open StdLabels

let patdiff_cmd ~use_color ~extra_patdiff_args =
  let args =
    List.concat [
      ["-keep-whitespace"];
      ["-location-style omake"];
      (if use_color then [] else ["-ascii"]);
      extra_patdiff_args
    ]
  in
  String.concat ~sep:" " ("patdiff" :: args)
;;

let print ?diff_command ?(extra_patdiff_args=[]) ?(use_color=false) ~file1 ~file2 () =
  let exec cmd =
    let cmd =
      Printf.sprintf "%s %s %s 1>&2" cmd (Filename.quote file1) (Filename.quote file2)
    in
    match Sys.command cmd with
    | 0 -> `Same
    | 1 -> `Different
    | n -> `Error (n, cmd)
  in
  match diff_command with
  | Some s -> ignore (exec s : [> `Same | `Different | `Error of int * string])
  | None ->
    begin match exec (patdiff_cmd ~use_color ~extra_patdiff_args) with
    | `Same ->
      (* patdiff produced no output, fallback to diff -u *)
      Printf.eprintf "File \"%s\", line 1, characters 0-0:\n%!" file1;
      ignore (exec "diff -u" : [> `Same | `Different | `Error of int * string])
    | `Different ->
      (* patdiff successfully found a difference *)
      ()
    | `Error (err_code, cmd) ->
      (* patdiff threw an error... perhaps it wasn't installed? fallback to diff -u *)
      Printf.eprintf "Error:\n\
                      > %S exited with code %d\n\
                      > Perhaps patdiff is not installed? Hint, try: opam install patdiff\n\
                      > Falling back to diff -u\n\
                      \n" cmd err_code;
      Printf.eprintf "File \"%s\", line 1, characters 0-0:\n%!" file1;
      ignore (exec "diff -u" : [> `Same | `Different | `Error of int * string])
    end
;;
