using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

​

​

//  https://lostechies.com/jimmybogard/2008/08/12/enumeration-classes/

public class DOWeek : IEnumerable

{

    public static DOWeek Monday { get; private set; } // = new DOWeek (1,"Monday");    // syntax not supported in .NET 4.5 ?

    public static DOWeek Tuesday { get; private set; }

    public static DOWeek Wednesday { get; private set; }

    public static DOWeek Thursday { get; private set; }

    public static DOWeek Friday { get; private set; }

    public static DOWeek Saturday { get; private set; }

    public static DOWeek Sunday { get; private set; }

​

    public const int ii=10;  // just test

    public static DOWeek[] ListOfDays;    // try readonly     compilation error: { get; private set; }

    public int Value {get; private set; }

    public string Name {get; private set; }

    public IEnumerator GetEnumerator()

    {

        return (IEnumerator)null;

    }

    // public int rtest {

    // static constructor can be skipped if syntax .NET 4.7 (above) can be used

    static DOWeek()    //access modifiers are not allowed on static constructors

    {

        Monday = new DOWeek(1, "Monday");

        Tuesday = new DOWeek(2, "Tuesday");

        Wednesday = new DOWeek(3, "Wednesday");

        Thursday = new DOWeek(4, "Thursday");

        Friday = new DOWeek(5, "Friday");

        Saturday = new DOWeek(6, "Saturday");

        Sunday = new DOWeek(7, "Sunday");

        ListOfDays = new [] { Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday};

    }

    private DOWeek (int pValue, string pName)

    {

        Value = pValue;

        Name = pName;

    }

    public DOWeek (int pValue)  // accepted also numbers not in 1..7

    {

        Value = (pValue-1) % 7 + 1;

        Name = ListOfDays.Single(dx => dx.Value == Value).Name;

    }

    public DOWeek (string pName)

    {

        DOWeek obx = ListOfDays.Single(dx => dx.Name==pName);

        Value = obx.Value;

        Name = obx.Name;

        // throw new NotImplementedException();

    }

    public string DayInfo()

    {

        return string.Format("Day:{0},{1}", this.Value, this.Name);  

    }

    public DOWeek Yesterday()

    {

        return ListOfDays.Single(dx => dx.Value == (Value-1-1+7)%7+1);

    }

    public DOWeek DayBeforeYesterday()

    {

        return ListOfDays.Single(dx => dx.Value == (Value-1-2+7)%7+1);

    }

    public DOWeek Tomorrow()

    {

        return ListOfDays.Single(dx => dx.Value == (Value-1+1)%7+1);

    }

    public DOWeek DayAfterTomorrow()

    {

        return ListOfDays.Single(dx => dx.Value == (Value-1+2)%7+1);

    }

    public static DOWeek operator + (DOWeek dayStart, int numofDays)

    {

        int n2 = (dayStart.Value -1 + numofDays) % 7 +1;

        return ListOfDays.Single(dx => dx.Value == n2);

    }

    public static explicit operator int(DOWeek xday)

    {

        return xday.Value;

    }

    public static void InvalidOperation()

    {

        // throw new NotImplementedException();   // Run-time exception (line 70): The method or operation is not implemented.

        // ListOfDays.OrderBy();

        ListOfDays[0].Value = 1;

​

    }

}

​

​

public class Program

{

    public enum DayOfWeek { Monday=1001, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday }

    public static void TestBasic()

    {

        DayOfWeek daya = DayOfWeek.Thursday;

        Console.WriteLine("(int)daya:{0}", (int)daya);    // 3 ! so Monday = 0 if not initialized with other value

        Console.WriteLine("daya:{0}", daya.ToString());    // daya:Thursday; enum.ToString gets the value: Thursday

        Console.WriteLine("daya:{0}", (daya-1).ToString());    // daya:Wednesday

        //DayOfWeek dayb = DayOfWeek.Sunday;

        DayOfWeek dayb = (DayOfWeek)DayOfWeek.Parse(typeof(DayOfWeek), "Friday");   //ArgumentException if 'Fridayaa'

        // dayb = (DayOfWeek)DayOfWeek.Parse(typeof(DayOfWeek), 1003);   // Parse requires string

        Console.WriteLine("Parse succedded");

        Console.WriteLine("dayb: {0}; (int)dayb:{1}", dayb, (int)dayb);    // 3 ! so Monday = 0 if not initialized with other value

    }

    public static void TestEnumClass()

    {

        DOWeek dx = new DOWeek(5);

        Console.WriteLine(dx.DayInfo());

        Console.WriteLine("+ {0} days : {1}", 9, (dx+9).DayInfo() );

        DOWeek dy = new DOWeek(2);

        Console.WriteLine("+ {0} days : {1}", 9, (dx+9).DayInfo() );

        Console.WriteLine("today: {0} ; -2,-1,1,2: {1},{2},{3},{4}", dy.DayInfo(), dy.DayBeforeYesterday().DayInfo(), dy.Yesterday().DayInfo(), dy.Tomorrow().DayInfo(), dx.DayAfterTomorrow().DayInfo());

        DOWeek.InvalidOperation();

        foreach(int i in Enumerable.Range(1,7))

        {

            DOWeek dyy = new DOWeek(i);

            Console.WriteLine(dyy.DayInfo());

        }

    }

​

    public static void Main()

    {

        Console.WriteLine("start");

        // TestBasic();

        TestEnumClass();

    }

}