#![no_std]
//! Exact builtin names and bounded external-command routing.

use turkos_os_shell_words::Words;

#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum Builtin { Cd, Exit, Help }

#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum Route<'a> { Builtin(Builtin), External(&'a str) }

#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub struct Decision<'a> { pub route: Route<'a>, pub argc: usize }

#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum Error { MissingCommand, InvalidName, BuiltinArity }

pub fn decide<const BYTES: usize, const COUNT: usize>(
    words: &Words<BYTES, COUNT>,
) -> Result<Decision<'_>, Error> {
    let Some(name) = words.get(0) else { return Err(Error::MissingCommand); };
    if name.is_empty() || name.bytes().any(|byte| byte == 0 || byte.is_ascii_whitespace())
    { return Err(Error::InvalidName); }
    let argc = words.len() - 1;
    let route = match name {
        "cd" if argc == 1 => Route::Builtin(Builtin::Cd),
        "cd" => return Err(Error::BuiltinArity),
        "exit" if argc <= 1 => Route::Builtin(Builtin::Exit),
        "exit" => return Err(Error::BuiltinArity),
        "help" if argc == 0 => Route::Builtin(Builtin::Help),
        "help" => return Err(Error::BuiltinArity),
        _ => Route::External(name),
    };
    Ok(Decision {route, argc})
}