impl/typescript.ts

import { type Countdown } from "./time_countdown_types.ts";

function pad2(n: number): string {
  return n < 10 ? "0" + n : String(n);
}

/**
 * The time left until `until`, as a number and as a timer's text. A moment is
 * reached at `until` itself, as a JWT's exp is (RFC 7519 4.1.4: "on or
 * after"), so `now === until` is expired with nothing left.
 */
export function countdown(until: number, now: number): Countdown {
  if (typeof until !== "number" || !Number.isSafeInteger(until)) throw new RangeError("until must be a whole number of seconds");
  if (typeof now !== "number" || !Number.isSafeInteger(now)) throw new RangeError("now must be a whole number of seconds");
  const seconds = until > now ? until - now : 0;
  const h = Math.floor(seconds / 3600);
  const m = Math.floor((seconds % 3600) / 60);
  const s = seconds % 60;
  const text = h > 0 ? `${h}:${pad2(m)}:${pad2(s)}` : `${m}:${pad2(s)}`;
  return { expired: seconds === 0, seconds, text };
}