calculateDerivedAddress.ts

import { blake2AsU8a, encodeAddress, decodeAddress } from '@polkadot/util-crypto';
import { u8aToHex, hexToU8a, bnToU8a } from '@polkadot/util';

import yargs from 'yargs';

const args = yargs
  .options({
    address: { type: 'string', demandOption: true, alias: 'a' },
    index: { type: 'array', demandOption: true, alias: 'i' },
  })
  .check((argv) => {
    // Ensure that index array is parsed correctly
    for (const i of argv['index'])
      if (typeof i !== 'number' || !Number.isInteger(i))
        throw new Error(`${i} is not an integer. Please try the command again with integers.`);
    return true;
  }).argv;

// If address does not start with 0x - decode it
let address = args['address'];
const ethAddress = address.length === 42;

const derivativeToEthAddress = (d: string) => d.slice(0, 42);
let derivative;

for (let l = 0; l < args['index'].length; l++) {
  if (!ethAddress) {
    address = decodeAddress(address);
  } else {
    address = hexToU8a(address);
  }

  // Calculate Derivative Address of Given Index
  derivative = u8aToHex(
    blake2AsU8a(
      new Uint8Array([
        ...new TextEncoder().encode('modlpy/utilisuba'),
        ...address,
        ...bnToU8a(args['index'][l], { bitLength: 16 }),
      ]),
      256
    )
  );

  if (ethAddress) address = derivativeToEthAddress(derivative);
  else address = derivative;
}

if (ethAddress) {
  console.log(
    `Moonbeam derivative at index ${args['index']}: ${derivativeToEthAddress(derivative)}`
  );
} else {
  console.log(`32 Bytes derivative at index ${args['index']}: ${derivative}`);
  console.log(`Encoded: ${encodeAddress(derivative)}`);
}