update_token_account_bal.ts

import { BN } from '@coral-xyz/anchor';
import { PublicKey } from '@solana/web3.js';
import { stringify, parse } from 'json-bigint';

import fs from 'fs';

const file = 'tests/accounts/token_account.json'; // Replace with the path to your JSON file

const account = fs.readFileSync(file, 'utf8');
const newU64 = new BN(90000000000); // Replace with the desired u64 value

const parsedAccount = parse(account);

console.log('Reading account data from:', file);

const prevBuffer = Buffer.from(parsedAccount.account.data[0], 'base64');

console.log(
  'Account mint:',
  new PublicKey(prevBuffer.subarray(0, 32)).toBase58()
);
console.log(
  'Account owner:',
  new PublicKey(prevBuffer.subarray(32, 64)).toBase58()
);
console.log(
  'Initial account value:',
  new BN(prevBuffer.subarray(64, 72), 'le').toString()
);

// Extract the 8 bytes as a big-endian u64
const uint8Array = new Uint8Array(prevBuffer);

console.log('New account value:', newU64.toString());

// Convert the new u64 to bytes and replace the original bytes
const nextAmount = newU64.toBuffer('le', 8);
uint8Array.set(nextAmount, 64);

const nextBuffer = Buffer.from(uint8Array);

console.log(
  'Updated account mint:',
  new PublicKey(nextBuffer.subarray(0, 32)).toBase58()
);
console.log(
  'Updated account owner:',
  new PublicKey(nextBuffer.subarray(32, 64)).toBase58()
);
console.log(
  'Updated account value:',
  new BN(nextBuffer.subarray(64, 72), 'le').toString()
);

const updatedAccount = {
  ...parsedAccount.account,
  data: [nextBuffer.toString('base64'), 'base64'],
};

const updatedJsonData = {
  ...parsedAccount,
  account: {
    ...updatedAccount,
    rentEpoch: parsedAccount.account.rentEpoch,
  },
  pubkey: parsedAccount.pubkey,
};

fs.writeFileSync(file, stringify(updatedJsonData, null, 2));
console.log('Account data updated and written back to:', file);