package drjava.util;

/**
 * Static methods for translating Base64 encoded strings to byte arrays
 * and vice-versa.
 * Copied from java.util.prefs.Base64
 *
 * @author  Josh Bloch
 * @see     java.util.prefs.Preferences
 * @since   1.4
 */
public class Base64 {
  /**
   * Translates the specified byte array into a Base64 string as per
   * Preferences.put(byte[]).
   */
  public static String byteArrayToBase64(byte[] a) {
    return byteArrayToBase64(a, false);
  }

  /**
   * Translates the specified byte array into an "alternate representation"
   * Base64 string.  This non-standard variant uses an alphabet that does
   * not contain the uppercase alphabetic characters, which makes it
   * suitable for use in situations where case-folding occurs.
   */
  public static String byteArrayToAltBase64(byte[] a) {
    return byteArrayToBase64(a, true);
  }

  private static String byteArrayToBase64(byte[] a, boolean alternate) {
    int aLen = a.length;
    int numFullGroups = aLen/3;
    int numBytesInPartialGroup = aLen - 3*numFullGroups;
    int resultLen = 4*((aLen + 2)/3);
    StringBuffer result = new StringBuffer(resultLen);
    char[] intToAlpha = (alternate ? intToAltBase64 : intToBase64);

    // Translate all full groups from byte array elements to Base64
    int inCursor = 0;
    for (int i=0; i<numFullGroups; i++) {
      int byte0 = a[inCursor++] & 0xff;
      int byte1 = a[inCursor++] & 0xff;
      int byte2 = a[inCursor++] & 0xff;
      result.append(intToAlpha[byte0 >> 2]);
      result.append(intToAlpha[(byte0 << 4)&0x3f | (byte1 >> 4)]);
      result.append(intToAlpha[(byte1 << 2)&0x3f | (byte2 >> 6)]);
      result.append(intToAlpha[byte2 & 0x3f]);
    }

    // Translate partial group if present
    if (numBytesInPartialGroup != 0) {
      int byte0 = a[inCursor++] & 0xff;
      result.append(intToAlpha[byte0 >> 2]);
      if (numBytesInPartialGroup == 1) {
        result.append(intToAlpha[(byte0 << 4) & 0x3f]);
        result.append("==");
      } else {
        // assert numBytesInPartialGroup == 2;
        int byte1 = a[inCursor++] & 0xff;
        result.append(intToAlpha[(byte0 << 4)&0x3f | (byte1 >> 4)]);
        result.append(intToAlpha[(byte1 << 2)&0x3f]);
        result.append('=');
      }
    }
    // assert inCursor == a.length;
    // assert result.length() == resultLen;
    return result.toString();
  }

  /**
   * This array is a lookup table that translates 6-bit positive integer
   * index values into their "Base64 Alphabet" equivalents as specified
   * in Table 1 of RFC 2045.
   */
  private static final char intToBase64[] = {
    'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M',
    'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z',
    'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm',
    'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z',
    '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '/'
  };

  /**
   * This array is a lookup table that translates 6-bit positive integer
   * index values into their "Alternate Base64 Alphabet" equivalents.
   * This is NOT the real Base64 Alphabet as per in Table 1 of RFC 2045.
   * This alternate alphabet does not use the capital letters.  It is
   * designed for use in environments where "case folding" occurs.
   */
  private static final char intToAltBase64[] = {
    '!', '"', '#', '$', '%', '&', '\'', '(', ')', ',', '-', '.', ':',
    ';', '<', '>', '@', '[', ']', '^',  '`', '_', '{', '|', '}', '~',
    'a', 'b', 'c', 'd', 'e', 'f', 'g',  'h', 'i', 'j', 'k', 'l', 'm',
    'n', 'o', 'p', 'q', 'r', 's', 't',  'u', 'v', 'w', 'x', 'y', 'z',
    '0', '1', '2', '3', '4', '5', '6',  '7', '8', '9', '+', '?'
  };

  /**
   * Translates the specified Base64 string (as per Preferences.get(byte[]))
   * into a byte array.
   *
   * @throw IllegalArgumentException if <tt>s</tt> is not a valid Base64
   *        string.
   */
  public static byte[] base64ToByteArray(String s) {
    return base64ToByteArray(s, false);
  }

