/*
 * Copyright (c) 2006-2011 Christian Plattner. All rights reserved.
 * Please refer to the LICENSE.txt for licensing details.
 */
package ch.ethz.ssh2.crypto;

import java.io.CharArrayWriter;
import java.io.IOException;

/**
 * Basic Base64 Support.
 *
 * @author Christian Plattner
 * @version 2.50, 03/15/10
 */
public class Base64 {
    static final char[] alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/".toCharArray();

    public static char[] encode(byte[] content) {
        CharArrayWriter cw = new CharArrayWriter((4 * content.length) / 3);
        int idx = 0;
        int x = 0;

        for (int i = 0; i < content.length; i++) {
            if (idx == 0)
                x = (content[i] & 0xff) << 16;
            else if (idx == 1)
                x = x | ((content[i] & 0xff) << 8);
            else
                x = x | (content[i] & 0xff);

            idx++;

            if (idx == 3) {
                cw.write(alphabet[x >> 18]);
                cw.write(alphabet[(x >> 12) & 0x3f]);
                cw.write(alphabet[(x >> 6) & 0x3f]);
                cw.write(alphabet[x & 0x3f]);
                idx = 0;
            }
        }

        if (idx == 1) {
            cw.write(alphabet[x >> 18]);
            cw.write(alphabet[(x >> 12) & 0x3f]);
            cw.write('=');
            cw.write('=');
        }

        if (idx == 2) {
            cw.write(alphabet[x >> 18]);
            cw.write(alphabet[(x >> 12) & 0x3f]);
            cw.write(alphabet[(x >> 6) & 0x3f]);
            cw.write('=');
        }

        return cw.toCharArray();
    }

    public static byte[] decode(char[] message) throws IOException {
        byte buff[] = new byte[4];
        byte dest[] = new byte[message.length];
        int bpos = 0;
        int destpos = 0;

        for (int i = 0; i < message.length; i++) {
            int c = message[i];

            if ((c == '\n') || (c == '\r') || (c == ' ') || (c == '\t'))
                continue;

            if ((c >= 'A') && (c <= 'Z')) {
                buff[bpos++] = (byte)(c - 'A');
            }
            else if ((c >= 'a') && (c <= 'z')) {
                buff[bpos++] = (byte)((c - 'a') + 26);
            }
            else if ((c >= '0') && (c <= '9')) {
                buff[bpos++] = (byte)((c - '0') + 52);
            }
            else if (c == '+') {
                buff[bpos++] = 62;
            }
            else if (c == '/') {
                buff[bpos++] = 63;
            }
            else if (c == '=') {
                buff[bpos++] = 64;
            }
            else {
                throw new IOException("Illegal char in base64 code.");
            }

            if (bpos == 4) {
                bpos = 0;

                if (buff[0] == 64)
                    break;

                if (buff[1] == 64)
                    throw new IOException("Unexpected '=' in base64 code.");

                if (buff[2] == 64) {
                    int v = (((buff[0] & 0x3f) << 6) | ((buff[1] & 0x3f)));
                    dest[destpos++] = (byte)(v >> 4);
                    break;
                }
                else if (buff[3] == 64) {
                    int v = (((buff[0] & 0x3f) << 12) | ((buff[1] & 0x3f) << 6) | ((buff[2] & 0x3f)));
                    dest[destpos++] = (byte)(v >> 10);
                    dest[destpos++] = (byte)(v >> 2);
                    break;
                }
                else {
                    int v = (((buff[0] & 0x3f) << 18) | ((buff[1] & 0x3f) << 12) | ((buff[2] & 0x3f) << 6) | ((buff[3] & 0x3f)));
                    dest[destpos++] = (byte)(v >> 16);
                    dest[destpos++] = (byte)(v >> 8);
                    dest[destpos++] = (byte)(v);
                }
            }
        }

        byte[] res = new byte[destpos];
        System.arraycopy(dest, 0, res, 0, destpos);
        return res;
    }
}