module Tty_str = struct

  type ttyfmt =
    | Plain
    | Red
    | Green
    | Yellow
    | Bold
    | Dim
    | Italic
    | Underline

  type t = { fmt : ttyfmt; data: string }

  let start_of fmt =
    match fmt with
    | Plain -> ""
    | Red -> "\x1b[31m"
    | Green -> "\x1b[32m"
    | Yellow -> "\x1b[33m"
    | Bold -> "\x1b[1m"
    | Dim -> "\x1b[2m"
    | Italic -> "\x1b[3m"
    | Underline -> "\x1b[4m"

  let end_of fmt =
    match fmt with
    | Plain -> ""
    | _ -> "\x1b[0m"

  let create ?(fmt = Plain) data = { fmt; data }

  let string_of ?(for_tty = false) t =
    let start_tag =
      match for_tty with
      | false -> ""
      | true -> start_of t.fmt
      in
    let end_tag =
      match for_tty with
      | false -> ""
      | true -> end_of t.fmt
      in
    Printf.sprintf "%s%s%s" start_tag t.data end_tag

end

let () =
  let line_1 = Tty_str.create "Some plain text" in
  let line_2 = Tty_str.create ~fmt:Red "Some red text" in
  let line_3 = Tty_str.create ~fmt:Green "Some green text" in
  let line_4 = Tty_str.create ~fmt:Yellow "Some yellow text" in
  let line_5 = Tty_str.create ~fmt:Bold "Some bold text" in
  let line_6 = Tty_str.create ~fmt:Italic "Some italic text" in
  let line_7 = Tty_str.create ~fmt:Dim "Some dim text" in
  let line_8 = Tty_str.create ~fmt:Underline "Some underlined text" in

  let lines =
    [line_1; line_2; line_3; line_4; line_5; line_6; line_7; line_8] in

  Printf.printf "Print with colors, for a TTY:\n----------------\n";
  List.iter
    (fun s -> Printf.printf "%s\n" (Tty_str.string_of ~for_tty:true s)) lines;

  Printf.printf "\nPrint without colors, for no TTY.\n----------------\n";
  List.iter
    (fun s -> Printf.printf "%s\n" (Tty_str.string_of s)) lines