{-# LANGUAGE DataKinds #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE TypeFamilies #-}

{- |
This module provides two things:

* Clocks that tick whenever events arrive on a 'Control.Concurrent.Chan',
  and useful utilities.
* Primitives to emit events.

Note that _events work across multiple clocks_,
i.e. it is possible (and encouraged) to emit events from signals
on a different clock than the event clock.
This is in line with the Rhine philosophy that _event sources are clocks_.

Events even work well across separate threads,
and constitute the recommended way of communication between threads in Rhine.

A simple example using events and threads can be found in rhine-examples.
-}
module FRP.Rhine.Clock.Realtime.Event (
  module FRP.Rhine.Clock.Realtime.Event,
  module Control.Monad.IO.Class,
  newChan,
)
where

-- base
import Control.Concurrent.Chan

-- time
import Data.Time.Clock

-- deepseq
import Control.DeepSeq

-- transformers
import Control.Monad.IO.Class
import Control.Monad.Trans.Reader

-- rhine
import FRP.Rhine.ClSF
import FRP.Rhine.Clock
import FRP.Rhine.Clock.Proxy

-- * Monads allowing for event emission and handling

-- | A monad transformer in which events can be emitted onto a 'Chan'.
type EventChanT event m = ReaderT (Chan event) m

{- | Escape the 'EventChanT' layer by explicitly providing a channel
   over which events are sent.
   Often this is not needed, and 'runEventChanT' can be used instead.
-}
withChan :: Chan event -> EventChanT event m a -> m a
withChan :: forall event (m :: Type -> Type) a.
Chan event -> EventChanT event m a -> m a
withChan = forall a b c. (a -> b -> c) -> b -> a -> c
flip forall r (m :: Type -> Type) a. ReaderT r m a -> r -> m a
runReaderT

{- | Create a channel across which events can be communicated,
and subsequently execute all event effects on this channel.

Ideally, this action is run _outside_ of 'flow',
e.g. @runEventChanT $ flow myRhine@.
This way, exactly one channel is created.

Caution: Don't use this with 'morphS',
since it would create a new channel every tick.
Instead, create one @chan :: Chan c@, e.g. with 'newChan',
and then use 'withChanS'.
-}
runEventChanT :: (MonadIO m) => EventChanT event m a -> m a
runEventChanT :: forall (m :: Type -> Type) event a.
MonadIO m =>
EventChanT event m a -> m a
runEventChanT EventChanT event m a
a = do
  Chan event
chan <- forall (m :: Type -> Type) a. MonadIO m => IO a -> m a
liftIO forall a. IO (Chan a)
newChan
  forall r (m :: Type -> Type) a. ReaderT r m a -> r -> m a
runReaderT EventChanT event m a
a Chan event
chan

{- | Remove ("run") an 'EventChanT' layer from the monad stack
by passing it explicitly the channel over which events are sent.

This is usually only needed if you can't use 'runEventChanT'
to create the channel.
Typically, create a @chan :: Chan c@ in your main program
before the main loop (e.g. 'flow') would be run,
then, by using this function,
pass the channel to every behaviour or 'ClSF' that wants to emit events,
and, by using 'eventClockOn', to every clock that should tick on the event.
-}
withChanS ::
  (Monad m) =>
  Chan event ->
  ClSF (EventChanT event m) cl a b ->
  ClSF m cl a b
withChanS :: forall (m :: Type -> Type) event cl a b.
Monad m =>
Chan event -> ClSF (EventChanT event m) cl a b -> ClSF m cl a b
withChanS = forall a b c. (a -> b -> c) -> b -> a -> c
flip forall (m :: Type -> Type) r cl a b.
Monad m =>
ClSF (ReaderT r m) cl a b -> r -> ClSF m cl a b
runReaderS_

-- * Event emission

{- | Emit a single event.
This causes every 'EventClock' on the same monad to tick immediately.

Be cautious when emitting events from a signal clocked by an 'EventClock'.
Nothing prevents you from emitting more events than are handled,
causing the event buffer to grow indefinitely.
-}
emit :: (MonadIO m) => event -> EventChanT event m ()
emit :: forall (m :: Type -> Type) event.
MonadIO m =>
event -> EventChanT event m ()
emit event
event = do
  Chan event
chan <- forall (m :: Type -> Type) r. Monad m => ReaderT r m r
ask
  forall (m :: Type -> Type) a. MonadIO m => IO a -> m a
liftIO forall a b. (a -> b) -> a -> b
$ forall a. Chan a -> a -> IO ()
writeChan Chan event
chan event
event

-- | Emit an event on every tick.
emitS :: (MonadIO m) => ClSF (EventChanT event m) cl event ()
emitS :: forall (m :: Type -> Type) event cl.
MonadIO m =>
ClSF (EventChanT event m) cl event ()
emitS = forall (m :: Type -> Type) a b cl.
Monad m =>
(a -> m b) -> ClSF m cl a b
arrMCl forall (m :: Type -> Type) event.
MonadIO m =>
event -> EventChanT event m ()
emit

