{-# LANGUAGE CPP #-}
{-# LANGUAGE TemplateHaskell #-}

module Test.Polysemy.Mock.TH (genMock) where

import Data.Bifunctor (first)
import Data.List (foldl')
import Language.Haskell.TH hiding (Strict)
import Polysemy (Embed, Members, Sem, interpret, pureT, reinterpretH)
import Polysemy.Internal (embed, send)
import Polysemy.Internal.TH.Common
import Polysemy.State (get, put)
import Test.Polysemy.Mock

-- | Generate mock using template-haskell.
-- Example usage:
--
-- > genMock ''Teletype
genMock :: Name -> Q [Dec]
genMock effName = do
  (_, constructors) <- getEffectMetadata effName
  -- MockImpl
  let mockImplEffectType = ConT ''MockImpl `AppT` ConT effName `AppT` returnsEffect
  let mockImplReturnType = mockImplEffectType `AppT` VarT (mkName "m")
  let mockImplDataType = mockImplReturnType `AppT` VarT (mkName "a")
  let mockImplConstructors =
        map (mkMockConstructor mockImplReturnType) constructors
          <> map (mkMockReturns mockImplReturnType) constructors
          <> map (mkMockCalls mockImplReturnType) constructors
  let mockImplD = DataInstD [] Nothing mockImplDataType Nothing mockImplConstructors []
  -- MockState
  mockStateConName <- newName (nameBase ''MockState <> nameBase effName)
  let mockStateRec =
        map mkMockStateCallsField constructors
          <> map mkMockStateReturnsField constructors
  let mockStateConstructor = RecC mockStateConName mockStateRec
  let mockStateType = ConT ''MockState `AppT` ConT effName `AppT` returnsEffect
  let mockStateD = DataInstD [] Nothing mockStateType Nothing [mockStateConstructor] []
  -- initialMockState
  let initialStateExps =
        map mkInitialCalls constructors
          <> map mkInitialReturns constructors
  let initialStateBody = NormalB (RecConE mockStateConName initialStateExps)
  let initialStateD = FunD 'initialMockState [Clause [] initialStateBody []]
  -- mock
  let mockMatches = map (mkMockMatch mockImplEffectType) constructors
  let mockBody = NormalB (AppE (VarE 'interpret) (LamCaseE mockMatches))
  let mockD = FunD 'mock [Clause [] mockBody []]
  -- mockToState
  let mockToStateMatches =
        map (mkMockToStateMatch mockStateType) constructors
          <> map (mkReturnsToStateMatch mockStateType) constructors
          <> map (mkCallsToStateMatch mockStateType) constructors
  let mockToStateBody = NormalB (AppE (VarE 'reinterpretH) (LamCaseE mockToStateMatches))
  let mockToStateD = FunD 'mockToState [Clause [] mockToStateBody []]
  -- instance
  let mockInstanceD =
        InstanceD
          Nothing
          [ConT ''Applicative `AppT` returnsEffect]
          (ConT ''Mock `AppT` ConT effName `AppT` returnsEffect)
          [ mockImplD,
            mockStateD,
            initialStateD,
            mockD,
            mockToStateD
          ]
  -- makeSem
  let semD =
        concatMap (mkReturnsSem mockImplEffectType) constructors
          <> concatMap (mkCallsSem mockImplEffectType) constructors
  -- Bring it together
  pure $ mockInstanceD : semD

mkMockConstructor :: Type -> ConLiftInfo -> Con
mkMockConstructor t c =
  let args = (map (first (const defaultBang)) $ cliFunArgs c)
   in GadtC [mockConName c] args (AppT t $ cliEffRes c)

mkMockReturns :: Type -> ConLiftInfo -> Con
mkMockReturns t c =
  GadtC [returnsConName c] [(defaultBang, returnsFunctionType c)] (AppT t $ TupleT 0)

