// Keep the store locked until writers finish, or until the process exits.
export function installShutdown(store, drain, { timeout = 5000 } = {}) {
  const release = () => {
    try { store.close(); }
    catch { console.error('Could not remove the access store lock. Check file permissions.'); process.exitCode = 1; }
  };
  process.once('exit', release);
  let stopping;
  const stop = () => {
    if (stopping) return stopping;
    const deadline = setTimeout(() => {
      console.error('Shutdown timed out; exiting and releasing the access store lock.');
      process.exit(1);
    }, timeout).unref();
    stopping = Promise.resolve().then(drain).catch(() => {
      console.error('Gateway shutdown failed.');
      // Do not unlock while unfinished jobs could still write to the store.
      process.exit(1);
    }).then(() => {
      clearTimeout(deadline);
      release();
    });
    return stopping;
  };
  // Keep handlers installed so repeated Ctrl+C cannot interrupt cleanup.
  process.on('SIGINT', stop);
  process.on('SIGTERM', stop);
  return stop;
}