previous method

@override DateTime previous(DateTime date)

Returns the previous date that fits the dayInYear.

• If the current date - DayInYear.dayInYear is greater than the dayInYear, it's returned the same year with the DayInYear.dayInYear being the dayInYear.
• If the current date - DayInYear.dayInYear is less than the dayInYear, it's returned the previous year with the DayInYear.dayInYear being the dayInYear.

Implementation

@override
DateTime previous(DateTime date) {
  final thisYearDay = date.firstDayOfYear
      .add(Duration(days: dayInYear - 1))
      .clamp(max: date.lastDayOfYear);
  if (date.dayInYear > dayInYear) return thisYearDay;
  return date
      .copyWith(year: date.year - 1)
      .firstDayOfYear
      .add(Duration(days: dayInYear - 1))
      .clamp(max: date.copyWith(year: date.year - 1).lastDayOfYear);
}