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.List;
  
  import org.jaxen.Context;
  import org.jaxen.Function;
  import org.jaxen.FunctionCallException;
  import org.jaxen.Navigator;
  
  /**
   * <p><b>4.2</b> <code><i>number</i> string-length(<i>string</i>)</code></p> 
   * 
   * <p>
   * The <b>string-length</b> function returns the number of <strong>Unicode characters</strong>
   * in its argument. This is <strong>not</strong> necessarily 
   * the same as the number <strong>Java chars</strong>
   * in the corresponding Java string. In particular, if the Java <code>String</code>
   * contains surrogate pairs each such pair will be counted as only one character
   * by this function. If the argument is omitted, 
   * it returns the length of the string-value of the context node.
   * </p>
   * 
   * @author bob mcwhirter (bob @ werken.com)
   * @see <a href="http://www.w3.org/TR/xpath#function-string-length" target="_top">Section 
   *      4.2 of the XPath Specification</a>
   */
  public class StringLengthFunction implements Function
  {
  
      
      /**
       * Create a new <code>StringLengthFunction</code> object.
       */
      public StringLengthFunction() {}
      
      
      /**
       * <p>
       * Returns the number of Unicode characters in the string-value of the argument.
       * </p>
       * 
       * @param context the context at the point in the
       *         expression when the function is called
       * @param args a list containing the item whose string-value is to be counted.
       *     If empty, the length of the context node's string-value is returned.
       * 
       * @return a <code>Double</code> giving the number of Unicode characters
       * 
       * @throws FunctionCallException if args has more than one item
       */
      public Object call(Context context,
                         List args) throws FunctionCallException
      {
          if (args.size() == 0)
          {
              return evaluate( context.getNodeSet(),
                               context.getNavigator() );
          } 
          else if (args.size() == 1)
          {
              return evaluate( args.get(0),
                               context.getNavigator() );
          }
  
          throw new FunctionCallException( "string-length() requires one argument." );
      }
  
      /**
       * <p>
       * Returns the number of Unicode characters in the string-value of 
       * an object.
       * </p>
       * 
       * @param obj the object whose string-value is counted
       * @param nav used to calculate the string-values of the first two arguments
       * 
       * @return a <code>Double</code> giving the number of Unicode characters
       * 
       * @throws FunctionCallException if the string contains mismatched surrogates
       */
      public static Double evaluate(Object obj, Navigator nav) throws FunctionCallException
      {
          String str = StringFunction.evaluate( obj, nav );
          // String.length() counts UTF-16 code points; not Unicode characters
          char[] data = str.toCharArray();
          int length = 0;
          for (int i = 0; i < data.length; i++) {
              char c = data[i];
              length++;
              // if this is a high surrogate; assume the next character is
              // is a low surrogate and skip it
              if (c >= 0xD800 && c <= 0xDFFF) {
                  try {
                      char low = data[i+1];
                      if (low < 0xDC00 || low > 0xDFFF) {
                          throw new FunctionCallException("Bad surrogate pair in string " + str);
                      }
                      i++; // increment past low surrogate
                  }
                  catch (ArrayIndexOutOfBoundsException ex) {
                      throw new FunctionCallException("Bad surrogate pair in string " + str);
                  }
              }
          }
          return new Double(length);
      }
      
  }
  