using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        FindCalendar(2018, 6);

    }

    public static DateTime ConvertToUserTime(DateTime dt) {

         var myConvertedDateTime = TimeZoneInfo.ConvertTimeFromUtc(dt,TimeZoneInfo.FindSystemTimeZoneById("SE Asia Standard Time"));

            myConvertedDateTime = DateTime.SpecifyKind(myConvertedDateTime, DateTimeKind.Unspecified);

            return myConvertedDateTime;

    }

    public static void FindCalendar(int year, int month) {

        var dayInLastMonth = new List<DateResultModel>();

        var dayInThisMonth = new List<DateResultModel>();

        var dayInNextMonth = new List<DateResultModel>();

        var date = new DateTime(year, month, 1);

        var userTime = ConvertToUserTime(date);

        Console.WriteLine(date);

        Console.WriteLine(userTime);

        var firstDayInThisMonth = new DateTime(userTime.Year, userTime.Month, 1).DayOfWeek;

        var prevNumOfDay = 0;

        var lastMonth = DateTime.UtcNow;

        if(month == 1) {

            prevNumOfDay = DateTime.DaysInMonth(year - 1, 12);

            lastMonth = new DateTime(year - 1, 12, 1);

        }

        else {

            prevNumOfDay = DateTime.DaysInMonth(userTime.Year, userTime.Month-1);

            lastMonth = new DateTime(userTime.Year, userTime.Month-1, 1);

        }

        for (var i = prevNumOfDay - ((int)firstDayInThisMonth - 1); i <= prevNumOfDay ; i++) {

            var dayInLastMonthItem = new DateResultModel{

                Day = i,

                DayOfWeek = (int) new DateTime(lastMonth.Year, lastMonth.Month, i).DayOfWeek,

                Date =  new DateTime(lastMonth.Year, lastMonth.Month, i)

            };

            dayInLastMonth.Add(dayInLastMonthItem);

        }

        Console.WriteLine("Day In Last Month");

        dayInLastMonth.ForEach(i => Console.WriteLine("Day: {0}\t DayOfWeek:{1}\t Date:{2}\t |", i.Day, i.DayOfWeek, i.Date));

        Console.WriteLine();

        Console.WriteLine();

        var totalThisMonthDay = DateTime.DaysInMonth(userTime.Year, userTime.Month);

        for(var i = 0 ; i < totalThisMonthDay ; i++) {

            var dayInThisMonthItem = new DateResultModel{

                Day = i+1,

                DayOfWeek = (int) new DateTime(userTime.Year, userTime.Month, i + 1).DayOfWeek,

                Date = new DateTime(userTime.Year, userTime.Month, i + 1)

            };

            dayInThisMonth.Add(dayInThisMonthItem);

        }

        Console.WriteLine("Day In This Month");

        dayInThisMonth.ForEach(i => Console.WriteLine("Day: {0}\t DayOfWeek:{1}\t Date:{2}\t |", i.Day, i.DayOfWeek, i.Date));

        Console.WriteLine();

        Console.WriteLine();

        Console.WriteLine("Day In Next Month");

        var lastDayInThisMonth = (int) new DateTime(userTime.Year, userTime.Month, totalThisMonthDay).DayOfWeek;

        if(month == 12) 

        {

            userTime = new DateTime(year + 1, 1, 1);

            for(var i = 0 ; i < (6 - lastDayInThisMonth) ; i++) {

                var dayInNextMonthItem = new DateResultModel{

                    Day = i +1,

                    DayOfWeek = (int) new DateTime(userTime.Year, userTime.Month, i+1).DayOfWeek,

                    Date = new DateTime(userTime.Year, userTime.Month, i+1)

                };

                dayInNextMonth.Add(dayInNextMonthItem);

            }

            dayInNextMonth.ForEach(i => Console.WriteLine("Day: {0}\t DayOfWeek:{1}\t Date:{2}\t |", i.Day, i.DayOfWeek, i.Date));

            var totalDays = dayInLastMonth.Count + dayInThisMonth.Count + dayInNextMonth.Count;

            if(totalDays < 36) {

            for(var i = (7-lastDayInThisMonth); i < ((7-lastDayInThisMonth)+7); i++) {

                var dayInNextMonthItem = new DateResultModel{

                    Day = i,

                    DayOfWeek = (int) new DateTime(userTime.Year, userTime.Month, i).DayOfWeek,

                    Date = new DateTime(userTime.Year, userTime.Month, i)

                };

                dayInNextMonth.Add(dayInNextMonthItem);

              }

            }

            dayInNextMonth.ForEach(i => Console.WriteLine("Day: {0}\t DayOfWeek:{1}\t Date:{2}\t |", i.Day, i.DayOfWeek, i.Date));

        }

        else

        {

            for(var i = 0 ; i < (6 - lastDayInThisMonth) ; i++) {

                var dayInNextMonthItem = new DateResultModel{

                    Day = i +1,

                    DayOfWeek = (int) new DateTime(userTime.Year, userTime.Month+1, i+1).DayOfWeek,

                    Date = new DateTime(userTime.Year, userTime.Month+1, i+1)

                };

                dayInNextMonth.Add(dayInNextMonthItem);

            }

​

            dayInNextMonth.ForEach(i => Console.WriteLine("Day: {0}\t DayOfWeek:{1}\t Date:{2}\t |", i.Day, i.DayOfWeek, i.Date));

            var totalDays = dayInLastMonth.Count + dayInThisMonth.Count + dayInNextMonth.Count;

            if(totalDays < 36) {

            for(var i = (7-lastDayInThisMonth); i < ((7-lastDayInThisMonth)+7); i++) {

                var dayInNextMonthItem = new DateResultModel{

                    Day = i,

                    DayOfWeek = (int) new DateTime(userTime.Year, userTime.Month+1, i).DayOfWeek,

                    Date = new DateTime(userTime.Year, userTime.Month+1, i)

                };

                dayInNextMonth.Add(dayInNextMonthItem);

              }

            }

            dayInNextMonth.ForEach(i => Console.WriteLine("Day: {0}\t DayOfWeek:{1}\t Date:{2}\t |", i.Day, i.DayOfWeek, i.Date));

        }

    }

}

​

public class DateResultModel {

    public int Day { get; set; }

    public int DayOfWeek { get; set;}

    public DateTime Date { get; set;}

}