using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        bool b = ValidateReturnPeriod("2019-12");

        Console.WriteLine(b);

    }

​

    private static bool ValidateReturnPeriod(string sReturnPeriod)

    {

        string sDateFrom, sDateTo;

        try

        {

            if (sReturnPeriod.Length != 7 || string.IsNullOrEmpty(sReturnPeriod.Trim()))

                throw new ArgumentException();

            if ((sReturnPeriod.Split('-')[0].Length != 4) || (sReturnPeriod.Split('-')[1].Length != 2))

                throw new ArgumentException();

            IEnumerable<DateTime> fdate = DateRange(sReturnPeriod);

            sDateFrom = string.Format("{0:yyyy-MM-dd}", fdate.ElementAt(0));

            sDateTo = string.Format("{0:yyyy-MM-dd}", fdate.ElementAt(1));

            return true;

        }

        catch (Exception __unusedException1__)

        {

            return false;

        }

    }

​

    private static IEnumerable<DateTime> DateRange(string returnPeriod)

    {

        const short QUARTER = 3;

        const short MIDYEAR = 20;

        const short JANUARY = 1;

        const short DECEMBER = 12;

        short year = Convert.ToInt16(returnPeriod.Substring(0, 4));

        short period = Convert.ToInt16(returnPeriod.Substring(5, 2));

        bool isQtr = false;

        DateTime dateFrom = new DateTime();

        DateTime dateTo = new DateTime();

        if (period > DECEMBER)

        {

            isQtr = true;

            period -= MIDYEAR;

        }

​

        dateFrom = new DateTime(year, period.Equals(MIDYEAR) ? JANUARY : period, JANUARY);

        if (Enumerable.Range(JANUARY, DECEMBER).Contains(period))

            dateTo = (isQtr ? dateFrom.AddMonths(QUARTER) : dateFrom.AddMonths(JANUARY)).AddDays(-JANUARY);

        else

            dateTo = dateFrom.AddMonths(DECEMBER).AddDays(-JANUARY);

        yield return dateFrom;

        yield return dateTo;

    }

}