open StdLabels
(** Common  module for ensuring that the function is evaluated only once *)

(** This represent a single path, which can be transformed throug a [repr]
    function. *)
module type PATH = sig
  type t

  (** Represent the path *)
  val repr
    : t -> (module Path.Repr.M
             with type point = Path.Point.t
              and type t = 's) -> 's -> 's
end

type printer =
  [ `Fill
  | `Line
  | `Ductus ]


module type P = sig
  include Path.Repr.M

  type repr

  val create_path
    : (repr -> repr) -> t

  val get
    : t -> repr
end


module MakePrinter(M:Repr.ENGINE) : P
  with type point = M.point
   and type t = M.t
   and type repr = M.repr = struct

  type t = M.t

  type point = M.point

  type repr = M.repr

  let get
    : t -> repr
    = M.get

  let create_path
    : (repr -> repr) -> t
    = M.create_path

  let start
    : Path.Point.t -> t -> t
    = fun pt t ->
      M.start pt pt t

  let line_to
    : Path.Point.t -> Path.Point.t -> t -> t
    = fun p0 p1 t ->

      M.line_to
        ( p0
        , p1 )
        ( Path.Point.copy p0 @@ Path.Point.get_coord' p0
        , Path.Point.copy p1 @@ Path.Point.get_coord' p1 )
        t

  let quadratic_to
    : (Path.Point.t * Gg.v2 * Gg.v2 * Path.Point.t) -> t -> t
    = fun (p0,  ctrl0, ctrl1, p1) t ->


      let ctrl0' = Path.Point.get_coord' @@ Path.Point.copy p0 ctrl0
      and ctrl1' = Path.Point.get_coord' @@ Path.Point.copy p1 ctrl1 in
      M.quadratic_to
        (p0, ctrl0, ctrl1, p1)
        (Path.Point.copy p0 @@ Path.Point.get_coord' p0, ctrl0', ctrl1', Path.Point.copy p1 @@ Path.Point.get_coord' p1)

        t

  let stop = M.stop
end

(** Transform the two path, into a single one. *)
module ReprSingle = struct

  type point = Path.Point.t

  type repr =
    | Move of (point)
    | Line_to of (point * point)
    | Quadratic of (point * Gg.v2 * Gg.v2 * point)

  module R = struct
    type t = repr list

    type point = Path.Point.t

    let start t actions =
      (Move t)::actions

    let line_to p0 p1 actions =
      Line_to (p0, p1)::actions

    let quadratic_to
      : (point * Gg.v2 * Gg.v2 * point) -> t -> t
      = fun q actions ->
        (Quadratic q)::actions

    let stop
      : t -> t
      = fun v -> v

  end

  let repr
    : (module PATH with type t = 't) -> 't -> 't -> repr list * repr list
    = fun (type t) (module P:PATH with type t = t) path back ->
      let path = P.repr path (module R) []
      and back = P.repr back (module R) [] in
      path, back
end

(* Canva representation *)

module FillCanva = FillEngine.Make(CanvaPrinter)
module LineCanva = LineEngine.Make(CanvaPrinter)
module DuctusCanva = DuctusEngine.Make(CanvaPrinter)

(* SVG representation *)

module FillSVG = FillEngine.Make(Svg)
module DuctusSVG = DuctusEngine.Make(Svg)


