/*-
 * 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.ArrayList;
import java.util.Iterator;

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

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

    private final Iterator<Option<T>> input;

    private Option<T> current;

    private Iterator<T> descendants;

    private final TreeProvider<T> provider;

    public DescendantsIterator(Iterator<Option<T>> input, Iterator<T> descendants, TreeProvider<T> provider) {
        this.input = input;
        this.current = null;
        this.descendants = new ArrayList<T>(new LazyList<T>(descendants)).iterator();
        this.provider = provider;
    }

    @Override
    protected Option<T> getElement() {
        if (current == null) {
            if (input.hasNext()) {
                current = input.next();
            } else {
                return null;
            }
        }
        return getDescendant();
    }

    private Option<T> getDescendant() {
        while (descendants.hasNext()) {
            T descendantCandidate = descendants.next();
            if (provider.isDescendant(current.getElement(), descendantCandidate)) {
                descendants.remove();
                return Option.of(descendantCandidate, current.getArgumentId());
            }
        }
        Option<T> result = Option.empty(current.getArgumentId());
        current = null;
        return result;
    }
}