namespace Exercise3
{
    class Program
    {
        static void Main(string[] args)
        {
            string inputString;
            int year = 0;
            int month = 0;
            int num = 1;
            int firstDay = 0;
            bool validYear = true;
            bool validMonth = true;
            string[] monthString = new string[] { "January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December" };
            int[,] calendar = new int[6, 7];

            Console.WriteLine("Program to print a calendar for a specified month in a specified year entered");
            Console.WriteLine();

            // Getting the chosen Year
            while (validYear)
            {
                Console.Write("Enter the year: ");
                inputString = Console.ReadLine();
                if (int.TryParse(inputString, out year))
                {
                    validYear = false;
                }
                else
                {
                    Console.WriteLine();
                    Console.WriteLine("You have entered an invalid value");
                    validYear = true;
                }
            }

            // Getting the chosen Month
            while (validMonth)
            {
                Console.Write("Enter the number of the month (Jan = 1, etc): ");
                inputString = Console.ReadLine();
                if (int.TryParse(inputString, out month))
                {
                    if (month < 1 || month > 12)
                    {
                        Console.WriteLine();
                        Console.WriteLine("Number entered must be between 1 and 12");
                        validMonth = true;
                    }
                    else
                    {
                        validMonth = false;
                    }
                }
                else
                {
                    Console.WriteLine();
                    Console.WriteLine("You have entered an invalid value");
                    validMonth = true;
                }
            }

            //DateTime for first day of Month and the amount of days in month
            DateTime dateGiven = new DateTime(year, month, 1);
            firstDay = (int)dateGiven.DayOfWeek - 1;
            if (firstDay == -1)
            {
                firstDay = 6;
            }
            int daysInMonth = System.DateTime.DaysInMonth(year, month);

            // Calculating
            for (int rows = 0; rows <= 5; rows++)
            {
                if (rows == 0)
                {
                    for (int columns = firstDay; columns <= 6; columns++)
                    {
                        calendar[rows, columns] = num++;
                    }
                }
                if (rows > 0 && rows <= 5)
                {
                    for (int columns = 0; columns <= 6; columns++)
                    {
                        if (num == daysInMonth + 1)
                        {
                            columns = 6;
                            rows = 5;
                        }
                        else
                        {
                            calendar[rows, columns] = num++;
                        }
                    }
                }
            }

            // Display
            Console.WriteLine();
            Console.WriteLine("           " + monthString[month - 1] + "          ");
            Console.WriteLine(" Mo  Tu  We  Th  Fr  Sa  Su ");

            for (int rows = 0; rows <= 5; rows++)
            {
                for (int columns = 0; columns <= 6; columns++)
                {
                    if (calendar[rows, columns] < 10)
                    {
                        Console.Write("  ");
                    }
                    else
                    {
                        Console.Write(" ");
                    }
                    if (calendar[rows, columns] == 0)
                    {
                        Console.Write("  ");
                    }
                    else
                    {
                        Console.Write(calendar[rows, columns]);
                        Console.Write(" ");
                    }
                }
                Console.WriteLine();
            }
            Console.WriteLine();
        }
    }
}