Code/net/minecraft/world/level/block/WitherSkullBlock.java

package net.minecraft.world.level.block;

import com.mojang.serialization.MapCodec;
import javax.annotation.Nullable;
import net.minecraft.advancements.CriteriaTriggers;
import net.minecraft.core.BlockPos;
import net.minecraft.core.Direction;
import net.minecraft.server.level.ServerPlayer;
import net.minecraft.tags.BlockTags;
import net.minecraft.world.Difficulty;
import net.minecraft.world.entity.EntitySpawnReason;
import net.minecraft.world.entity.EntityType;
import net.minecraft.world.entity.LivingEntity;
import net.minecraft.world.entity.boss.wither.WitherBoss;
import net.minecraft.world.item.ItemStack;
import net.minecraft.world.item.Items;
import net.minecraft.world.level.Level;
import net.minecraft.world.level.block.entity.SkullBlockEntity;
import net.minecraft.world.level.block.state.BlockBehaviour;
import net.minecraft.world.level.block.state.BlockState;
import net.minecraft.world.level.block.state.pattern.BlockInWorld;
import net.minecraft.world.level.block.state.pattern.BlockPattern;
import net.minecraft.world.level.block.state.pattern.BlockPatternBuilder;
import net.minecraft.world.level.block.state.predicate.BlockStatePredicate;

public class WitherSkullBlock extends SkullBlock {
    public static final MapCodec<WitherSkullBlock> CODEC = simpleCodec(WitherSkullBlock::new);
    @Nullable
    private static BlockPattern witherPatternFull;
    @Nullable
    private static BlockPattern witherPatternBase;

    @Override
    public MapCodec<WitherSkullBlock> codec() {
        return CODEC;
    }

    protected WitherSkullBlock(BlockBehaviour.Properties p_58254_) {
        super(SkullBlock.Types.WITHER_SKELETON, p_58254_);
    }

    @Override
    public void setPlacedBy(Level p_58260_, BlockPos p_58261_, BlockState p_58262_, @Nullable LivingEntity p_58263_, ItemStack p_58264_) {
        checkSpawn(p_58260_, p_58261_);
    }

    public static void checkSpawn(Level p_335323_, BlockPos p_328733_) {
        if (p_335323_.getBlockEntity(p_328733_) instanceof SkullBlockEntity skullblockentity) {
            checkSpawn(p_335323_, p_328733_, skullblockentity);
        }
    }

    public static void checkSpawn(Level p_58256_, BlockPos p_58257_, SkullBlockEntity p_58258_) {
        if (!p_58256_.isClientSide) {
            BlockState blockstate = p_58258_.getBlockState();
            boolean flag = blockstate.is(Blocks.WITHER_SKELETON_SKULL) || blockstate.is(Blocks.WITHER_SKELETON_WALL_SKULL);
            if (flag && p_58257_.getY() >= p_58256_.getMinY() && p_58256_.getDifficulty() != Difficulty.PEACEFUL) {
                BlockPattern.BlockPatternMatch blockpattern$blockpatternmatch = getOrCreateWitherFull().find(p_58256_, p_58257_);
                if (blockpattern$blockpatternmatch != null) {
                    WitherBoss witherboss = EntityType.WITHER.create(p_58256_, EntitySpawnReason.TRIGGERED);
                    if (witherboss != null) {
                        CarvedPumpkinBlock.clearPatternBlocks(p_58256_, blockpattern$blockpatternmatch);
                        BlockPos blockpos = blockpattern$blockpatternmatch.getBlock(1, 2, 0).getPos();
                        witherboss.snapTo(
                            blockpos.getX() + 0.5,
                            blockpos.getY() + 0.55,
                            blockpos.getZ() + 0.5,
                            blockpattern$blockpatternmatch.getForwards().getAxis() == Direction.Axis.X ? 0.0F : 90.0F,
                            0.0F
                        );
                        witherboss.yBodyRot = blockpattern$blockpatternmatch.getForwards().getAxis() == Direction.Axis.X ? 0.0F : 90.0F;
                        witherboss.makeInvulnerable();

                        for (ServerPlayer serverplayer : p_58256_.getEntitiesOfClass(ServerPlayer.class, witherboss.getBoundingBox().inflate(50.0))) {
                            CriteriaTriggers.SUMMONED_ENTITY.trigger(serverplayer, witherboss);
                        }

                        p_58256_.addFreshEntity(witherboss);
                        CarvedPumpkinBlock.updatePatternBlocks(p_58256_, blockpattern$blockpatternmatch);
                    }
                }
            }
        }
    }

    public static boolean canSpawnMob(Level p_58268_, BlockPos p_58269_, ItemStack p_58270_) {
        return p_58270_.is(Items.WITHER_SKELETON_SKULL)
                && p_58269_.getY() >= p_58268_.getMinY() + 2
                && p_58268_.getDifficulty() != Difficulty.PEACEFUL
                && !p_58268_.isClientSide
            ? getOrCreateWitherBase().find(p_58268_, p_58269_) != null
            : false;
    }

    private static BlockPattern getOrCreateWitherFull() {
        if (witherPatternFull == null) {
            witherPatternFull = BlockPatternBuilder.start()
                .aisle("^^^", "###", "~#~")
                .where('#', p_58272_ -> p_58272_.getState().is(BlockTags.WITHER_SUMMON_BASE_BLOCKS))
                .where('^', BlockInWorld.hasState(BlockStatePredicate.forBlock(Blocks.WITHER_SKELETON_SKULL).or(BlockStatePredicate.forBlock(Blocks.WITHER_SKELETON_WALL_SKULL))))
                .where('~', p_360475_ -> p_360475_.getState().isAir())
                .build();
        }

        return witherPatternFull;
    }

    private static BlockPattern getOrCreateWitherBase() {
        if (witherPatternBase == null) {
            witherPatternBase = BlockPatternBuilder.start()
                .aisle("   ", "###", "~#~")
                .where('#', p_58266_ -> p_58266_.getState().is(BlockTags.WITHER_SUMMON_BASE_BLOCKS))
                .where('~', p_360474_ -> p_360474_.getState().isAir())
                .build();
        }

        return witherPatternBase;
    }
}