of method
- DateTime date
override
    Returns the period of the given date considering the generator type.
Implementation
@override
WeekPeriod of(DateTime date) {
  var difference = weekStart - date.weekday;
  if (difference > 0) difference -= DateTime.daysPerWeek;
  final day = date.day + difference;
  final start = date.copyWith(day: day).date;
  final end = start.addDays(DateTime.daysPerWeek - 1).endOfDay;
  return WeekPeriod(start: start, end: end);
}