{-# LANGUAGE UndecidableInstances #-}

-- |
-- Module      : Streamly.Internal.Data.Stream.ZipAsync
-- Copyright   : (c) 2017 Composewell Technologies
-- License     : BSD-3-Clause
-- Maintainer  : streamly@composewell.com
-- Stability   : experimental
-- Portability : GHC
--
-- To run examples in this module:
--
-- >>> import qualified Streamly.Prelude as Stream
--
module Streamly.Internal.Data.Stream.ZipAsync
    ( ZipAsyncM(..)
    , ZipAsync
    , consMZipAsync
    , zipAsyncWithK
    , zipAsyncWithMK
    )
where

#if __GLASGOW_HASKELL__ < 808
import Data.Semigroup (Semigroup(..))
#endif
import Streamly.Internal.Control.Concurrent (MonadAsync)
import Streamly.Internal.Data.Stream.Serial (SerialT(..))
import Streamly.Internal.Data.Stream.StreamK.Type (Stream)

import qualified Streamly.Internal.Data.Stream.StreamK.Type as K
import qualified Streamly.Internal.Data.Stream.StreamK as K
import qualified Streamly.Internal.Data.Stream.StreamD as D
import qualified Streamly.Internal.Data.Stream.Serial as Serial
import qualified Streamly.Internal.Data.Stream.SVar.Eliminate as SVar
import qualified Streamly.Internal.Data.Stream.SVar.Generate as SVar
import Streamly.Internal.Data.SVar

import Prelude hiding (map, repeat, zipWith, errorWithoutStackTrace)

#include "Instances.hs"

-- $setup
-- >>> import qualified Streamly.Prelude as Stream
-- >>> import Control.Concurrent (threadDelay)
-- >>> :{
--  delay n = do
--      threadDelay (n * 1000000)   -- sleep for n seconds
--      putStrLn (show n ++ " sec") -- print "n sec"
--      return n                    -- IO Int
-- :}

------------------------------------------------------------------------------
-- Parallel Zipping
------------------------------------------------------------------------------

-- | Like 'zipAsyncWith' but with a monadic zipping function.
--
-- @since 0.4.0
{-# INLINE zipAsyncWithMK #-}
zipAsyncWithMK :: MonadAsync m
    => (a -> b -> m c) -> Stream m a -> Stream m b -> Stream m c
zipAsyncWithMK f m1 m2 = K.mkStream $ \st yld sng stp -> do
    sv <- newParallelVar StopNone (adaptState st)
    SVar.toSVarParallel (adaptState st) sv $ D.fromStreamK m2
    K.foldStream st yld sng stp $ K.zipWithM f m1 (getSerialT (SVar.fromSVar sv))

-- XXX Should we rename this to zipParWith or zipParallelWith? This can happen
-- along with the change of behvaior to end the stream concurrently.
--
-- | Like 'zipWith' but zips concurrently i.e. both the streams being zipped
-- are evaluated concurrently using the 'ParallelT' concurrent evaluation
-- style. The maximum number of elements of each stream evaluated in advance
-- can be controlled by 'maxBuffer'.
--
-- The stream ends if stream @a@ or stream @b@ ends. However, if stream @b@
-- ends while we are still evaluating stream @a@ and waiting for a result then
-- stream will not end until after the evaluation of stream @a@ finishes. This
-- behavior can potentially be changed in future to end the stream immediately
-- as soon as any of the stream end is detected.
--
-- @since 0.1.0
{-# INLINE zipAsyncWithK #-}
zipAsyncWithK :: MonadAsync m
    => (a -> b -> c) -> Stream m a -> Stream m b -> Stream m c
zipAsyncWithK f = zipAsyncWithMK (\a b -> return (f a b))

------------------------------------------------------------------------------
-- Parallely Zipping Streams
------------------------------------------------------------------------------
--
-- | For 'ZipAsyncM' streams:
--
-- @
-- (<>) = 'Streamly.Prelude.serial'
-- (<*>) = 'Streamly.Prelude.serial.zipAsyncWith' id
-- @
--
-- Applicative evaluates the streams being zipped concurrently, the following
-- would take half the time that it would take in serial zipping:
--
-- >>> s = Stream.fromFoldableM $ Prelude.map delay [1, 1, 1]
-- >>> Stream.toList $ Stream.fromZipAsync $ (,) <$> s <*> s
-- ...
-- [(1,1),(1,1),(1,1)]
--
-- /Since: 0.2.0 ("Streamly")/
--
-- @since 0.8.0
newtype ZipAsyncM m a = ZipAsyncM {getZipAsyncM :: Stream m a}
        deriving (Semigroup, Monoid)

-- | An IO stream whose applicative instance zips streams wAsyncly.
--
-- /Since: 0.2.0 ("Streamly")/
--
-- @since 0.8.0
type ZipAsync = ZipAsyncM IO

consMZipAsync :: Monad m => m a -> ZipAsyncM m a -> ZipAsyncM m a
consMZipAsync m (ZipAsyncM r) = ZipAsyncM $ K.consM m r

instance Monad m => Functor (ZipAsyncM m) where
    {-# INLINE fmap #-}
    fmap f (ZipAsyncM m) = ZipAsyncM $ getSerialT $ fmap f (SerialT m)

instance MonadAsync m => Applicative (ZipAsyncM m) where
    pure = ZipAsyncM . getSerialT . Serial.repeat

    {-# INLINE (<*>) #-}
    ZipAsyncM m1 <*> ZipAsyncM m2 = ZipAsyncM $ zipAsyncWithK id m1 m2