-- | Emit an event whenever the input value is @Just event@.
emitSMaybe :: (MonadIO m) => ClSF (EventChanT event m) cl (Maybe event) ()
emitSMaybe :: forall (m :: Type -> Type) event cl.
MonadIO m =>
ClSF (EventChanT event m) cl (Maybe event) ()
emitSMaybe = forall (m :: Type -> Type) cl a b.
Monad m =>
ClSF m cl a b -> ClSF m cl (Maybe a) (Maybe b)
mapMaybe forall (m :: Type -> Type) event cl.
MonadIO m =>
ClSF (EventChanT event m) cl event ()
emitS forall {k} (cat :: k -> k -> Type) (a :: k) (b :: k) (c :: k).
Category cat =>
cat a b -> cat b c -> cat a c
>>> forall (a :: Type -> Type -> Type) b c.
Arrow a =>
(b -> c) -> a b c
arr (forall a b. a -> b -> a
const ())

-- | Like 'emit', but completely evaluates the event before emitting it.
emit' :: (NFData event, MonadIO m) => event -> EventChanT event m ()
emit' :: forall event (m :: Type -> Type).
(NFData event, MonadIO m) =>
event -> EventChanT event m ()
emit' event
event =
  event
event forall a b. NFData a => a -> b -> b
`deepseq` do
    Chan event
chan <- forall (m :: Type -> Type) r. Monad m => ReaderT r m r
ask
    forall (m :: Type -> Type) a. MonadIO m => IO a -> m a
liftIO forall a b. (a -> b) -> a -> b
$ forall a. Chan a -> a -> IO ()
writeChan Chan event
chan event
event

-- | Like 'emitS', but completely evaluates the event before emitting it.
emitS' :: (NFData event, MonadIO m) => ClSF (EventChanT event m) cl event ()
emitS' :: forall event (m :: Type -> Type) cl.
(NFData event, MonadIO m) =>
ClSF (EventChanT event m) cl event ()
emitS' = forall (m :: Type -> Type) a b cl.
Monad m =>
(a -> m b) -> ClSF m cl a b
arrMCl forall event (m :: Type -> Type).
(NFData event, MonadIO m) =>
event -> EventChanT event m ()
emit'

-- | Like 'emitSMaybe', but completely evaluates the event before emitting it.
emitSMaybe' ::
  (NFData event, MonadIO m) =>
  ClSF (EventChanT event m) cl (Maybe event) ()
emitSMaybe' :: forall event (m :: Type -> Type) cl.
(NFData event, MonadIO m) =>
ClSF (EventChanT event m) cl (Maybe event) ()
emitSMaybe' = forall (m :: Type -> Type) cl a b.
Monad m =>
ClSF m cl a b -> ClSF m cl (Maybe a) (Maybe b)
mapMaybe forall event (m :: Type -> Type) cl.
(NFData event, MonadIO m) =>
ClSF (EventChanT event m) cl event ()
emitS' forall {k} (cat :: k -> k -> Type) (a :: k) (b :: k) (c :: k).
Category cat =>
cat a b -> cat b c -> cat a c
>>> forall (a :: Type -> Type -> Type) b c.
Arrow a =>
(b -> c) -> a b c
arr (forall a b. a -> b -> a
const ())

-- * Event clocks

{- | A clock that ticks whenever an @event@ is emitted.
   It is not yet bound to a specific channel,
   since ideally, the correct channel is created automatically
   by 'runEventChanT'.
   If you want to create the channel manually and bind the clock to it,
   use 'eventClockOn'.
-}
data EventClock event = EventClock

instance Semigroup (EventClock event) where
  <> :: EventClock event -> EventClock event -> EventClock event
(<>) EventClock event
_ EventClock event
_ = forall event. EventClock event
EventClock

instance (MonadIO m) => Clock (EventChanT event m) (EventClock event) where
  type Time (EventClock event) = UTCTime
  type Tag (EventClock event) = event
  initClock :: EventClock event
-> RunningClockInit
     (EventChanT event m)
     (Time (EventClock event))
     (Tag (EventClock event))
initClock EventClock event
_ = do
    UTCTime
initialTime <- forall (m :: Type -> Type) a. MonadIO m => IO a -> m a
liftIO IO UTCTime
getCurrentTime
    forall (m :: Type -> Type) a. Monad m => a -> m a
return
      ( forall (m :: Type -> Type) b a. Monad m => m b -> MSF m a b
constM forall a b. (a -> b) -> a -> b
$ do
          Chan event
chan <- forall (m :: Type -> Type) r. Monad m => ReaderT r m r
ask
          event
event <- forall (m :: Type -> Type) a. MonadIO m => IO a -> m a
liftIO forall a b. (a -> b) -> a -> b
$ forall a. Chan a -> IO a
readChan Chan event
chan
          UTCTime
time <- forall (m :: Type -> Type) a. MonadIO m => IO a -> m a
liftIO IO UTCTime
getCurrentTime
          forall (m :: Type -> Type) a. Monad m => a -> m a
return (UTCTime
time, event
event)
      , UTCTime
initialTime
      )

instance GetClockProxy (EventClock event)

{- | Create an event clock that is bound to a specific event channel.
   This is usually only useful if you can't apply 'runEventChanT'
   to the main loop (see 'withChanS').
-}
eventClockOn ::
  (MonadIO m) =>
  Chan event ->
  HoistClock (EventChanT event m) m (EventClock event)
eventClockOn :: forall (m :: Type -> Type) event.
MonadIO m =>
Chan event -> HoistClock (EventChanT event m) m (EventClock event)
eventClockOn Chan event
chan =
  HoistClock
    { unhoistedClock :: EventClock event
unhoistedClock = forall event. EventClock event
EventClock
    , monadMorphism :: forall a. EventChanT event m a -> m a
monadMorphism = forall event (m :: Type -> Type) a.
Chan event -> EventChanT event m a -> m a
withChan Chan event
chan
    }