Store additional spawn-information along with an entity

src/main/java/ru/bclib/api/biomes/BCLBiomeBuilder.java

@@ -30,6 +30,7 @@ import net.minecraft.world.level.levelgen.SurfaceRules;
 import net.minecraft.world.level.levelgen.carver.ConfiguredWorldCarver;
 import net.minecraft.world.level.levelgen.feature.ConfiguredStructureFeature;
 import net.minecraft.world.level.levelgen.placement.PlacedFeature;
+import ru.bclib.entity.BCLEntityWrapper;
 import ru.bclib.util.ColorUtil;
 import ru.bclib.world.biomes.BCLBiome;
 import ru.bclib.world.features.BCLFeature;
@@ -131,6 +132,22 @@ public class BCLBiomeBuilder {
 		return this;
 	}
 	
+	/**
+	 * Adds mob spawning to biome.
+	 * @param wrapper {@link BCLEntityWrapper} mob type.
+	 * @param weight spawn weight.
+	 * @param minGroupCount minimum mobs in group.
+	 * @param maxGroupCount maximum mobs in group.
+	 * @return same {@link BCLBiomeBuilder} instance.
+	 */
+	public <M extends Mob> BCLBiomeBuilder spawn(BCLEntityWrapper<M> wrapper, int weight, int minGroupCount, int maxGroupCount) {
+		if (wrapper.canSpawn()) {
+			return spawn(wrapper.type(), weight, minGroupCount, maxGroupCount);
+		}
+		
+		return this;
+	}
+	
 	/**
 	 * Adds ambient particles to thr biome.
 	 * @param particle {@link ParticleOptions} particles (or {@link net.minecraft.core.particles.ParticleType}).

src/main/java/ru/bclib/api/biomes/BiomeAPI.java

@@ -61,6 +61,7 @@ import net.minecraft.world.level.levelgen.placement.PlacedFeature;
 import org.apache.commons.lang3.mutable.MutableInt;
 import ru.bclib.BCLib;
 import ru.bclib.config.Configs;
+import ru.bclib.entity.BCLEntityWrapper;
 import ru.bclib.interfaces.SurfaceMaterialProvider;
 import ru.bclib.interfaces.SurfaceProvider;
 import ru.bclib.interfaces.SurfaceRuleProvider;
@@ -626,6 +627,10 @@ public class BiomeAPI {
 	 * @param structure {@link ConfiguredStructureFeature} to add.
 	 */
 	public static void addBiomeStructure(ResourceKey biomeKey, ConfiguredStructureFeature structure) {
+		if (biomeKey==null){
+			BCLib.LOGGER.error("null is not a valid biomeKey for " + structure);
+			return;
+		}
 		changeStructureStarts(structureMap -> {
 			Multimap<ConfiguredStructureFeature<?, ?>, ResourceKey<Biome>> configuredMap = structureMap.computeIfAbsent(structure.feature, k -> HashMultimap.create());
 			
@@ -699,6 +704,20 @@ public class BiomeAPI {
 		return SURFACE_RULES.get(biomeID);
 	}
 	
+	/**
+	 * Adds mob spawning to specified biome.
+	 * @param biome {@link Biome} to add mob spawning.
+	 * @param entityType {@link BCLEntityWrapper} mob type.
+	 * @param weight spawn weight.
+	 * @param minGroupCount minimum mobs in group.
+	 * @param maxGroupCount maximum mobs in group.
+	 */
+	public static <M extends Mob> void addBiomeMobSpawn(Biome biome, BCLEntityWrapper<M> entityType, int weight, int minGroupCount, int maxGroupCount) {
+		if (entityType.canSpawn()){
+			addBiomeMobSpawn(biome, entityType.type(), weight, minGroupCount, maxGroupCount);
+		}
+	}
+	
 	/**
 	 * Adds mob spawning to specified biome.
 	 * @param biome {@link Biome} to add mob spawning.

src/main/java/ru/bclib/api/spawning/SpawnRuleBuilder.java

@@ -13,6 +13,7 @@ import net.minecraft.world.entity.SpawnPlacements.Type;
 import net.minecraft.world.level.block.Block;
 import net.minecraft.world.level.levelgen.Heightmap.Types;
 import net.minecraft.world.phys.AABB;
+import ru.bclib.entity.BCLEntityWrapper;
 import ru.bclib.interfaces.SpawnRule;
 
 import java.util.Arrays;
@@ -33,6 +34,7 @@ public class SpawnRuleBuilder<M extends Mob> {
 	
 	/**
 	 * Starts new rule building process.
+	 * @param entityType The entity you want to build a rule for
 	 * @return prepared {@link SpawnRuleBuilder} instance.
 	 */
 	public static SpawnRuleBuilder start(EntityType<? extends Mob> entityType) {
@@ -41,6 +43,15 @@ public class SpawnRuleBuilder<M extends Mob> {
 		return INSTANCE;
 	}
 	
+	/**
+	 * Starts new rule building process.
+	 * @param entityType The entity you want to build a rule for
+	 * @return prepared {@link SpawnRuleBuilder} instance.
+	 */
+	public static SpawnRuleBuilder start(BCLEntityWrapper<? extends Mob> entityType) {
+		return start(entityType.type());
+	}
+	
 	/**
 	 * Stop entity spawn on peaceful {@link Difficulty}
 	 * @return same {@link SpawnRuleBuilder} instance.

src/main/java/ru/bclib/entity/BCLEntityWrapper.java

@@ -0,0 +1,7 @@
+package ru.bclib.entity;
+
+import net.minecraft.world.entity.Entity;
+import net.minecraft.world.entity.EntityType;
+
+public record BCLEntityWrapper<T extends Entity>(EntityType<T> type, boolean canSpawn)  {
+}

src/main/java/ru/bclib/world/biomes/BCLBiome.java

@@ -11,6 +11,7 @@ import net.minecraft.world.level.levelgen.SurfaceRules;
 import net.minecraft.world.level.levelgen.SurfaceRules.RuleSource;
 import net.minecraft.world.level.levelgen.feature.ConfiguredStructureFeature;
 import org.jetbrains.annotations.Nullable;
+import ru.bclib.BCLib;
 import ru.bclib.api.biomes.BiomeAPI;
 import ru.bclib.util.WeightedList;
 
@@ -226,6 +227,9 @@ public class BCLBiome {
 			edge.updateActualBiomes(biomeRegistry);
 		}
 		this.actualBiome = biomeRegistry.get(biomeID);
+		if (actualBiome==null) {
+			BCLib.LOGGER.error("Unable to find actual Biome for " + biomeID);
+		}
 		
 		if (!this.structures.isEmpty()) {
 			structures.forEach(s -> BiomeAPI.addBiomeStructure(BiomeAPI.getBiomeKey(actualBiome), s));