/**
 * The one invariant that makes a shiftSchedule period mean something: every Shift hanging off a ShiftSchedule
 * falls inside that ShiftSchedule's dates. Overlapping shiftSchedules are allowed (membership is the explicit
 * shiftScheduleId FK), so this is what keeps a period honest rather than a uniqueness rule.
 */
export function isWithinPeriod(date: Date, startDate: Date, endDate: Date): boolean {
  const at = date.getTime();
  return at >= startDate.getTime() && at <= endDate.getTime();
}