Hash Time Locked Contract

import { Script } from '@scure/btc-signer';
import { hash160 } from '@scure/btc-signer/utils.js';
import { hex } from '@scure/base';
import {
  RestArkProvider,
  RestIndexerProvider,
  MnemonicIdentity,
  VtxoScript,
  networks
} from '@arkade-os/sdk';

// Setup
const arkProvider = new RestArkProvider('https://arkade.computer');
const info = await arkProvider.getInfo();
const serverPubkey = hex.decode(info.signerPubkey).slice(1); // x-only
const exitDelay = BigInt(info.exitDelay);

// Identities
const receiver = MnemonicIdentity.fromMnemonic("abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon about");
const receiverPubkey = await receiver.xOnlyPublicKey();

// The secret (in production, receiver generates this)
const preimage = crypto.getRandomValues(new Uint8Array(32));

const preimageHash = hash160(preimage); // RIPEMD160(SHA256(preimage)), 20 bytes

OP_HASH160 <preimageHash> OP_EQUALVERIFY <receiverPubkey> OP_CHECKSIGVERIFY <serverPubkey> OP_CHECKSIG

// Collaborative: preimage + receiverSig + serverSig
const collaborativePath = Script.encode([
  'HASH160',
  preimageHash,
  'EQUALVERIFY',
  receiverPubkey,
  'CHECKSIGVERIFY',
  serverPubkey,
  'CHECKSIG'
]);

<exitDelay> OP_CHECKSEQUENCEVERIFY OP_DROP OP_HASH160 <preimageHash> OP_EQUALVERIFY <receiverPubkey> OP_CHECKSIG

// Unilateral: after exitDelay, preimage + receiverSig
const unilateralPath = Script.encode([
  exitDelay,
  'CHECKSEQUENCEVERIFY',
  'DROP',
  'HASH160',
  preimageHash,
  'EQUALVERIFY',
  receiverPubkey,
  'CHECKSIG'
]);

// Build the VTXO with both paths
const vhtlcScript = new VtxoScript([collaborativePath, unilateralPath]);
const vhtlcAddress = vhtlcScript.address(networks.bitcoin.hrp, serverPubkey).encode();

console.log('VHTLC address:', vhtlcAddress);
console.log('Preimage (save this!):', hex.encode(preimage));

import {
  buildOffchainTx,
  CSVMultisigTapscript,
  Transaction
} from '@arkade-os/sdk';
import { base64 } from '@scure/base';

// Query the VTXO
const indexerProvider = new RestIndexerProvider('https://arkade.computer');
const result = await indexerProvider.getVtxos({
  scripts: [hex.encode(vhtlcScript.pkScript)],
  spendableOnly: true,
});

const vtxo = result.vtxos[0];

// Recipient script (where funds go after claim)
const recipientScript = /* your destination VtxoScript */;

// Build the transaction
const serverUnrollScript = CSVMultisigTapscript.decode(
  hex.decode(info.checkpointTapscript)
);

const input = {
  txid: vtxo.txid,
  vout: vtxo.vout,
  value: vtxo.value,
  tapLeafScript: vhtlcScript.findLeaf(hex.encode(collaborativePath)),
  tapTree: vhtlcScript.encode(),
};

const outputs = [{ amount: vtxo.value, script: recipientScript.pkScript }];

const { arkTx, checkpoints } = buildOffchainTx(
  [input],
  outputs,
  serverUnrollScript
);

// Sign with receiver
const psbt = arkTx.toPSBT();
const tx = Transaction.fromPSBT(psbt);
const signedTx = await receiver.sign(tx);

// Submit to server (server co-signs)
const { arkTxid, signedCheckpointTxs } = await arkProvider.submitTx(
  base64.encode(signedTx.toPSBT()),
  checkpoints.map(c => base64.encode(c.toPSBT()))
);

// Finalize checkpoints
const finalCheckpoints = await Promise.all(
  signedCheckpointTxs.map(async (cpB64) => {
    const cpTx = Transaction.fromPSBT(base64.decode(cpB64));
    const signed = await receiver.sign(cpTx, [0]);
    return base64.encode(signed.toPSBT());
  })
);

await arkProvider.finalizeTx(arkTxid, finalCheckpoints);
console.log('VHTLC claimed!', arkTxid);