// Synchronize at receipt using a bounded estimate of the return journey. The
// countdown uses performance.now(), so changing the OS clock cannot extend it.
export function roundClock(
  serverNow: number,
  sentAt: number,
  receivedAt: number,
) {
  const serverAtReceipt = serverNow + Math.max(0, receivedAt - sentAt) / 2;
  return {
    remaining(deadline: string, now: number) {
      return Math.max(
        0,
        Math.ceil(
          (Date.parse(deadline) - serverAtReceipt - (now - receivedAt)) / 1000,
        ),
      );
    },
  };
}