001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.text.translate;
018
019import java.io.IOException;
020import java.io.Writer;
021
022/**
023 * Translates escaped Unicode values of the form \\u+\d\d\d\d back to
024 * Unicode. It supports multiple 'u' characters and will work with or
025 * without the +.
026 *
027 * @since 1.0
028 */
029public class UnicodeUnescaper extends CharSequenceTranslator {
030
031    /**
032     * {@inheritDoc}
033     */
034    @Override
035    public int translate(final CharSequence input, final int index, final Writer writer) throws IOException {
036        if (input.charAt(index) == '\\' && index + 1 < input.length() && input.charAt(index + 1) == 'u') {
037            // consume optional additional 'u' chars
038            int i = 2;
039            while (index + i < input.length() && input.charAt(index + i) == 'u') {
040                i++;
041            }
042
043            if (index + i < input.length() && input.charAt(index + i) == '+') {
044                i++;
045            }
046
047            if (index + i + 4 <= input.length()) {
048                // Get 4 hex digits
049                final CharSequence unicode = input.subSequence(index + i, index + i + 4);
050
051                try {
052                    final int value = Integer.parseInt(unicode.toString(), 16);
053                    writer.write((char) value);
054                } catch (final NumberFormatException nfe) {
055                    throw new IllegalArgumentException("Unable to parse unicode value: " + unicode, nfe);
056                }
057                return i + 4;
058            }
059            throw new IllegalArgumentException("Less than 4 hex digits in unicode value: '"
060                    + input.subSequence(index, input.length())
061                    + "' due to end of CharSequence");
062        }
063        return 0;
064    }
065}