--
-- Author: Michael Sloan <mgsloan@gmail.com>
--
-- This code is in the public domain.
--
-- Based off Johan Bockgård's Drawing2.hs
--
-- updated to GTK 3 by Catherine Holloway
--
import qualified Graphics.UI.Gtk as G
import qualified Graphics.Rendering.Cairo as C
import qualified Graphics.Rendering.Cairo.Matrix as M

f x = sin (x*5) / (x*5)

main = graph f

windowSize :: Int
windowSize = 400

graph :: (Double -> Double) -> IO ()
graph f = do
  G.initGUI
  window <- G.windowNew
  canvas <- G.drawingAreaNew
  -- Gtk3 no longer has size requests, and window does not have a drawable
  -- area to fill, thus we must explicitly tell it how to draw the window size.
  G.windowSetDefaultSize window windowSize windowSize
  G.windowSetGeometryHints window (Just window)
    (Just (0, 0)) (Just (windowSize, windowSize))
    Nothing Nothing (Just (1,1))
  -- press any key to quit
  window `G.on` G.keyPressEvent $ G.tryEvent $ do C.liftIO G.mainQuit
  canvas `G.on` G.draw $ (prologue canvas >> renderG f)
  G.set window [G.containerChild G.:= canvas, G.windowResizable G.:= False]
  G.widgetShowAll window
  G.mainGUI

foreach :: (Monad m) => [a] -> (a -> m b) -> m [b]
foreach = flip mapM

deriv :: (Double -> Double) -> Double -> Double
deriv f x = ((f $ x + 0.05) - (f $ x - 0.05)) * 10

gen :: Double -> Double -> (Double -> Double) -> [Double]
gen v t f | v > t = []
gen v t f = v : (gen (f v) t f)

skipBy f = foldr (\x c -> if f x then c else x : c) []

falloff x = 0.25 * (x + 1.5) / ((x+0.5)^5 + 1)

renderG :: (Double -> Double) -> C.Render ()
renderG f = do
  C.moveTo (-5) (f (-5))
  sequence_ $ map (\d -> C.lineTo d $ f d) $ skipBy (isInfinite . f) [-4.9,-4.8..5]
  --Adaptive attempt (falloff func is what really needs work)
  --sequence_ $ map (\d -> C.lineTo d $ f d) $ skipBy (isInfinite . f) $ tail $ gen (-5) 5 (\x -> x + (falloff $ abs $ deriv (deriv f) x))
  C.stroke

-- Set up stuff
prologue canvas = do
  wWidth'  <- C.liftIO $ G.widgetGetAllocatedWidth  canvas
  wHeight' <- C.liftIO $ G.widgetGetAllocatedHeight canvas
  let wWidth  = realToFrac wWidth'
      wHeight = realToFrac wHeight'
      width   = 10
      height  = 10
      xmax    = width / 2
      xmin    = - xmax
      ymax    = height / 2
      ymin    = - ymax
      scaleX  = realToFrac wWidth  / width
      scaleY  = realToFrac wHeight / height

  -- style and color
  C.setLineCap C.LineCapRound
  C.setLineJoin C.LineJoinRound
  C.setLineWidth $ 1 / max scaleX scaleY

  -- Set up user coordinates
  C.scale scaleX scaleY
  -- center origin
  C.translate (width / 2) (height / 2)
  -- positive y-axis upwards
  let flipY = M.Matrix 1 0 0 (-1) 0 0
  C.transform flipY
  C.setSourceRGBA 0 0 0 1
  grid xmin xmax ymin ymax

-- Grid and axes
grid xmin xmax ymin ymax = do
  -- axes
  C.moveTo 0 ymin; C.lineTo 0 ymax; C.stroke
  C.moveTo xmin 0; C.lineTo xmax 0; C.stroke
  -- grid
  C.setDash [0.01, 0.99] 0
  foreach [xmin .. xmax] $ \ x ->
      do C.moveTo x ymin
         C.lineTo x ymax
         C.stroke
  C.setDash [] 0