startDate method

@override DateTime startDate(DateTime date)

Returns the next date that fits the dueDay.

• If the date - DateTime.day is less than the dueDay, it's returned the same month with the DateTime.day being dueDay, clamped to the months length.
• If the date - DateTime.day is greater than the dueDay, it's returned the next month with the DateTime.day being dueDay, clamped to the months length.

Implementation

@override
DateTime startDate(DateTime date) {
  if (valid(date)) return date;
  return next(date);
}