module Graphics.UI.AF.General.EditFile
    ( editFile
    )
where

import Graphics.UI.AF.General.AutoForm
import Graphics.UI.AF.General.Misc
import Graphics.UI.AF.General.MySYB
import Graphics.UI.AF.General.CustomTypes

import Control.Monad.Error

editFile :: ( Read t, AutoForm wxAct comH builder satCxt com
            , Sat (satCxt t), Eq t, Show t, MonadIO builder, MonadIO wxAct
            , TypePresentation t wxAct comH builder satCxt com) =>
	    FilePath
         -> t
         -> builder ()
editFile filename defaultValue =
       do entry          <- fromFile filename defaultValue (errorDialog "Error loading file")
          entryHandle    <- builderCom entry  -- FIXME: should be changed to mkCom laiter
          chState        <- makeChangedState entryHandle
          
          let saveFile = do x <- getValue entryHandle
                            liftIO $ writeFile filename $ show x
                            setValue chState $ Unchanged x
          button "Save" saveFile >>= enabledWhen chState (== Changed)
          -- FIXME: missing saveAs button
          button "Quit" closeWindow
          return ()

-- |Tries to read a file from disc. If an error occurs the 'onError' function is called.
fromFile :: (MonadIO m, Read a)
         => FilePath            -- ^The file to read.
         -> a                   -- ^Default value.
         -> (String -> m ())    -- ^This is called if an error occurs while trying to read the file.
         -> m a
fromFile filename defaultValue onError =
      do entry <- liftIO $ (do entryText <- readFile filename
                               e <- readIO entryText
                               return $ Right e
                           ) `catch` (return . Left . show)
         case entry of
           Left "" -> return defaultValue
           Left s  -> do onError s
                         return defaultValue
           Right x -> return x