001///////////////////////////////////////////////////////////////////////////////////////////////
002// checkstyle: Checks Java source code and other text files for adherence to a set of rules.
003// Copyright (C) 2001-2024 the original author or authors.
004//
005// This library is free software; you can redistribute it and/or
006// modify it under the terms of the GNU Lesser General Public
007// License as published by the Free Software Foundation; either
008// version 2.1 of the License, or (at your option) any later version.
009//
010// This library is distributed in the hope that it will be useful,
011// but WITHOUT ANY WARRANTY; without even the implied warranty of
012// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
013// Lesser General Public License for more details.
014//
015// You should have received a copy of the GNU Lesser General Public
016// License along with this library; if not, write to the Free Software
017// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
018///////////////////////////////////////////////////////////////////////////////////////////////
019
020package com.puppycrawl.tools.checkstyle.xpath.iterators;
021
022import java.util.LinkedList;
023import java.util.Queue;
024
025import net.sf.saxon.om.AxisInfo;
026import net.sf.saxon.om.NodeInfo;
027import net.sf.saxon.tree.iter.AxisIterator;
028import net.sf.saxon.tree.iter.SingleNodeIterator;
029
030/**
031 * Recursive-free implementation of the descendant axis iterator.
032 */
033public class DescendantIterator implements AxisIterator {
034
035    /**
036     * Enum defines starting node for iterator.
037     */
038    public enum StartWith {
039        /** Start with current node. */
040        CURRENT_NODE,
041        /** Omit current node and start with child nodes. */
042        CHILDREN,
043    }
044
045    /**
046     * Queue for sibling nodes.
047     */
048    private final Queue<NodeInfo> queue = new LinkedList<>();
049    /**
050     * Descendant axis iterator.
051     */
052    private AxisIterator descendantEnum;
053
054    /**
055     * Create an iterator over the "descendant" axis.
056     *
057     * @param start the initial context node.
058     * @param startWith mode of the iterator, see {@link StartWith}.
059     */
060    public DescendantIterator(NodeInfo start, StartWith startWith) {
061        if (startWith == StartWith.CURRENT_NODE) {
062            descendantEnum = SingleNodeIterator.makeIterator(start);
063        }
064        else if (startWith == StartWith.CHILDREN) {
065            descendantEnum = start.iterateAxis(AxisInfo.CHILD);
066        }
067    }
068
069    /**
070     * Get the next item in the sequence.
071     *
072     * @return the next Item. If there are no more nodes, return null.
073     */
074    @Override
075    public NodeInfo next() {
076        NodeInfo result = null;
077        do {
078            if (descendantEnum == null) {
079                if (queue.isEmpty()) {
080                    break;
081                }
082                descendantEnum = queue.poll().iterateAxis(AxisInfo.CHILD);
083            }
084            else {
085                result = descendantEnum.next();
086                if (result == null) {
087                    descendantEnum = null;
088                }
089            }
090        } while (result == null);
091
092        if (result != null) {
093            queue.add(result);
094        }
095        return result;
096    }
097}