import Graphics.UI.Gtk
import Graphics.UI.Gtk.Gdk.Events
-- import Graphics.Rendering.Cairo
import Graphics.UI.Gtk.Gdk.GC

import Control.Monad.Trans
import Data.IORef

main = do
  initGUI
      
  -- create main window
  win <- windowNew
  onDestroy win mainQuit
  
  -- create state variables
  linesRef <- newIORef []
  widthRef <- newIORef 1
  
  -- create the drawing area
  drawingArea <- drawingAreaNew
  let height = 200
  let width  = 400
  onSizeRequest drawingArea $
    return (Requisition width height)
  onButtonPress drawingArea $ \e -> do
    lines <- readIORef linesRef
    let lines' = (round (eventX e), round (eventY e)) : lines
    writeIORef linesRef lines'
    print lines'
    widgetQueueDraw drawingArea
    return True
  onExpose drawingArea $ \e -> do
    dw <- widgetGetDrawWindow drawingArea
    gc <- gcNew dw
    lines        <- readIORef linesRef
    currentWidth <- readIORef widthRef
    gcSetValues gc $ newGCValues {
      lineWidth = currentWidth
    }
    drawLines dw gc lines
    --sequence_ (zipWith (drawLine dw gc) lines (tail lines))
    return True
  
  entry <- entryNew
  
  btn <- buttonNew
  buttonSetLabel btn "Set Width"
  onClicked btn $ do
    txt <- entryGetText entry
    case reads txt of
      [(n,"")] -> do writeIORef widthRef n
                     widgetQueueDraw drawingArea
      _        -> do dlg <- messageDialogNew (Just win) [] MessageError ButtonsOk "This is not an integer"
                     dialogRun dlg
                     widgetDestroy dlg
  -- describe layout of widgets
  let spacing = 10
  vbox <- vBoxNew False spacing
  boxPackStart vbox drawingArea PackGrow 0
  hbox <- hBoxNew False spacing
  boxPackStart hbox entry PackGrow 0
  boxPackStart hbox btn PackNatural 0
  boxPackStart vbox hbox PackNatural 0
  
  containerAdd win vbox

  widgetShowAll win
  mainGUI

  
{-
GTK is written in C and available in many languages
initialization of GTK
main loop of GTK
for reference use the documentation and the examples
how to add widgets in containers


Steps
-----

1. initGUI and mainGUI
2. windowNew & widgetShowAll
3. onDestroy win mainQuit
4. drawingAreaNew & containerAdd
5. onButtonPress drawingArea $ \e ->
    print (eventX e, eventY e) >> return True
6. modeling state -> IORef
-}