根据指定日期计算周数

/// <summary>
        /// 计算当前周
        /// </summary>
        /// <returns></returns>
        public static int GetWeekNoNow(string time)
        {
            string systemStartDate = CCAConfig.SystemStartDate;
            if (string.IsNullOrEmpty(systemStartDate)) throw new Exception("Not config system start date");

            DateTime startDate = DateTime.Parse(systemStartDate);
            int str = new System.Globalization.GregorianCalendar().GetWeekOfYear(startDate, System.Globalization.CalendarWeekRule.FirstDay, DayOfWeek.Monday);

            int strNow = new System.Globalization.GregorianCalendar().GetWeekOfYear(DateTime.Now, System.Globalization.CalendarWeekRule.FirstDay, DayOfWeek.Monday);

            int weekNo = strNow - str + 1; // base on 1

            return weekNo;
        }