module AFRPSpec (spec) where

import Control.Category ((>>>))
import Data.Foldable (for_)
import AFRP
import Data.Functor.Identity (Identity (..))
import Data.Time (UTCTime (..))
import Data.UUID (nil)
import Hedgehog
import qualified Hedgehog.Gen as Gen
import qualified Hedgehog.Range as Range
import Test.Hspec
import Test.Hspec.Hedgehog

fakeRequest :: Request
fakeRequest = Request (UTCTime (toEnum 0) 0) nil

runPure :: Mealy Identity a b -> [a] -> [b]
runPure _ [] = []
runPure m (a : as) = case runIdentity (AFRP.runMealy m id fakeRequest a) of
  (b, m') -> b : runPure m' as

spec :: Spec
spec = describe "AFRP" $ do
  holdSpec
  eventsSpec
  isEventSpec
  tagSpec
  toEventSpec
  lMergeSpec
  changesSpec
  edgeSpec
  filterASpec
  slidingSpec
  mapAccumSpec
  preMapAccumSpec
  -- time-dependent: delayEvent, debounce, rollup, fixed — skipped for now

holdSpec :: Spec
holdSpec = describe "hold" $ do
  it "holds initial value until an Event arrives" $
    runPure (hold 'a') [Tick, Event 'b', Tick, Event 'c']
      `shouldBe` ['a', 'b', 'b', 'c']

  it "never changes on Tick" $
    runPure (hold (0 :: Int)) (replicate 5 Tick) `shouldBe` replicate 5 (0 :: Int)

eventsSpec :: Spec
eventsSpec = describe "events" $ do
  it "converts Tick to Left () and Event a to Right a" $
    runPure events [Tick, Event 'a', Tick, Event 'b']
      `shouldBe` [Left (), Right 'a', Left (), Right 'b']

isEventSpec :: Spec
isEventSpec = describe "isEvent" $ do
  it "returns False for Tick" $
    isEvent Tick `shouldBe` False

  it "returns True for Event x" $
    isEvent (Event ()) `shouldBe` True

tagSpec :: Spec
tagSpec = describe "tag" $ do
  it "replaces value preserving structure" $ do
    tag 'b' Tick `shouldBe` Tick
    tag 'b' (Event 'a') `shouldBe` Event 'b'

toEventSpec :: Spec
toEventSpec = describe "toEvent" $ do
  it "round-trips through events" $
    runPure toEvent [Left (), Right 'a', Left ()]
      `shouldBe` [Tick, Event 'a', Tick]

  it "is inverse of events modulo Event/Either" $
    runPure (events >>> toEvent) [Tick, Event 'a', Event 'b']
      `shouldBe` [Tick, Event 'a', Event 'b']

lMergeSpec :: Spec
lMergeSpec = describe "lMerge" $ do
  it "both Tick gives Tick" $
    lMerge (Tick :: Event Int) (Tick :: Event Int) `shouldBe` Tick

  it "prefers left Event" $
    lMerge (Event (1 :: Int)) (Event (2 :: Int)) `shouldBe` Event (1 :: Int)

  it "prefers right Event if left is Tick" $
    lMerge Tick (Event (2 :: Int)) `shouldBe` Event (2 :: Int)

changesSpec :: Spec
changesSpec = describe "changes" $ do
  it "first output is always Tick" $
    runPure changes "hello" !! 0 `shouldBe` Tick

  it "outputs Event only on value change" $
    runPure changes "aaaabbbcca"
      `shouldBe` [Tick, Tick, Tick, Tick
                 , Event 'b', Tick, Tick
                 , Event 'c', Tick
                 , Event 'a'
                 ]

  it "first output is Tick, subsequent outputs are Event iff value changed" $
    hedgehog $ do
      xs <- forAll $ Gen.list (Range.linear 0 100) Gen.alpha
      let out = runPure changes xs
      length out === length xs
      case out of
        [] -> pure ()
        (Tick : rest) -> do
          let triples = zip3 xs (drop 1 xs) rest
          for_ triples $ \(prev, curr, o) ->
            if prev /= curr
              then o === Event curr
              else o === Tick
        _ -> failure

edgeSpec :: Spec
edgeSpec = describe "edge" $ do
  it "emits Event () only on rising edge" $
    runPure edge [False, True, True, False, True]
      `shouldBe` [Tick, Event (), Tick, Tick, Event ()]

