/*

 * Copyright (c) 1995, 2011, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package sun.misc;

import java.io.OutputStream;

import java.io.PushbackInputStream;

import java.io.PrintStream;

/**

 * This class implements a BASE64 Character decoder as specified in RFC1521.

 *

 * This RFC is part of the MIME specification which is published by the

 * Internet Engineering Task Force (IETF). Unlike some other encoding

 * schemes there is nothing in this encoding that tells the decoder

 * where a buffer starts or stops, so to use it you will need to isolate

 * your encoded data into a single chunk and then feed them this decoder.

 * The simplest way to do that is to read all of the encoded data into a

 * string and then use:

 * <pre>

 *      byte    mydata[];

 *      BASE64Decoder base64 = new BASE64Decoder();

 *

 *      mydata = base64.decodeBuffer(bufferString);

 * </pre>

 * This will decode the String in <i>bufferString</i> and give you an array

 * of bytes in the array <i>myData</i>.

 *

 * On errors, this class throws a CEFormatException with the following detail

 * strings:

 * <pre>

 *    "BASE64Decoder: Not enough bytes for an atom."

 * </pre>

 *

 * @author      Chuck McManis

 * @see         CharacterEncoder

 * @see         BASE64Decoder

 */

public class BASE64Decoder extends CharacterDecoder {

    /** This class has 4 bytes per atom */

    protected int bytesPerAtom() {

        return (4);

    }

    /** Any multiple of 4 will do, 72 might be common */

    protected int bytesPerLine() {

        return (72);

    }

    /**

     * This character array provides the character to value map

     * based on RFC1521.

     */

    private final static char pem_array[] = {

        //       0   1   2   3   4   5   6   7

                'A','B','C','D','E','F','G','H', // 0

                'I','J','K','L','M','N','O','P', // 1

                'Q','R','S','T','U','V','W','X', // 2

                'Y','Z','a','b','c','d','e','f', // 3

                'g','h','i','j','k','l','m','n', // 4

                'o','p','q','r','s','t','u','v', // 5

                'w','x','y','z','0','1','2','3', // 6

                '4','5','6','7','8','9','+','/'  // 7

        };

    private final static byte pem_convert_array[] = new byte[256];

    static {

        for (int i = 0; i < 255; i++) {

            pem_convert_array[i] = -1;

        }

        for (int i = 0; i < pem_array.length; i++) {

            pem_convert_array[pem_array[i]] = (byte) i;

        }

    }

    byte decode_buffer[] = new byte[4];

    /**

     * Decode one BASE64 atom into 1, 2, or 3 bytes of data.

     */

    @SuppressWarnings("fallthrough")

    protected void decodeAtom(PushbackInputStream inStream, OutputStream outStream, int rem)

        throws java.io.IOException

    {

        int     i;

        byte    a = -1, b = -1, c = -1, d = -1;

        if (rem < 2) {

            throw new CEFormatException("BASE64Decoder: Not enough bytes for an atom.");

        }

        do {

            i = inStream.read();

            if (i == -1) {

                throw new CEStreamExhausted();

            }

        } while (i == '\n' || i == '\r');

        decode_buffer[0] = (byte) i;

        i = readFully(inStream, decode_buffer, 1, rem-1);

        if (i == -1) {

            throw new CEStreamExhausted();

        }

        if (rem > 3 && decode_buffer[3] == '=') {

            rem = 3;

        }

        if (rem > 2 && decode_buffer[2] == '=') {

            rem = 2;

        }

        switch (rem) {

        case 4:

            d = pem_convert_array[decode_buffer[3] & 0xff];

            // NOBREAK

        case 3:

            c = pem_convert_array[decode_buffer[2] & 0xff];

            // NOBREAK

        case 2:

            b = pem_convert_array[decode_buffer[1] & 0xff];

            a = pem_convert_array[decode_buffer[0] & 0xff];

            break;

        }

        switch (rem) {

        case 2:

            outStream.write( (byte)(((a << 2) & 0xfc) | ((b >>> 4) & 3)) );

            break;

        case 3:

            outStream.write( (byte) (((a << 2) & 0xfc) | ((b >>> 4) & 3)) );

            outStream.write( (byte) (((b << 4) & 0xf0) | ((c >>> 2) & 0xf)) );

            break;

        case 4:

            outStream.write( (byte) (((a << 2) & 0xfc) | ((b >>> 4) & 3)) );

            outStream.write( (byte) (((b << 4) & 0xf0) | ((c >>> 2) & 0xf)) );

            outStream.write( (byte) (((c << 6) & 0xc0) | (d  & 0x3f)) );

            break;

        }

        return;

    }

}