package coffee.liz.ecs.events;

import java.util.Set;
import java.util.concurrent.CopyOnWriteArraySet;
import java.util.function.Consumer;

/**
 * Minimal observable contract for event emission.
 *
 * @param <E>
 *            emitted event type
 */
public class EventBus<E> {
    protected final Set<Consumer<E>> subscriptions = new CopyOnWriteArraySet<>();

    /**
     * Register a hook to receive future events.
     *
     * @param hook
     *            callback to invoke for each emitted event
     * @return subscribed hook.
     */
    public Consumer<E> subscribe(final Consumer<E> hook) {
        subscriptions.add(hook);
        return hook;
    }

    /**
     * Remove a previously registered hook.
     *
     * @param hook callback to remove
     */
    public void unsubscribe(final Consumer<E> hook) {
        subscriptions.remove(hook);
    }

    /**
     * Publish an event to all currently subscribed hooks.
     *
     * @param event
     *            event to publish
     */
    public void emit(final E event) {
        subscriptions.forEach(s -> s.accept(event));
    }
}