using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var date = DateTime.Parse("12/25/2019");

        Console.WriteLine(UKBankHoliday.IsBankHoliday(date));

    }

}

​

public static class UKBankHoliday

    {

        #region Holiday Adjustments

        private static DateTime FixWeekend(DateTime hol)

        {

            if (hol.DayOfWeek == DayOfWeek.Sunday)

                hol = hol.AddDays(1);

            else if (hol.DayOfWeek == DayOfWeek.Saturday)

                hol = hol.AddDays(2);

            return hol;

        }

        private static DateTime FindFirstMonday(DateTime hol)

        {

            while (hol.DayOfWeek != DayOfWeek.Monday)

            {

                hol = hol.AddDays(1);

            }

            return hol;

        }

        #endregion

​

        #region Individual Holidays

        /// <summary>

        /// Christmas day

        /// </summary>

        /// <param name="year"></param>

        /// <returns></returns>

        public static DateTime Christmas(int year)

        {

            DateTime hol = new DateTime(year, 12, 25);

            hol = FixWeekend(hol);

            return hol;

        }

​

        /// <summary>

        /// Boxing Day

        /// </summary>

        /// <param name="year"></param>

        /// <returns></returns>

        public static DateTime BoxingDay(int year)

        {

            DateTime hol = new DateTime(year, 12, 26);

            //if Xmas=Sun, it's shifted to Mon and 26 also gets shifted

            bool isSundayOrMonday =

                hol.DayOfWeek == DayOfWeek.Sunday ||

                hol.DayOfWeek == DayOfWeek.Monday;

            hol = FixWeekend(hol);

            if (isSundayOrMonday)

                hol = hol.AddDays(1);

            return hol;

        }

​

        /// <summary>

        /// Date of New Year bank holiday. This is 1974 on only but will return pre 1974 dates.

        /// </summary>

        /// <param name="year"></param>

        /// <returns></returns>

        public static DateTime NewYear(int year)

        {

            //since 1974 only

            DateTime hol = new DateTime(year, 1, 1);

            hol = FixWeekend(hol);

            return hol;

        }

        /// <summary>

        /// Returns "Early Spring"/"May Day" holiday (first Monday in May). Created in 1978.

        /// </summary>

        /// <param name="year"></param>

        /// <returns>(Nullable)date for Early May Bank Holiday (null before 1978)</returns>

        public static DateTime? MayDay(int year)

        {

            //warning- should be null for < 1977

            if (year < 1978) return null;

            if (year == 1995)

                return new DateTime(1995, 5, 8); //1995 moved for 50th anniversary of VE day

            DateTime hol = new DateTime(year, 5, 1);

            hol = FindFirstMonday(hol);

            return hol;

        }

        /// <summary>

        /// The Spring/Last Monday in May holiday (replaced variable Whit Monday in 1971)

        /// </summary>

        /// <param name="year"></param>

        /// <returns></returns>

        public static DateTime Spring(int year)

        {

            if (year == 2002) return new DateTime(2002, 6, 4); //Golden Jubilee of Elizabeth II

            if (year == 2012) return new DateTime(2012, 6, 4); //Queen's Diamond Jubilee

            DateTime hol = new DateTime(year, 5, 24);

            hol = FindFirstMonday(hol);

            return hol;

        }

​

        /// <summary>

        /// Summer bank holiday (last Monday in August)

        /// </summary>

        /// <param name="year"></param>

        /// <returns></returns>

        public static DateTime Summer(int year)

        {

            DateTime hol = new DateTime(year, 8, 25);

            hol = FindFirstMonday(hol);

            return hol;

        }

​

        /// <summary>

        /// Good Friday (Friday before Easter)

        /// </summary>

        /// <param name="year"></param>

        /// <returns></returns>

        public static DateTime GoodFriday(int year)

        {

            DateTime hol = GetEaster(year);

            hol = hol.AddDays(-2);

            return hol;

        }

​

        /// <summary>

        /// Easter Monday (Monday after Easter)

