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The XPath engine used by HtmlUnit.
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/*
 * 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.htmlunit.xpath.axes;

import org.htmlunit.xpath.XPathContext;
import org.htmlunit.xpath.objects.XObject;
import org.htmlunit.xpath.patterns.NodeTest;
import org.htmlunit.xpath.xml.dtm.DTMIterator;

/**
 * This class defines a simplified type of union iterator that only tests along the child axes. If
 * the conditions are right, it is much faster than using a UnionPathIterator.
 */
public class UnionChildIterator extends ChildTestIterator {

  /**
   * Even though these may hold full LocPathIterators, this array does not have to be cloned, since
   * only the node test and predicate portion are used, and these only need static information.
   * However, also note that index predicates can not be used!
   */
  private PredicatedNodeTest[] m_nodeTests = null;

  /** Constructor for UnionChildIterator */
  public UnionChildIterator() {
    super(null);
  }

  /**
   * Add a node test to the union list.
   *
   * @param test reference to a NodeTest, which will be added directly to the list of node tests (in
   *     other words, it will not be cloned). The parent of this test will be set to this object.
   */
  public void addNodeTest(final PredicatedNodeTest test) {

    // Increase array size by only 1 at a time. Fix this
    // if it looks to be a problem.
    if (null == m_nodeTests) {
      m_nodeTests = new PredicatedNodeTest[1];
      m_nodeTests[0] = test;
    }
    else {
      final PredicatedNodeTest[] tests = m_nodeTests;
      final int len = m_nodeTests.length;

      m_nodeTests = new PredicatedNodeTest[len + 1];

      System.arraycopy(tests, 0, m_nodeTests, 0, len);

      m_nodeTests[len] = test;
    }
    test.exprSetParent(this);
  }

  /** {@inheritDoc} */
  @Override
  public short acceptNode(final int n) {
    final XPathContext xctxt = getXPathContext();
    try {
      xctxt.pushCurrentNode(n);
      for (final PredicatedNodeTest pnt : m_nodeTests) {
        final XObject score = pnt.execute(xctxt, n);
        if (score != NodeTest.SCORE_NONE) {
          // Note that we are assuming there are no positional predicates!
          if (pnt.getPredicateCount() > 0) {
            if (pnt.executePredicates(n, xctxt)) {
                return DTMIterator.FILTER_ACCEPT;
            }
          }
          else {
            return DTMIterator.FILTER_ACCEPT;
        }
        }
      }
    }
    catch (final javax.xml.transform.TransformerException se) {

      // TODO: Fix this.
      throw new RuntimeException(se.getMessage());
    }
    finally {
      xctxt.popCurrentNode();
    }
    return DTMIterator.FILTER_SKIP;
  }
}