/*

  * Licensed to the Apache Software Foundation (ASF) under one or more

  * contributor license agreements.  See the NOTICE file distributed with

  * this work for additional information regarding copyright ownership.

  * The ASF licenses this file to You under the Apache License, Version 2.0

  * (the "License"); you may not use this file except in compliance with

  * the License.  You may obtain a copy of the License at

  * 

  *      http://www.apache.org/licenses/LICENSE-2.0

  * 

  * Unless required by applicable law or agreed to in writing, software

  * distributed under the License is distributed on an "AS IS" BASIS,

  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

  * See the License for the specific language governing permissions and

  * limitations under the License.

  */

 package org.apache.commons.lang3.text.translate;

 import java.io.IOException;

 import java.io.Writer;

 /**

  * Translates escaped Unicode values of the form \\u+\d\d\d\d back to 

  * Unicode. It supports multiple 'u' characters and will work with or 

  * without the +.

  * 

  * @since 3.0

  * @version $Id: UnicodeUnescaper.java 1436770 2013-01-22 07:09:45Z ggregory $

  */

 public class UnicodeUnescaper extends CharSequenceTranslator {

     /**

      * {@inheritDoc}

      */

     @Override

     public int translate(final CharSequence input, final int index, final Writer out) throws IOException {

         if (input.charAt(index) == '\\' && index + 1 < input.length() && input.charAt(index + 1) == 'u') {

             // consume optional additional 'u' chars

             int i = 2;

             while (index + i < input.length() && input.charAt(index + i) == 'u') {

                 i++;

             }

             if (index + i < input.length() && input.charAt(index + i) == '+') {

                 i++;

             }

             if (index + i + 4 <= input.length()) {

                 // Get 4 hex digits

                 final CharSequence unicode = input.subSequence(index + i, index + i + 4);

                 try {

                     final int value = Integer.parseInt(unicode.toString(), 16);

                     out.write((char) value);

                 } catch (final NumberFormatException nfe) {

                     throw new IllegalArgumentException("Unable to parse unicode value: " + unicode, nfe);

                 }

                 return i + 4;

             } else {

                 throw new IllegalArgumentException("Less than 4 hex digits in unicode value: '" + input.subSequence(index, input.length())

                         + "' due to end of CharSequence");

             }

         }

         return 0;

     }

 }