From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Jake Potrebic <jake.m.potrebic@gmail.com>
Date: Thu, 2 Jul 2020 16:12:10 -0700
Subject: [PATCH] Add PlayerTradeEvent and PlayerPurchaseEvent

Co-authored-by: Alexander <protonull@protonmail.com>

diff --git a/src/main/java/net/minecraft/world/entity/npc/AbstractVillager.java b/src/main/java/net/minecraft/world/entity/npc/AbstractVillager.java
index 742ffe531bb8f3a9ca34dea99b044123d90cfff9..bd283f71cb05ffbe1fed39afb41ae54dc52ec297 100644
--- a/src/main/java/net/minecraft/world/entity/npc/AbstractVillager.java
+++ b/src/main/java/net/minecraft/world/entity/npc/AbstractVillager.java
@@ -138,11 +138,24 @@ public abstract class AbstractVillager extends AgeableMob implements InventoryCa
     @Override
     public void overrideXp(int experience) {}
 
+    // Paper start
+    @Override
+    public void processTrade(MerchantOffer recipe, @Nullable io.papermc.paper.event.player.PlayerPurchaseEvent event) { // The MerchantRecipe passed in here is the one set by the PlayerPurchaseEvent
+        if (event == null || event.willIncreaseTradeUses()) {
+            recipe.increaseUses();
+        }
+        if (event == null || event.isRewardingExp()) {
+            this.rewardTradeXp(recipe);
+        }
+        this.notifyTrade(recipe);
+    }
+    // Paper end
+
     @Override
     public void notifyTrade(MerchantOffer offer) {
-        offer.increaseUses();
+        // offer.increaseUses(); // Paper - handled in processTrade
         this.ambientSoundTime = -this.getAmbientSoundInterval();
-        this.rewardTradeXp(offer);
+        // this.rewardTradeXp(offer); // Paper - handled in processTrade
         if (this.tradingPlayer instanceof ServerPlayer) {
             CriteriaTriggers.TRADE.trigger((ServerPlayer) this.tradingPlayer, this, offer.getResult());
         }
diff --git a/src/main/java/net/minecraft/world/inventory/AbstractContainerMenu.java b/src/main/java/net/minecraft/world/inventory/AbstractContainerMenu.java
index 36834f30ccefd229df4da2dbc7b22edcb83429c3..49ac1e922c0c3b38ed48adda46870e1fc0fb09dc 100644
--- a/src/main/java/net/minecraft/world/inventory/AbstractContainerMenu.java
+++ b/src/main/java/net/minecraft/world/inventory/AbstractContainerMenu.java
@@ -741,6 +741,14 @@ public abstract class AbstractContainerMenu {
     public abstract boolean stillValid(Player player);
 
     protected boolean moveItemStackTo(ItemStack stack, int startIndex, int endIndex, boolean fromLast) {
+        // Paper start
+        return this.moveItemStackTo(stack, startIndex, endIndex, fromLast, false);
+    }
+    protected boolean moveItemStackTo(ItemStack stack, int startIndex, int endIndex, boolean fromLast, boolean isCheck) {
+        if (isCheck) {
+            stack = stack.copy();
+        }
+        // Paper end
         boolean flag1 = false;
         int k = startIndex;
 
@@ -763,18 +771,27 @@ public abstract class AbstractContainerMenu {
 
                 slot = (Slot) this.slots.get(k);
                 itemstack1 = slot.getItem();
+                // Paper start - clone if only a check
+                if (isCheck) {
+                    itemstack1 = itemstack1.copy();
+                }
+                // Paper end
                 if (!itemstack1.isEmpty() && ItemStack.isSameItemSameTags(stack, itemstack1)) {
                     int l = itemstack1.getCount() + stack.getCount();
 
                     if (l <= stack.getMaxStackSize()) {
                         stack.setCount(0);
                         itemstack1.setCount(l);
+                        if (!isCheck) { // Paper - dont update if only a check
                         slot.setChanged();
+                        } // Paper
                         flag1 = true;
                     } else if (itemstack1.getCount() < stack.getMaxStackSize()) {
                         stack.shrink(stack.getMaxStackSize() - itemstack1.getCount());
                         itemstack1.setCount(stack.getMaxStackSize());
+                        if (!isCheck) { // Paper - dont update if only a check
                         slot.setChanged();
+                        } // Paper
                         flag1 = true;
                     }
                 }
@@ -805,14 +822,33 @@ public abstract class AbstractContainerMenu {
 
