using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        //Console.WriteLine(new DateTime(2023,6,19).AddDays(7).GetNextDayOfWeek(DayOfWeek.Monday));

        DateRange dr = new DateRange();

        dr.PrepareSlots (DateTime.UtcNow, DateTime.UtcNow.AddYears(1), RecurenceTypes.Monthly, new List<DayOfWeek>() { DayOfWeek.Monday, DayOfWeek.Wednesday });

        Console.WriteLine("Current " + DateTime.UtcNow + " Next " + DateTime.UtcNow.AddYears(1));

        dr.Print();

    }

}

​

public class DateRange

{

    private Dictionary<DateTime, DayOfWeek> Range { get; set; }

​

    public DateRange()

    {

        Range = new Dictionary<DateTime, DayOfWeek>();

    }

​

    public void PrepareWeeklySlots(DateTime start, DateTime end, IEnumerable<DayOfWeek> dayOfWeeks)

    {

        var date = start;

        while (date.Date >= DateTime.Now.Date && date.Date <= end.Date)

        {

            foreach (var dayOfWeek in dayOfWeeks)

            {

                var nextDay = date.Date.GetNextDayOfWeek(dayOfWeek);

                if (dayOfWeek == nextDay.DayOfWeek && nextDay.Date >= date.Date && nextDay.Date <= end.Date)

                {

                    Range.Add(nextDay, dayOfWeek);

                }

            }

            date = date.AddDays(7).GetNextWeekStartingDate();

        }

    }

​

    public void PrepareMonthlySlots(DateTime start, DateTime end, IEnumerable<DayOfWeek> dayOfWeeks)

    {

        var date = start;

        while (date.Date >= DateTime.UtcNow.Date && date.Date <= end.Date)

        {

            //if (date.Date >= DateTime.UtcNow.Date && date.Date <= end.Date)

            {

                PrepareWeeklySlots(date, date.GetFirstDayOfNextMonth().AddDays(-1), dayOfWeeks);

            }

            date = date.GetFirstDayOfNextMonth();

        }

    }

​

    public void PrepareYearlySlots(DateTime start, DateTime end, IEnumerable<DayOfWeek> dayOfWeeks)

    {

        var date = start;

        while (date.Date < end.Date)

        {

            if (date.Date >= DateTime.UtcNow.Date && date.Date <= end.Date)

            {

                PrepareWeeklySlots(start, date.GetNextYear(), dayOfWeeks);

            }

            date = date.GetNextYear();

        }

    }

​

    public void PrepareSlots(DateTime start, DateTime end, RecurenceTypes recType, IEnumerable<DayOfWeek> dayOfWeeks)

    {

        if (recType == RecurenceTypes.Monthly)

        {

            PrepareMonthlySlots(start, end, dayOfWeeks);

        }

        else if (recType == RecurenceTypes.Daily)

        {

            PrepareWeeklySlots(start, end, dayOfWeeks);

        }

        else if (recType == RecurenceTypes.YearlyOnce)

        {

            PrepareYearlySlots(start, end, dayOfWeeks);

        }

    }

​

​

​

    public void Print()

    {

        int index = 0;

        foreach (var da in Range)

        {

            index++;

            Console.WriteLine(index + ". " + da.Key.Date.ToString("dd-MMM-yyyy") + " is " + (int)da.Value);

        }

        Console.WriteLine("Recurence Count " + Range.Count);

    }

}

​

public static class DateRangeExtensions

{

    public static DateTime GetNextDayOfWeek(this DateTime startDate, DayOfWeek dayOfWeek)

    {

        int daysToAdd = (int)dayOfWeek - 1;

        var weekStartDate = startDate.AddDays((int)DayOfWeek.Monday - (int)startDate.DayOfWeek);

        return weekStartDate.AddDays(daysToAdd);

    }

​

    public static DateTime GetNextWeekStartingDate(this DateTime startDate)

    {

        int daysToAdd = (int)DayOfWeek.Monday - (int)startDate.DayOfWeek;

        return startDate.AddDays(daysToAdd);

    }

​

    public static DateTime GetNextMonth(this DateTime startDate)

    {

        return startDate.AddMonths(1);

    }

​

    public static DateTime GetFirstDayOfNextMonth(this DateTime startDate)

    {

        var newDate = startDate.AddMonths(1);

        return newDate.AddDays(startDate.Day > 2 ? 1 - startDate.Day : 0);

    }

​

    public static DateTime GetNextYear(this DateTime startDate)

    {

        return startDate.AddYears(1);

    }

}

​

public enum RecurenceTypes

{

    None,

    Daily,

    Monthly,

    OnlyWeekends,

    OnlyWeekdays,

    YearlyOnce,

}

​

​