PdfRpt.Core.Helper.PersianDate.Find1StDayOfMonth C# (CSharp) Method

        public static int Find1StDayOfMonth(int year, int monthIndex, CalendarType calendarType = CalendarType.PersianCalendar)
        {
            if (calendarType == CalendarType.GregorianCalendar)
                return (int)new DateTime(year, monthIndex, 1).DayOfWeek;

            int outYear, outMonth, outDay, dayWeek = 1;
            HijriToGregorian(year, monthIndex, 1, out outYear, out outMonth, out outDay);

            var res = new DateTime(outYear, outMonth, outDay);

            switch (res.DayOfWeek)
            {
                case DayOfWeek.Saturday:
                    dayWeek = 0;
                    break;

                case DayOfWeek.Sunday:
                    dayWeek = 1;
                    break;

                case DayOfWeek.Monday:
                    dayWeek = 2;
                    break;

                case DayOfWeek.Tuesday:
                    dayWeek = 3;
                    break;

                case DayOfWeek.Wednesday:
                    dayWeek = 4;
                    break;

                case DayOfWeek.Thursday:
                    dayWeek = 5;
                    break;

                case DayOfWeek.Friday:
                    dayWeek = 6;
                    break;
            }

            return dayWeek;
        }