using System;

​

public class Program

{

    static DateTime todaysDate = new DateTime(2016,03,31,11,33,11);

    public static void Main()

    {

        DateTime startDate = new DateTime();

        DateTime aDueDate = new DateTime();

        startDate = DateTime.Now;               

        startDate = new DateTime(2016,04,01,08,26,44);

        Console.WriteLine( "Start Date : " + startDate.ToString("dd-MMM-yyyy HH:mm:ss")  + "           Todays Date: " + todaysDate.ToString("dd-MMM-yyyy HH:mm:ss") );

        Console.WriteLine();

​

        //-----------------------------------------------------------------------------------------------------------------------------------------------

        int result = DateTime.Compare(startDate, todaysDate );

        string relationship;

        if (result < 0)

            relationship = "is earlier than";

        else if (result == 0)

            relationship = "is the same time as";         

            else

            relationship = "is later than";

            //Console.WriteLine("{0} {1} {2}", startDate, relationship,  todaysDate);

        //-----------------------------------------------------------------------------------------------------------------------------------------------

        Console.WriteLine(System.Environment.NewLine);

​

        Schedule sType = new Schedule();

        sType.TypeName = "hour";

        sType.HourInterval = 12;

        aDueDate = CalculateDueDateBySchedule(startDate, sType);        

        Console.WriteLine( sType.TypeName + " " + sType.HourInterval+  " Due Date:      " + aDueDate.ToString("dd-MMM-yyyy HH:mm:ss") );

        sType.TypeName = "hour";

        sType.HourInterval = 24;

        aDueDate = CalculateDueDateBySchedule(startDate, sType);        

        Console.WriteLine( sType.TypeName + " " + sType.HourInterval+  " Due Date:      " + aDueDate.ToString("dd-MMM-yyyy HH:mm:ss") );

​

        Console.WriteLine(System.Environment.NewLine);

        sType.TypeName = "week";

        sType.DayName = "Friday";

        Console.WriteLine(sType.DayName + " "+ GetDayOftheWeekInt(sType.DayName ) );

        sType.WeekInterval = 1;     

        aDueDate = CalculateDueDateBySchedule(startDate, sType);        

        Console.WriteLine( sType.TypeName + " " +  sType.DayName + "  Week Interval: " + sType.WeekInterval+  " First Due Date:      " + aDueDate.ToString("dd-MMM-yyyy HH:mm:ss") );

        Console.WriteLine(System.Environment.NewLine);

        sType.TypeName = "month";

        sType.MonthDate = "first";

        sType.MonthInterval = 1;        

        aDueDate = CalculateDueDateBySchedule(startDate, sType);        

        Console.WriteLine( sType.TypeName + " " +  sType.MonthDate + " " + sType.MonthInterval+  " Due Date:      " + aDueDate.ToString("dd-MMM-yyyy HH:mm:ss") );

        sType.TypeName = "month";

        sType.MonthDate = "last";

        sType.MonthInterval = 1;        

        aDueDate = CalculateDueDateBySchedule(startDate, sType);        

        Console.WriteLine( sType.TypeName + " " +  sType.MonthDate + " " + sType.MonthInterval+  " Due Date:      " + aDueDate.ToString("dd-MMM-yyyy HH:mm:ss") );

    }

    public static int GetDayOftheWeekInt(string daySelected)

    {

       int dayInt =0 ;

            switch(daySelected.ToLower())

        {

            case "monday" :

                dayInt = (int) DayOfWeek.Monday;            

            break;

            case "tuesday" :

                dayInt = (int) DayOfWeek.Tuesday;           

            break;

​

            case "wednesday" :

                dayInt = (int) DayOfWeek.Wednesday;         

            break;

​

            case "thursday" :

                dayInt = (int) DayOfWeek.Thursday;          

            break;

            case "friday" :

                dayInt = (int) DayOfWeek.Friday;            

            break;

​

            case "saturday" :

                dayInt = (int) DayOfWeek.Saturday;          

            break;

​

            case "sunday" :

                dayInt = (int) DayOfWeek.Sunday;            

            break;              

            }

        return dayInt;

