README.txt

Yes, this is all registered
Yes, this is all added to the biomes
No, the create method does not work

TestStructure.java

package com.bytelaw.bytesstructures.feature.structure;

import com.google.common.collect.Lists;
import com.mojang.datafixers.Dynamic;
import net.minecraft.util.math.BlockPos;
import net.minecraft.util.math.ChunkPos;
import net.minecraft.util.math.MutableBoundingBox;
import net.minecraft.world.biome.Biome;
import net.minecraft.world.biome.BiomeManager;
import net.minecraft.world.gen.ChunkGenerator;
import net.minecraft.world.gen.Heightmap;
import net.minecraft.world.gen.feature.ProbabilityConfig;
import net.minecraft.world.gen.feature.structure.Structure;
import net.minecraft.world.gen.feature.structure.StructureStart;
import net.minecraft.world.gen.feature.template.TemplateManager;
import net.minecraftforge.registries.ForgeRegistries;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;

import java.util.List;
import java.util.Random;
import java.util.function.Function;

public class TestStructure extends AbstractStructure<ProbabilityConfig> {
    private static final Logger LOGGER = LogManager.getLogger();

    public TestStructure(Function<Dynamic<?>, ? extends ProbabilityConfig> configFactoryIn) {
        super(configFactoryIn);
    }

    @Override
    public List<Biome> getBiomesToSpawnAt() {
        return Lists.newArrayList(ForgeRegistries.BIOMES.getValues());
    }

    @Override
    protected int getSeedModifier() {
        return 165745293;
    }

    @Override
    public IStartFactory getStartFactory() {
        return Start::new;
    }

    @Override
    public String getStructureName() {
        return "bytesstructures:test_structure";
    }

    @Override
    public int getSize() {
        return 2;
    }

    @Override
    public boolean canBeGenerated(BiomeManager biomeManagerIn, ChunkGenerator<?> generatorIn, Random randIn, int chunkX, int chunkZ, Biome biomeIn) {
        ChunkPos chunkpos = this.getStartPositionForPosition(generatorIn, randIn, chunkX, chunkZ, 0, 0);
        if (chunkX == chunkpos.x && chunkZ == chunkpos.z) {
            int i = chunkX >> 4;
            int j = chunkZ >> 4;
            randIn.setSeed((long)(i ^ j << 4) ^ generatorIn.getSeed());
            randIn.nextInt();
            if (randIn.nextInt(5) != 0) {
                return false;
            }

            return generatorIn.hasStructure(biomeIn, this);
        }

        return false;
    }

    public static class Start extends StructureStart {
        public Start(Structure<?> structure, int cx, int cz, MutableBoundingBox boundingBox, int references, long seed) {
            super(structure, cx, cz, boundingBox, references, seed);
        }

        @Override
        public void init(ChunkGenerator<?> generator, TemplateManager templateManagerIn, int chunkX, int chunkZ, Biome biomeIn) {
            int i = chunkX * 16;
            int j = chunkZ * 16;

            int k = generator.func_222531_c(i, j, Heightmap.Type.WORLD_SURFACE_WG);
            BlockPos pos = new BlockPos(i, k, j);

            TestStructurePieces.addStructurePieces(templateManagerIn, pos, this.components);
            this.recalculateStructureSize();
        }
    }
}

TestStructurePieces.java

package com.bytelaw.bytesstructures.feature.structure;

import com.bytelaw.bytesstructures.BytesStructures;
import net.minecraft.nbt.CompoundNBT;
import net.minecraft.tileentity.ChestTileEntity;
import net.minecraft.tileentity.TileEntity;
import net.minecraft.util.Mirror;
import net.minecraft.util.ResourceLocation;
import net.minecraft.util.Rotation;
import net.minecraft.util.math.BlockPos;
import net.minecraft.util.math.ChunkPos;
import net.minecraft.util.math.MutableBoundingBox;
import net.minecraft.world.IWorld;
import net.minecraft.world.gen.ChunkGenerator;
import net.minecraft.world.gen.Heightmap;
import net.minecraft.world.gen.feature.structure.StructurePiece;
import net.minecraft.world.gen.feature.structure.TemplateStructurePiece;
import net.minecraft.world.gen.feature.template.BlockIgnoreStructureProcessor;
import net.minecraft.world.gen.feature.template.PlacementSettings;
import net.minecraft.world.gen.feature.template.Template;
import net.minecraft.world.gen.feature.template.TemplateManager;
import net.minecraft.world.storage.loot.LootTables;

import java.util.List;
import java.util.Random;

public class TestStructurePieces {
    private static final ResourceLocation
            LOCATION = BytesStructures.resource("teststructureroom"),
            LOCATION_2 = BytesStructures.resource("teststructureroom2");

    public static void addStructurePieces(TemplateManager manager, BlockPos pos, List<StructurePiece> pieces) {
        pieces.add(new Piece(pos, manager));
        pieces.add(new AncientPiece(pos, manager));
    }

