstack, amount
+            );
+            int i = Math.min(possibleDurabilityFromXp, itemstack.getDamageValue());
+            org.bukkit.event.player.PlayerItemMendEvent event = org.bukkit.craftbukkit.event.CraftEventFactory.callPlayerItemMendEvent(handle, orb, itemstack, stackEntry.get().inSlot(), i);
+            i = event.getRepairAmount();
+            orb.discard(org.bukkit.event.entity.EntityRemoveEvent.Cause.DESPAWN);
+            if (!event.isCancelled()) {
+                amount -= i * amount / possibleDurabilityFromXp;
+                itemstack.setDamageValue(itemstack.getDamageValue() - i);
+            }
+        }
+        return amount;
+    }
+
+    @Override
+    public void giveExp(int exp, boolean applyMending) {
+        if (applyMending) {
+            exp = this.applyMending(exp);
+        }
+        // Paper end
         this.getHandle().giveExperiencePoints(exp);
     }