automaton-1.7: test/Stream.hs

module Stream where

-- base
import Control.Monad (when)
import Control.Monad.Identity (Identity (..))

-- transformers
import Control.Monad.Trans.Class (lift)
import Control.Monad.Trans.Except (ExceptT (..), throwE)
import Control.Monad.Trans.Reader (ReaderT (..), ask)
import Control.Monad.Trans.Writer.Lazy (runWriter, tell)

-- selective
import Control.Selective

-- tasty
import Test.Tasty (testGroup)

-- tasty-hunit
import Test.Tasty.HUnit (testCase, (@?=))

-- automaton
import Data.Stream (StreamT (..), constM, foreverExceptE, handleExceptT, handleWriterT, mmap, snapshot, streamToList, unfold, unfold_)
import Data.Stream.Except qualified as StreamExcept
import Data.Stream.Optimized qualified as StreamOptimized
import Data.Stream.Result

tests =
  testGroup
    "Stream"
    [ testGroup
        "Selective"
        [ testCase "Selects second stream based on first stream" $
            let automaton1 = unfold 0 (\n -> Result (n + 1) (if even n then Right n else Left n))
                automaton2 = pure (* 10)
             in take 10 (runIdentity (streamToList (automaton1 <*? automaton2))) @?= [0, 10, 2, 30, 4, 50, 6, 70, 8, 90]
        , testCase "Progresses state of second stream only when first stream returns Left" $
            let automaton1 = unfold 0 (\n -> Result (n + 1) (if even n then Right n else Left n))
                automaton2 = unfold 1 (\n -> Result (n + 2) (* n))
             in take 10 (runIdentity (streamToList (automaton1 <*? automaton2))) @?= [0, 1, 2, 9, 4, 25, 6, 49, 8, 81]
        ]
    , testGroup
        "snapshot"
        [ testCase "Shows the current effect in the output" $
            let stream = snapshot $ constM $ tell [()]
             in take 3 (fmap runWriter $ fst $ runWriter $ streamToList stream) @?= [((), [()]), ((), [()]), ((), [()])]
        ]
    , testGroup
        "handleEffect"
        [ testGroup
            "handleExceptT"
            [ testCase "Switches to constantly Left after exception has been triggered" $
                let stream = mmap (\i -> when (i > 2) (throwE ())) nats
                 in take 5 (runIdentity $ streamToList $ handleExceptT stream) @?= [Right (), Right (), Left (), Left (), Left ()]
            ]
        , testGroup
            "handleWriterT"
            [ testCase "Returns the current log on the output" $
                let stream = mmap (tell . pure) nats
                 in take 3 (fmap fst $ runIdentity $ streamToList $ handleWriterT stream) @?= [[1], [1, 2], [1, 2, 3]]
            ]
        ]
    , testGroup
        "foreverExceptE"
        [ testCase "Uses initial ReaderT value, stores exceptions, and resets state" $
            take 5 (runIdentity $ streamToList $ foreverExceptE 0 throwsNext)
              @?= [0, 1, 2, 3, 4]
        , testCase "StreamExcept.foreverE behaves the same for stateful streams" $
            let streamExcept = StreamExcept.CoalgebraicExcept $ StreamOptimized.Stateful throwsNext
             in take 5 (runIdentity $ streamToList $ StreamOptimized.toStreamT $ StreamExcept.foreverE 0 streamExcept)
                  @?= [0, 1, 2, 3, 4]
        , testCase "StreamExcept.foreverE handles stateless streams" $
            let stateless =
                  StreamExcept.CoalgebraicExcept $
                    StreamOptimized.Stateless $ do
                      ExceptT $ ReaderT $ \e -> if e > 10 then pure $ Right e else pure $ Left $ e + 1
             in take 4 (runIdentity $ streamToList $ StreamOptimized.toStreamT $ StreamExcept.foreverE 0 stateless)
                  @?= [11, 11, 11, 11]
        , testCase "StreamExcept.foreverE handles RecursiveExcept via bind" $
            let recursive = StreamExcept.RecursiveExcept $
                  StreamOptimized.toRecursive $
                    StreamOptimized.Stateful $
                      StreamT 0 $ \n -> ExceptT $ ReaderT $ \lastE ->
                        if n < lastE
                          then pure $ Right $ Result (n + 1) n
                          else pure $ Left $ lastE + 1
             in take 10 (runIdentity $ streamToList $ StreamOptimized.toStreamT $ StreamExcept.foreverE 0 recursive)
                  @?= [0, 0, 1, 0, 1, 2, 0, 1, 2, 3]
        ]
    ]

nats :: (Applicative m) => StreamT m Int
nats = unfold_ 0 (+ 1)

-- | Emit the current ReaderT value when 'shouldThrow' is False; otherwise throw its successor.
throwsNext :: StreamT (ExceptT Int (ReaderT Int Identity)) Int
throwsNext = StreamT False $ \shouldThrow ->
  do
    exceptionValue <- lift ask
    if shouldThrow
      then throwE (exceptionValue + 1)
      else
        pure $ Result True exceptionValue