    public static class Piece extends TemplateStructurePiece {
        public Piece(BlockPos pos, TemplateManager manager) {
            super(BytesFeatures.TEST_STRUCTURE_ROOM, 0);
            this.templatePosition = new BlockPos(pos.getX(), pos.getY(), pos.getZ());
            setup(manager);
        }

        public Piece(TemplateManager manager, CompoundNBT nbt) {
            super(BytesFeatures.TEST_STRUCTURE_ROOM, nbt);
            setup(manager);
        }

        protected void setup(TemplateManager manager) {
            Template template = manager.getTemplateDefaulted(LOCATION);
            PlacementSettings settings = new PlacementSettings().setRotation(Rotation.NONE).setMirror(Mirror.NONE).setCenterOffset(BlockPos.ZERO).addProcessor(BlockIgnoreStructureProcessor.STRUCTURE_BLOCK);
            setup(template, this.templatePosition, settings);
        }

        @Override
        public boolean create(IWorld worldIn, ChunkGenerator<?> chunkGeneratorIn, Random randomIn, MutableBoundingBox mutableBoundingBoxIn, ChunkPos chunkPosIn) {
            PlacementSettings placementsettings = (new PlacementSettings()).setRotation(Rotation.NONE).setMirror(Mirror.NONE).setCenterOffset(BlockPos.ZERO).addProcessor(BlockIgnoreStructureProcessor.STRUCTURE_BLOCK);
            BlockPos blockpos1 = this.templatePosition.add(Template.transformedBlockPos(placementsettings, new BlockPos(3, 0, 0)));
            int strucHeight = worldIn.getHeight(Heightmap.Type.WORLD_SURFACE_WG, blockpos1.getX(), blockpos1.getZ());
            this.templatePosition = this.templatePosition.add(0, strucHeight, 0);
            return super.create(worldIn, chunkGeneratorIn, randomIn, boundingBox, chunkPosIn);
        }

        @Override
        protected void handleDataMarker(String function, BlockPos pos, IWorld worldIn, Random rand, MutableBoundingBox sbb) {
            if("chest".equals(function)) {
                TileEntity te = worldIn.getTileEntity(pos);
                if(te instanceof ChestTileEntity) {
                    ((ChestTileEntity)te).setLootTable(LootTables.CHESTS_BURIED_TREASURE, rand.nextLong());
                }
            }
        }
    }

    public static class AncientPiece extends TemplateStructurePiece {
        public AncientPiece(BlockPos pos, TemplateManager manager) {
            super(BytesFeatures.TEST_STRUCTURE_ANCIENT_ROOM, 1);
            this.templatePosition = new BlockPos(pos.getX(), pos.getY(), pos.getZ());
            setup(manager);
        }

        public AncientPiece(TemplateManager manager, CompoundNBT nbt) {
            super(BytesFeatures.TEST_STRUCTURE_ANCIENT_ROOM, nbt);
            setup(manager);
        }

        protected void setup(TemplateManager manager) {
            Template template = manager.getTemplateDefaulted(LOCATION);
            PlacementSettings settings = new PlacementSettings().setRotation(Rotation.NONE).setMirror(Mirror.NONE).setCenterOffset(BlockPos.ZERO).addProcessor(BlockIgnoreStructureProcessor.STRUCTURE_BLOCK);
            setup(template, this.templatePosition, settings);
        }

        @Override
        public boolean create(IWorld worldIn, ChunkGenerator<?> chunkGeneratorIn, Random randomIn, MutableBoundingBox mutableBoundingBoxIn, ChunkPos chunkPosIn) {
            PlacementSettings placementsettings = (new PlacementSettings()).setRotation(Rotation.NONE).setMirror(Mirror.NONE).setCenterOffset(BlockPos.ZERO).addProcessor(BlockIgnoreStructureProcessor.STRUCTURE_BLOCK);
            BlockPos blockpos1 = this.templatePosition.add(Template.transformedBlockPos(placementsettings, new BlockPos(3, 0, 0)));
            int strucHeight = worldIn.getHeight(Heightmap.Type.WORLD_SURFACE_WG, blockpos1.getX(), blockpos1.getZ());
            this.templatePosition = this.templatePosition.add(0, strucHeight, 0);
            return super.create(worldIn, chunkGeneratorIn, randomIn, boundingBox, chunkPosIn);
        }

        @Override
        protected void handleDataMarker(String function, BlockPos pos, IWorld worldIn, Random rand, MutableBoundingBox sbb) {
            if("chest".equals(function)) {
                TileEntity te = worldIn.getTileEntity(pos);
                if(te instanceof ChestTileEntity) {
                    ((ChestTileEntity)te).setLootTable(LootTables.CHESTS_BURIED_TREASURE, rand.nextLong());
                }
            }
        }
    }
}