Base36.java

package io.multibase;

import java.math.BigInteger;

public class Base36 {

  public static byte[] decode(String in) {
    byte[] withoutLeadingZeroes = new BigInteger(in, 36).toByteArray();
    int zeroPrefixLength = zeroPrefixLength(in);
    byte[] res = new byte[zeroPrefixLength + withoutLeadingZeroes.length];
    System.arraycopy(withoutLeadingZeroes, 0, res, zeroPrefixLength, withoutLeadingZeroes.length);
    return res;
  }

  public static String encode(byte[] in) {
    String withoutLeadingZeroes = new BigInteger(1, in).toString(36);
    int zeroPrefixLength = zeroPrefixLength(in);
    StringBuilder b = new StringBuilder();
    for (int i = 0; i < zeroPrefixLength; i++) b.append("0");
    b.append(withoutLeadingZeroes);
    return b.toString();
  }

  private static int zeroPrefixLength(byte[] bytes) {
    for (int i = 0; i < bytes.length; i++) {
      if (bytes[i] != 0) {
        return i;
      }
    }
    return bytes.length;
  }

  private static int zeroPrefixLength(String in) {
    for (int i = 0; i < in.length(); i++) {
      if (in.charAt(i) != '0') {
        return i;
      }
    }
    return in.length();
  }
}