package org.gcube.data.streams.delegates;

import org.gcube.data.streams.Stream;

/**
 * A {@link Stream} that notifies an {@link StreamListener} of key iteration events.
 * 
 * @author Fabio Simeoni
 *
 * @param <E> the type of stream elements
 */
public class MonitoredStream<E> extends AbstractDelegateStream<E,E> {

	private final StreamListener listener;
	
	private boolean started=false;
	
	/**
	 * Creates an instance with a {@link Stream} and a {@link StreamListener}.
	 * @param stream the stream
	 * @param listener the listener
	 * @throws IllegalArgumentException if the stream or the listener are {@code null}
	 */
	public MonitoredStream(Stream<E> stream,StreamListener listener) throws IllegalArgumentException {
		
		super(stream);
		
		if (listener==null)
			throw new IllegalArgumentException("invalid null listener");
		
		this.listener=listener;
	}
	
	@Override
	protected E delegateNext() {
		
		E element = stream().next();
		
		if (!started) {
			listener.onStart();
			started=true;
		}
		
		if (!delegateHasNext())
			listener.onEnd();
		
		return element;
		
	}
	
	@Override
	protected boolean delegateHasNext() {
		return stream().hasNext();
	}
	
	@Override
	public void close() {
		super.close();
		listener.onClose();
	}
}