use orchid_base::{name_char, name_start};
use orchid_base::{OrcRes, is};
use orchid_extension::gen_expr::new_atom;
use orchid_extension::{LexContext, LexedData, Lexer, err_not_applicable};
use orchid_extension::tree::GenTok;

use crate::std::string::str_atom::IntStrAtom;

#[derive(Default, Debug)]
pub struct SubscriptLexer;
impl Lexer for SubscriptLexer {
	const CHAR_FILTER: &'static [std::ops::RangeInclusive<char>] = &['.'..='.'];
	async fn lex<'a>(tail: &'a str, lctx: &'a LexContext<'a>) -> OrcRes<(&'a str, impl LexedData)> {
		if tail.len() <= 1 || !name_start(tail.chars().nth(1).unwrap()) {
			return Err(err_not_applicable().await);
		}
		let name_len = match tail[1..].char_indices().find(|(_, c)| !name_char(*c)) {
			None => tail.len() - 1,
			Some((pos, _)) => pos,
		};
		let new_tail = &tail[name_len + 1..];
		Ok((new_tail, [
			GenTok::Name(is(".").await).at(lctx.pos_lt(1, &tail[1..])),
			GenTok::NewExpr(new_atom(IntStrAtom(is(&tail[1..name_len + 1]).await)))
				.at(lctx.pos_tt(&tail[1..], new_tail)),
		]))
	}
}