content: -- | Running your app inside GHCi.
  --
  -- To start up GHCi for usage with Yesod, first make sure you are in dev mode:
  --
  -- > cabal configure -fdev
  --
  -- Note that @yesod devel@ automatically sets the dev flag.
  -- Now launch the repl:
  --
  -- > cabal repl --ghc-options="-O0 -fobject-code"
  --
  -- To start your app, run:
  --
  -- > :l DevelMain
  -- > DevelMain.update
  --
  -- You can also call @DevelMain.shutdown@ to stop the app
  --
  -- You will need to add the foreign-store package to your .cabal file.
  -- It is very light-weight.
  --
  -- If you don't use cabal repl, you will need
  -- to run the following in GHCi or to add it to
  -- your .ghci file.
  --
  -- :set -DDEVELOPMENT
  --
  -- There is more information about this approach,
  -- on the wiki: https://github.com/yesodweb/yesod/wiki/ghci
  
  module DevelMain where
  
  import Prelude
  import Application (getApplicationRepl, shutdownApp)
  
  import Control.Monad ((>=>))
  import Control.Concurrent
  import Data.IORef
  import Foreign.Store
  import Network.Wai.Handler.Warp
  import GHC.Word
  
  -- | Start or restart the server.
  -- newStore is from foreign-store.
  -- A Store holds onto some data across ghci reloads
  update :: IO ()
  update = do
      mtidStore <- lookupStore tidStoreNum
      case mtidStore of
        -- no server running
        Nothing -> do
            done <- storeAction doneStore newEmptyMVar
            tid <- start done
            _ <- storeAction (Store tidStoreNum) (newIORef tid)
            return ()
        -- server is already running
        Just tidStore -> restartAppInNewThread tidStore
    where
      doneStore :: Store (MVar ())
      doneStore = Store 0
  
      -- shut the server down with killThread and wait for the done signal
      restartAppInNewThread :: Store (IORef ThreadId) -> IO ()
      restartAppInNewThread tidStore = modifyStoredIORef tidStore $ \tid -> do
          killThread tid
          withStore doneStore takeMVar
          readStore doneStore >>= start
  
  
      -- | Start the server in a separate thread.
      start :: MVar () -- ^ Written to when the thread is killed.
            -> IO ThreadId
      start done = do
          (port, site, app) <- getApplicationRepl
    -- https://github.com/parsonsmatt/servant-persistent/pull/33
          forkFinally
            (runSettings (setPort port defaultSettings) app)
            -- Note that this implies concurrency
            -- between shutdownApp and the next app that is starting.
            -- Normally this should be fine
            (\_ -> putMVar done () >> shutdownApp site)
  
  -- | kill the server
  shutdown :: IO ()
  shutdown = do
      mtidStore <- lookupStore tidStoreNum
      case mtidStore of
        -- no server running
        Nothing -> putStrLn "no Yesod app running"
        Just tidStore -> do
            withStore tidStore $ readIORef >=> killThread
            putStrLn "Yesod app is shutdown"
  
  tidStoreNum :: Word32
  tidStoreNum = 1
  
  modifyStoredIORef :: Store (IORef a) -> (a -> IO a) -> IO ()
  modifyStoredIORef store f = withStore store $ \ref -> do
      v <- readIORef ref
      f v >>= writeIORef ref
  