let read_all_lines file_name =
  let in_channel = open_in file_name in
  let rec read_recursive lines =
    try
      Scanf.fscanf in_channel "%[^\r\n]\n" (fun x -> read_recursive (x :: lines))
    with
      End_of_file ->
      lines in
  let lines = read_recursive [] in
  let _ = close_in_noerr in_channel in
  List.rev (lines)

type lineresult = Ok of (string * string * string) | No of string | Skip

let read_line_content (lst: string list) : lineresult =
  match lst with
  | [] -> Skip
  | domain::ip::cidr::[] -> Ok (domain, ip, cidr)
  | _ -> No (String.concat " " lst)

let parse_config_file (fname: string) : lineresult list =
  let content = read_all_lines fname in
  let remove_comments (str:string) : string =
    match String.index_opt str '#' with
    | None -> str
    | Some n -> String.sub str 0 n
  in
  let parse_line line =
    line |>
      remove_comments |>
      String.split_on_char ' ' |>
      List.filter (fun s -> not (List.mem s ["\t"; ""; "\n"])) |> (* strip spaces *)
      read_line_content
  in
  content |> List.map parse_line