                 slot = (Slot) this.slots.get(k);
                 itemstack1 = slot.getItem();
+                // Paper start - clone if only a check
+                if (isCheck) {
+                    itemstack1 = itemstack1.copy();
+                }
+                // Paper end
                 if (itemstack1.isEmpty() && slot.mayPlace(stack)) {
                     if (stack.getCount() > slot.getMaxStackSize()) {
+                        // Paper start - dont set slot if only check
+                        if (isCheck) {
+                            stack.shrink(slot.getMaxStackSize());
+                        } else {
+                        // Paper end
                         slot.set(stack.split(slot.getMaxStackSize()));
+                        } // Paper
                     } else {
+                        // Paper start - dont set slot if only check
+                        if (isCheck) {
+                            stack.shrink(stack.getCount());
+                        } else {
+                        // Paper end
                         slot.set(stack.split(stack.getCount()));
+                        } // Paper
                     }
 
+                    if (!isCheck) { // Paper - dont update if only check
                     slot.setChanged();
+                    } // Paper
                     flag1 = true;
                     break;
                 }
diff --git a/src/main/java/net/minecraft/world/inventory/MerchantMenu.java b/src/main/java/net/minecraft/world/inventory/MerchantMenu.java
index 589527215b10aa848a079b964e748c8c2e6137a1..a6e036165ce1a387195cf3db190a42c5d8249b95 100644
--- a/src/main/java/net/minecraft/world/inventory/MerchantMenu.java
+++ b/src/main/java/net/minecraft/world/inventory/MerchantMenu.java
@@ -134,12 +134,12 @@ public class MerchantMenu extends AbstractContainerMenu {
 
             itemstack = itemstack1.copy();
             if (index == 2) {
-                if (!this.moveItemStackTo(itemstack1, 3, 39, true)) {
+                if (!this.moveItemStackTo(itemstack1, 3, 39, true, true)) { // Paper
                     return ItemStack.EMPTY;
                 }
 
-                slot.onQuickCraft(itemstack1, itemstack);
-                this.playTradeSound();
+                // slot.onQuickCraft(itemstack1, itemstack); // Paper - moved to after the non-check moveItemStackTo call
+                // this.playTradeSound();
             } else if (index != 0 && index != 1) {
                 if (index >= 3 && index < 30) {
                     if (!this.moveItemStackTo(itemstack1, 30, 39, false)) {
@@ -152,6 +152,7 @@ public class MerchantMenu extends AbstractContainerMenu {
                 return ItemStack.EMPTY;
             }
 
+            if (index != 2) { // Paper - moved down for slot 2
             if (itemstack1.isEmpty()) {
                 slot.set(ItemStack.EMPTY);
             } else {
@@ -163,6 +164,21 @@ public class MerchantMenu extends AbstractContainerMenu {
             }
 
             slot.onTake(player, itemstack1);
+            } // Paper start - handle slot 2
+            if (index == 2) { // is merchant result slot
+                slot.onTake(player, itemstack1);
+                if (itemstack1.isEmpty()) {
+                    slot.set(ItemStack.EMPTY);
+                    return ItemStack.EMPTY;
+                }
+
+                this.moveItemStackTo(itemstack1, 3, 39, true, false); // This should always succeed because it's checked above
+
+                slot.onQuickCraft(itemstack1, itemstack);
+                this.playTradeSound();
+                slot.set(ItemStack.EMPTY); // itemstack1 should ALWAYS be empty
+            }
+            // Paper end
         }
 
         return itemstack;
diff --git a/src/main/java/net/minecraft/world/inventory/MerchantResultSlot.java b/src/main/java/net/minecraft/world/inventory/MerchantResultSlot.java
index 74b28315197b81f80334ae6023113904e4fac4c3..7acf5ab9339e0134819aab5f270e99e927cc7a62 100644
--- a/src/main/java/net/minecraft/world/inventory/MerchantResultSlot.java
+++ b/src/main/java/net/minecraft/world/inventory/MerchantResultSlot.java
@@ -47,13 +47,32 @@ public class MerchantResultSlot extends Slot {
 
