DateTime utils

public static class DateTimeUtils
    {
        public static DateTime NSDateToDateTime(this NSDate date)
        {
            var reference = TimeZone.CurrentTimeZone.ToLocalTime(new DateTime(2001, 1, 1, 0, 0, 0));
            return reference.AddSeconds(date.SecondsSinceReferenceDate);
        }

        public static NSDate DateTimeToNSDate(this DateTime date)
        {
            var reference = TimeZone.CurrentTimeZone.ToLocalTime(new DateTime(2001, 1, 1, 0, 0, 0));
            return NSDate.FromTimeIntervalSinceReferenceDate((date - reference).TotalSeconds);
        }

        public static DateTime StartOfWeek(this DateTime dt, DayOfWeek startOfWeek)
        {
            var ci = System.Threading.Thread.CurrentThread.CurrentCulture;
            var fdow = ci.DateTimeFormat.FirstDayOfWeek;
            return DateTime.Today.AddDays(-(DateTime.Today.DayOfWeek - fdow));
        }
    }