mkMockCalls :: Type -> ConLiftInfo -> Con
mkMockCalls t c =
  GadtC [callsConName c] [] (AppT t (functionCallType c))

mkMockStateCallsField :: ConLiftInfo -> (Name, Bang, Type)
mkMockStateCallsField c =
  (callsFieldName c, defaultBang, functionCallType c)

mkMockStateReturnsField :: ConLiftInfo -> (Name, Bang, Type)
mkMockStateReturnsField c =
  (returnsFieldName c, defaultBang, returnsFunctionType c)

mkInitialCalls :: ConLiftInfo -> (Name, Exp)
mkInitialCalls c =
  (callsFieldName c, ListE [])

mkInitialReturns :: ConLiftInfo -> (Name, Exp)
mkInitialReturns c =
  let returnsFn =
        case cliEffRes c of
          (TupleT 0) -> LamE (map (const WildP) $ cliFunArgs c) $ AppE (VarE 'pure) (TupE [])
          _ -> AppE (VarE 'error) (LitE (StringL $ "Unexpected mock invocation: " <> nameBase (cliFunName c)))
   in (returnsFieldName c, returnsFn)

mkMockMatch :: Type -> ConLiftInfo -> Match
mkMockMatch t c =
  let pat = ConP (cliConName c) (map (VarP . fst) (cliFunArgs c))
      sendFn = VarE 'send
      args = map (VarE . fst) (cliFunArgs c)
      theMock = foldl' AppE (ConE $ mockConName c) args
      body = NormalB (AppE (AppTypeE sendFn t) theMock)
   in Match pat body []

mkMockToStateMatch :: Type -> ConLiftInfo -> Match
mkMockToStateMatch t c =
  let pat = ConP (mockConName c) (map VarP vars)
      --
      vars = map fst (cliFunArgs c)
      newArgs = if length (cliFunArgs c) == 1
                   then ListE [ VarE . fst . head . cliFunArgs $ c]
                   else
#if MIN_VERSION_template_haskell(2,16,0)
                      ListE [TupE (map (Just . VarE . fst) $ cliFunArgs c)]
#else
                      ListE [TupE (map (VarE . fst) $ cliFunArgs c)]
#endif
      oldArgs = AppE (VarE (callsFieldName c)) (VarE stateName)
      allArgs = InfixE (Just oldArgs) (VarE '(++)) (Just newArgs)
      newState = RecUpdE (VarE stateName) [(callsFieldName c, allArgs)]
      --
      applyReturnsFn = foldl' AppE (VarE (returnsFieldName c)) (VarE stateName : map VarE vars)
      embedReturnsFn = AppE (VarE 'embed) applyReturnsFn
      returnAsPureT = NoBindS $ InfixE (Just (VarE 'pureT)) (VarE '(=<<)) (Just embedReturnsFn)
      body =
        NormalB
          ( DoE
              [ getState t,
                putState newState,
                returnAsPureT
              ]
          )
   in Match pat body []

mkReturnsToStateMatch :: Type -> ConLiftInfo -> Match
mkReturnsToStateMatch t c =
  let f = mkName "f"
      pat = ConP (returnsConName c) [VarP f]
      newState = RecUpdE (VarE stateName) [(returnsFieldName c, VarE f)]
      returnNothing = NoBindS $ AppE (VarE 'pureT) (TupE [])
      body =
        NormalB
          ( DoE
              [ getState t,
                putState newState,
                returnNothing
              ]
          )
   in Match pat body []

mkCallsToStateMatch :: Type -> ConLiftInfo -> Match
mkCallsToStateMatch t c =
  let pat = ConP (callsConName c) []
      returnCalls = NoBindS $ AppE (VarE 'pureT) (AppE (VarE (callsFieldName c)) (VarE stateName))
      body =
        NormalB
          ( DoE
              [ getState t,
                returnCalls
              ]
          )
   in Match pat body []

