using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var now = DateTime.Now;

        Console.WriteLine("Today is " + now.Date);

        var offers = new List<Offer> {

            new Offer(State.Available, now),

            new Offer(State.Available, now.AddDays(2)),

            new Offer(State.Available, now.AddDays(4)),

            new Offer(State.Activated, now),

            new Offer(State.Activated, now.AddDays(2)),

            new Offer(State.Activated, now.AddDays(4)),

            new Offer(State.Expired, now.AddDays(-1)),

            new Offer(State.Expired, now.AddDays(-3)),

            new Offer(State.Expired, now.AddDays(-6)),

            new Offer(State.Declined, now),

            new Offer(State.Declined, now.AddDays(2)),

            new Offer(State.Declined, now.AddDays(4))

        };

        offers.Sort();

        foreach(var offer in offers)

        {

            Console.WriteLine($"State: {offer.OfferState}, ValidTo: {offer.ValidTo}, DaysLeft: {offer.DaysLeft}");  

        }

    }

}

​

public enum State

{

    Unknown = 0,

    Available = 1,

    Activated = 2,

    Expired = 3,

    Declined = 4,

}

​

public class Offer : IComparable<Offer>

{

    public Offer(State state, DateTime validTo)

    {

        OfferState = state;

        ValidTo = validTo;

    }

    public State OfferState { get; }

    public DateTime ValidTo { get; }

    public int DaysLeft {

        get

        {

            return ValidTo.Date.Subtract(DateTime.Now.Date).Days + 1;

        }

    }

    public int CompareTo(Offer other)

        {

            if (OfferState == other.OfferState)

            {

                switch (OfferState)

                {

                    case State.Available:

                    case State.Activated:

                    case State.Declined:

                        return DaysLeft.CompareTo(other.DaysLeft);

                    case State.Expired:

                        return other.DaysLeft.CompareTo(DaysLeft);

                    default:

                        return DaysLeft.CompareTo(other.DaysLeft);

                }

            }

​

            return CompareOfferSate(OfferState, other.OfferState);

        }

​

        private int CompareOfferSate(State a, State b)

        {

            /*

             * Map represents the order: Available; Activated; Declined; Expired; Redeemed

             * */

            var offerStateMapper = new[] { 99, 0, 1, 3, 2, 4, 99, 99, 99, 99 };

            var aOrder = offerStateMapper[(int)a];

            var bOrder = offerStateMapper[(int)b];

            return aOrder.CompareTo(bOrder);

        }

}