dorfteich/apps/backup/src/scheduler.ts

/**
 * Daily scheduling without a cron dependency: one `setTimeout` to the next
 * HH:MM occurrence (container-local time via TZ), re-armed after every run.
 * A run that crosses midnight simply shifts the next one — backups are
 * hours apart, drift by seconds is irrelevant.
 */

/** Milliseconds from `now` to the next local-time occurrence of `time` (HH:MM). */
export function msUntilNext(now: Date, time: string): number {
  const [hours = 0, minutes = 0] = time.split(':').map(Number);
  const next = new Date(now);
  next.setHours(hours, minutes, 0, 0);
  if (next.getTime() <= now.getTime()) next.setDate(next.getDate() + 1);
  return next.getTime() - now.getTime();
}

export function scheduleDaily(
  time: string,
  task: () => Promise<void>,
  log: { info(details: object, message: string): void },
): { stop(): void } {
  let timer: NodeJS.Timeout;
  const arm = (): void => {
    const delay = msUntilNext(new Date(), time);
    log.info({ nextRunInMs: delay }, 'next backup run scheduled');
    timer = setTimeout(() => {
      void task().finally(arm);
    }, delay);
  };
  arm();
  return { stop: () => clearTimeout(timer) };
}