using System;

using System.Text;

public class Program

{

    public static void Main()

    {

        var skigym = new Serie("Skigymnastik", "Antje", 10, new DateTime(2017,10,10));

        skigym.Print();

        var hupf = new Serie("Rumhupf", "DrillSarge", -5, DateTime.Now);

        hupf.Print();

        var muscle = new Serie("Mehr Muskeln", "Arnie Schwarzenegger", 4, new DateTime(2017,02,03));

        muscle.Print(); 

        var SkigymDauer = new Dauer(skigym);

        SkigymDauer.Print();

        var print = new Printer();

    }

}

​

public class Serie : Printer

{

    public string KursTitel {get; private set;}

    public string TrainerName {get; private set;}

    public int AnzahlSessions {get; private set;}

    public DateTime StartTermin {get; private set;}

    public StringBuilder sb = new StringBuilder();

    public Serie(string kurs, string trainer, int anzahlSessions, DateTime start)

    {

        this.KursTitel = kurs;

        this.TrainerName = trainer;

        this.StartTermin = start;   

        if (anzahlSessions < 1)

        {

            this.AnzahlSessions = 0;

            sb.AppendFormat("Kurs {0}: No sessions planned!", this.KursTitel);

            sb.AppendLine();

        }

        else 

        {

            this.AnzahlSessions = anzahlSessions;

        }       

    }

    public override void Print()

    {

        sb = GatherKursInfo();

        Console.WriteLine(sb);          

    }

    private StringBuilder GatherKursInfo()

    {

        sb.AppendFormat("Kurs: {0}. ", this.KursTitel);

        sb.AppendFormat("Trainer: {0}. ", this.TrainerName);

        sb.AppendFormat("Sessions: {0}. ", this.AnzahlSessions); 

        sb.AppendFormat("Start: {0:dd-MMM-yyyy}. ", this.StartTermin);

        sb.AppendLine();

        return sb;

    }

}

​

public class Dauer : Printer

{

    public Serie Kurs;

    public StringBuilder sb = new StringBuilder();

    public DateTime EndDate;

    public Dauer (Serie kurs)

    {

        this.Kurs = kurs;

        this.EndDate = CalculateEndDate();

    }

    private DateTime CalculateEndDate()

    {

        DateTime heute = DateTime.Now;

        var StartTermin = this.Kurs.StartTermin;

        var DauerInTagen = (this.Kurs.AnzahlSessions-1) * 7;

        var DeltaInMonaten = DauerInTagen / 28;

        var RestDeltaInTagen = DauerInTagen % 28;

        var EndTermin = new DateTime(StartTermin.Year, StartTermin.Month + DeltaInMonaten, StartTermin.Day + RestDeltaInTagen);

        return EndTermin;

    }

    public override void  Print()

    {

        Console.WriteLine(KursDauer());

    }

    private StringBuilder KursDauer()

    {

        sb.AppendFormat("Kurs: {0}. ", this.Kurs.KursTitel);

        sb.AppendFormat("Sessions: {0}. ", this.Kurs.AnzahlSessions); 

        sb.AppendFormat("Start: {0:dd-MMM-yyyy}. ", this.Kurs.StartTermin);

        sb.AppendFormat("Ende: {0:dd-MMM-yyyy}. ", this.EndDate);

        sb.AppendLine();

        return sb;

    }

}

​

public class Printer

{   

    public virtual void Print()

    {

        Console.WriteLine();

    }

}

​