// Parse an "HH:mm" (24h) string into minutes-since-midnight, or null if malformed.
export function parseHHMM(value: string): number | null {
  const m = /^(\d{2}):(\d{2})$/.exec(value);
  if (!m) return null;
  const hours = Number(m[1]);
  const minutes = Number(m[2]);
  if (hours > 23 || minutes > 59) return null;
  return hours * 60 + minutes;
}

// Is `now`'s wall-clock time inside the [start, end) window? The window may wrap
// past midnight (start > end, e.g. 21:00 → 07:00). A zero-length window
// (start === end) is treated as never active. Malformed inputs → false.
export function isWithinTimeWindow(start: string, end: string, now: Date = new Date()): boolean {
  const s = parseHHMM(start);
  const e = parseHHMM(end);
  if (s === null || e === null || s === e) return false;
  const cur = now.getHours() * 60 + now.getMinutes();
  if (s < e) return cur >= s && cur < e;
  // Overnight wrap: active from start until midnight, then midnight until end.
  return cur >= s || cur < e;
}