/*
 * Copyright (C) 2004 Joe Walnes. Copyright (C) 2006, 2007 XStream Committers. All rights reserved.
 * 
 * The software in this package is published under the terms of the BSD style license a copy of
 * which has been included with this distribution in the LICENSE.txt file.
 * 
 * Created on 06. August 2004 by Joe Walnes
 */
// original package name: com.thoughtworks.xstream.core.util
package io.selendroid.server.android.internal;



import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.Reader;
import java.io.StringReader;

/**
 * Encodes binary data to plain text as Base64.
 * 
 * <p>
 * Despite there being a gazillion other Base64 implementations out there, this has been written as
 * part of XStream as it forms a core part but is too trivial to warrant an extra dependency.
 * </p>
 * 
 * <p>
 * This meets the standard as described in RFC 1521, section 5.2
 * <http://www.freesoft.org/CIE/RFC/1521/7.htm>, allowing other Base64 tools to manipulate the data.
 * </p>
 * 
 * Original code from <a href="http://xstream.codehaus.org/">XStream</a>
 */
public class Base64Encoder {

  // Here's how encoding works:
  //
  // 1) Incoming bytes are broken up into groups of 3 (each byte having 8 bits).
  //
  // 2) The combined 24 bits (3 * 8) are split into 4 groups of 6 bits.
  //
  // input |------||------||------| (3 values each with 8 bits)
  // 101010101010101010101010
  // output |----||----||----||----| (4 values each with 6 bits)
  //
  // 3) Each of these 4 groups of 6 bits are converted back to a number, which will fall in the
  // range of 0 - 63.
  //
  // 4) Each of these 4 numbers are converted to an alphanumeric char in a specified mapping table,
  // to create
  // a 4 character string.
  //
  // 5) This is repeated for all groups of three bytes.
  //
  // 6) Special padding is done at the end of the stream using the '=' char.

  private static final char[] SIXTY_FOUR_CHARS =
      "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/".toCharArray();
  private static final int[] REVERSE_MAPPING = new int[123];

  static {
    for (int i = 0; i < SIXTY_FOUR_CHARS.length; i++)
      REVERSE_MAPPING[SIXTY_FOUR_CHARS[i]] = i + 1;
  }

  public String encode(byte[] input) {
    StringBuffer result = new StringBuffer();
    int outputCharCount = 0;
    for (int i = 0; i < input.length; i += 3) {
      int remaining = Math.min(3, input.length - i);
      int oneBigNumber =
          (input[i] & 0xff) << 16 | (remaining <= 1 ? 0 : input[i + 1] & 0xff) << 8
              | (remaining <= 2 ? 0 : input[i + 2] & 0xff);
      for (int j = 0; j < 4; j++)
        result.append(remaining + 1 > j
            ? SIXTY_FOUR_CHARS[0x3f & oneBigNumber >> 6 * (3 - j)]
            : '=');
      if ((outputCharCount += 4) % 76 == 0) result.append('\n');
    }
    return result.toString();
  }

  public byte[] decode(String input) {
    try {
      ByteArrayOutputStream out = new ByteArrayOutputStream();
      StringReader in = new StringReader(input);
      for (int i = 0; i < input.length(); i += 4) {
        int a[] = {mapCharToInt(in), mapCharToInt(in), mapCharToInt(in), mapCharToInt(in)};
        int oneBigNumber =
            (a[0] & 0x3f) << 18 | (a[1] & 0x3f) << 12 | (a[2] & 0x3f) << 6 | (a[3] & 0x3f);
        for (int j = 0; j < 3; j++)
          if (a[j + 1] >= 0) out.write(0xff & oneBigNumber >> 8 * (2 - j));
      }
      return out.toByteArray();
    } catch (IOException e) {
      throw new Error(e + ": " + e.getMessage());
    }
  }

  private int mapCharToInt(Reader input) throws IOException {
    int c;
    while ((c = input.read()) != -1) {
      int result = REVERSE_MAPPING[c];
      if (result != 0) return result - 1;
      if (c == '=') return -1;
    }
    return -1;
  }
}