  /**
   * Translates the specified "alternate representation" Base64 string
   * into a byte array.
   *
   * @throw IllegalArgumentException or ArrayOutOfBoundsException
   *        if <tt>s</tt> is not a valid alternate representation
   *        Base64 string.
   */
  public static byte[] altBase64ToByteArray(String s) {
    return base64ToByteArray(s, true);
  }

  private static byte[] base64ToByteArray(String s, boolean alternate) {
    byte[] alphaToInt = (alternate ?  altBase64ToInt : base64ToInt);
    int sLen = s.length();
    int numGroups = sLen/4;
    if (4*numGroups != sLen)
      throw new IllegalArgumentException(
        "String length must be a multiple of four.");
    int missingBytesInLastGroup = 0;
    int numFullGroups = numGroups;
    if (sLen != 0) {
      if (s.charAt(sLen-1) == '=') {
        missingBytesInLastGroup++;
        numFullGroups--;
      }
      if (s.charAt(sLen-2) == '=')
        missingBytesInLastGroup++;
    }
    byte[] result = new byte[3*numGroups - missingBytesInLastGroup];

    // Translate all full groups from base64 to byte array elements
    int inCursor = 0, outCursor = 0;
    for (int i=0; i<numFullGroups; i++) {
      int ch0 = base64toInt(s.charAt(inCursor++), alphaToInt);
      int ch1 = base64toInt(s.charAt(inCursor++), alphaToInt);
      int ch2 = base64toInt(s.charAt(inCursor++), alphaToInt);
      int ch3 = base64toInt(s.charAt(inCursor++), alphaToInt);
      result[outCursor++] = (byte) ((ch0 << 2) | (ch1 >> 4));
      result[outCursor++] = (byte) ((ch1 << 4) | (ch2 >> 2));
      result[outCursor++] = (byte) ((ch2 << 6) | ch3);
    }

    // Translate partial group, if present
    if (missingBytesInLastGroup != 0) {
      int ch0 = base64toInt(s.charAt(inCursor++), alphaToInt);
      int ch1 = base64toInt(s.charAt(inCursor++), alphaToInt);
      result[outCursor++] = (byte) ((ch0 << 2) | (ch1 >> 4));

      if (missingBytesInLastGroup == 1) {
        int ch2 = base64toInt(s.charAt(inCursor++), alphaToInt);
        result[outCursor++] = (byte) ((ch1 << 4) | (ch2 >> 2));
      }
    }
    // assert inCursor == s.length()-missingBytesInLastGroup;
    // assert outCursor == result.length;
    return result;
  }

  /**
   * Translates the specified character, which is assumed to be in the
   * "Base 64 Alphabet" into its equivalent 6-bit positive integer.
   *
   * @throw IllegalArgumentException or ArrayOutOfBoundsException if
   *        c is not in the Base64 Alphabet.
   */
  private static int base64toInt(char c, byte[] alphaToInt) {
    int result = alphaToInt[c];
    if (result < 0)
      throw new IllegalArgumentException("Illegal character " + c);
    return result;
  }

  /**
   * This array is a lookup table that translates unicode characters
   * drawn from the "Base64 Alphabet" (as specified in Table 1 of RFC 2045)
   * into their 6-bit positive integer equivalents.  Characters that
   * are not in the Base64 alphabet but fall within the bounds of the
   * array are translated to -1.
   */
  private static final byte base64ToInt[] = {
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63, 52, 53, 54,
    55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1, -1, 0, 1, 2, 3, 4,
    5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23,
    24, 25, -1, -1, -1, -1, -1, -1, 26, 27, 28, 29, 30, 31, 32, 33, 34,
    35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51
  };

  /**
   * This array is the analogue of base64ToInt, but for the nonstandard
   * variant that avoids the use of uppercase alphabetic characters.
   */
  private static final byte altBase64ToInt[] = {
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 0, 1,
    2, 3, 4, 5, 6, 7, 8, -1, 62, 9, 10, 11, -1 , 52, 53, 54, 55, 56, 57,
    58, 59, 60, 61, 12, 13, 14, -1, 15, 63, 16, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, 17, -1, 18, 19, 21, 20, 26, 27, 28, 29, 30, 31, 32, 33,
    34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50,
    51, 22, 23, 24, 25
  };

  public static void main(String args[]) {
    int numRuns  = Integer.parseInt(args[0]);
    int numBytes = Integer.parseInt(args[1]);
    java.util.Random rnd = new java.util.Random();
    for (int i=0; i<numRuns; i++) {
      for (int j=0; j<numBytes; j++) {
        byte[] arr = new byte[j];
        for (int k=0; k<j; k++)
          arr[k] = (byte)rnd.nextInt();

        String s = byteArrayToBase64(arr);
        byte [] b = base64ToByteArray(s);
        if (!java.util.Arrays.equals(arr, b))
          System.out.println("Dismal failure!");

        s = byteArrayToAltBase64(arr);
        b = altBase64ToByteArray(s);
        if (!java.util.Arrays.equals(arr, b))
          System.out.println("Alternate dismal failure!");
      }
    }
  }
}