/*
 * LangFunction.java
 * Copyright (C) 2004 The Free Software Foundation
 * 
 * This file is part of GNU JAXP, a library.
 *
 * GNU JAXP 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 of the License, or
 * (at your option) any later version.
 * 
 * GNU JAXP 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 this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 * Linking this library statically or dynamically with other modules is
 * making a combined work based on this library.  Thus, the terms and
 * conditions of the GNU General Public License cover the whole
 * combination.
 *
 * 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
 * modules, and to copy and distribute the resulting executable under
 * terms of your choice, provided that you also meet, for each linked
 * independent module, the terms and conditions of the license of that
 * module.  An independent module is a module which is not derived from
 * or based on this library.  If you modify this library, you may extend
 * this exception to your version of the library, but you are not
 * obliged to do so.  If you do not wish to do so, delete this
 * exception statement from your version. 
 */

package gnu.xml.xpath;

import java.util.List;
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)
  {
    if (node.getNodeType() == Node.ELEMENT_NODE)
      {
        return ((Element) node).getAttribute("xml:lang");
      }
    return null;
  }
  
  public Expr clone(Object context)
  {
    return new IdFunction(arg.clone(context));
  }

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