splitUTXO.ts

import { getScriptPubkey, getUtxos, pushBTCpmt } from "./utils/utxo";
import { Wallet } from "./utils/wallet";
import * as Bitcoin from "bitcoinjs-lib";
import * as ecc from "tiny-secp256k1";

Bitcoin.initEccLib(ecc);

const COUNT = 6;
const UTXO_OUTPUT = 546;
const SIGNATURE_SIZE = 126;
const TESTNET_FEERATE = 1


const main = async () => {
  const wallet = new Wallet();

  console.log('address', wallet.address)

  const utxos = await getUtxos(wallet.address);

  const utxo = utxos.find((utxo) => utxo.value > 10000);

  if (utxo === undefined) throw new Error("No btcs");

  const psbt = new Bitcoin.Psbt({ network: Bitcoin.networks.testnet });

  psbt.addInput({
    hash: utxo.txid,
    index: utxo.vout,
    witnessUtxo: {
      value: utxo.value,
      script: wallet.output,
    },
    tapInternalKey: Buffer.from(wallet.publicKey, "hex").slice(1, 33),
  });

  for (let i = 0; i < 6; i++) {
    psbt.addOutput({
      address: wallet.address,
      value: 546,
    });
  }

  const fee = calculateTxFee(psbt, TESTNET_FEERATE)

  psbt.addOutput({
    address: wallet.address,
    value: utxo.value - UTXO_OUTPUT * COUNT - fee,
  });

  const signedPsbt = wallet.signPsbt(psbt);

  const tx = signedPsbt.extractTransaction();
  const txHex = tx.toHex();

  const txId = await pushBTCpmt(txHex);

  console.log(`Successfully split. Txid:${txId}`)
};

const calculateTxFee = (psbt: Bitcoin.Psbt, feeRate: number): number => {
  const tx = new Bitcoin.Transaction();

  for (let i = 0; i < psbt.txInputs.length; i++) {
    const txInput = psbt.txInputs[i];

    tx.addInput(txInput.hash, txInput.index, txInput.sequence);
    tx.setWitness(i, [Buffer.alloc(SIGNATURE_SIZE)]);
  }

  for (let txOutput of psbt.txOutputs) {
    tx.addOutput(txOutput.script, txOutput.value);
  }
  tx.addOutput(psbt.txOutputs[0].script, psbt.txOutputs[0].value);

  return tx.virtualSize() * feeRate;
};

main();