Fun C# Caesar Cipher command line tool in a functional programming style

Rot13.CLI.cs

using CaesarCipher;

if (args?.Length > 0)
    Console.WriteLine(args[0].Rot13());
else
{
    Console.WriteLine("Start typing (Return key to exit)");
    PresentUntilReturnKey();
}

static void PresentUntilReturnKey(char output = '\0')
{
    if (output != 0)
    {
        if (output == '\r') return;
        Present(
            output,
            Console.Write,
            Console.GetCursorPosition,
            Console.SetCursorPosition);
    }
    PresentUntilReturnKey(Console.ReadKey().Rot13());
}

static void Present(
    char output,
    Action<string> writer,
    Func<(int Left, int Top)> cursorPositionGetter,
    Action<int, int> cursorPositionSetter) =>
    KeyPressPresenter.Present(
        output, writer, cursorPositionGetter, cursorPositionSetter);

internal class KeyPressPresenter
{
    public static void Present(
        char output,
        Action<string> writer,
        Func<(int Left, int Top)>? cursorPositionGetter = null,
        Action<int, int>? cursorPositionSetter = null)
    {
        if (output == 127)
        {
            writer($"\b\b");
            return;
        }
        if (cursorPositionGetter == null
            || cursorPositionSetter == null)
        {
            writer($"\b{output}");
            return;
        }
        Write(output,
            cursorPositionGetter(),
            writer,
            cursorPositionSetter);
    }

    private static void Write(
        char output,
        (int Left, int Top) origPos,
        Action<string> writer,
        Action<int, int> cursorPositionSetter)
    {
        SetPosition(cursorPositionSetter, origPos);
        writer($"{output}");
        ResetPosition(cursorPositionSetter, origPos);
    }

    private static void SetPosition(
        Action<int, int> cursorPositionSetter,
        (int Left, int Top) origPos)
    {
        try
        {
            cursorPositionSetter(origPos.Left - 1, origPos.Top + 1);
        }
        catch (ArgumentOutOfRangeException)
        {
            cursorPositionSetter(1, 1);
        }
    }

    private static void ResetPosition(
        Action<int, int> cursorPositionSetter,
        (int Left, int Top) origPos)
    {
        cursorPositionSetter(origPos.Left, origPos.Top);
    }
}

namespace CaesarCipher
{
    public static class Extensions
    {
        public static char[] Rot13(this string self) =>
            self.ToCharArray().Rot13();

        public static char Rot13(this ConsoleKeyInfo self) =>
            self.KeyChar.Rot13();

        private static char[] Rot13(this IEnumerable<char> self) =>
            self.Select(c => c.Rot13()).ToArray();

        private static char Rot13(this char self) =>
            self switch
            {
                >= 'a' and <= 'm' or >= 'A' and <= 'M' => (char)(self + 13),
                >= 'n' and <= 'z' or >= 'N' and <= 'Z' => (char)(self - 13),
                _ => self
            };
    }
}