simple.ml

open Str
open Types

let hex6 = regexp "\\([0-9a-f]\\)\\1\\([0-9a-f]\\)\\2\\([0-9a-f]\\)\\3"

let is_num = function
  | Number (n, (None | Some "%")) -> true
  | _ -> false

let clip = function
  | Number (n, u) when n < 0.          -> Number (0., u)
  | Number (n, None) when n > 255.     -> Number (255., None)
  | Number (n, Some "%") when n > 100. -> Number (100., Some "%")
  | value -> value

let rec shorten_expr = function
  (* #aabbcc -> #abc *)
  | Hexcolor h when string_match hex6 h 0 ->
    let gr n = matched_group n h in
    shorten_expr (Hexcolor (gr 1 ^ gr 2 ^ gr 3))

  (* rgb(r,g,b) -> #rrggbb *)
  | Function ("rgb", Nary (",", [r; g; b]))
    when is_num r && is_num g && is_num b ->
    let i c =
      match clip c with
      | Number (n, None) -> int_of_float n
      | Number (n, Some "%") -> int_of_float (n *. 2.55 +. 0.5)
      | _ -> assert false
    in
    shorten_expr (Hexcolor (Printf.sprintf "%02x%02x%02x" (i r) (i g) (i b)))

  (* clip rgb values, e.g. rgb(-1,256,0) -> rgb(0,255,0) *)
  | Function ("rgb", Nary (",", [r; g; b])) ->
    Function ("rgb", Nary (",", [clip r; clip g; clip b]))

  (* rgba(r,g,b,1.0) -> rgb(r,g,b) *)
  | Function ("rgba", Nary (",", [r; g; b; Number (1., None)])) ->
    shorten_expr (Function ("rgb", Nary (",", [r; g; b])))

  (* TODO: hsl[a](...) *)

  (* 0px -> 0 *)
  | Number (0., Some _) -> Number (0., None)

  (* transform color names to shorter hex codes and vice-versa *)
  | v -> Color_names.compress v

let shorten_font_weight = function
  | Ident "normal" -> Number (400.0, None)
  | Ident "bold"   -> Number (700.0, None)
  | v -> v

let shorten_nth = function
  (* even -> 2n *)
  | Even                  -> Formula (2, 0)
  (* 2n+1 | 2n-1 -> odd *)
  | Formula (2, (1 | -1)) -> Odd
  (* -n+1 -> 1 *)
  | Formula (-1, 1)       -> Formula (0, 1)
  | v -> v

let compress =
  Util.transform_stylesheet begin function
    | Expr value ->
      Expr (shorten_expr value)
    | Declaration ("font-weight", value, imp) ->
      Declaration ("font-weight", shorten_font_weight value, imp)
    | Declaration (("border" | "outline") as name, Ident "none", imp) ->
      Declaration (name, Number (0., None), imp)
    | Pseudo_class_arg (Nth nth) ->
      Pseudo_class_arg (Nth (shorten_nth nth))
    (* Remove rulesets with :nth-child(0) selector *)
    | Selector (Pseudo_class (_, cls, Some [Nth (Formula (0, 0))]))
      when string_match (regexp "nth-") cls 0 ->
      Clear
    (* Remove rulesets with no selectors or declarations *)
    | Statement (Ruleset ([], _))
    | Statement (Ruleset (_, [])) ->
      Clear
    | v -> v
  end