open Sexp

let rec sexp_of_json j =
  match j with
  | Json.Num f -> Hint {hint = Bytes.of_string "num"; body = Bytes.of_string (Json.to_string j)}
  | Json.Str s -> str s
  | Json.Arr js -> Arr (List.map sexp_of_json js)
  | Json.Rec kvs -> Arr ((Hint {hint = Bytes.of_string "obj"; body = Bytes.empty}) ::
			    (List.map (fun (k, v) -> Arr [str k; sexp_of_json v]) kvs))
  | Json.Flg f -> Hint {hint = (Bytes.of_string "bool"); body = (Bytes.of_string (string_of_bool f))}
  | Json.Nil -> Hint {hint = (Bytes.of_string "null"); body = Bytes.empty}

let json_of_sexp x =
  let rec walk x =
    match x with
      | Hint {hint = hint; body = n} when hint = Bytes.of_string "num" ->
        Json.Num (float_of_string (Bytes.to_string n))
      | Str s -> Json.Str (Bytes.to_string s)
      | Arr ((Hint {hint = hint; body = bs}) :: kvs) when hint = Bytes.of_string "obj" && bs = Bytes.empty ->
	Json.Rec (List.map
		    (fun kv ->
		      (match kv with
			| Arr [Str k; v] -> (Bytes.to_string k, walk v)
			| _ -> raise (Syntax_error "Bad JSON-SEXP key-value")))
		    kvs)
      | Arr xs -> Json.Arr (List.map walk xs)
      | Hint {hint = hint; body = bs} when hint = Bytes.of_string "bool" -> Json.Flg (bool_of_string (Bytes.to_string bs))
      | Hint {hint = hint; body = bs} when hint = Bytes.of_string "null" && bs = Bytes.empty -> Json.Nil
      | Hint {hint = h; body = b} -> Json.Rec ["_hint", Json.Str (Bytes.to_string h); "_body", Json.Str (Bytes.to_string b)]
  in
  Lwt.wrap1 walk x