module Main where

import Graphics.UI.Gtk (initGUI, mainGUI)
import System.Gnome.GConf (GConf, gconfGetDefault, gconfSet)
import System.Glib.MainLoop (timeoutAdd, timeoutRemove, HandlerId)
import System.Directory (getHomeDirectory, getDirectoryContents, doesFileExist)
import System.Random
import System.Environment
import Control.Monad (filterM)
import Data.IORef

main :: IO ()
main = do
  random_generator <- getStdGen
  random_generator_ior <- newIORef random_generator
  home <- getHomeDirectory
  args <- getArgs
  let seconds = case length args of
                  0 -> 50 :: Int
                  _ -> read (head args) :: Int
      minutes = case length args of
                  n | n < 2 -> 1440
                  _ -> read (head $ drop 1 args) :: Int
      picture_directory = case length args of
                            n | n == 3 -> head $ drop 2 args
                            n | n > 3 -> error "Usage: gnome_desktop [redisplay-seconds] [reread-minutes] [directory]"
                            n | otherwise -> "Pictures"
      pictures = home ++ "/" ++ picture_directory ++ "/"
  set_timeouts random_generator_ior seconds minutes pictures
  initGUI
  mainGUI

set_timeouts :: IORef StdGen -> Int -> Int -> FilePath -> IO ()
set_timeouts random_generator_ior seconds minutes pictures = do
  real_files <- get_pictures pictures
  conf <- gconfGetDefault
  set_picture conf real_files (length real_files) random_generator_ior
  picture_timeout <- timeoutAdd (set_picture conf real_files (length real_files) random_generator_ior) (seconds * 1000)
  timeout_handler_ior <- newIORef picture_timeout
  timeoutAdd (read_directory seconds pictures conf timeout_handler_ior random_generator_ior) (minutes * 60000)
  return ()

read_directory :: Int -> FilePath -> GConf -> IORef HandlerId -> IORef StdGen -> IO Bool
read_directory seconds pictures conf timeout_handler_ior random_generator_ior = do
  real_files <- get_pictures pictures
  handler_id <- readIORef timeout_handler_ior
  timeoutRemove handler_id
  handler_id <- timeoutAdd (set_picture conf real_files (length real_files) random_generator_ior) (seconds * 1000) 
  return True

get_pictures :: FilePath -> IO [FilePath]
get_pictures pictures = do
  files <- getDirectoryContents pictures
  let abs_files = map (absolute_file pictures) files
  filterM doesFileExist abs_files


set_picture :: GConf -> [FilePath] -> Int -> IORef StdGen -> IO Bool
set_picture conf files len random_generator_ior = do
  g <- readIORef random_generator_ior
  let (n, g') = randomR (1, len) g
      file = head $ drop (n - 1) files
  writeIORef random_generator_ior g'
  gconfSet conf "/desktop/gnome/background/picture_filename" file
  return True

absolute_file :: FilePath -> FilePath -> FilePath
absolute_file pictures file = pictures ++ file