module MusicScroll.EventLoop where

import Control.Concurrent.Async
import Control.Concurrent.STM

import MusicScroll.Pipeline

-- | This callbacks ought to update the UI themselves via postGUI
type UICallback = AppState -> IO ()

data EventLoopState = EventLoopState
  { evAppState    :: AppState
  , evUiCallbacks :: TBQueue UICallback
  , evEphemeral   :: Maybe (Async ()) }

eventLoop :: EventLoopState -> IO a
eventLoop st =
  do newCallback <- atomically . readTBQueue $ evUiCallbacks st
     maybe (pure ()) cancel (evEphemeral st)
     newAsync <- async (newCallback (evAppState st))
     let st' = st { evEphemeral = Just newAsync }
     eventLoop st'