  it "starts from False, so first True is a rising edge" $
    runPure edge [True, False, True]
      `shouldBe` [Event (), Tick, Event ()]

  it "Event () only on False -> True transition" $
    hedgehog $ do
      bs <- forAll $ Gen.list (Range.linear 0 50) Gen.bool
      let out = runPure edge bs
      length out === length bs
      case (bs, out) of
        ([], []) -> pure ()
        (b : _, o : _) -> do
          if b then o === Event () else o === Tick
          let triples = zip3 bs (drop 1 bs) (drop 1 out)
          for_ triples $ \(prev, curr, o') ->
            if not prev && curr
              then o' === Event ()
              else o' === Tick
        _ -> failure

filterASpec :: Spec
filterASpec = describe "filterA" $ do
  it "lets through values matching predicate" $
    runPure (filterA (even @Int)) [1, 2, 3, 4]
      `shouldBe` [Left (), Right 2, Left (), Right 4]

  it "output is Right a iff predicate holds" $
    hedgehog $ do
      threshold <- forAll $ Gen.int (Range.linear (-10) 10)
      let p = (> threshold)
      xs <- forAll $ Gen.list (Range.linear 0 50) (Gen.int (Range.linear (-20) 20))
      let out = runPure (filterA p) xs
      length out === length xs
      for_ (zip xs out) $ \(x, o) ->
        if p x
          then o === Right x
          else o === Left ()

slidingSpec :: Spec
slidingSpec = describe "sliding" $ do
  it "accumulates events up to the window size" $
    runPure (sliding (3 :: Int)) [Event (1 :: Int), Event 2, Event 3, Event 4]
      `shouldBe` [[1], [1, 2], [1, 2, 3], [2, 3, 4]]

  it "Ticks don't change the accumulator" $
    runPure (sliding 2) [Event (1 :: Int), Tick, Event 2]
      `shouldBe` [[1], [1], [1, 2]]

  it "empty list stays empty" $
    runPure (sliding (5 :: Int)) ([] :: [Event Int]) `shouldBe` []

  it "output length never exceeds window size" $
    hedgehog $ do
      n <- forAll $ Gen.int (Range.constant 1 10)
      evs <- forAll $ Gen.list (Range.linear 0 20) (Gen.frequency
        [(3, Event <$> Gen.alpha), (1, pure Tick)])
      let out = runPure (sliding n) evs
      for_ out $ \xs -> assert (length xs <= n)

mapAccumSpec :: Spec
mapAccumSpec = describe "mapAccum" $ do
  it "running sum" $
    runPure (mapAccum (+) (0 :: Int) id) [1, 2, 3]
      `shouldBe` [1, 3, 6]

  it "post-state extraction: output uses state after applying f" $
    runPure (mapAccum (\s x -> s ++ [x]) ([] :: [Int]) id) [1, 2, 3]
      `shouldBe` [[1], [1, 2], [1, 2, 3]]

  it "output equals running sum of all inputs so far" $
    hedgehog $ do
      xs <- forAll $ Gen.list (Range.linear 0 50) (Gen.int (Range.linear (-100) 100))
      let out = runPure (mapAccum (+) (0 :: Int) id) xs
      length out === length xs
      for_ (zip3 [0 ..] xs out) $ \(i, _x, cur) ->
        cur === sum (take (i + 1) xs)

preMapAccumSpec :: Spec
preMapAccumSpec = describe "preMapAccum" $ do
  it "running sum with pre-state extraction" $
    runPure (preMapAccum (+) (0 :: Int) id) [1, 2, 3]
      `shouldBe` [0, 1, 3]

  it "pre-state extraction: output uses state before applying f" $
    runPure (preMapAccum (\s x -> s ++ [x]) ([] :: [Int]) id) [1, 2, 3]
      `shouldBe` [[], [1], [1, 2]]

  it "output equals running sum before current input" $
    hedgehog $ do
      xs <- forAll $ Gen.list (Range.linear 0 50) (Gen.int (Range.linear (-100) 100))
      let out = runPure (preMapAccum (+) (0 :: Int) id) xs
      length out === length xs
      for_ (zip3 [0 ..] xs out) $ \(i, _x, cur) ->
        cur === sum (take i xs)