/*
 * Hibernate, Relational Persistence for Idiomatic Java
 *
 * Copyright (c) 2011, Red Hat Inc. or third-party contributors as
 * indicated by the @author tags or express copyright attribution
 * statements applied by the authors.  All third-party contributions are
 * distributed under license by Red Hat Inc.
 *
 * This copyrighted material is made available to anyone wishing to use, modify,
 * copy, or redistribute it subject to the terms and conditions of the GNU
 * Lesser General Public License, as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License
 * for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this distribution; if not, write to:
 * Free Software Foundation, Inc.
 * 51 Franklin Street, Fifth Floor
 * Boston, MA  02110-1301  USA
 */
package org.hibernate.internal.util.collections;

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


An JoinedIterable is an Iterable that wraps a number of Iterables. This class makes multiple iterables look like one to the caller. When any method from the Iterator interface is called on the Iterator object returned by iterator(), the JoinedIterable will delegate to a single underlying Iterator. The JoinedIterable will invoke the iterator on each Iterable, in sequence, until all Iterators are exhausted. 
Author:
Gail Badner (adapted from JoinedIterator)/**
 * An JoinedIterable is an Iterable that wraps a number of Iterables.
 *
 * This class makes multiple iterables look like one to the caller.
 * When any method from the Iterator interface is called on the
 * Iterator object returned by {@link #iterator()}, the JoinedIterable
 * will delegate to a single underlying Iterator. The JoinedIterable will
 * invoke the iterator on each Iterable, in sequence, until all Iterators
 * are exhausted.
 *
 * @author Gail Badner (adapted from JoinedIterator)
 */
public class JoinedIterable<T> implements Iterable<T> {
	private final TypeSafeJoinedIterator<T> iterator;

	public JoinedIterable(List<Iterable<T>> iterables) {
		if ( iterables == null ) {
			throw new NullPointerException( "Unexpected null iterables argument" );
		}
		iterator = new TypeSafeJoinedIterator<T>( iterables );
	}

	public Iterator<T> iterator() {
		return iterator;
	}

	private class TypeSafeJoinedIterator<T> implements Iterator<T> {

		// wrapped iterators
		private List<Iterable<T>> iterables;

		// index of current iterator in the wrapped iterators array
		private int currentIterableIndex;

		// the current iterator
		private Iterator<T> currentIterator;

		// the last used iterator
		private Iterator<T> lastUsedIterator;

		public TypeSafeJoinedIterator(List<Iterable<T>> iterables) {
			this.iterables = iterables;
		}

		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
		@SuppressWarnings( {"unchecked"})
		protected void updateCurrentIterator() {

			if ( currentIterator == null) {
				if( iterables.size() == 0  ) {
					currentIterator = EmptyIterator.INSTANCE;
				}
				else {
					currentIterator = iterables.get( 0 ).iterator();
				}
				// 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() && currentIterableIndex < iterables.size() - 1) {
				currentIterableIndex++;
				currentIterator = iterables.get( currentIterableIndex ).iterator();
			}
		}
	}
}