     @Override
     public void onTake(Player player, ItemStack stack) {
-        this.checkTakeAchievements(stack);
+        // this.checkTakeAchievements(stack); // Paper - move to after event is called and not cancelled
         MerchantOffer merchantOffer = this.slots.getActiveOffer();
+        // Paper start
+        io.papermc.paper.event.player.PlayerPurchaseEvent event = null;
+        if (merchantOffer != null && player instanceof net.minecraft.server.level.ServerPlayer serverPlayer) {
+            if (this.merchant instanceof net.minecraft.world.entity.npc.AbstractVillager abstractVillager) {
+                event = new io.papermc.paper.event.player.PlayerTradeEvent(serverPlayer.getBukkitEntity(), (org.bukkit.entity.AbstractVillager) abstractVillager.getBukkitEntity(), merchantOffer.asBukkit(), true, true);
+            } else if (this.merchant instanceof org.bukkit.craftbukkit.inventory.CraftMerchantCustom.MinecraftMerchant) {
+                event = new io.papermc.paper.event.player.PlayerPurchaseEvent(serverPlayer.getBukkitEntity(), merchantOffer.asBukkit(), false, true);
+            }
+            if (event != null) {
+                if (!event.callEvent()) {
+                    stack.setCount(0);
+                    event.getPlayer().updateInventory();
+                    return;
+                }
+                merchantOffer = org.bukkit.craftbukkit.inventory.CraftMerchantRecipe.fromBukkit(event.getTrade()).toMinecraft();
+            }
+        }
+        this.checkTakeAchievements(stack);
+        // Paper end
         if (merchantOffer != null) {
             ItemStack itemStack = this.slots.getItem(0);
             ItemStack itemStack2 = this.slots.getItem(1);
             if (merchantOffer.take(itemStack, itemStack2) || merchantOffer.take(itemStack2, itemStack)) {
-                this.merchant.notifyTrade(merchantOffer);
+                this.merchant.processTrade(merchantOffer, event); // Paper
                 player.awardStat(Stats.TRADED_WITH_VILLAGER);
                 this.slots.setItem(0, itemStack);
                 this.slots.setItem(1, itemStack2);
diff --git a/src/main/java/net/minecraft/world/item/trading/Merchant.java b/src/main/java/net/minecraft/world/item/trading/Merchant.java
index d41f44ed2e497ba3373d170c08488b49e88334c4..d3a99ba6f3085ad12b67ddc94cc4ab393ec7ecbe 100644
--- a/src/main/java/net/minecraft/world/item/trading/Merchant.java
+++ b/src/main/java/net/minecraft/world/item/trading/Merchant.java
@@ -20,6 +20,7 @@ public interface Merchant {
 
     void overrideOffers(MerchantOffers offers);
 
+    default void processTrade(MerchantOffer merchantRecipe, @Nullable io.papermc.paper.event.player.PlayerPurchaseEvent event) { this.notifyTrade(merchantRecipe); } // Paper
     void notifyTrade(MerchantOffer offer);
 
     void notifyTradeUpdated(ItemStack stack);
diff --git a/src/main/java/org/bukkit/craftbukkit/inventory/CraftMerchantCustom.java b/src/main/java/org/bukkit/craftbukkit/inventory/CraftMerchantCustom.java
index 552851cff3678d605428866999951fefd4375d7a..9f6ce6c4cba1e6fe83fbac129da990748681ce94 100644
--- a/src/main/java/org/bukkit/craftbukkit/inventory/CraftMerchantCustom.java
+++ b/src/main/java/org/bukkit/craftbukkit/inventory/CraftMerchantCustom.java
@@ -79,10 +79,25 @@ public class CraftMerchantCustom extends CraftMerchant {
             return this.trades;
         }
 
+        // Paper start
+        @Override
+        public void processTrade(MerchantOffer merchantRecipe, @javax.annotation.Nullable io.papermc.paper.event.player.PlayerPurchaseEvent event) { // The MerchantRecipe passed in here is the one set by the PlayerPurchaseEvent
+            /** Based on {@link net.minecraft.world.entity.npc.AbstractVillager#processTrade(MerchantOffer, io.papermc.paper.event.player.PlayerPurchaseEvent)} */
+            if (getTradingPlayer() instanceof net.minecraft.server.level.ServerPlayer) {
+                if (event == null || event.willIncreaseTradeUses()) {
+                    merchantRecipe.increaseUses();
+                }
+                if (event == null || event.isRewardingExp()) {
+                    this.tradingWorld.addFreshEntity(new net.minecraft.world.entity.ExperienceOrb(tradingWorld, tradingPlayer.getX(), tradingPlayer.getY(), tradingPlayer.getZ(), merchantRecipe.getXp(), org.bukkit.entity.ExperienceOrb.SpawnReason.VILLAGER_TRADE, this.tradingPlayer, null));
+                }
+            }
+            this.notifyTrade(merchantRecipe);
+        }
+        // Paper end
         @Override
         public void notifyTrade(MerchantOffer offer) {
             // increase recipe's uses
-            offer.increaseUses();
+            // offer.increaseUses(); // Paper - handled above in processTrade
         }
 
         @Override
