/*
 * Copyright (C) 2000 - 2026 Silverpeas
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 *
 * As a special exception to the terms and conditions of version 3.0 of
 * the GPL, you may redistribute this Program in connection with Free/Libre
 * Open Source Software ("FLOSS") applications as described in Silverpeas's
 * FLOSS exception.  You should have received a copy of the text describing
 * the FLOSS exception, and it is also available here:
 * "https://www.silverpeas.org/legal/floss_exception.html"
 *
 * This program 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 Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
package org.silverpeas.sso.kerberos.spnego;

public final class Base64 {

  private static final String ALPHABET =
      "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

  private Base64() {
    // default private
  }

  /**
   * Base-64 encodes the supplied block of data.  Line wrapping is not
   * applied on output.
   * @param bytes The block of data that is to be Base-64 encoded.
   * @return A <code>String</code> containing the encoded data.
   */
  public static String encode(final byte[] bytes) {
    int length = bytes.length;

    if (length == 0) {
      return "";
    }

    final StringBuilder buffer = new StringBuilder((int) Math.ceil(length / 3d) * 4);
    final int remainder = length % 3;
    length -= remainder;
    int block;
    int idx = 0;
    while (idx < length) {
      block = ((bytes[idx++] & 0xff) << 16) | ((bytes[idx++] & 0xff) << 8) | (bytes[idx++] & 0xff);
      buffer.append(ALPHABET.charAt(block >>> 18));
      buffer.append(ALPHABET.charAt((block >>> 12) & 0x3f));
      buffer.append(ALPHABET.charAt((block >>> 6) & 0x3f));
      buffer.append(ALPHABET.charAt(block & 0x3f));
    }
    if (remainder == 0) {
      return buffer.toString();
    }
    if (remainder == 1) {
      block = (bytes[idx] & 0xff) << 4;
      buffer.append(ALPHABET.charAt(block >>> 6));
      buffer.append(ALPHABET.charAt(block & 0x3f));
      buffer.append("==");
      return buffer.toString();
    }
    block = (((bytes[idx++] & 0xff) << 8) | ((bytes[idx]) & 0xff)) << 2;
    buffer.append(ALPHABET.charAt(block >>> 12));
    buffer.append(ALPHABET.charAt((block >>> 6) & 0x3f));
    buffer.append(ALPHABET.charAt(block & 0x3f));
    buffer.append("=");
    return buffer.toString();
  }

  /**
   * Decodes the supplied Base-64 encoded string.
   * @param string The Base-64 encoded string that is to be decoded.
   * @return A <code>byte[]</code> containing the decoded data block.
   */
  public static byte[] decode(final String string) {
    final int length = string.length();
    if (length == 0) {
      return new byte[0];
    }

    final int pad =
        (string.charAt(length - 2) == '=') ? 2 : (string.charAt(length - 1) == '=') ? 1 : 0;
    final int size = length * 3 / 4 - pad;
    byte[] buffer = new byte[size];
    int block;
    int idx = 0;
    int index = 0;
    while (idx < length) {
      block = (ALPHABET.indexOf(string.charAt(idx++)) & 0xff) << 18 |
          (ALPHABET.indexOf(string.charAt(idx++)) & 0xff) << 12 |
          (ALPHABET.indexOf(string.charAt(idx++)) & 0xff) << 6 |
          (ALPHABET.indexOf(string.charAt(idx++)) & 0xff);
      buffer[index++] = (byte) (block >>> 16);
      if (index < size) {
        buffer[index++] = (byte) ((block >>> 8) & 0xff);
      }
      if (index < size) {
        buffer[index++] = (byte) (block & 0xff);
      }
    }
    return buffer;
  }
}
