-- |
-- Module:
--   Reflex.Test.Monad.Host
-- Description:
--   This module contains a monad for testing reflex networks

module Reflex.Test.Monad.Host
  ( TestGuestT
  , TestGuestConstraints
  , ReflexTriggerRef

  , MonadReflexTest(..)
  , AppState(..)
  , ReflexTestT(..)
  , runReflexTestT
  , ReflexTestApp(..)
  , runReflexTestApp
  )
where



import           Prelude


import           Control.Concurrent.Chan
import           Control.Monad.IO.Class

import           Control.Monad.Fix
import           Control.Monad.Primitive
import           Control.Monad.Reader
import           Control.Monad.Ref
import           Control.Monad.State.Strict
import           Data.Dependent.Sum
import           Data.Functor.Identity
import           Data.Kind

import           Reflex
import           Reflex.Class               ()
import           Reflex.Host.Class


type TestGuestT t (m :: Type -> Type)
  = TriggerEventT t (PostBuildT t (PerformEventT t m))

type TestGuestConstraints t (m :: Type -> Type)
  = ( MonadReflexHost t m
    , MonadHold t m
    , MonadSample t m
    , Ref m ~ Ref IO
    , MonadRef m
    , MonadRef (HostFrame t)
    , Ref (HostFrame t) ~ Ref IO
    , MonadIO (HostFrame t)
    , PrimMonad (HostFrame t)
    , MonadIO m
    , MonadFix m
    )

-- | since we work with this type directly a lot, it helps to wrap it around a type synonym
type ReflexTriggerRef t (m :: Type -> Type) a = Ref m (Maybe (EventTrigger t a))

-- |
class MonadReflexTest t m | m -> t  where
  -- | since event subscriptions also happen within the monad, input triggers created via 'newEventWithTriggerRef' may be stuck in the 'Nothing' state as there are no listeners yet
  -- therefore it's necessary to pass in IORefs to the EventTriggers, thus the name of this type
  -- in practice, this will likely be a record containing many trigger refs and the monad user must deref them all
  type InputTriggerRefs m :: Type
  -- | in practice, this will likely be a record containing events and behaviors for the monad user to build a 'ReadPhase' that is passed into 'fireQueuedEventsAndRead'
  type OutputEvents m :: Type
  -- | the inner monad that reflex is running in
  -- likely 'SpiderHost Global'
  type InnerMonad m :: Type -> Type
  -- | see comments for 'InputTriggerRefs'
  inputTriggerRefs :: m (InputTriggerRefs m)
  -- | all queued triggers will fire simultaneous on the next execution of 'fireQueuedEventsAndRead'
  queueEventTrigger :: DSum (EventTrigger t) Identity -> m ()
  -- | same as 'queueEventTrigger' except works with trigger refs
  -- if the trigger ref derefs to 'Nothing', the event does not get queued
  queueEventTriggerRef :: Ref (InnerMonad m) (Maybe (EventTrigger t a)) -> a -> m ()
  -- | see comments for 'OutputEvents'
  outputs :: m (OutputEvents m)
  -- | fire all queued events and run a ReadPhase to produce results from the execution frames
  -- readphase takes place in the inner monad
  fireQueuedEventsAndRead :: ReadPhase (InnerMonad m) a -> m [a]
  -- | same as above with no ReadPhase
  fireQueuedEvents :: (Monad (ReadPhase (InnerMonad m))) => m [()]
  fireQueuedEvents = fireQueuedEventsAndRead (return ())

-- m is 'InnerMonad' from above
data AppState t m = AppState
    { _appState_queuedEvents :: [DSum (EventTrigger t) Identity] -- ^ events to fire in next 'FireCommand'
    -- ^ 'FireCommand' to fire events and run next frame
    , _appState_fire         :: FireCommand t m -- ^ 'FireCommand' to fire events and run next frame
    }

