package dev.kske.chess.event;

import java.util.ArrayList;
import java.util.List;

/**
 * Dispatches {@link Event}s to various {@link Subscriber}s.<br>
 * <br>
 * Project: <strong>Chess</strong><br>
 * File: <strong>EventBus.java</strong><br>
 * Created: <strong>7 Aug 2019</strong><br>
 *
 * @since Chess v0.4-alpha
 * @author Kai S. K. Engelbart
 */
public class EventBus {

	private List<Subscriber> subscribers;

	private static EventBus instance;

	/**
	 * @return a singleton instance of {@link EventBus}
	 */
	public static EventBus getInstance() {
		if (instance == null)
			instance = new EventBus();
		return instance;
	}

	private EventBus() {
		subscribers = new ArrayList<>();
	}

	/**
	 * Registers a subscriber to which future events will be dispatched.
	 *
	 * @param subscribable the subscriber to register
	 */
	public void register(Subscriber subscribable) {
		subscribers.add(subscribable);
	}

	/**
	 * Dispatches an event to all {@Subscriber}s registered at this event bus.
	 *
	 * @param event the event to dispatch
	 */
	public void dispatch(Event<?> event) {
		subscribers.stream()
			.filter(e -> e.supports().contains(event.getClass()))
			.forEach(e -> e.handle(event));
	}

	/**
	 * @return a list of all registered subscribers
	 */
	public List<Subscriber> getSubscribers() { return subscribers; }
}