checksum.ts

import { sshash } from './sshash.ts';

export function checkAddressChecksum (decoded: Uint8Array): [boolean, number, number, number] {
  const ss58Length = (decoded[0] & 0b0100_0000) ? 2 : 1;
  const ss58Decoded = ss58Length === 1
    ? decoded[0]
    : ((decoded[0] & 0b0011_1111) << 2) | (decoded[1] >> 6) | ((decoded[1] & 0b0011_1111) << 8);

  // 32/33 bytes public + 2 bytes checksum + prefix
  const isPublicKey = [34 + ss58Length, 35 + ss58Length].includes(decoded.length);
  const length = decoded.length - (isPublicKey ? 2 : 1);

  // calculate the hash and do the checksum byte checks
  const hash = sshash(decoded.subarray(0, length));
  const isValid = (decoded[0] & 0b1000_0000) === 0 && ![46, 47].includes(decoded[0]) && (
    isPublicKey
      ? decoded[decoded.length - 2] === hash[0] && decoded[decoded.length - 1] === hash[1]
      : decoded[decoded.length - 1] === hash[0]
  );

  return [isValid, length, ss58Length, ss58Decoded];
}