-- | implementation of 'MonadReflexTest'
newtype ReflexTestT t intref out m a = ReflexTestT { unReflexTestM :: ReaderT (intref, out) (StateT (AppState t m) m) a }
  deriving
    ( Functor
    , Applicative
    , Monad
    , MonadIO
    , MonadFix
    , MonadReader (intref, out)
    , MonadState (AppState t m))

deriving instance MonadSample t m => MonadSample t (ReflexTestT t intref out m)
deriving instance MonadHold t m => MonadHold t (ReflexTestT t intref out m)
deriving instance MonadReflexCreateTrigger t m => MonadReflexCreateTrigger t (ReflexTestT t intref out m)

instance MonadTrans (ReflexTestT t intref out) where
  lift = ReflexTestT . lift . lift

instance (MonadSubscribeEvent t m) => MonadSubscribeEvent t (ReflexTestT t intref out m) where
  subscribeEvent = lift . subscribeEvent

instance (MonadRef m) => MonadReflexTest t (ReflexTestT t intref out m) where
  type InputTriggerRefs (ReflexTestT t intref out m) = intref
  type OutputEvents (ReflexTestT t intref out m) = out
  type InnerMonad (ReflexTestT t intref out m) = m
  inputTriggerRefs = do
    (intref,_) <- ask
    return intref
  queueEventTrigger evt = do
    as <- get
    put $ as { _appState_queuedEvents = evt : _appState_queuedEvents as }
  queueEventTriggerRef ref a = do
    mpulse <- lift $ readRef ref
    case mpulse of
      Nothing    -> return ()
      Just pulse -> do
        as <- get
        put $ as { _appState_queuedEvents = (pulse :=> Identity a) : _appState_queuedEvents as }
  outputs = do
    (_,out) <- ask
    return out
  fireQueuedEventsAndRead rp = do
    as <- get
    put $ as { _appState_queuedEvents = [] }
    lift $ (runFireCommand $ _appState_fire as) (_appState_queuedEvents as) rp

runReflexTestT
  :: forall intref inev out t m a
   . (TestGuestConstraints t m)
  => (inev, intref) -- ^ make sure intref match inev, i.e. return values of newEventWithTriggerRef
  -> (inev -> TestGuestT t m out) -- ^ network to test
  -> ReflexTestT t intref out m a -- ^ test monad to run
  -> m ()
runReflexTestT (input, inputTRefs) app rtm = do
  (postBuild, postBuildTriggerRef) <- newEventWithTriggerRef

  events                           <- liftIO newChan
  (output, fc@(FireCommand fire))  <- do
    hostPerformEventT
      $ flip runPostBuildT    postBuild
      $ flip runTriggerEventT events
      $ app input

  -- handle post build
  -- TODO consider adding some way to test 'PostBuild' results
  mPostBuildTrigger <- readRef postBuildTriggerRef
  _                 <- case mPostBuildTrigger of
    Nothing -> return [()] -- no subscribers
    Just postBuildTrigger ->
      fire [postBuildTrigger :=> Identity ()] $ return ()

  -- TODO maybe find a way to handle trigger events
  -- one solution is to implement non-blocking variant of TriggerEventT
  -- and then pass as part of AppState such that each call to readPhase will fire any trigger events
  -- another option is just to start a thread and output warnings anytime triggerEvs are created
  --triggerEvs <- liftIO $ readChan events

  -- run the test monad
  flip runStateT (AppState [] fc)
    $ flip runReaderT (inputTRefs, output)
      $ unReflexTestM rtm

  return ()



-- | class to help bind network and types to a 'ReflexTestT'
-- see test/Reflex/Test/Monad/HostSpec.hs for usage example
class ReflexTestApp app t m | app -> t m where
  data AppInputTriggerRefs app :: Type
  data AppInputEvents app :: Type
  data AppOutput app :: Type
  getApp :: AppInputEvents app -> TestGuestT t m (AppOutput app)
  makeInputs :: m (AppInputEvents app, AppInputTriggerRefs app)

runReflexTestApp
  :: (ReflexTestApp app t m, TestGuestConstraints t m)
  => ReflexTestT t (AppInputTriggerRefs app) (AppOutput app) m ()
  -> m ()
runReflexTestApp rtm = do
  i <- makeInputs
  runReflexTestT i getApp rtm