using System;
using System.Collections.Generic;

public class Wagon
{
    Train Train { get; }
    public Stage LogisticDeck { get; } = null;
    public Stage MainDeck { get; private set; } = null;
    List<Stage> UpperDecks { get; } = new List<Stage>();

    public Wagon(Train train)
    {
        Train = train;
    }

    public Stage GetDeck(int level)
    {
        if (level < -1 || level > UpperDecks.Count)
            throw new System.ArgumentOutOfRangeException(nameof(level));
        if(level == -1) 
            return LogisticDeck;
        if (level == 0)
            return MainDeck;

        return UpperDecks[level - 1];
    }

    public void Populate()
    {
        MainDeck = new Stage();
        MainDeck.Populate();
    }
}