Compute Black Friday date

BlackFriday.cs

namespace ExportDatabase
{ 


    class AmHoliday
    {


        public static System.DateTime Thanksgiving(int year)
        {
            if (year < 1942)
                throw new System.ArgumentException("Year must be 1942 or later.", nameof(year));

            System.DateTime dt = new System.DateTime(year, 11, 1, 0, 0, 0, System.DateTimeKind.Local);

            int diff = System.DayOfWeek.Thursday - dt.DayOfWeek;
            if (diff < 0)
                diff += 7;

            diff += 22;

            System.DateTime thanksGiving = new System.DateTime(year, 11, diff, 0, 0, 0, System.DateTimeKind.Local);
            return thanksGiving;
        } // End Function Thanksgiving


        private static System.DateTime Thanksgiving2(int year)
        {
            if (year < 1942)
                throw new System.ArgumentException("Year must be 1942 or later.", nameof(year));

            System.DateTime dt = new System.DateTime(year, 11, 1, 0, 0, 0, System.DateTimeKind.Local);
            int[] thanks = new int[] { 26, 25, 24, 23, 22, 28, 27 };
            System.DateTime thanksGiving = new System.DateTime(year, 11, thanks[(int)dt.DayOfWeek], 0, 0, 0, System.DateTimeKind.Local);
            return thanksGiving;
        } // End Function Thanksgiving2 


        public static System.DateTime BlackFriday(int year)
        {
            if (year < 1942)
                throw new System.ArgumentException("Year must be 1942 or later.", nameof(year));

            System.DateTime dt = Thanksgiving(year).AddDays(1);
            return dt;
        } // End Function BlackFriday 


        internal static void Test()
        {
            System.DateTime tg = Thanksgiving(2024);
            System.DateTime tg2 = Thanksgiving2(tg.Year);

            System.DateTime bf = tg.AddDays(1);

            System.DateTime dt = new System.DateTime(tg.Year, 11, 1, 0, 0, 0, System.DateTimeKind.Local);

            string[] weekDays = new string[] {
                 "Sunday" // 0
                ,"Monday" // 1 
                ,"Tuesday" // 2
                ,"Wednesday" // 3
                ,"Thursday" // 4
                ,"Friday" // 5
                ,"Saturday" // 6
                
            };

            int thanks = -1;
            switch (dt.DayOfWeek)
            {
                case System.DayOfWeek.Thursday: // 22 + (thursday - weekday)
                    thanks = 22;
                    break;
                case System.DayOfWeek.Wednesday:// 22 + (thursday - weekday)
                    thanks = 23;
                    break;
                case System.DayOfWeek.Tuesday:// 22 + (thursday - weekday)
                    thanks = 24;
                    break;
                case System.DayOfWeek.Monday: // 22 + (thursday - weekday)
                    thanks = 25;
                    break;
                case System.DayOfWeek.Sunday: // 22 + (thursday - weekday)
                    thanks = 26;
                    break;
                case System.DayOfWeek.Saturday: // 22 +  7 - (thursday - weekday)
                    thanks = 27;
                    break;
                case System.DayOfWeek.Friday: // 22 +  7 - (thursday - weekday)
                    thanks = 28;
                    break;
            } // End switch 

            int diff = System.DayOfWeek.Thursday - dt.DayOfWeek;
            if (diff < 0)
                diff += 7;

            System.Console.WriteLine("November 1st {0} is a {1}.", dt.Year, weekDays[(int)dt.DayOfWeek]);
            System.Console.WriteLine("Thanksgiving {0} is on November {1}.", dt.Year, 22 + diff);
            System.Console.WriteLine("Thanksgiving {0} is on November {1}.", dt.Year, thanks);
            System.Console.WriteLine("Thanksgiving {0} is on {1}.", tg.Year, tg.ToString("dddd' 'dd' 'MMMM' 'yyyy"));
            System.Console.WriteLine("Thanksgiving (2) {0} is on {1}.", tg2.Year, tg2.ToString("dddd' 'dd' 'MMMM' 'yyyy"));
            System.Console.WriteLine("Black Friday {0} is on {1}.", bf.Year, bf.ToString("dddd' 'dd' 'MMMM' 'yyyy"));
        } // End Sub Test 


    } // End Class AmHoliday 


} // End Namespace ExportDatabase