// How far server F's clock is from this machine's: the moment F's Date header
// turns to the next second, against our clock at that moment (the middle of
// the two requests around it). A ticket carries whole seconds, and F refuses
// one from its future, so F must not be behind the dashboard's machine.
//
//   node tools/live/clock.mjs [host] [port]
import http from 'node:http';
const [host = '172.22.0.38', port = '8081'] = process.argv.slice(2);
const agent = new http.Agent({ keepAlive: true, maxSockets: 1 });
const ask = () =>
  new Promise((resolve, reject) => {
    const sent = Date.now();
    http
      .get({ host, port, path: '/healthz', agent }, (r) => {
        r.resume();
        r.on('end', () => resolve({ sent, got: Date.now(), date: Date.parse(r.headers.date) }));
      })
      .on('error', reject);
  });
let last = await ask();
const offsets = [];
for (const end = Date.now() + 6000; Date.now() < end;) {
  const now = await ask();
  if (now.date !== last.date) offsets.push(Math.round(now.date - (last.got + now.sent) / 2) + `±${Math.ceil((now.sent - last.got) / 2)}`);
  last = now;
}
agent.destroy();
console.log(`${host}:${port} clock minus ours (ms): ${offsets.join(' ')}`);