using System;

public class DateTransform

{

    public static void Main()

    {

        new DateTransform("2015-07-01", "2015-07-04");

        new DateTransform("2015-12-01", "2016-02-03");

        new DateTransform("2015-12-01", "2017-02-03");

        new DateTransform("2016-03-01", "2016-05-05");

        new DateTransform("2017-01-01", "2017-01-01");

        new DateTransform("2022-09-05", "2023-09-04");

        new DateTransform("2015-04-01", "2020-09-10");

        new DateTransform("2015-12-11", "2016-12-11");

    }

    public DateTransform(string start, string end)

    {

        var startDate = DateTime.Parse(start);

        var endDate = DateTime.Parse(end);

        var startDateRep = new StartDateRepresentation(startDate, endDate);

        var endDateRep = new EndDateRepresentation(startDate, endDate);

        var output = startDateRep.ToString();

        if(startDate != endDate)

        {

            output = string.Format("{0} - {1}", output, endDateRep.ToString());

        }

        Console.WriteLine(output);

    }

}

​

public class StartDateRepresentation

{

    public DateTime StartDate { get; set; }

    public DateTime EndDate { get; set; }

    public bool StartYearCurrentYear { get { return StartDate.Year == DateTime.Today.Year; } }

    public bool SameYear { get { return StartDate.Year == EndDate.Year; } }

    public bool SameMonth { get { return SameYear && StartDate.Month == EndDate.Month; } }

    public bool SameDate { get { return StartDate == EndDate; } }

    public bool AtLeastYearApart { get { return (EndDate.Year - StartDate.Year > 1) || (StartDate.Year == EndDate.Year -1) && ((StartDate.Month < EndDate.Month) || (StartDate.Month == EndDate.Month && StartDate.Date < EndDate.Date)); } }

    public virtual bool ShowYear

    {

        get

        {

            if(SameDate) return true;

            else if(SameYear) return false;

            return !StartYearCurrentYear || (StartYearCurrentYear && AtLeastYearApart);

        }

    }

    public StartDateRepresentation(DateTime startDate, DateTime endDate)

    {

        StartDate = startDate;

        EndDate = endDate;

    }

    public override string ToString()

    {

        var month = StartDate.ToString("MMMM");

        var output = string.Format("{0} {1}", month, StartDate.ToStringWithOrdinal());

        if(ShowYear) output += string.Format(", {0}", StartDate.Year);

        return output;

    }

}

​

public class EndDateRepresentation : StartDateRepresentation

{

    public override bool ShowYear

    {

        get

        {

            if(!StartYearCurrentYear && !AtLeastYearApart) return true;

            if(SameYear) return false;

            return !StartYearCurrentYear || (StartYearCurrentYear && AtLeastYearApart);

        }

    }

    public EndDateRepresentation(DateTime startDate, DateTime endDate) : base(startDate, endDate)

    {

    }

    public override string ToString()

    {

        var month = EndDate.ToString("MMMM");

        var output = string.Empty;

        if(SameMonth) output = EndDate.ToStringWithOrdinal();

        else output = string.Format("{0} {1}", month, EndDate.ToStringWithOrdinal());

        if(ShowYear) output += string.Format(", {0}", EndDate.Year);

        return output;

    }

}

​

public static class Extensions

{   

    public static string ToStringWithOrdinal(this DateTime d)

    {

        switch (d.Day)

        {

            case 1: case 21: case 31:

              return d.ToString("d'st'");

            case 2: case 22:

              return d.ToString("d'nd'");

            case 3: case 23:

              return d.ToString("d'rd'");

            default:

              return d.ToString("d'th'");

        }

    }

}