public static DateTimeOffset StartOfWeek(this DateTimeOffset dt, DayOfWeek firstDayOfWeek = DayOfWeek.Monday)
{
int diff = (7 + (dt.DayOfWeek - firstDayOfWeek)) % 7;
return(new DateTimeOffset(dt.AddDays(-1 * diff).Date, dt.Offset));
}
/// <summary>
/// 요일을 기준으로 해당 주의 첫번째 날짜와 시간을 반환한다.
/// </summary>
public static DateTimeOffset BeginOfWeek(this DateTimeOffset self, DayOfWeek startOfWeek)
{
int diff = (7 + (self.DayOfWeek - startOfWeek)) % 7;
return(self.AddDays(-1 * diff));
}