001///////////////////////////////////////////////////////////////////////////////////////////////
002// checkstyle: Checks Java source code and other text files for adherence to a set of rules.
003// Copyright (C) 2001-2023 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 net.sf.saxon.om.AxisInfo;
023import net.sf.saxon.om.NodeInfo;
024import net.sf.saxon.tree.iter.AxisIterator;
025
026/**
027 * Recursive-free implementation of the preceding axis iterator.
028 */
029public class PrecedingIterator implements AxisIterator {
030    /**
031     * Ancestor axis iterator.
032     */
033    private final AxisIterator ancestorEnum;
034    /**
035     * Preceding-sibling axis iterator.
036     */
037    private AxisIterator previousSiblingEnum;
038    /**
039     * Descendant axis iterator.
040     */
041    private AxisIterator descendantEnum;
042
043    /**
044     * Create an iterator over the "preceding" axis.
045     *
046     * @param start the initial context node.
047     */
048    public PrecedingIterator(NodeInfo start) {
049        ancestorEnum = start.iterateAxis(AxisInfo.ANCESTOR);
050        previousSiblingEnum = start.iterateAxis(AxisInfo.PRECEDING_SIBLING);
051        descendantEnum = null;
052    }
053
054    /**
055     * Get the next item in the sequence.
056     *
057     * @return the next Item. If there are no more nodes, return null.
058     */
059    @Override
060    public NodeInfo next() {
061        NodeInfo result = null;
062
063        while (result == null) {
064            if (descendantEnum != null) {
065                result = descendantEnum.next();
066            }
067
068            if (result == null && previousSiblingEnum != null) {
069                result = previousSiblingEnum.next();
070                if (result == null) {
071                    previousSiblingEnum = null;
072                }
073                else {
074                    descendantEnum = new ReverseDescendantIterator(result);
075                }
076            }
077
078            if (result == null) {
079                result = ancestorEnum.next();
080                if (result == null) {
081                    break;
082                }
083                previousSiblingEnum = result.iterateAxis(AxisInfo.PRECEDING_SIBLING);
084            }
085        }
086        return result;
087    }
088}