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1   ///////////////////////////////////////////////////////////////////////////////////////////////
2   // checkstyle: Checks Java source code and other text files for adherence to a set of rules.
3   // Copyright (C) 2001-2024 the original author or authors.
4   //
5   // This library is free software; you can redistribute it and/or
6   // modify it under the terms of the GNU Lesser General Public
7   // License as published by the Free Software Foundation; either
8   // version 2.1 of the License, or (at your option) any later version.
9   //
10  // This library is distributed in the hope that it will be useful,
11  // but WITHOUT ANY WARRANTY; without even the implied warranty of
12  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
13  // Lesser General Public License for more details.
14  //
15  // You should have received a copy of the GNU Lesser General Public
16  // License along with this library; if not, write to the Free Software
17  // Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
18  ///////////////////////////////////////////////////////////////////////////////////////////////
19  
20  package com.puppycrawl.tools.checkstyle.xpath.iterators;
21  
22  import net.sf.saxon.om.AxisInfo;
23  import net.sf.saxon.om.NodeInfo;
24  import net.sf.saxon.tree.iter.AxisIterator;
25  
26  /**
27   * Recursive-free implementation of the preceding axis iterator.
28   */
29  public class PrecedingIterator implements AxisIterator {
30      /**
31       * Ancestor axis iterator.
32       */
33      private final AxisIterator ancestorEnum;
34      /**
35       * Preceding-sibling axis iterator.
36       */
37      private AxisIterator previousSiblingEnum;
38      /**
39       * Descendant axis iterator.
40       */
41      private AxisIterator descendantEnum;
42  
43      /**
44       * Create an iterator over the "preceding" axis.
45       *
46       * @param start the initial context node.
47       */
48      public PrecedingIterator(NodeInfo start) {
49          ancestorEnum = start.iterateAxis(AxisInfo.ANCESTOR);
50          previousSiblingEnum = start.iterateAxis(AxisInfo.PRECEDING_SIBLING);
51      }
52  
53      /**
54       * Get the next item in the sequence.
55       *
56       * @return the next Item. If there are no more nodes, return null.
57       */
58      @Override
59      public NodeInfo next() {
60          NodeInfo result = null;
61  
62          while (result == null) {
63              if (descendantEnum != null) {
64                  result = descendantEnum.next();
65              }
66  
67              if (result == null && previousSiblingEnum != null) {
68                  result = previousSiblingEnum.next();
69                  if (result == null) {
70                      previousSiblingEnum = null;
71                  }
72                  else {
73                      descendantEnum = new ReverseDescendantIterator(result);
74                  }
75              }
76  
77              if (result == null) {
78                  result = ancestorEnum.next();
79                  if (result == null) {
80                      break;
81                  }
82                  previousSiblingEnum = result.iterateAxis(AxisInfo.PRECEDING_SIBLING);
83              }
84          }
85          return result;
86      }
87  }