(** Draw a path to a canva.contents

    The code may seems scary, but is very repetitive. Firt, all points (from the
    main stroke, and the interior one) are evaluated. Then, they are both rendered
    using the selected engine.
*)
let to_canva
  : (module PATH with type t = 's) -> 's * 's -> Brr_canvas.C2d.t -> printer -> unit
  = fun (type s) (module R:PATH with type t = s) (path, back) ctx engine ->
    let f, b = ReprSingle.repr (module R) path back in
    match engine with
    | `Fill ->
      let t = List.fold_left2 f b
          ~init:(FillCanva.create_path (fun p -> Brr_canvas.C2d.fill ctx p; p))
          ~f:(fun ctx f b ->
              match (f, b) with
              | ReprSingle.Move p0, ReprSingle.Move p0' -> FillCanva.start p0 p0' ctx
              | ReprSingle.Line_to l, ReprSingle.Line_to l' -> FillCanva.line_to l l' ctx
              | ReprSingle.Quadratic q, ReprSingle.Quadratic q' -> FillCanva.quadratic_to q q' ctx
              | _ -> ctx
            ) in
      FillCanva.get t
      |> Brr_canvas.C2d.stroke ctx
    | `Line ->
      let t = List.fold_left2 f b
          ~init:(LineCanva.create_path (fun p -> Brr_canvas.C2d.fill ctx p; p))
          ~f:(fun ctx f b ->
              match (f, b) with
              | ReprSingle.Move p0, ReprSingle.Move p0' -> LineCanva.start p0 p0' ctx
              | ReprSingle.Line_to l, ReprSingle.Line_to l' -> LineCanva.line_to l l' ctx
              | ReprSingle.Quadratic q, ReprSingle.Quadratic q' -> LineCanva.quadratic_to q q' ctx
              | _ -> ctx
            ) in
      LineCanva.get t
      |> Brr_canvas.C2d.stroke ctx
    | `Ductus ->
      let t = List.fold_left2 f b
          ~init:(DuctusCanva.create_path (fun p -> Brr_canvas.C2d.fill ctx p; p))
          ~f:(fun ctx f b ->
              match (f, b) with
              | ReprSingle.Move p0, ReprSingle.Move p0' -> DuctusCanva.start p0 p0' ctx
              | ReprSingle.Line_to l, ReprSingle.Line_to l' -> DuctusCanva.line_to l l' ctx
              | ReprSingle.Quadratic q, ReprSingle.Quadratic q' -> DuctusCanva.quadratic_to q q' ctx
              | _ -> ctx
            ) in
      DuctusCanva.get t
      |> Brr_canvas.C2d.stroke ctx



(** Draw a path and represent it as SVG *)
let to_svg
  : (module PATH with type t = 's) -> color:Jstr.t -> 's * 's -> printer -> Brr.El.t
  = fun (type s) (module R:PATH with type t = s) ~color (path, back) engine ->
    let f, b = ReprSingle.repr (module R) path back in
    match engine with
    | `Fill ->

      (* In order to deal with over crossing path, I cut the path in as
         many segment as there is curve, and fill them all. Then, all of theme
         are grouped inside a single element *)
      let paths = ref [] in
      let init = (FillSVG.create_path
                    (fun p ->
                       let repr = Svg.path
                           ~at:Brr.At.[ v (Jstr.v "d") p ]
                           [] in

                       paths := repr::!paths;
                       Jstr.empty)) in
      let _ = List.fold_left2 f b
          ~init
          ~f:(fun ctx f b ->
              match (f, b) with
              | ReprSingle.Move p0, ReprSingle.Move p0' -> FillSVG.start p0 p0' ctx
              | ReprSingle.Line_to l, ReprSingle.Line_to l' -> FillSVG.line_to l l' ctx
              | ReprSingle.Quadratic q, ReprSingle.Quadratic q' -> FillSVG.quadratic_to q q' ctx
              | _ -> ctx
            ) in

      Brr.El.v (Jstr.v "g")
        ~at:Brr.At.[
            v (Jstr.v "fill")  color
          ; v (Jstr.v "stroke") color]
        !paths

    | `Ductus ->
      let init = DuctusSVG.create_path (fun _ -> Jstr.empty) in
      let svg_path = List.fold_left2 f b
          ~init
          ~f:(fun ctx f b ->
              match (f, b) with
              | ReprSingle.Move p0, ReprSingle.Move p0' -> DuctusSVG.start p0 p0' ctx
              | ReprSingle.Line_to l, ReprSingle.Line_to l' -> DuctusSVG.line_to l l' ctx
              | ReprSingle.Quadratic q, ReprSingle.Quadratic q' -> DuctusSVG.quadratic_to q q' ctx
              | _ -> ctx
            )
                     |> DuctusSVG.get in

      Svg.path
        ~at:Brr.At.[
            v (Jstr.v "fill")  color
          ; v (Jstr.v "stroke") color
          ; v (Jstr.v "d") svg_path ]
        []
    | `Line ->
      raise Not_found