minecraft-src/net/minecraft/world/entity/ai/behavior/ShowTradesToPlayer.java

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

import com.google.common.collect.ImmutableMap;
import com.google.common.collect.Lists;
import java.util.List;
import net.minecraft.server.level.ServerLevel;
import net.minecraft.world.entity.EntityType;
import net.minecraft.world.entity.EquipmentSlot;
import net.minecraft.world.entity.LivingEntity;
import net.minecraft.world.entity.ai.Brain;
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.item.ItemStack;
import net.minecraft.world.item.trading.MerchantOffer;
import org.jetbrains.annotations.Nullable;

public class ShowTradesToPlayer extends Behavior<Villager> {
	private static final int MAX_LOOK_TIME = 900;
	private static final int STARTING_LOOK_TIME = 40;
	@Nullable
	private ItemStack playerItemStack;
	private final List<ItemStack> displayItems = Lists.<ItemStack>newArrayList();
	private int cycleCounter;
	private int displayIndex;
	private int lookTime;

	public ShowTradesToPlayer(int minDuration, int maxDuration) {
		super(ImmutableMap.of(MemoryModuleType.INTERACTION_TARGET, MemoryStatus.VALUE_PRESENT), minDuration, maxDuration);
	}

	public boolean checkExtraStartConditions(ServerLevel level, Villager owner) {
		Brain<?> brain = owner.getBrain();
		if (brain.getMemory(MemoryModuleType.INTERACTION_TARGET).isEmpty()) {
			return false;
		} else {
			LivingEntity livingEntity = (LivingEntity)brain.getMemory(MemoryModuleType.INTERACTION_TARGET).get();
			return livingEntity.getType() == EntityType.PLAYER
				&& owner.isAlive()
				&& livingEntity.isAlive()
				&& !owner.isBaby()
				&& owner.distanceToSqr(livingEntity) <= 17.0;
		}
	}

	public boolean canStillUse(ServerLevel level, Villager entity, long gameTime) {
		return this.checkExtraStartConditions(level, entity) && this.lookTime > 0 && entity.getBrain().getMemory(MemoryModuleType.INTERACTION_TARGET).isPresent();
	}

	public void start(ServerLevel level, Villager entity, long gameTime) {
		super.start(level, entity, gameTime);
		this.lookAtTarget(entity);
		this.cycleCounter = 0;
		this.displayIndex = 0;
		this.lookTime = 40;
	}

	public void tick(ServerLevel level, Villager owner, long gameTime) {
		LivingEntity livingEntity = this.lookAtTarget(owner);
		this.findItemsToDisplay(livingEntity, owner);
		if (!this.displayItems.isEmpty()) {
			this.displayCyclingItems(owner);
		} else {
			clearHeldItem(owner);
			this.lookTime = Math.min(this.lookTime, 40);
		}

		this.lookTime--;
	}

	public void stop(ServerLevel level, Villager entity, long gameTime) {
		super.stop(level, entity, gameTime);
		entity.getBrain().eraseMemory(MemoryModuleType.INTERACTION_TARGET);
		clearHeldItem(entity);
		this.playerItemStack = null;
	}

	private void findItemsToDisplay(LivingEntity entity, Villager villager) {
		boolean bl = false;
		ItemStack itemStack = entity.getMainHandItem();
		if (this.playerItemStack == null || !ItemStack.isSameItem(this.playerItemStack, itemStack)) {
			this.playerItemStack = itemStack;
			bl = true;
			this.displayItems.clear();
		}

		if (bl && !this.playerItemStack.isEmpty()) {
			this.updateDisplayItems(villager);
			if (!this.displayItems.isEmpty()) {
				this.lookTime = 900;
				this.displayFirstItem(villager);
			}
		}
	}

	private void displayFirstItem(Villager villager) {
		displayAsHeldItem(villager, (ItemStack)this.displayItems.get(0));
	}

	private void updateDisplayItems(Villager villager) {
		for (MerchantOffer merchantOffer : villager.getOffers()) {
			if (!merchantOffer.isOutOfStock() && this.playerItemStackMatchesCostOfOffer(merchantOffer)) {
				this.displayItems.add(merchantOffer.assemble());
			}
		}
	}

	private boolean playerItemStackMatchesCostOfOffer(MerchantOffer offer) {
		return ItemStack.isSameItem(this.playerItemStack, offer.getCostA()) || ItemStack.isSameItem(this.playerItemStack, offer.getCostB());
	}

	private static void clearHeldItem(Villager villager) {
		villager.setItemSlot(EquipmentSlot.MAINHAND, ItemStack.EMPTY);
		villager.setDropChance(EquipmentSlot.MAINHAND, 0.085F);
	}

	private static void displayAsHeldItem(Villager villager, ItemStack item) {
		villager.setItemSlot(EquipmentSlot.MAINHAND, item);
		villager.setDropChance(EquipmentSlot.MAINHAND, 0.0F);
	}

	private LivingEntity lookAtTarget(Villager villager) {
		Brain<?> brain = villager.getBrain();
		LivingEntity livingEntity = (LivingEntity)brain.getMemory(MemoryModuleType.INTERACTION_TARGET).get();
		brain.setMemory(MemoryModuleType.LOOK_TARGET, new EntityTracker(livingEntity, true));
		return livingEntity;
	}

	private void displayCyclingItems(Villager villager) {
		if (this.displayItems.size() >= 2 && ++this.cycleCounter >= 40) {
			this.displayIndex++;
			this.cycleCounter = 0;
			if (this.displayIndex > this.displayItems.size() - 1) {
				this.displayIndex = 0;
			}

			displayAsHeldItem(villager, (ItemStack)this.displayItems.get(this.displayIndex));
		}
	}
}