/*
 * 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.tika.parser.pdf;

import static java.nio.charset.StandardCharsets.ISO_8859_1;

import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;

import org.apache.pdfbox.cos.COSString;
import org.apache.pdfbox.io.RandomAccessBuffer;
import org.apache.pdfbox.io.RandomAccessRead;
import org.apache.pdfbox.pdfparser.COSParser;

/**
 * In fairly rare cases, a PDF's XMP will contain a string that
 * has incorrectly been encoded with PDFEncoding: an octal for non-ascii and
 * ascii for ascii, e.g. "\376\377\000M\000i\000c\000r\000o\000s\000o\000f\000t\000"
 * <p>
 * This class can be used to decode those strings.
 * <p>
 * See TIKA-1678.  Many thanks to Andrew Jackson for raising this issue
 * and Tilman Hausherr for the solution.
 * <p>
 * As of this writing, we are only handling strings that start with
 * an encoded BOM.  Andrew Jackson found a handful of other examples (e.g.
 * this ISO-8859-7 string:
 * "Microsoft Word - \\323\\365\\354\\354\\345\\364\\357\\367\\336
 * \\364\\347\\362 PRAKSIS \\363\\364\\357")
 * that we aren't currently handling.
 */
class PDFEncodedStringDecoder {

    private static final String[] PDF_ENCODING_BOMS = {
            "\\376\\377", //UTF-16BE
            "\\377\\376", //UTF-16LE
            "\\357\\273\\277"//UTF-8
    };

    /**
     * Does this string contain an octal-encoded UTF BOM?
     * Call this statically to determine if you should bother creating a new parser to parse it.
     * @param s
     * @return
     */
    static boolean shouldDecode(String s) {
        if (s == null || s.length() < 8) {
            return false;
        }
        for (String BOM : PDF_ENCODING_BOMS) {
            if (s.startsWith(BOM)) {
                return true;
            }
        }
        return false;
    }

    /**
     * This assumes that {@link #shouldDecode(String)} has been called
     * and has returned true.  If you run this on a non-octal encoded string,
     * disaster will happen!
     *
     * @param value
     * @return
     */
    String decode(String value) {
        try {
            byte[] bytes = new String("(" + value + ")").getBytes(ISO_8859_1);
            InputStream is = new ByteArrayInputStream(bytes);
            COSStringParser p = new COSStringParser(new RandomAccessBuffer(is));
            String parsed = p.myParseCOSString();
            if (parsed != null) {
                return parsed;
            }
        } catch (IOException e) {
            //oh well, we tried.
        }
        //just return value if something went wrong
        return value;
    }

    class COSStringParser extends COSParser {

        COSStringParser(RandomAccessRead buffer) throws IOException {
            super(buffer);
        }

        /**
         *
         * @return parsed string or null if something went wrong.
         */
        String myParseCOSString() {
            try {
                COSString cosString = parseCOSString();
                if (cosString != null) {
                    return cosString.getString();
                }
            } catch (IOException e) {
            }
            return null;
        }
    }
}