/*
 * Hibernate, Relational Persistence for Idiomatic Java
 *
 * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
 * See the lgpl.txt file in the root directory or <http://www.gnu.org/licenses/lgpl-2.1.html>.
 */
package org.hibernate.internal.util.collections;

import java.util.Collections;
import java.util.Iterator;
import java.util.List;

An Iterator implementation that wraps other Iterators, and presents them all as one
continuous Iterator.  When any method from Iterator is called, we delegate to each
wrapped Iterator in turn until all wrapped Iterators are exhausted.
Author:
Gavine King, Steve Ebersole/**
 * An Iterator implementation that wraps other Iterators, and presents them all as one
 * continuous Iterator.  When any method from Iterator is called, we delegate to each
 * wrapped Iterator in turn until all wrapped Iterators are exhausted.
 *
 * @author Gavine King
 * @author Steve Ebersole
 */
public class JoinedIterator<T> implements Iterator<T> {
	private Iterator<T>[] wrappedIterators;

	private int currentIteratorIndex;
	private Iterator<T> currentIterator;
	private Iterator<T> lastUsedIterator;

	@SuppressWarnings("unchecked")
	public JoinedIterator(List<Iterator<T>> wrappedIterators) {
		this( wrappedIterators.toArray( new Iterator[ wrappedIterators.size() ]) );
	}

	public JoinedIterator(Iterator<T>... iteratorsToWrap) {
		if( iteratorsToWrap == null ) {
			throw new NullPointerException( "Iterators to join were null" );
		}
		this.wrappedIterators = iteratorsToWrap;
	}

	public boolean hasNext() {
		updateCurrentIterator();
		return currentIterator.hasNext();
	}

	public T next() {
		updateCurrentIterator();
		return currentIterator.next();
	}

	public void remove() {
		updateCurrentIterator();
		lastUsedIterator.remove();
	}


	// call this before any Iterator method to make sure that the current Iterator
	// is not exhausted
	protected void updateCurrentIterator() {
		if ( currentIterator == null ) {
			if( wrappedIterators.length == 0  ) {
				currentIterator = Collections.<T>emptyList().iterator();
			}
			else {
				currentIterator = wrappedIterators[0];
			}
			// set last used iterator here, in case the user calls remove
			// before calling hasNext() or next() (although they shouldn't)
			lastUsedIterator = currentIterator;
		}

		while (! currentIterator.hasNext() && currentIteratorIndex < wrappedIterators.length - 1) {
			currentIteratorIndex++;
			currentIterator = wrappedIterators[currentIteratorIndex];
		}
	}

}