signature GRAPH_LINES =
sig
  val generate: AppType.app_type -> Real32.real vector
end

structure GraphLines :> GRAPH_LINES =
struct
  fun toNdc (cur, half) = (cur - half) / half

  fun helpGenGraphLinesX (pos, xClickPoints, yClickPoints, acc,
    windowWidth, windowHeight) =
    if pos = Vector.length xClickPoints then
      Vector.concat acc
    else
      let
        val halfWidth = windowHeight div 2
        val halfWidth = Real32.fromInt halfWidth
        val halfHeight = windowHeight div 2
        val halfHeight = Real32.fromInt halfHeight

        val curX = Vector.sub (xClickPoints, pos)
        val curYNdc = toNdc (curX, halfWidth)

        val minY = Vector.sub (xClickPoints, 0)
        val minY = toNdc (minY, halfWidth)
        val maxY = Vector.sub (xClickPoints, Vector.length xClickPoints - 1)
        val maxY = toNdc (maxY, halfWidth)

        val acc =
            #[ curYNdc - 0.001, minY
             , curYNdc + 0.001, minY
             , curYNdc + 0.001, maxY

             , curYNdc + 0.001, maxY
             , curYNdc - 0.001, maxY
             , curYNdc - 0.001, minY
             ] :: acc
      in
        helpGenGraphLinesX
          (pos + 1, xClickPoints, yClickPoints, acc, windowWidth, windowHeight)
      end

  fun helpGenGraphLinesY (pos, yClickPoints, xClickPoints, acc,
    windowWidth, windowHeight) =
    if pos = Vector.length yClickPoints then
      acc
    else
      let
        val halfWidth = windowHeight div 2
        val halfWidth = Real32.fromInt halfWidth
        val halfHeight = windowHeight div 2
        val halfHeight = Real32.fromInt halfHeight

        val curY = Vector.sub (yClickPoints, pos)
        val curYNdc = toNdc (curY, halfHeight)

        val minX = Vector.sub (xClickPoints, 0)
        val minX = toNdc (minX, halfWidth)
        val maxX = Vector.sub (xClickPoints, Vector.length xClickPoints - 1)
        val maxX = toNdc (maxX, halfWidth)

        val acc =
            #[ minX, curYNdc - 0.001
             , minX, curYNdc + 0.001
             , maxX, curYNdc + 0.001

             , maxX, curYNdc + 0.001
             , maxX, curYNdc - 0.001
             , minX, curYNdc - 0.001 
             ] :: acc
      in
        helpGenGraphLinesY
          (pos + 1, yClickPoints, xClickPoints, acc, windowWidth, windowHeight)
      end

  fun helpGenerate (windowWidth, windowHeight, xClickPoints, yClickPoints) =
  let
    val acc = helpGenGraphLinesY (0, yClickPoints, xClickPoints, [], windowWidth, windowHeight)
  in
    helpGenGraphLinesX (0, xClickPoints, yClickPoints, acc, windowWidth, windowHeight)
  end

  fun generate (app: AppType.app_type) = 
    let
      val {windowWidth, windowHeight, xClickPoints, yClickPoints, ...} = app
    in
      helpGenerate (windowWidth, windowHeight, xClickPoints, yClickPoints)
    end
end