import type { ServiceAlert } from './ridebus';

export function isAlertActive(alert: ServiceAlert, now: number): boolean {
  return (
    Date.parse(alert.startTime) <= now &&
    (alert.endTime === null || now < Date.parse(alert.endTime))
  );
}

export function getActiveAlerts(
  alerts: ServiceAlert[],
  cityId: number,
  now: number
): ServiceAlert[] {
  const seen = new Set<number>();
  return alerts.filter((alert) => {
    if (
      alert.cityId !== cityId ||
      seen.has(alert.id) ||
      !isAlertActive(alert, now)
    )
      return false;
    seen.add(alert.id);
    return true;
  });
}

export function formatAlertRouteNumbers(alert: ServiceAlert): string {
  return alert.routeNumbers.map((number) => `№${number}`).join(' · ');
}

// Recheck the current data at each start/end boundary, independently of polling.
// Long timers are capped because browsers store their delay as a signed int32.
export function watchAlertValidity(
  alerts: ServiceAlert[],
  onChange: () => void
) {
  let timer: ReturnType<typeof setTimeout>;
  function schedule() {
    const now = Date.now();
    const next = alerts
      .flatMap((alert) => [alert.startTime, alert.endTime])
      .filter((time): time is string => time !== null)
      .map(Date.parse)
      .filter((time) => time > now)
      .reduce((earliest, time) => Math.min(earliest, time), Infinity);
    if (Number.isFinite(next))
      timer = setTimeout(refresh, Math.min(next - now, 2147483647));
  }
  function refresh() {
    onChange();
    schedule();
  }
  // Also cover a boundary crossed between render and effect subscription.
  timer = setTimeout(refresh, 0);
  return () => clearTimeout(timer);
}