/* LangFunction.java -- 
   Copyright (C) 2004,2006 Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.

GNU Classpath is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU Classpath; see the file COPYING.  If not, write to the
Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
02110-1301 USA.

Linking this library statically or dynamically with other modules is
making a combined work based on this library.  Thus, the terms and
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As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
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package gnu.xml.xpath;

import java.util.List;
import javax.xml.namespace.QName;
import org.w3c.dom.Element;
import org.w3c.dom.Node;

/**
 * The <code>lang</code> function returns true or false depending on whether
 * the language of the context node as specified by xml:lang attributes is
 * the same as or is a sublanguage of the language specified by the argument
 * string. The language of the context node is determined by the value of
 * the xml:lang attribute on the context node, or, if the context node has
 * no xml:lang attribute, by the value of the xml:lang attribute on the
 * nearest ancestor of the context node that has an xml:lang attribute. If
 * there is no such attribute, then lang returns false. If there is such an
 * attribute, then lang returns true if the attribute value is equal to the
 * argument ignoring case, or if there is some suffix starting with - such
 * that the attribute value is equal to the argument ignoring that suffix of
 * the attribute value and ignoring case.
 *
 * @author <a href='mailto:dog@gnu.org'>Chris Burdess</a>
 */
final class LangFunction
  extends Expr
{

  final Expr arg;

  LangFunction(List args)
  {
    this((Expr) args.get(0));
  }

  LangFunction(Expr arg)
  {
    this.arg = arg;
  }

  public Object evaluate(Node context, int pos, int len)
  {
    Object val = arg.evaluate(context, pos, len);
    String lang = _string(context, val);
    String clang = getLang(context);
    while (clang == null && context != null)
      {
        context = context.getParentNode();
        clang = getLang(context);
      }
    boolean ret = (clang == null) ? false :
      clang.toLowerCase().startsWith(lang.toLowerCase());
    return ret ? Boolean.TRUE : Boolean.FALSE;
  }

  String getLang(Node node)
  {
    while (node != null)
      {
        if (node.getNodeType() == Node.ELEMENT_NODE)
          {
            String lang = ((Element) node).getAttribute("xml:lang");
            if (lang != null)
              return lang;
          }
        node = node.getParentNode();
      }
    return null;
  }
  
  public Expr clone(Object context)
  {
    return new IdFunction(arg.clone(context));
  }

  public boolean references(QName var)
  {
    return arg.references(var);
  }

  public String toString()
  {
    return "lang(" + arg + ")";
  }
  
}