signature TRIANGLES =
sig
  val toVector: AppType.app_type -> Real32.real vector
end

structure Triangles :> TRIANGLES =
struct
  open AppType

  fun helpToVector (lst, acc, windowWidth, windowHeight, halfWidth, halfHeight) =
    case lst of
      {x1, y1, x2, y2, x3, y3, r, g, b} :: tl =>
        let
          val x1 = Ndc.centreAlignX (x1, windowWidth, windowHeight, halfWidth)
          val x2 = Ndc.centreAlignX (x2, windowWidth, windowHeight, halfWidth)
          val x3 = Ndc.centreAlignX (x3, windowWidth, windowHeight, halfWidth)

          val y1 = Ndc.centreAlignY (y1, windowWidth, windowHeight, halfHeight)
          val y2 = Ndc.centreAlignY (y2, windowWidth, windowHeight, halfHeight)
          val y3 = Ndc.centreAlignY (y3, windowWidth, windowHeight, halfHeight)

          val vec =
           #[ x1 / halfWidth
            , y1 / halfHeight
            , r
            , g
            , b
            , x2 / halfWidth
            , y2 / halfHeight
            , r
            , g
            , b
            , x3 / halfWidth
            , y3 / halfHeight
            , r
            , g
            , b
            ]
          val acc = vec :: acc
        in
          helpToVector
            (tl, acc, windowWidth, windowHeight, halfWidth, halfHeight)
        end
    | [] => acc

  fun toVector (app: app_type) =
    let
      val windowWidth = #windowWidth app
      val windowHeight = #windowHeight app
      val halfWidth = Real32.fromInt (windowWidth div 2)
      val halfHeight = Real32.fromInt (windowHeight div 2)
      val lst = helpToVector
        (#triangles app, [], windowWidth, windowHeight, halfWidth, halfHeight)
    in
      Vector.concat lst
    end
end