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{-# LANGUAGE ViewPatterns #-}
module Thermoprint.Server.Push
( Notification
, withPush
, protocolSpec
, notifyOnChange
) where
import Network.WebSockets
import Network.Wai.Handler.WebSockets
import Network.Wai (Application)
import Network.URI
import Control.Concurrent.STM
import Thermoprint.Server.Queue
import Control.Monad.IO.Class
import Control.Monad
import Paths_thermoprint_server (version)
import Data.Version (showVersion)
import Data.ByteString.Char8 (ByteString)
import qualified Data.ByteString.Char8 as CBS
import Data.Text (Text)
import qualified Data.Text as Text
type Notification = URI
withPush :: TChan Notification -> Application -> Application
withPush chan = websocketsOr defaultConnectionOptions $ flip acceptRequestWith (AcceptRequest $ Just protocolSpec) >=> handleClient chan
protocolSpec :: ByteString
protocolSpec = CBS.pack $ "thermoprint-server.notification." ++ showVersion version
handleClient :: TChan Notification -> Connection -> IO ()
handleClient chan conn = do
cChan <- atomically $ dupTChan chan
forkPingThread conn 10
forever . void $ atomically (readTChan cChan) >>= sendTextData conn . packNotification
packNotification :: Notification -> Text
packNotification = Text.pack . show
notifyOnChange :: MonadIO m => TChan Notification -> (a -> a -> Bool) -> Notification -> TVar a -> m ()
notifyOnChange chan cmp n q = void . liftIO $ readTVarIO q >>= notifyOnChange'
where
notifyOnChange' last = do
current <- atomically $ (\current -> current <$ check (not $ cmp last current)) =<< readTVar q
atomically $ writeTChan chan n
notifyOnChange' current
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