structure AppUpdate =
struct
  open AppType

  local
    fun helpGetTrianglesVector (lst, acc) =
      case lst of
        {x1, y1, x2, y2, x3, y3} :: tl =>
          let val vec = Vector.fromList [x1, y1, x2, y2, x3, y3]
          in helpGetTrianglesVector (tl, vec :: acc)
          end
      | [] => acc
  in
    fun getTrianglesVector (app: app_type) =
      let val lst = helpGetTrianglesVector (#triangles app, [])
      in Vector.concat lst
      end
  end

  local
    val clickPoints =
     #[ 25,  50,  75,  100
      , 125, 150, 175, 200
      , 225, 250, 275, 300
      , 325, 350, 375, 400
      , 425, 450, 475
      ]

    fun getVerticalClickPos (idx, horizontalPos, mouseX, mouseY, r, g, b) =
      if idx = Vector.length clickPoints then
        #[]
      else
        let
          val curVerticalPos = Vector.sub (clickPoints, idx)
        in
          if mouseY < curVerticalPos - 10 orelse mouseY > curVerticalPos + 10 then
            getVerticalClickPos
              (idx + 1, horizontalPos, mouseX, mouseY, r, g, b)
          else
            let
              val left = Real32.fromInt (horizontalPos - 10) / 500.0
              val right = Real32.fromInt (horizontalPos + 10) / 500.0
              val bottom = Real32.fromInt (curVerticalPos - 10) / 500.0
              val top = Real32.fromInt (curVerticalPos + 10) / 500.0
            in
              #[ left, bottom, r, g, b
               , right, bottom, r, g, b
               , left, top, r, g, b

               , left, top, r, g, b
               , right, bottom, r, g, b
               , right, top, r, g, b
               ]
            end
        end

    fun getHorizontalClickPos (idx, mouseX, mouseY, r, g, b) =
      if idx = Vector.length clickPoints then
        #[]
      else
        let
          val curPos = Vector.sub (clickPoints, idx)
        in
          if mouseX < curPos - 10 orelse mouseX > curPos + 10 then
            getHorizontalClickPos (idx + 1, mouseX, mouseY, r, g, b)
          else
            getVerticalClickPos (0, curPos, mouseX, mouseY, r, g, b)
        end
  in
    (*
     * This function returns a vector containing the position data of the
     * clicked square.
     * If a square wasn't found at the clicked position, 
     * an empty vector is returned.
     *)
    fun getClickPos (mouseX, mouseY, r, g, b) =
      getHorizontalClickPos (0, mouseX, mouseY, r, g, b)
  end

  fun update (model, mouseX, mouseY, inputMsg) =
    let
      open DrawMessage
      open InputMessage
    in
      case inputMsg of
        MOUSE_MOVE {x = mouseX, y = mouseY} =>
          let
            val _ = print "mouse moved\n"
            val drawMsg = 
              DRAW_BUTTON (getClickPos (mouseX, mouseY, 1.0, 0.0, 0.0))
          in
            (model, drawMsg, mouseX, mouseY)
          end
      | MOUSE_LEFT_RELEASE =>
          let
            val _ = print "mouse released\n"
            val drawMsg = 
              DRAW_BUTTON (getClickPos (mouseX, mouseY, 1.0, 0.0, 0.0))
          in
            (model, drawMsg, mouseX, mouseY)
          end
      | MUSE_LEFT_CLICK =>
          let
            val _ = print "mouse clicked\n"
            val buttonVec = getClickPos (mouseX, mouseY, 1.0, 0.0, 0.0)
            val drawMsg = DRAW_BUTTON buttonVec
          in
            (model, drawMsg, mouseX, mouseY)
          end
    end
end