public static DateTime CalculateDateTime(this DateTime datetime, DOWEnum dayOfWeek, bool IsEOD) =>
 (IsEOD) ?
 datetime.Date.AddDays((int)dayOfWeek).AddHours(23).AddMinutes(59).AddSeconds(59)
     :
 datetime.Date.AddDays((int)dayOfWeek).AddHours(0).AddMinutes(0).AddSeconds(0);
 private DateTime CalcDateTime(int week, DOWEnum dow, bool eod = false) =>
 (eod ?
  ClassStartDay.Date.AddHours(23).AddMinutes(59).AddSeconds(59)
     : ClassStartDay.Date.AddHours(0).AddMinutes(0).AddSeconds(0))
 .AddDays((week - 1) * 7)
 .AddDays(((int)dow < 0) ? 0 : (int)dow);