src/main/java/org/apache/sling/query/impl/iterator/ReverseIterator.java

/*-
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package org.apache.sling.query.impl.iterator;

import java.util.Iterator;

import org.apache.sling.query.api.internal.IteratorToIteratorFunction;
import org.apache.sling.query.api.internal.Option;
import org.apache.sling.query.impl.util.LazyList;

public class ReverseIterator<T> extends AbstractIterator<Option<T>> {

	private final Iterator<Option<T>> filtered;

	private final Iterator<Option<T>> original;

	public ReverseIterator(IteratorToIteratorFunction<T> function, Iterator<Option<T>> input) {
		LazyList<Option<T>> lazyList = new LazyList<Option<T>>(input);
		filtered = function.apply(lazyList.listIterator());
		original = lazyList.listIterator();
	}

	@Override
	protected Option<T> getElement() {
		if (original.hasNext()) {
			Option<T> originalElement = original.next();
			Option<T> filteredElement = null;
			if (filtered.hasNext()) {
				filteredElement = filtered.next();
			}
			if (filteredElement == null || filteredElement.isEmpty()) {
				return originalElement;
			} else {
				return Option.empty(originalElement.getArgumentId());
			}
		}
		return null;
	}
}