import java.util.Arrays;

public class Base64Test {

  private static char[] nrToChar;
  private static int[] charToNr;

  static {
    nrToChar = new char[64];
    for (char i = 'A'; i <= 'Z'; i++) {
      nrToChar[i - 'A'] = i;
    }
    int offset = 'Z' - 'A' + 1; // 26
    for (char i = 'a'; i <= 'z'; i++) {
      nrToChar[offset + (i - 'a')] = i;
    }
    offset = offset + 'z' - 'a' + 1; // 52
    for (char i = '0'; i <= '9'; i++) {
      nrToChar[offset + (i - '0')] = i;
    }
    nrToChar[62] = '+';
    nrToChar[63] = '/';

    charToNr = new int[256];

    for (int i = 0; i < 64; i++) {
      char c = nrToChar[i];
      charToNr[c] = findNr(c);
    }
  }

  private static byte findNr(char c) {
    for (int i = 0; i < nrToChar.length; i++) {
      if (nrToChar[i] == c) {
        return (byte) i;
      }
    }
    throw new Error("Char not found");
  }

  /**
   * requires: - input is a Base64 encoding.
   * ensurse:  - result is the decoded data from the input.
   **/
  public static byte[] base64Decode(String in) {
    int len = (in.length() / 4) * 3;
    byte[] out = new byte[len];
    int j = 0;
    for (int i = 0; i < out.length; i += 3) {
      int a = charToNr[(int) in.charAt(j)];
      int b = charToNr[(int) in.charAt(j + 1)];
      int c = charToNr[(int) in.charAt(j + 2)];
      int d = charToNr[(int) in.charAt(j + 3)];
      out[i] = (byte) ((a << 2) | (b >> 4));
      out[i + 1] = (byte) ((b << 4) | (c >> 2));
      out[i + 2] = (byte) ((c << 6) | d);
      j += 4;
    }
    return out;
  }

  public static int unsignedByte2Int(byte a) {
    return (int) a & 0xFF;
  }

  /***
   * requires: - input divisible by 3 (in.length % 3 == 0)
   * ensures:  - result is a Base64 encoding of the input.
   *           - input is not modified
   **/
  public static String base64Encode(byte[] in) {
    int resLength = (in.length / 3) * 4;
    StringBuffer out = new StringBuffer(resLength);
    for (int i = 0; i < in.length; i += 3) {
      out.append(nrToChar[(in[i] >> 2) & 63]);
      out.append(nrToChar[((in[i] & 3) << 4) | ((in[i + 1] >> 4) & 15)]);
      out.append(nrToChar[((in[i + 1] & 15) << 2)
          | ((in[i + 2] >> 6) & 3)]);
      out.append(nrToChar[in[i + 2] & 63]);
    }
    return out.toString();
  }

  public static void printByteArray(byte[] in) {
    for (int i = 0; i < in.length; i++) {
      System.out.print(in[i]);
    }
  }

  public static byte[] generate() {
    // TODO generate a random byte array. Note any input requirements to the
    // Base 64 function.
    return null;
  }

  public static boolean test(byte[] input) {
    try {
      // TODO Write a test for the Base64 encoder / decoder.
      return false;
    } catch (Exception e) {
      e.printStackTrace();
      return false;
    }
  }

  public static void main(String[] args) {
    for (int i = 0; i < 10000; i++) {
      byte[] array = generate();
      if (!test(array)) {
        System.out.println("Failed: " + Arrays.toString(array));
        System.exit(0);
      }
    }
    System.out.println("Done.");
  }

}