Add example code to get writable block registry during bootstrap

Author: UnknownSilicon

api/src/main/java/parallelmc/parallelutils/ParallelUtilsBootstrapper.java

@@ -3,16 +3,64 @@
 import io.papermc.paper.plugin.bootstrap.BootstrapContext;
 import io.papermc.paper.plugin.bootstrap.PluginBootstrap;
 import io.papermc.paper.plugin.bootstrap.PluginProviderContext;
+import io.papermc.paper.registry.RegistryAccess;
+import io.papermc.paper.registry.event.RegistryEvents;
+import io.papermc.paper.registry.keys.EnchantmentKeys;
+import net.minecraft.core.Holder;
+import net.minecraft.core.MappedRegistry;
+import net.minecraft.core.WritableRegistry;
+import net.minecraft.core.registries.BuiltInRegistries;
+import net.minecraft.core.registries.Registries;
+import net.minecraft.resources.ResourceKey;
+import net.minecraft.world.level.block.Block;
 import org.bukkit.plugin.java.JavaPlugin;
+import org.jetbrains.annotations.Nullable;
+
+import java.lang.reflect.Field;
+import java.util.Map;
 
 public class ParallelUtilsBootstrapper implements PluginBootstrap {
     @Override
     public void bootstrap(BootstrapContext context) {
+        MappedRegistry<WritableRegistry<?>> writable_registry = (MappedRegistry<WritableRegistry<?>>) getPrivateField("WRITABLE_REGISTRY", BuiltInRegistries.class, null, WritableRegistry.class);
+
+        Map<WritableRegistry<?>, Holder.Reference<WritableRegistry<?>>> byValue = getPrivateField("byValue", MappedRegistry.class, writable_registry, Map.class);
+
+        WritableRegistry<Block> blockRegistry = null;
+
+        for (WritableRegistry i : byValue.keySet()) {
+            if (String.valueOf(i.key().location()).equals(String.valueOf(Registries.BLOCK.location()))) {
+                blockRegistry = i;
+                break;
+            }
+        }
+
+        if (blockRegistry == null) {
+            return;
+        }
 
     }
 
     @Override
     public JavaPlugin createPlugin(PluginProviderContext context) {
         return PluginBootstrap.super.createPlugin(context);
     }
+
+    @Nullable
+    public static <T, U> U getPrivateField(String fieldName, Class<T> clazz, T object, Class<U> retClazz) throws ClassCastException{
+        Field field;
+
+        try {
+            field = clazz.getDeclaredField(fieldName);
+
+            field.setAccessible(true);
+
+            Object o = field.get(object);
+
+            return (U) o;
+        } catch (NoSuchFieldException | IllegalAccessException e) {
+            e.printStackTrace();
+            return null;
+        }
+    }
 }