Gregorian constructor

Gregorian(int year, [ int month = 1, int day = 1, int hour = 0, int minute = 0, int second = 0, ])

Create a Gregorian date by using year, month and day

year and month default to 1

Implementation

Gregorian(this.year,
    [this.month = 1,
    this.day = 1,
    this.hour = 0,
    this.minute = 0,
    this.second = 0]) {
  // should be between: Gregorian(560,3,20) and Gregorian(3798,12,31)
  if (year < 560 || year > 3798) {
    throw DateException('Gregorian date is out of computable range.');
  }

  if (month < 1 || month > 12) {
    throw DateException('Gregorian month is out of valid range.');
  }

  // monthLength is very cheap
  // isLeapYear is also very cheap
  final ml = monthLength;

  if (day < 1 || day > ml) {
    throw DateException('Gregorian day is out of valid range.');
  }

  // no need for further analysis for MAX, but for MIN being in year 560:
  if (year == 560) {
    if (month < 3 || (month == 3 && day < 20)) {
      throw DateException('Gregorian date is out of computable range.');
    }
  }
}