fix mobs not spawning in structures

src/main/java/carpet/utils/SpawnOverrides.java

@@ -0,0 +1,74 @@
+package carpet.utils;
+
+import carpet.CarpetSettings;
+import it.unimi.dsi.fastutil.longs.LongSet;
+import net.minecraft.core.BlockPos;
+import net.minecraft.core.Holder;
+import net.minecraft.data.worldgen.StructureFeatures;
+import net.minecraft.util.random.WeightedRandomList;
+import net.minecraft.world.entity.EntityType;
+import net.minecraft.world.entity.MobCategory;
+import net.minecraft.world.level.StructureFeatureManager;
+import net.minecraft.world.level.biome.MobSpawnSettings;
+import net.minecraft.world.level.levelgen.feature.ConfiguredStructureFeature;
+import net.minecraft.world.level.levelgen.feature.StructureFeature;
+import net.minecraft.world.level.levelgen.structure.StructureSpawnOverride;
+import net.minecraft.world.level.levelgen.structure.StructureStart;
+import org.apache.commons.lang3.tuple.Pair;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.function.BooleanSupplier;
+
+public class SpawnOverrides {
+    final private static Map<Pair<MobCategory, StructureFeature<?>>, Pair<BooleanSupplier, StructureSpawnOverride>> carpetOverrides = new HashMap<>();
+    static {
+        addOverride(() -> CarpetSettings.huskSpawningInTemples, MobCategory.MONSTER, StructureFeatures.DESERT_PYRAMID, StructureSpawnOverride.BoundingBoxType.STRUCTURE,
+                        WeightedRandomList.create(new MobSpawnSettings.SpawnerData(EntityType.HUSK, 1, 1, 1))
+        );
+        addOverride(() -> CarpetSettings.shulkerSpawningInEndCities, MobCategory.MONSTER, StructureFeatures.END_CITY, StructureSpawnOverride.BoundingBoxType.PIECE,
+                WeightedRandomList.create(new MobSpawnSettings.SpawnerData(EntityType.SHULKER, 10, 4, 4))
+        );
+        addOverride(() -> CarpetSettings.piglinsSpawningInBastions, MobCategory.MONSTER, StructureFeatures.BASTION_REMNANT, StructureSpawnOverride.BoundingBoxType.PIECE,
+                WeightedRandomList.create(
+                        new MobSpawnSettings.SpawnerData(EntityType.PIGLIN_BRUTE, 5, 1, 2),
+                        new MobSpawnSettings.SpawnerData(EntityType.PIGLIN, 10, 2, 4),
+                        new MobSpawnSettings.SpawnerData(EntityType.HOGLIN, 2, 1, 2)
+                )
+        );
+
+    }
+
+    public static void addOverride(BooleanSupplier when, MobCategory cat, Holder<ConfiguredStructureFeature<?,?>> poo,
+                                   StructureSpawnOverride.BoundingBoxType type, WeightedRandomList<MobSpawnSettings.SpawnerData> spawns)
+    {
+        carpetOverrides.put(Pair.of(cat, poo.value().feature), Pair.of(when, new StructureSpawnOverride(type, spawns)));
+    }
+
+    public static WeightedRandomList<MobSpawnSettings.SpawnerData> test(StructureFeatureManager structureFeatureManager, LongSet foo,
+            MobCategory cat, ConfiguredStructureFeature<?,?> confExisting, BlockPos where)
+    {
+        final Pair<BooleanSupplier, StructureSpawnOverride> spawnData = carpetOverrides.get(Pair.of(cat, confExisting.feature));
+        if (spawnData == null || !spawnData.getKey().getAsBoolean()) return null;
+        StructureSpawnOverride override = spawnData.getRight();
+        if (override.boundingBox() == StructureSpawnOverride.BoundingBoxType.STRUCTURE)
+        {
+            if (structureFeatureManager.getStructureAt(where, confExisting).isValid())
+                return override.spawns();
+        }
+        else
+        {
+            List<StructureStart> starts = new ArrayList<>(1);
+            structureFeatureManager.fillStartsForFeature(confExisting, foo, starts::add);
+            for (StructureStart start: starts)
+            {
+                if (start != null && start.isValid() && structureFeatureManager.structureHasPieceAt(where, start)) {
+                    return override.spawns();
+                }
+            }
+        }
+        return null;
+    }
+}