mkReturnsSem ::
  -- | Should look like: @MockImpl Teletype n@
  -- n is assumed to be 'stateEffectName', maybe this is problematic, but it works for now
  Type ->
  ConLiftInfo ->
  [Dec]
mkReturnsSem mockImplEffType c =
  let funcName = mkName ("mock" <> nameBase (cliConName c) <> "Returns")
      body = NormalB (InfixE (Just $ VarE 'send) (VarE '(.)) (Just $ ConE (returnsConName c)))
      appArrowT = AppT . AppT ArrowT
      r = VarT $ mkName "r"
      semr t = ConT ''Sem `AppT` r `AppT` t
      typ = ForallT [] [membersEffListType mockImplEffType r] (returnsFunctionType c `appArrowT` semr (TupleT 0))
   in [ SigD funcName typ,
        FunD funcName [Clause [] body []]
      ]

mkCallsSem ::
  -- | Should look like: @MockImpl Teletype n@
  -- n is assumed to be 'stateEffectName', maybe this is problematic, but it works for now
  Type ->
  ConLiftInfo ->
  [Dec]
mkCallsSem mockImplEffType c =
  let funcName = mkName ("mock" <> nameBase (cliConName c) <> "Calls")
      typeAppliedSend = VarE 'send `AppTypeE` mockImplEffType
      body = NormalB $ typeAppliedSend `AppE` ConE (callsConName c)
      r = VarT $ mkName "r"
      semr t = ConT ''Sem `AppT` r `AppT` t
      typ = ForallT [PlainTV returnsEffectName, PlainTV $ mkName "r"] [membersEffListType mockImplEffType r] (semr $ functionCallType c)
   in [ SigD funcName typ,
        FunD funcName [Clause [] body []]
      ]

membersEffListType :: Type -> Type -> Type
membersEffListType mockImplEffType r =
  let embededStateEffect = ConT ''Embed `AppT` VarT returnsEffectName
      appConsT = AppT . AppT PromotedConsT
      effList = foldr appConsT PromotedNilT [mockImplEffType, embededStateEffect]
   in ConT ''Members `AppT` effList `AppT` r

getState :: Type -> Stmt
getState t = BindS (VarP stateName) (VarE 'get `AppTypeE` t)

putState :: Exp -> Stmt
putState newState = NoBindS (AppE (VarE 'put) newState)

stateName :: Name
stateName = mkName "state"

callsConName :: ConLiftInfo -> Name
callsConName c = mkName ("Mock" <> nameBase (cliConName c) <> "Calls")

returnsConName :: ConLiftInfo -> Name
returnsConName c = mkName ("Mock" <> nameBase (cliConName c) <> "Returns")

mockConName :: ConLiftInfo -> Name
mockConName c = mkName ("Mock" <> nameBase (cliConName c))

callsFieldName :: ConLiftInfo -> Name
callsFieldName c = mkName (nameBase (cliFunName c) <> "Calls")

returnsFieldName :: ConLiftInfo -> Name
returnsFieldName c = mkName (nameBase (cliFunName c) <> "Returns")

defaultBang :: Bang
defaultBang = Bang NoSourceUnpackedness NoSourceStrictness

functionCallType :: ConLiftInfo -> Type
functionCallType c =
  let arity = length $ cliFunArgs c
   in if arity == 1
        then AppT ListT $ snd $ head $ cliFunArgs c
        else AppT ListT $ foldl' AppT (TupleT arity) (map snd $ cliFunArgs c)

returnsFunctionType :: ConLiftInfo -> Type
returnsFunctionType c =
  let argTypes = (map snd $ cliFunArgs c)
      returnType = (AppT returnsEffect $ cliEffRes c)
   in foldr (AppT . AppT ArrowT) returnType argTypes

returnsEffect :: Type
returnsEffect = VarT returnsEffectName

returnsEffectName :: Name
returnsEffectName = mkName "n"