Make, accept and cancel offers

// node offers.mjs make <outpoint> <price> [<days>|never]
// node offers.mjs accept <offer id>
// node offers.mjs cancel <offer id> [<offer id> …]
// WIF: the private key (mainnet WIF) of your Taproot address.
import * as bitcoin from 'bitcoinjs-lib';
import * as ecc from 'tiny-secp256k1';
import { ECPairFactory } from 'ecpair';

bitcoin.initEccLib(ecc);
const ECPair = ECPairFactory(ecc);
const BASE = process.env.RARESATS_URL ?? 'https://raresats.net';
const [command, ...args] = process.argv.slice(2);

const key = ECPair.fromWIF(process.env.WIF);
const internalKey = key.publicKey.subarray(1, 33);
const { address, output } = bitcoin.payments.p2tr({ internalPubkey: internalKey });
const publicKey = Buffer.from(key.publicKey).toString('hex');
const signer = key.tweak(bitcoin.crypto.taggedHash('TapTweak', internalKey));

async function call(path, body) {
  const response = await fetch(`${BASE}${path}`, body === undefined ? {} : {
    method: 'POST',
    headers: { 'content-type': 'application/json' },
    body: JSON.stringify(body)
  });
  const json = await response.json();
  if (!response.ok) {
    throw Object.assign(new Error(`${path}: ${response.status} ${json.code}: ${json.error}`), { code: json.code });
  }
  return json;
}

// Sign exactly the inputs listed, with the default sighash; never finalize.
function sign({ psbt, sign: inputs }) {
  const parsed = bitcoin.Psbt.fromBase64(psbt);
  for (const { index } of inputs) {
    parsed.signInput(index, signer);
  }
  return parsed.toBase64();
}

// BIP-322 simple: sign the virtual to_sign transaction; the signature is its witness.
function signBip322(message) {
  const tag = bitcoin.crypto.sha256(Buffer.from('BIP0322-signed-message'));
  const hash = bitcoin.crypto.sha256(Buffer.concat([tag, tag, Buffer.from(message, 'utf8')]));
  const toSpend = new bitcoin.Transaction();
  toSpend.version = 0;
  toSpend.addInput(new Uint8Array(32), 0xffffffff, 0, Uint8Array.from([0x00, 0x20, ...hash]));
  toSpend.addOutput(output, 0n);
  const toSign = new bitcoin.Psbt();
  toSign.setVersion(0);
  toSign.addInput({ hash: toSpend.getHash(), index: 0, sequence: 0, witnessUtxo: { script: output, value: 0n }, tapInternalKey: internalKey });
  toSign.addOutput({ script: Uint8Array.from([0x6a]), value: 0n });
  toSign.signInput(0, signer);
  toSign.finalizeAllInputs();
  const witness = toSign.extractTransaction(true).ins[0].witness;
  return Buffer.concat([Buffer.from([witness.length]), ...witness.flatMap(item => [Buffer.from([item.length]), Buffer.from(item)])]).toString('base64');
}

if (command === 'make') {
  const [outpoint, price, days = '7'] = args;
  const fees = await call('/api/market/fees');
  const prepared = await call('/api/market/offers/prepare', {
    outpoint,
    price: Number(price),
    bidder: { payment_address: address, payment_public_key: publicKey, ordinals_address: address, ordinals_public_key: publicKey },
    fee_rate: fees.normal,
    expires_in: days === 'never' ? 'never' : Number(days) * 86400
  });
  const { summary } = prepared;
  console.log(`price ${summary.price} + platform fee ${summary.platform_fee} + network fee ${summary.network_fee} = ${summary.total} sats`);
  const { offer } = await call('/api/market/offers', { id: prepared.id, psbt: sign(prepared) });
  console.log(`${offer.id} ${offer.outpoint}: ${offer.status}, expires ${offer.expires_at === null ? 'never' : new Date(offer.expires_at * 1000).toISOString()}`);
} else if (command === 'accept') {
  const [id] = args;
  const prepared = await call(`/api/market/offers/${id}/accept/prepare`, { seller_address: address, seller_public_key: publicKey });
  console.log(`you receive ${prepared.summary.price} sats for ${prepared.summary.outpoint}`);
  const body = { psbt: sign(prepared) };
  // Resubmitting is idempotent: retry while the outcome is unknown.
  for (let attempt = 1; ; attempt++) {
    try {
      console.log('accepted', (await call(`/api/market/offers/${id}/accept`, body)).txid);
      break;
    } catch (error) {
      if (error.code !== 'broadcast_unknown' || attempt === 5) {
        throw error;
      }
      await new Promise(resolve => setTimeout(resolve, 10_000));
    }
  }
} else if (command === 'cancel') {
  const message = `raresats.net cancel-offer ${args.join(',')} ${Math.floor(Date.now() / 1000)}`;
  const { offers } = await call('/api/market/offers/cancel', { ids: args, address, message, signature: signBip322(message) });
  for (const offer of offers) {
    console.log(`${offer.id}: ${offer.status}`);
  }
} else {
  console.error('usage: node offers.mjs make <outpoint> <price> [<days>|never] | accept <offer id> | cancel <offer id> …');
  process.exit(1);
}