    }

    public static DateTime CalculateDueDateBySchedule(DateTime aDate, Schedule sType)

    {

       DateTime aDueDate = new DateTime();

        switch(sType.TypeName)

        {

            case "hour":

                        aDueDate = CalculateDueDateHour(aDate, sType.HourInterval);

                        break;

            case "week":

                        aDueDate = ClosestWeekDay(aDate, sType.DayName, sType.WeekInterval);    

                        break;

            case "month":

                        aDueDate = CalculateDueDateMonth(aDate, sType.MonthDate, sType.MonthInterval);  

                        break;

        }

        return aDueDate;

    }

    public static DateTime  CalculateDueDateWeek(DateTime startDate, string daySelected, int weekInterval){

        DateTime nextWeekDate  =  new DateTime();

        int weekFraction  = weekInterval*7;

        int dayInt  = GetDayOftheWeekInt(daySelected);

        int dayIntofStartDate = GetDayOftheWeekInt(startDate.DayOfWeek.ToString());     

        Console.WriteLine(dayInt + " "+ dayIntofStartDate);

        nextWeekDate = startDate.AddDays(( dayInt - dayIntofStartDate) + weekFraction)  ;

        return nextWeekDate;

    }

    public static DateTime ClosestWeekDay(DateTime startDate, string daySelected, int weekInterval)

    {

        int daySelectedInt  = GetDayOftheWeekInt(daySelected);

        int dayIntStartDate = GetDayOftheWeekInt(startDate.DayOfWeek.ToString());       

        //Console.WriteLine("dayIntStartDate   " + dayIntStartDate + "  daySelectedInt  "+ daySelectedInt );

        if(dayIntStartDate > daySelectedInt)

            return startDate.AddDays(7*weekInterval - ( dayIntStartDate - daySelectedInt));

        else

        {

            if(dayIntStartDate == daySelectedInt)

            {

                if(startDate > todaysDate)

                    return startDate.AddDays( daySelectedInt - dayIntStartDate);

                else

                    return startDate.AddDays(7*weekInterval - ( dayIntStartDate - daySelectedInt));

            }

            else

            {                           

                return startDate.AddDays( daySelectedInt - dayIntStartDate);

            }

        }   

    }

    public static DateTime CalculateDueDateMonth(DateTime aDate, string MonthDate, int monthInterval)

    {

        DateTime dueDate = new DateTime();

        int hours = aDate.Hour;

        int mins  = aDate.Minute;

        int secs  = aDate.Second;

        int year = aDate.AddMonths(monthInterval).Year;

        int month = aDate.AddMonths(monthInterval).Month;

      if(MonthDate.ToLower() == "first")

      {                           

          year = aDate.AddMonths(monthInterval).Year;

          month = aDate.AddMonths(monthInterval).Month;

          dueDate = new DateTime(year, month, 1, hours, mins, secs);

          if(dueDate <= aDate)

          {       

              dueDate = new DateTime(year, month - 1, DateTime.DaysInMonth(System.DateTime.Now.Year, month -1), hours, mins, secs);       

          }

      }

      if(MonthDate.ToLower() == "last")

      {

          year = aDate.Year;

          month = aDate.Month;        

          dueDate = new DateTime(year, month, DateTime.DaysInMonth(System.DateTime.Now.Year, month), hours, mins, secs);;     

          if(dueDate <= aDate)

          {       

              dueDate = new DateTime(year, month + 1, DateTime.DaysInMonth(System.DateTime.Now.Year, month+1), hours, mins, secs);        

          }

      } 

       return dueDate;

    }

​

    public static DateTime CalculateDueDateHour(DateTime aDate, int hourInterval){

        return aDate.AddHours(hourInterval);    

    }

​

    public class Schedule

    {

        public string TypeName {get; set;}  // 12 hours, 24 hours, 1 week, 2 week, 1 month, 3 month         

        public int HourInterval{get;set;} // 1,2,3,4 week

        public string DayName {get; set;} // Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday     

        public int WeekInterval{get;set;} // 1,2,3,4 week

        public string MonthDate {get; set;} // First Date, Last Date    

        public int MonthInterval {get; set;}    // 1,3,6 month

    }

}