/*

  * $Header: /home/projects/jaxen/scm/jaxen/src/java/main/org/jaxen/function/LangFunction.java,v 1.13 2006/02/05 21:47:41 elharo Exp $

  * $Revision: 1.13 $

  * $Date: 2006/02/05 21:47:41 $

  *

  * ====================================================================

  *

  * 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: LangFunction.java,v 1.13 2006/02/05 21:47:41 elharo Exp $

  */

 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>

  *  <para xml:lang="en"/>

  *  <div xml:lang="en"><para/></div>

  *  <para xml:lang="EN"/>

  *  <para xml:lang="en-us"/>

  * </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);

     }

 }