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.HashMap;
  import java.util.List;
  import java.util.Map;
  
  import org.jaxen.Context;
  import org.jaxen.Function;
  import org.jaxen.FunctionCallException;
  import org.jaxen.Navigator;
  
  /**
   * <p>
   * <b>4.2</b>
   * <code><i>string</i> translate(<i>string</i>,<i>string</i>,<i>string</i>)</code>
   * </p>
   * 
   * <blockquote src="http://www.w3.org/TR/xpath#function-translate">
   * <p>
   * The <b><a href="http://www.w3.org/TR/xpath#function-translate">translate</a></b> function
   * returns the first argument string with occurrences of characters in
   * the second argument string replaced by the character at the
   * corresponding position in the third argument string. For example,
   * <code>translate("bar","abc","ABC")</code> returns the string
   * <code>BAr</code>. If there is a character in the second argument
   * string with no character at a corresponding position in the third
   * argument string (because the second argument string is longer than
   * the third argument string), then occurrences of that character in the
   * first argument string are removed. For example,
   * <code>translate("--aaa--","abc-","ABC")</code> returns
   * <code>"AAA"</code>. If a character occurs more than once in the
   * second argument string, then the first occurrence determines the
   * replacement character. If the third argument string is longer than
   * the second argument string, then excess characters are ignored.
   * </p>
   * 
   * <blockquote> <b>NOTE: </b>The <b>translate</b> function is not a
   * sufficient solution for case conversion in all languages. A future
   * version of XPath may provide additional functions for case
   * conversion.</blockquote>
   * 
   * </blockquote>
   * 
   * @author Jan Dvorak ( jan.dvorak @ mathan.cz )
   * 
   * @see <a href="http://www.w3.org/TR/xpath#function-translate"
   *      target="_top">Section 4.2 of the XPath Specification</a>
   */
  public class TranslateFunction implements Function
  {
  
       /* The translation is done thru a HashMap. Performance tip (for anyone
        * who needs to improve the performance of this particular function):
        * Cache the HashMaps, once they are constructed. */
      
      /**
       * Create a new <code>TranslateFunction</code> object.
       */
      public TranslateFunction() {}
      
      
      /** Returns a copy of the first argument in which
       * characters found in the second argument are replaced by
       * corresponding characters from the third argument.
       *
       * @param context the context at the point in the
       *         expression when the function is called
       * @param args a list that contains exactly three items
       * 
       * @return a <code>String</code> built from <code>args.get(0)</code> 
       *     in which occurrences of characters in <code>args.get(1)</code> 
       *     are replaced by the corresponding characters in <code>args.get(2)</code> 
       * 
       * @throws FunctionCallException if <code>args</code> does not have exactly three items
       */
      public Object call(Context context,
                         List args) throws FunctionCallException
      {
          if (args.size() == 3) {
              return evaluate( args.get(0),
                               args.get(1),
                               args.get(2),
                               context.getNavigator() );
          }
  
          throw new FunctionCallException( "translate() requires three arguments." );
      }
  
      /** 
       * Returns a copy of <code>strArg</code> in which
       * characters found in <code>fromArg</code> are replaced by
       * corresponding characters from <code>toArg</code>.
       * If necessary each argument is first converted to it string-value
       * as if by the XPath <code>string()</code> function.
       * 
       * @param strArg the base string
       * @param fromArg the characters to be replaced
       * @param toArg the characters they will be replaced by
       * @param nav the <code>Navigator</code> used to calculate the string-values of the arguments.
       * 
       * @return a copy of <code>strArg</code> in which
       *  characters found in <code>fromArg</code> are replaced by
       *  corresponding characters from <code>toArg</code>
       *  
       * @throws FunctionCallException if one of the arguments is a malformed Unicode string;
       *     that is, if surrogate characters don't line up properly
       * 
       */
      public static String evaluate(Object strArg,
                                    Object fromArg,
                                    Object toArg,
                                    Navigator nav) throws FunctionCallException
      {
          String inStr = StringFunction.evaluate( strArg, nav );
          String fromStr = StringFunction.evaluate( fromArg, nav );
          String toStr = StringFunction.evaluate( toArg, nav );
      
          // Initialize the mapping in a HashMap
          Map characterMap = new HashMap();
          String[] fromCharacters = toUnicodeCharacters(fromStr);
          String[] toCharacters = toUnicodeCharacters(toStr);
          int fromLen = fromCharacters.length;
          int toLen = toCharacters.length;
          for ( int i = 0; i < fromLen; i++ ) {
              String cFrom = fromCharacters[i];
              if ( characterMap.containsKey( cFrom ) ) {
                  // We've seen the character before, ignore
                  continue;
              }
              
              if ( i < toLen ) {
                  // Will change
                  characterMap.put( cFrom, toCharacters[i] );
              } 
              else {
                  // Will delete
                  characterMap.put( cFrom, null );
              }
          }
  
          // Process the input string thru the map
          StringBuffer outStr = new StringBuffer( inStr.length() );
          String[] inCharacters = toUnicodeCharacters(inStr);
          int inLen = inCharacters.length;
          for ( int i = 0; i < inLen; i++ ) {
              String cIn = inCharacters[i];
              if ( characterMap.containsKey( cIn ) ) {
                  String cTo = (String) characterMap.get( cIn );
                  if ( cTo != null ) {
                      outStr.append( cTo );
                  }
              } 
              else {
                  outStr.append( cIn );
              }
          }
      
          return outStr.toString();
      }
  
      private static String[] toUnicodeCharacters(String s) throws FunctionCallException {
  
          String[] result = new String[s.length()];
          int stringLength = 0;
          for (int i = 0; i < s.length(); i++) {
              char c1 = s.charAt(i);
              if (isHighSurrogate(c1)) {
                  try {
                      char c2 = s.charAt(i+1);
                      if (isLowSurrogate(c2)) {
                          result[stringLength] = (c1 + "" + c2).intern();
                          i++;
                      }
                      else {
                          throw new FunctionCallException("Mismatched surrogate pair in translate function");
                      }
                  }
                  catch (StringIndexOutOfBoundsException ex) {
                      throw new FunctionCallException("High surrogate without low surrogate at end of string passed to translate function");
                  }
              }
              else {
                  result[stringLength]=String.valueOf(c1).intern();
              }
              stringLength++;
          }
          
          if (stringLength == result.length) return result;
          
          // trim array
          String[] trimmed = new String[stringLength];
          System.arraycopy(result, 0, trimmed, 0, stringLength);
          return trimmed;
          
      }
  
      private static boolean isHighSurrogate(char c) {
          return c >= 0xD800 && c <= 0xDBFF;
      }
       
      private static boolean isLowSurrogate(char c) {
          return c >= 0xDC00 && c <= 0xDFFF;
      }
       
  }