        /// </summary>

        /// <param name="year"></param>

        /// <returns></returns>

        public static DateTime EasterMonday(int year)

        {

            DateTime hol = GetEaster(year);

            hol = hol.AddDays(1);

            return hol;

        }

        /// <summary>

        /// Private overloads of GoodFriday and EasterMonday reusing Easter calculation

        /// </summary>

        private static DateTime GoodFriday(DateTime easter)

        {

            DateTime hol = easter.AddDays(-2);

            return hol;

        }

        private static DateTime EasterMonday(DateTime easter)

        {

            DateTime hol = easter.AddDays(1);

            return hol;

        }

        #endregion

​

        /// <summary>

        /// Get a list of dates for all holidays in a year.

        /// </summary>

        /// <param name="year">The year</param>

        /// <returns>List of bank holidays</returns>

        public static IList<DateTime> BankHolidays(int year)

        {

            List<DateTime> bHols = new List<DateTime>();

            if (year > 1973)

                bHols.Add(NewYear(year)); //New Year only in 1974

​

            DateTime easter = GetEaster(year);

            bHols.Add(GoodFriday(easter));

            bHols.Add(EasterMonday(easter));

​

            DateTime? dt = MayDay(year);

            if (dt.HasValue)

                bHols.Add(dt.Value);

            bHols.Add(Spring(year));

​

            if (year == 2002)

                bHols.Add(new DateTime(2002, 6, 3)); //Golden Jubilee of Elizabeth II

            if (year == 2011)

                bHols.Add(new DateTime(2012, 4, 29)); //Royal Wedding

            if (year == 2012)

                bHols.Add(new DateTime(2012, 6, 5)); //Queen's Diamond Jubilee

​

            bHols.Add(Summer(year));

            bHols.Add(Christmas(year));

            bHols.Add(BoxingDay(year));

            return bHols;

        }

        /// <summary>

        /// Get a list of dates for all holidays in a year.

        /// </summary>

        /// <param name="year">The year</param>

        /// <returns>Dictionary of bank holidays</returns>

        public static IDictionary<DateTime, string> BankHolidayNames(int year)

        {

            var bHols = new Dictionary<DateTime, string>();

            if (year > 1973)

                bHols.Add(NewYear(year), "New Year"); //New Year only in 1974

​

            DateTime easter = GetEaster(year);

            bHols.Add(GoodFriday(easter), "Good Friday");

            bHols.Add(EasterMonday(easter), "Easter Monday");

​

            if (year == 2011)

                bHols.Add(new DateTime(2011, 4, 29), "Royal Wedding"); //Royal Wedding

​

            DateTime? dt = MayDay(year);

            if (dt.HasValue)

                bHols.Add(dt.Value, "Early May");

            bHols.Add(Spring(year), "Spring");

​

            if (year == 2002)

                bHols.Add(new DateTime(2002, 6, 3), "Golden Jubilee"); //Golden Jubilee of Elizabeth II

            if (year == 2012)

                bHols.Add(new DateTime(2012, 6, 5), "Queen's Diamond Jubilee"); //Queen's Diamond Jubilee

​

            bHols.Add(Summer(year), "Summer");

            bHols.Add(Christmas(year), "Christmas");

            bHols.Add(BoxingDay(year), "Boxing Day");

            return bHols;

        }

​

        /// <summary>

        /// Returns the next working day (Mon-Fri, not bank holiday)

        /// after the specified date (or the same date)

        /// </summary>

        /// <param name="dt">The date you wish to check</param>

        /// <returns>A date that is a working day</returns>

        public static DateTime NextWorkingDay(DateTime dt)

        {

            bool isWorkingDay = false;

            //loops through

            //(not ideal as a March/April date that hits Easter Friday

            //will have to calculate Easter three times-

            // first for the Friday, then for Easter Monday, then again to clear the Tuesday.

            // Easter Monday will calculate twice.

