content: /*
   * $Header$
   * $Revision$
   * $Date$
   *
   * ====================================================================
   *
   * Copyright 2000-2002 bob mcwhirter & James Strachan.
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions are
   * met:
   * 
   *   * Redistributions of source code must retain the above copyright
   *     notice, this list of conditions and the following disclaimer.
   * 
   *   * Redistributions in binary form must reproduce the above copyright
   *     notice, this list of conditions and the following disclaimer in the
   *     documentation and/or other materials provided with the distribution.
   * 
   *   * Neither the name of the Jaxen Project nor the names of its
   *     contributors may be used to endorse or promote products derived 
   *     from this software without specific prior written permission.
   * 
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
   * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
   * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
   * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER
   * OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
   * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
   * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
   * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
   * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
   * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
   * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   *
   * ====================================================================
   * This software consists of voluntary contributions made by many 
   * individuals on behalf of the Jaxen Project and was originally 
   * created by bob mcwhirter <bob@werken.com> and 
   * James Strachan <jstrachan@apache.org>.  For more information on the 
   * Jaxen Project, please see <http://www.jaxen.org/>.
   * 
   * $Id$
   */
  
  
  package org.jaxen.function;
  
  import java.util.Iterator;
  import java.util.List;
  
  import org.jaxen.Context;
  import org.jaxen.Function;
  import org.jaxen.FunctionCallException;
  import org.jaxen.Navigator;
  import org.jaxen.UnsupportedAxisException;
  
  /**
   * <p>
   * <b>4.3</b> <code><i>boolean</i> lang(<i>string</i>)</code>
   * </p>
   * 
   * <blockquote src="http://www.w3.org/TR/xpath#function-lang">
   * <p>
   * The <b>lang</b> function returns true or false depending on whether
   * the language of the context node as specified by
   * <code>xml:lang</code> 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 <code>xml:lang</code>
   * 
   * attribute on the context node, or, if the context node has no
   * <code>xml:lang</code> attribute, by the value of the
   * <code>xml:lang</code> attribute on the nearest ancestor of the
   * context node that has an <code>xml:lang</code> attribute. If there
   * is no such attribute, then <b><a href="#function-lang">lang</a></b>
   * returns false. If there is such an attribute, then <b><a
   * href="#function-lang">lang</a></b> returns true if the attribute
   * value is equal to the argument ignoring case, or if there is some
   * suffix starting with <code>-</code> such that the attribute value
   * is equal to the argument ignoring that suffix of the attribute value
   * and ignoring case. For example, <code>lang("en")</code> would
   * return true if the context node is any of these five elements:
   * </p>
   * 
   * <pre>
   *  &lt;para xml:lang=&quot;en&quot;/&gt;
   *  &lt;div xml:lang=&quot;en&quot;&gt;&lt;para/&gt;&lt;/div&gt;
   *  &lt;para xml:lang=&quot;EN&quot;/&gt;
   *  &lt;para xml:lang=&quot;en-us&quot;/&gt;
   * </pre>
   * 
   * </blockquote>
   * 
   * @author Attila Szegedi (szegedia @ freemail.hu)
   * @see <a href="http://www.w3.org/TR/xpath#function-lang"
   *      target="_top">XPath Specification</a>
   */
  public class LangFunction implements Function
  {
      private static final String LANG_LOCALNAME = "lang";
      private static final String XMLNS_URI = 
          "http://www.w3.org/XML/1998/namespace";
      
  
      /**
       * Create a new <code>LangFunction</code> object.
       */
      public LangFunction() {}
      
      
      /**
       * <p>
       * Determines whether or not the context node is written in the language specified
       * by the XPath string-value of <code>args.get(0)</code>,
       * as determined by the nearest <code>xml:lang</code> attribute in scope. 
       * </p>
       * 
       * @param context the context in which to evaluate the <code>lang()</code> function
       * @param args the arguments to the lang function
       * @return a <code>Boolean</code> indicating whether the context node is written in
       *     the specified language
       * @throws FunctionCallException if <code>args</code> does not have length one
       * 
       */
      public Object call(Context context,
                         List args) throws FunctionCallException
      {
          if (args.size() != 1) {
              throw new FunctionCallException("lang() requires exactly one argument.");   
          }
          
          Object arg = args.get(0);
              
          try {
              return evaluate(context.getNodeSet(), arg, context.getNavigator() );
          }
          catch(UnsupportedAxisException e) {
              throw new FunctionCallException("Can't evaluate lang()", 
                                                   e);
          }
         
      }
  
      private static Boolean evaluate(List contextNodes, Object lang, Navigator nav)
        throws UnsupportedAxisException
      {
          return evaluate(contextNodes.get(0), 
              StringFunction.evaluate(lang, nav), nav)
              ? Boolean.TRUE : Boolean.FALSE;
      }
  
      private static boolean evaluate(Object node, String lang, Navigator nav)
        throws UnsupportedAxisException
      {
          
          Object element = node;
          if (! nav.isElement(element)) {
              element = nav.getParentNode(node);
          }
          while (element != null && nav.isElement(element)) 
          {
              Iterator attrs = nav.getAttributeAxisIterator(element);
              while(attrs.hasNext())
              {
                  Object attr = attrs.next();
                  if(LANG_LOCALNAME.equals(nav.getAttributeName(attr)) && 
                     XMLNS_URI.equals(nav.getAttributeNamespaceUri(attr)))
                  {
                      return 
                          isSublang(nav.getAttributeStringValue(attr), lang);
                  }
              }
              element = nav.getParentNode(element);
          }
          return false;
      }
      
      private static boolean isSublang(String sublang, String lang)
      {
          if(sublang.equalsIgnoreCase(lang))
          {
              return true;
          }
          int ll = lang.length();
          return 
              sublang.length() > ll && 
              sublang.charAt(ll) == '-' && 
              sublang.substring(0, ll).equalsIgnoreCase(lang);
      }
      
  }
  
  