module Image where

import System.Process
import System.Exit
import Control.Concurrent.STM

newtype ImageQueue = ImageQueue (TQueue (IO Bool, TMVar Bool))

mkImageQueue :: IO ImageQueue
mkImageQueue = ImageQueue <$> newTQueueIO

queueAction :: ImageQueue -> IO Bool -> IO Bool
queueAction (ImageQueue q) a = do
	v <- newEmptyTMVarIO
	atomically $ writeTQueue q (a, v)
	atomically $ takeTMVar v

queueRunnerThread :: ImageQueue -> IO ()
queueRunnerThread q@(ImageQueue qv) = do
	(a, v) <- atomically $ readTQueue qv
	r <- a
	_ <- atomically $ tryPutTMVar v r
	queueRunnerThread q

scaleImage :: Int -> FilePath -> FilePath -> IO Bool
scaleImage maxsz src dst = do
	p <- spawnProcess "convert"
		[ src
		, "-resize"
		-- The ">" makes it only shrink large images, not scale up
		-- small.
		, show maxsz ++ "x" ++ show maxsz ++ ">"
		, dst
		]
	(== ExitSuccess) <$> waitForProcess p