Base62.java

package io.kaif.token;

public class Base62 {

  public static final String ALPHABET = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";

  public static final long BASE = ALPHABET.length();

  public static String fromBase10(long i) {
    StringBuilder sb = new StringBuilder("");
    while (i > 0) {
      i = fromBase10(i, sb);
    }
    return sb.reverse().toString();
  }

  private static long fromBase10(long i, final StringBuilder sb) {
    int rem = (int) (i % BASE);
    sb.append(ALPHABET.charAt(rem));
    return i / BASE;
  }

  public static long toBase10(String str) {
    return toBase10(new StringBuilder(str).reverse().toString().toCharArray());
  }

  private static long toBase10(char[] chars) {
    long n = 0;
    for (int i = chars.length - 1; i >= 0; i--) {
      n += toBase10(ALPHABET.indexOf(chars[i]), i);
    }
    return n;
  }

  private static long toBase10(long n, int pow) {
    return n * (long) Math.pow(BASE, pow);
  }

  private Base62() {
  }
}