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(** Strings of printable characters *)

type repr = string (* Invariant: contains only printable characters *)

type t = String_tag of repr [@@ocaml.unboxed]

type error += Non_printable_character of (int * string)

let () =
  let open Data_encoding in
  register_error_kind
    `Permanent
    ~id:"michelson_v1.non_printable_character"
    ~title:"Non printable character in a Michelson string"
    ~description:
      "Michelson strings are only allowed to contain printable characters \
       (either the newline character or characters in the [32, 126] ASCII \
       range)."
    ~pp:(fun ppf (pos, s) ->
      Format.fprintf
        ppf
        "In Michelson string \"%s\", character at position %d has ASCII code \
         %d. Expected: either a newline character (ASCII code 10) or a \
         printable character (ASCII code between 32 and 126)."
        s
        pos
        (Char.code s.[pos]))
    (obj2 (req "position" int31) (req "string" (string Plain)))
    (function Non_printable_character (pos, s) -> Some (pos, s) | _ -> None)
    (fun (pos, s) -> Non_printable_character (pos, s))

let empty = String_tag ""

let of_string v =
  let open Result_syntax in
  let rec check_printable_ascii i =
    if Compare.Int.(i < 0) then return (String_tag v)
    else
      match v.[i] with
      | '\n' | '\x20' .. '\x7E' -> check_printable_ascii (i - 1)
      | _ -> tzfail @@ Non_printable_character (i, v)
  in
  check_printable_ascii (String.length v - 1)

let to_string (String_tag s) = s

let compare (String_tag x) (String_tag y) = Compare.String.compare x y

let length (String_tag s) = String.length s

let concat_pair (String_tag x) (String_tag y) = String_tag (x ^ y)

let concat l =
  let l = List.map (fun (String_tag s) -> s) l in
  String_tag (String.concat "" l)

let sub (String_tag s) offset length = String_tag (String.sub s offset length)