src/game/java/net/minecraft/world/item/EndCrystalItem.java

package net.minecraft.world.item;

import java.util.List;
import net.minecraft.core.BlockPos;
import net.minecraft.server.level.ServerLevel;
import net.minecraft.world.InteractionResult;
import net.minecraft.world.entity.Entity;
import net.minecraft.world.entity.boss.enderdragon.EndCrystal;
import net.minecraft.world.item.context.UseOnContext;
import net.minecraft.world.level.Level;
import net.minecraft.world.level.block.Blocks;
import net.minecraft.world.level.block.state.BlockState;
import net.minecraft.world.level.dimension.end.EndDragonFight;
import net.minecraft.world.level.gameevent.GameEvent;
import net.minecraft.world.phys.AABB;

public class EndCrystalItem extends Item {
    public EndCrystalItem(Item.Properties p_41174_) {
        super(p_41174_);
    }

    @Override
    public InteractionResult useOn(UseOnContext p_41176_) {
        Level level = p_41176_.getLevel();
        BlockPos blockpos = p_41176_.getClickedPos();
        BlockState blockstate = level.getBlockState(blockpos);
        if (!blockstate.is(Blocks.OBSIDIAN) && !blockstate.is(Blocks.BEDROCK)) {
            return InteractionResult.FAIL;
        } else {
            BlockPos blockpos1 = blockpos.above();
            if (!level.isEmptyBlock(blockpos1)) {
                return InteractionResult.FAIL;
            } else {
                double d0 = (double)blockpos1.getX();
                double d1 = (double)blockpos1.getY();
                double d2 = (double)blockpos1.getZ();
                List<Entity> list = level.getEntities(null, new AABB(d0, d1, d2, d0 + 1.0, d1 + 2.0, d2 + 1.0));
                if (!list.isEmpty()) {
                    return InteractionResult.FAIL;
                } else {
                    if (level instanceof ServerLevel) {
                        EndCrystal endcrystal = new EndCrystal(level, d0 + 0.5, d1, d2 + 0.5);
                        endcrystal.setShowBottom(false);
                        level.addFreshEntity(endcrystal);
                        level.gameEvent(p_41176_.getPlayer(), GameEvent.ENTITY_PLACE, blockpos1);
                        EndDragonFight enddragonfight = ((ServerLevel)level).getDragonFight();
                        if (enddragonfight != null) {
                            enddragonfight.tryRespawn();
                        }
                    }

                    p_41176_.getItemInHand().shrink(1);
                    return InteractionResult.SUCCESS;
                }
            }
        }
    }
}