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package io.ipfs.multibase;
import java.math.BigInteger;
public class Base36 {
public static byte[] decode(String in) {
if (in.isEmpty()) {
return new byte[0];
}
BigInteger value = new BigInteger(in, 36);
byte[] withoutLeadingZeroes = value.signum() == 0 ? new byte[0] : value.toByteArray();
// BigInteger.toByteArray() prepends a 0x00 sign byte when the top magnitude byte has its
// high bit set; strip it so the only leading zeroes are the ones recorded in the string.
int start = withoutLeadingZeroes.length > 0 && withoutLeadingZeroes[0] == 0 ? 1 : 0;
int magnitudeLength = withoutLeadingZeroes.length - start;
int zeroPrefixLength = zeroPrefixLength(in);
byte[] res = new byte[zeroPrefixLength + magnitudeLength];
System.arraycopy(withoutLeadingZeroes, start, res, zeroPrefixLength, magnitudeLength);
return res;
}
public static String encode(byte[] in) {
BigInteger value = new BigInteger(1, in);
String withoutLeadingZeroes = value.signum() == 0 ? "" : value.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();
}
}
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