(*
 * SPDX-FileCopyrightText: 2024 The Forester Project Contributors
 *
 * SPDX-License-Identifier: GPL-3.0-or-later
 *)

open Forester_prelude

type t = Word of string | Symbol of char [@@deriving repr]

let pp fmt = function
  | Word x -> Format.fprintf fmt "%s" x
  | Symbol x -> Format.fprintf fmt "%c" x

let show = Format.asprintf "%a" pp

let is_alpha c =
  let i = Char.code c in
  (i >= 65 && i <= 90) || (i >= 97 && i <= 122)

let rec parse_word acc xs =
  match xs with
  | [] -> (Word (String_util.implode_bwd acc), "")
  | x :: xs ->
    if is_alpha x then parse_word (Bwd.Snoc (acc, x)) xs
    else (Word (String_util.implode_bwd acc), String_util.implode (x :: xs))

let parse input =
  match String_util.explode input with
  | x :: xs ->
    if is_alpha x then Some (parse_word (Bwd.Snoc (Bwd.Emp, x)) xs)
    else Some (Symbol x, String_util.implode xs)
  | [] -> None