Code/net/minecraft/world/entity/ai/behavior/TradeWithVillager.java

package net.minecraft.world.entity.ai.behavior;

import com.google.common.collect.ImmutableMap;
import com.google.common.collect.ImmutableSet;
import java.util.Set;
import java.util.stream.Collectors;
import net.minecraft.server.level.ServerLevel;
import net.minecraft.world.SimpleContainer;
import net.minecraft.world.entity.EntityType;
import net.minecraft.world.entity.LivingEntity;
import net.minecraft.world.entity.ai.memory.MemoryModuleType;
import net.minecraft.world.entity.ai.memory.MemoryStatus;
import net.minecraft.world.entity.npc.Villager;
import net.minecraft.world.entity.npc.VillagerProfession;
import net.minecraft.world.item.Item;
import net.minecraft.world.item.ItemStack;
import net.minecraft.world.item.Items;

public class TradeWithVillager extends Behavior<Villager> {
    private Set<Item> trades = ImmutableSet.of();

    public TradeWithVillager() {
        super(ImmutableMap.of(MemoryModuleType.INTERACTION_TARGET, MemoryStatus.VALUE_PRESENT, MemoryModuleType.NEAREST_VISIBLE_LIVING_ENTITIES, MemoryStatus.VALUE_PRESENT));
    }

    protected boolean checkExtraStartConditions(ServerLevel p_24416_, Villager p_24417_) {
        return BehaviorUtils.targetIsValid(p_24417_.getBrain(), MemoryModuleType.INTERACTION_TARGET, EntityType.VILLAGER);
    }

    protected boolean canStillUse(ServerLevel p_24419_, Villager p_24420_, long p_24421_) {
        return this.checkExtraStartConditions(p_24419_, p_24420_);
    }

    protected void start(ServerLevel p_24437_, Villager p_24438_, long p_24439_) {
        Villager villager = (Villager)p_24438_.getBrain().getMemory(MemoryModuleType.INTERACTION_TARGET).get();
        BehaviorUtils.lockGazeAndWalkToEachOther(p_24438_, villager, 0.5F, 2);
        this.trades = figureOutWhatIAmWillingToTrade(p_24438_, villager);
    }

    protected void tick(ServerLevel p_24445_, Villager p_24446_, long p_24447_) {
        Villager villager = (Villager)p_24446_.getBrain().getMemory(MemoryModuleType.INTERACTION_TARGET).get();
        if (!(p_24446_.distanceToSqr(villager) > 5.0)) {
            BehaviorUtils.lockGazeAndWalkToEachOther(p_24446_, villager, 0.5F, 2);
            p_24446_.gossip(p_24445_, villager, p_24447_);
            boolean flag = p_24446_.getVillagerData().profession().is(VillagerProfession.FARMER);
            if (p_24446_.hasExcessFood() && (flag || villager.wantsMoreFood())) {
                throwHalfStack(p_24446_, Villager.FOOD_POINTS.keySet(), villager);
            }

            if (flag && p_24446_.getInventory().countItem(Items.WHEAT) > Items.WHEAT.getDefaultMaxStackSize() / 2) {
                throwHalfStack(p_24446_, ImmutableSet.of(Items.WHEAT), villager);
            }

            if (!this.trades.isEmpty() && p_24446_.getInventory().hasAnyOf(this.trades)) {
                throwHalfStack(p_24446_, this.trades, villager);
            }
        }
    }

    protected void stop(ServerLevel p_24453_, Villager p_24454_, long p_24455_) {
        p_24454_.getBrain().eraseMemory(MemoryModuleType.INTERACTION_TARGET);
    }

    private static Set<Item> figureOutWhatIAmWillingToTrade(Villager p_24423_, Villager p_24424_) {
        ImmutableSet<Item> immutableset = p_24424_.getVillagerData().profession().value().requestedItems();
        ImmutableSet<Item> immutableset1 = p_24423_.getVillagerData().profession().value().requestedItems();
        return immutableset.stream().filter(p_24431_ -> !immutableset1.contains(p_24431_)).collect(Collectors.toSet());
    }

    private static void throwHalfStack(Villager p_24426_, Set<Item> p_24427_, LivingEntity p_24428_) {
        SimpleContainer simplecontainer = p_24426_.getInventory();
        ItemStack itemstack = ItemStack.EMPTY;
        int i = 0;

        while (i < simplecontainer.getContainerSize()) {
            ItemStack itemstack1;
            Item item;
            int j;
            label28: {
                itemstack1 = simplecontainer.getItem(i);
                if (!itemstack1.isEmpty()) {
                    item = itemstack1.getItem();
                    if (p_24427_.contains(item)) {
                        if (itemstack1.getCount() > itemstack1.getMaxStackSize() / 2) {
                            j = itemstack1.getCount() / 2;
                            break label28;
                        }

                        if (itemstack1.getCount() > 24) {
                            j = itemstack1.getCount() - 24;
                            break label28;
                        }
                    }
                }

                i++;
                continue;
            }

            itemstack1.shrink(j);
            itemstack = new ItemStack(item, j);
            break;
        }

        if (!itemstack.isEmpty()) {
            BehaviorUtils.throwItem(p_24426_, itemstack, p_24428_.position());
        }
    }
}