getIsoWeekNumber function

int getIsoWeekNumber(
  1. DateTime date
)

Implementation

int getIsoWeekNumber(DateTime date) {
  // Get the Thursday of the current week (ISO week starts near the closest Thursday)
  DateTime thursdayOfCurrentWeek = date.add(Duration(days: (4 - date.weekday)));

  // Get January 4th of the year (since ISO weeks always start around this date)
  DateTime firstThursdayOfYear = DateTime(thursdayOfCurrentWeek.year, 1, 4);

  // Find the Thursday of the first week of the year
  DateTime firstWeekThursday = firstThursdayOfYear.add(Duration(days: (4 - firstThursdayOfYear.weekday)));

  // Calculate the difference in days between the current week's Thursday and the year's first week Thursday
  int weekNumber = ((thursdayOfCurrentWeek.difference(firstWeekThursday).inDays) ~/ 7) + 1;

  return weekNumber;
}