module List =
  struct include List
  let singleton x = List.cons x []
  end

module Grep =
  struct

  open Cprg
  open Cprg.Syntax

  let blank, blank0 =
    let ignore = lift (fun _ -> ()) in
    let is_ws = function ' ' | '\t' -> true | _ -> false in
    ignore @@ take_while1 is_ws, ignore @@ take_while is_ws

  let word = take_while1 @@ function
    'a' .. 'z' | '_' | '-' -> true | _ -> false

  let equal = char '='

  let listitem : (_ * [ `flag | `pair of string ]) code =
    (lift2 (fun x y -> x, \`pair y) (word <* equal) word)
    or (lift (fun x -> x, \`flag) word)

  let chain = fix @@ fun chain ->
    (lift2 List.cons (listitem <* blank) chain)
    or (lift List.singleton listitem)

  let chain' =
    blank0 *> ((char 's' *> char 'e' *> char 't' *> blank *> chain) or chain) <* blank0

  let parse_inner =
    let [@warning "-26"] to_string = String.concat ";" % List.map (function
      | x, \`flag -> "'" ^ x ^ "'"
      | x, \`pair y -> "'" ^ x ^ "','" ^ y ^ "'") in
    Cprg.parse_string ~consume:\`All chain'
    %> function Result.Ok x ->
        (* Eio.traceln "oar: oar-code: grep: cprg dict is [%s]" (to_string x); *) x
      | Result.Error e -> failwith (Printf.sprintf "oar: oar-code: grep: cprg error is '%s'" e)

  open Re

  let vi_sign = alt [str "vim"; str "vi"]

  let pat = seq [vi_sign; char ':'; group (any |> rep1); char ':']

  let parse_outer_opt =
    Re.exec_opt (Re.compile pat)
    %> Option.map (fun g ->
      let content = Re.Group.get g 1 in
      (* Eio.traceln "oar: oar-code: grep: regexp content output is '%s'" content; *) content)

  let vimline_opt = parse_outer_opt %> Option.map parse_inner

end

(* let filetype_to_language = function *)
(*   | ("ocaml" | "typst") as x -> x *)
(*   | s -> failwith (Printf.sprintf "oar: oar-code: filetype_to_language: unhandled filetype '%s'" s) *)

let extension_to_language filename =
  match Filename.extension filename with
  | ".ml" -> "ocaml"
  | ".typ" -> "typst"
  | ".yml" -> "yaml"
  | ".org" -> "org"
  | s -> failwith (Printf.sprintf "oar: oar-code: extension_to_language: unhandled extension '%s' of filename '%s'" s filename)

open Eio

include struct
  module Language_infer = struct end end

let%include [@in (module Language_infer) [@as? of_file]]
lang_infer__of_file path =
  let lang = Option.bind (Grep.vimline_opt @@ Path.load path) (
    List.assoc_opt "ft" %> function Some (\`pair lang) -> Some lang | _ -> None) in
  match lang with Some l -> l | None ->
  extension_to_language @@ Path.native_exn path