open! Stdune

let quote_length s =
  let n = ref 0 in
  let len = String.length s in
  for i = 0 to len - 1 do
    n
      := !n
         +
         match String.unsafe_get s i with
         | '\"' | '\\' | '\n' | '\t' | '\r' | '\b' -> 2
         | '%' -> if i + 1 < len && s.[i + 1] = '{' then 2 else 1
         | ' ' .. '~' -> 1
         | _ -> 4
  done;
  !n
;;

let escape_to s ~dst:s' ~ofs =
  let n = ref ofs in
  let len = String.length s in
  for i = 0 to len - 1 do
    (match String.unsafe_get s i with
     | ('\"' | '\\') as c ->
       Bytes.unsafe_set s' !n '\\';
       incr n;
       Bytes.unsafe_set s' !n c
     | '\n' ->
       Bytes.unsafe_set s' !n '\\';
       incr n;
       Bytes.unsafe_set s' !n 'n'
     | '\t' ->
       Bytes.unsafe_set s' !n '\\';
       incr n;
       Bytes.unsafe_set s' !n 't'
     | '\r' ->
       Bytes.unsafe_set s' !n '\\';
       incr n;
       Bytes.unsafe_set s' !n 'r'
     | '\b' ->
       Bytes.unsafe_set s' !n '\\';
       incr n;
       Bytes.unsafe_set s' !n 'b'
     | '%' when i + 1 < len && s.[i + 1] = '{' ->
       Bytes.unsafe_set s' !n '\\';
       incr n;
       Bytes.unsafe_set s' !n '%'
     | ' ' .. '~' as c -> Bytes.unsafe_set s' !n c
     | c ->
       let a = Char.code c in
       Bytes.unsafe_set s' !n '\\';
       incr n;
       Bytes.unsafe_set s' !n (Char.unsafe_chr (48 + (a / 100)));
       incr n;
       Bytes.unsafe_set s' !n (Char.unsafe_chr (48 + (a / 10 mod 10)));
       incr n;
       Bytes.unsafe_set s' !n (Char.unsafe_chr (48 + (a mod 10))));
    incr n
  done
;;

(* Escape [s] if needed. *)
let escaped s =
  let n = quote_length s in
  if n = 0 || n > String.length s
  then (
    let s' = Bytes.create n in
    escape_to s ~dst:s' ~ofs:0;
    Bytes.unsafe_to_string s')
  else s
;;

(* Surround [s] with quotes, escaping it if necessary. *)
let quoted s =
  let len = String.length s in
  let n = quote_length s in
  let s' = Bytes.create (n + 2) in
  Bytes.unsafe_set s' 0 '"';
  if len = 0 || n > len
  then escape_to s ~dst:s' ~ofs:1
  else Bytes.blit_string ~src:s ~src_pos:0 ~dst:s' ~dst_pos:1 ~len;
  Bytes.unsafe_set s' (n + 1) '"';
  Bytes.unsafe_to_string s'
;;
