src/main/java/org/apache/sling/query/impl/iterator/SiblingsIterator.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 java.util.ListIterator;
import java.util.function.Predicate;

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

public class SiblingsIterator<T> extends AbstractIterator<T> {

    private final Predicate<T> until;

    private final ListIterator<T> siblings;

    private final Type type;

    private final TreeProvider<T> provider;

    private boolean finished;

    public SiblingsIterator(Predicate<T> until, T resource, Type type, TreeProvider<T> provider) {
        this.provider = provider;
        this.until = until;
        this.siblings = getRewindedIterator(resource, type);
        this.finished = false;
        this.type = type;
    }

    @Override
    protected T getElement() {
        if (finished) {
            return null;
        }
        while (type.canAdvance(siblings)) {
            T resource = type.advance(siblings);
            if (until != null && until.test(resource)) {
                finished = true;
                return null;
            }
            if (until == null) {
                finished = true;
            }
            return resource;
        }
        return null;
    }

    private ListIterator<T> getRewindedIterator(T resource, Type type) {
        String resourceName = provider.getName(resource);
        T parent = provider.getParent(resource);
        Iterator<T> iterator;
        if (parent == null) {
            iterator = IteratorUtils.singleElementIterator(resource);
        } else {
            iterator = provider.listChildren(parent);
        }
        ListIterator<T> listIterator = new LazyList<T>(iterator).listIterator();
        while (listIterator.hasNext()) {
            T sibling = listIterator.next();
            if (provider.getName(sibling).equals(resourceName)) {
                break;
            }
        }
        if (type == Type.PREV) {
            listIterator.previous();
        }
        return listIterator;
    }

    public enum Type {
        NEXT {
            @Override
            public boolean canAdvance(ListIterator<?> iterator) {
                return iterator.hasNext();
            }

            @Override
            public <T> T advance(ListIterator<T> iterator) {
                return iterator.next();
            }
        },
        PREV {
            @Override
            public boolean canAdvance(ListIterator<?> iterator) {
                return iterator.hasPrevious();
            }

            @Override
            public <T> T advance(ListIterator<T> iterator) {
                return iterator.previous();
            }
        };

        public abstract boolean canAdvance(ListIterator<?> iterator);

        public abstract <T> T advance(ListIterator<T> iterator);
    }
}