StarWarsList.cs

// never use this btw

public class StarWarsList<T> : IList<T>
{
    private readonly List<T> _BaseList = new List<T>();

    private static int _FromStarWarsNumbering(int i) => i switch
    {
        4 => 0,
        5 => 1,
        6 => 2,
        1 => 3,
        2 => 4,
        3 => 5,
        _ => i - 1
    };

    private static int _ToStarWarsNumbering(int i) => i switch
    {
        0 => 4,
        1 => 5,
        2 => 6,
        3 => 1,
        4 => 2,
        5 => 3,
        -1 => -1, // required for IndexOf
        _ => i + 1
    };

    public T this[int index]
    {
        get => _BaseList[_FromStarWarsNumbering(index)];
        set => _BaseList[_ToStarWarsNumbering(index)] = value;
    }

    public int Count => _BaseList.Count;
    bool ICollection<T>.IsReadOnly => ((ICollection<T>)_BaseList).IsReadOnly;

    public void Add(T item) => _BaseList.Add(item);
    public void Clear() => _BaseList.Clear();
    public bool Contains(T item) => _BaseList.Contains(item);
    public void CopyTo(T[] array, int arrayIndex) => _BaseList.CopyTo(array, arrayIndex);
    public int IndexOf(T item) => _ToStarWarsNumbering(_BaseList.IndexOf(item));
    public void Insert(int index, T item) => _BaseList.Insert(_FromStarWarsNumbering(index), item);
    public bool Remove(T item) => _BaseList.Remove(item);
    public void RemoveAt(int index) => _BaseList.RemoveAt(_FromStarWarsNumbering(index));

    public IEnumerator<T> GetEnumerator() => _BaseList.GetEnumerator();
    IEnumerator IEnumerable.GetEnumerator() => _BaseList.GetEnumerator();
}