ECS - Asset manager pattern

AssetManager.java

/**
 * Manages reference components to assets.
 *
 * - Adds asset reference component to entities with metadata component.
 * - Reloads asset reference if removed.
 * - Removes asset reference when metadata component is removed.
 *
 * @author Daan van Yperen
 *
 * @param <A> Identifying metadata component type.
 * @param <B> Asset reference component type (typically transient).
 */
@SkipWire
public abstract class AssetManager<A extends Component, B extends Component> extends Manager {

	private final Class<A> metadataType;
	private final Class<B> referenceType;

	protected M<A> mMetadataType;
	protected M<B> mReferenceType;

	/**
	 * @param metadataType Identifying component type.
	 * @param referenceType Asset reference component type (typically transient).
	 */
	public AssetManager(Class<A> metadataType, Class<B> referenceType) {
		this.metadataType = metadataType;
		this.referenceType = referenceType;
	}

	/**
	 * Setup new asset reference component by identifying component.
	 *
	 * @param entity Altered entity.
	 * @param a Existing asset identifying component.
	 * @param b New asset reference component to setup.
	 */
	protected abstract void setup(Entity entity, A a, B b);

	@Override
	protected void setWorld(World world) {
		super.setWorld(world);

		mReferenceType = new M<>(referenceType, world);
		mMetadataType = new M<>(metadataType, world);

		listenForResolveJobs();
		listenForCleanupJobs();
	}

	/**
	 * Cause cleanup of asset reference without asset metadata.
	 */
	private void listenForCleanupJobs() {
		world.getManager(AspectSubscriptionManager.class).get(Aspect.all(referenceType).exclude(metadataType))
				.addSubscriptionListener(new EntitySubscription.SubscriptionListener() {
					@Override
					public void inserted(IntBag entities) {
						int[] ids = entities.getData();
						for (int i = 0, s = entities.size(); s > i; i++) {
							remove(ids[i]);
						}
					}

					@Override
					public void removed(IntBag entities) {
					}
				});
	}

	/**
	 * Cause population of missing references.
	 */
	private void listenForResolveJobs() {
		world.getManager(AspectSubscriptionManager.class).get(Aspect.all(metadataType).exclude(referenceType))
				.addSubscriptionListener(new EntitySubscription.SubscriptionListener() {
					@Override
					public void inserted(IntBag entities) {
						int[] ids = entities.getData();
						for (int i = 0, s = entities.size(); s > i; i++) {
							create(ids[i]);
						}
					}

					@Override
					public void removed(IntBag entities) {
					}
				});
	}

	protected void create(int entityId) {
		setup(world.getEntity(entityId), mMetadataType.get(entityId), mReferenceType.create(entityId));
	}

	protected void remove(int entityId) {
		Entity entity = world.getEntity(entityId);
		if (entity != null) {
			mReferenceType.remove(entity);
		}
	}
}

ExampleManager.java

public class ExampleManager extends AssetManager<Font, BitmapFontAsset> {

	public ExampleManager() {
		super(Font.class, BitmapFontAsset.class);
	}

	@Override
	protected void setup(Entity entity, Font font, BitmapFontAsset bitmapFontAsset) {
		bitmapFontAsset.bitmapFont = getFont(font.fontName);
	}