package envoy.event;

import java.io.Serializable;
import java.util.Objects;

/**
 * This class serves as a convenience base class for all events. It provides a generic value. For
 * events without a value there also is {@link envoy.event.Event.Valueless}.
 *
 * @author Kai S. K. Engelbart
 * @param <T> the type of the Event
 * @since Envoy v0.2-alpha
 */
public abstract class Event<T> implements Serializable {

	protected final T value;

	private static final long serialVersionUID = 0L;

	protected Event(T value) {
		this(value, false);
	}

	/**
	 * This constructor is reserved for {@link Valueless} events. No other event should contain null
	 * values. Only use if really necessary. Using this constructor with {@code true} implies that
	 * the user has to manually check if the value of the event is null.
	 */
	protected Event(T value, boolean canBeNull) {
		this.value = canBeNull ? value : Objects.requireNonNull(value);
	}

	/**
	 * @return the data associated with this event
	 */
	public T get() {
		return value;
	}

	@Override
	public String toString() {
		return String.format("%s[value=%s]", this.getClass().getSimpleName(), value);
	}

	/**
	 * Serves as a super class for events that do not carry a value.
	 *
	 * @author Kai S. K. Engelbart
	 * @since Envoy Common v0.2-alpha
	 */
	public static abstract class Valueless extends Event<Void> {

		private static final long serialVersionUID = 0L;

		protected Valueless() {
			super(null, true);
		}

		@Override
		public String toString() {
			return this.getClass().getSimpleName();
		}
	}
}