            // To avoid the recalculation, make these methods non-static and cache the date)

            while (isWorkingDay == false)

            {

                //Mon-Fri and not bank holiday, it's okay

                if (dt.DayOfWeek != DayOfWeek.Saturday &&

                    dt.DayOfWeek != DayOfWeek.Sunday &&

                    !IsBankHoliday(dt))

                    isWorkingDay = true;

                //it's Saturday, so skip to Monday

                else if (dt.DayOfWeek == DayOfWeek.Saturday)

                    dt = dt.AddDays(2);

                //it's Sunday, so skip to Monday

                else if (dt.DayOfWeek == DayOfWeek.Sunday)

                    dt = dt.AddDays(1);

                //it's Friday (bank holiday), so skip to Monday

                else if (dt.DayOfWeek == DayOfWeek.Friday)

                    dt = dt.AddDays(3);

                //it's Mon-Thu (bank holiday), so next day

                else

                    dt = dt.AddDays(1);

                //any of the addDays should now loop and retest

                //only Good Friday and Christmas Day should loop twice

                //(2 adjacent bank holidays)

            }

            return dt;

        }

​

        /// <summary>

        /// Check if a specific date is a bank holiday.

        /// Obviously the BankHoliday list is more efficient for repeated checks

        /// </summary>

        /// <param name="dt">The date you wish to check</param>

        /// <returns>True if date is a bank holiday (excluding weekends)</returns>

        public static bool IsBankHoliday(DateTime dt)

        {

            int year = dt.Year;

​

            switch (dt.Month)

            {

                case 1:

                    if ((year > 1973) && (NewYear(year) == dt))

                        return true;

                    break;

                case 3:

                case 4:

                    //only Mondays and Fridays are bank holidays

                    if (dt.DayOfWeek != DayOfWeek.Monday &&

                        dt.DayOfWeek != DayOfWeek.Friday)

                        return false;

                    //easter can be in March or April

                    DateTime easter = GetEaster(year);

                    if (GoodFriday(easter) == dt)

                        return true;

                    if (EasterMonday(easter) == dt)

                        return true;

                    break;

                case 5:

                    if (dt.DayOfWeek != DayOfWeek.Monday)

                        return false;

                    if (MayDay(year) == dt)

                        return true;

                    if (Spring(year) == dt)

                        return true;

                    break;

                case 8:

                    if (dt.DayOfWeek != DayOfWeek.Monday)

                        return false;

                    if (Summer(year) == dt)

                        return true;

                    break;

                case 12:

                    if (Christmas(year) == dt)

                        return true;

                    if (BoxingDay(year) == dt)

                        return true;

                    break;

            }

            if ((year == 2002) &&

               (dt.Month == 6) &&

               ((dt.Day == 3) || (dt.Day == 4)))

                return true; //Golden Jubilee of Elizabeth II

            if ((year == 2011) &&

               (dt.Month == 4) &&

               ((dt.Day == 29)))

                return true; //Royal Wedding

            if ((year == 2012) &&

               (dt.Month == 6) &&

               ((dt.Day == 5)))

                return true; //Queen's Diamond Jubilee

​

            return false;

        }

​

        /// <summary>

        /// Work out the date for Easter Sunday for specified year

        /// </summary>

        /// <param name="year">The year as an integer</param>

        /// <returns>Returns a datetime of Easter Sunday.</returns>

        private static DateTime GetEaster(int year)

        {

            //should be

            //Easter Monday  28 Mar 2005  17 Apr 2006  9 Apr 2007  24 Mar 2008

​

            //Oudin's Algorithm - http://www.smart.net/~mmontes/oudin.html

            int g = year % 19;

            int c = year / 100;

            int h = (c - c / 4 - (8 * c + 13) / 25 + 19 * g + 15) % 30;

            int i = h - (h / 28) * (1 - (h / 28) * (29 / (h + 1)) * ((21 - g) / 11));

            int j = (year + year / 4 + i + 2 - c + c / 4) % 7;

            int p = i - j;

            int easterDay = 1 + (p + 27 + (p + 6) / 40) % 31;

            int easterMonth = 3 + (p + 26) / 30;

​

            return new DateTime(year, easterMonth, easterDay);

        }

    }