{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE Rank2Types #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeApplications #-}
{-# LANGUAGE RecordWildCards #-}

module Haddock.Interface.Specialize
    ( specializeInstHead
    ) where


import Haddock.Syb
import Haddock.Types

import GHC
import Name
import FastString
import TysPrim ( funTyConName )
import TysWiredIn ( listTyConName )

import Control.Monad
import Control.Monad.Trans.State

import Data.Data
import qualified Data.List as List
import Data.Maybe
import Data.Map (Map)
import qualified Data.Map as Map
import Data.Set (Set)
import qualified Data.Set as Set

-- | Instantiate all occurrences of given names with corresponding types.
specialize :: Data a => [(Name, HsType GhcRn)] -> a -> a
specialize specs = go spec_map0
  where
    go :: forall x. Data x => Map Name (HsType GhcRn) -> x -> x
    go spec_map = everywhereButType @Name $ mkT $ sugar . strip_kind_sig . specialize_ty_var spec_map

    strip_kind_sig :: HsType name -> HsType name
    strip_kind_sig (HsKindSig _ (L _ t) _) = t
    strip_kind_sig typ = typ

    specialize_ty_var :: Map Name (HsType GhcRn) -> HsType GhcRn -> HsType GhcRn
    specialize_ty_var spec_map (HsTyVar _ _ (L _ name'))
      | Just t <- Map.lookup name' spec_map = t
    specialize_ty_var _ typ = typ

    -- This is a tricky recursive definition. By adding in the specializations
    -- one by one, we should avoid infinite loops.
    spec_map0 = foldr (\(n,t) acc -> Map.insert n (go acc t) acc) mempty specs

{-# SPECIALIZE specialize :: [(Name, HsType GhcRn)] -> HsType GhcRn -> HsType GhcRn #-}

-- | Instantiate given binders with corresponding types.
--
-- Again, it is just a convenience function around 'specialize'. Note that
-- length of type list should be the same as the number of binders.
specializeTyVarBndrs :: LHsQTyVars GhcRn -> [HsType GhcRn] -> HsType GhcRn -> HsType GhcRn
specializeTyVarBndrs bndrs typs =
    specialize $ zip bndrs' typs
  where
    bndrs' = map (bname . unLoc) . hsq_explicit $ bndrs
    bname (UserTyVar _ (L _ name)) = name
    bname (KindedTyVar _ (L _ name) _) = name
    bname (XTyVarBndr _) = error "haddock:specializeTyVarBndrs"



specializePseudoFamilyDecl :: LHsQTyVars GhcRn -> [HsType GhcRn]
                           -> PseudoFamilyDecl GhcRn
                           -> PseudoFamilyDecl GhcRn
specializePseudoFamilyDecl bndrs typs decl =
  decl {pfdTyVars = map (fmap (specializeTyVarBndrs bndrs typs)) (pfdTyVars decl)}

specializeSig :: LHsQTyVars GhcRn -> [HsType GhcRn]
              -> Sig GhcRn
              -> Sig GhcRn
specializeSig bndrs typs (TypeSig _ lnames typ) =
  TypeSig noExt lnames (typ {hswc_body = (hswc_body typ) {hsib_body = noLoc typ'}})
  where
    true_type :: HsType GhcRn
    true_type = unLoc (hsSigWcType typ)
    typ' :: HsType GhcRn
    typ' = rename fv $ specializeTyVarBndrs bndrs typs true_type
    fv = foldr Set.union Set.empty . map freeVariables $ typs
specializeSig _ _ sig = sig


-- | Make all details of instance head (signatures, associated types)
-- specialized to that particular instance type.
specializeInstHead :: InstHead GhcRn -> InstHead GhcRn
specializeInstHead ihd@InstHead { ihdInstType = clsi@ClassInst { .. }, .. } =
    ihd { ihdInstType = instType' }
  where
    instType' = clsi
        { clsiSigs = map specializeSig' clsiSigs
        , clsiAssocTys = map specializeFamilyDecl' clsiAssocTys
        }
    specializeSig' = specializeSig clsiTyVars ihdTypes
    specializeFamilyDecl' = specializePseudoFamilyDecl clsiTyVars ihdTypes
specializeInstHead ihd = ihd


-- | Make given type use tuple and list literals where appropriate.
--
-- After applying 'specialize' function some terms may not use idiomatic list
-- and tuple literals resulting in types like @[] a@ or @(,,) a b c@. This
-- can be fixed using 'sugar' function, that will turn such types into @[a]@
-- and @(a, b, c)@.
sugar :: HsType GhcRn -> HsType GhcRn
sugar = sugarOperators . sugarTuples . sugarLists

sugarLists :: NamedThing (IdP (GhcPass p)) => HsType (GhcPass p) -> HsType (GhcPass p)
sugarLists (HsAppTy _ (L _ (HsTyVar _ _ (L _ name))) ltyp)
    | getName name == listTyConName = HsListTy NoExt ltyp
sugarLists typ = typ


sugarTuples :: NamedThing (IdP (GhcPass p)) => HsType (GhcPass p) -> HsType (GhcPass p)
sugarTuples typ =
    aux [] typ
  where
    aux apps (HsAppTy _ (L _ ftyp) atyp) = aux (atyp:apps) ftyp
    aux apps (HsParTy _ (L _ typ')) = aux apps typ'
    aux apps (HsTyVar _ _ (L _ name))
        | isBuiltInSyntax name' && suitable = HsTupleTy NoExt HsBoxedTuple apps
      where
        name' = getName name
        strName = getOccString name
        suitable = case parseTupleArity strName of
            Just arity -> arity == length apps
            Nothing -> False
    aux _ _ = typ


sugarOperators :: NamedThing (IdP (GhcPass p)) => HsType (GhcPass p) -> HsType (GhcPass p)
sugarOperators (HsAppTy _ (L _ (HsAppTy _ (L _ (HsTyVar _ _ (L l name))) la)) lb)
    | isSymOcc $ getOccName name' = mkHsOpTy la (L l name) lb
    | funTyConName == name' = HsFunTy NoExt la lb
  where
    name' = getName name
sugarOperators typ = typ


-- | Compute arity of given tuple operator.
--
-- >>> parseTupleArity "(,,)"
-- Just 3
--
-- >>> parseTupleArity "(,,,,)"
-- Just 5
--
-- >>> parseTupleArity "abc"
-- Nothing
--
-- >>> parseTupleArity "()"
-- Nothing
parseTupleArity :: String -> Maybe Int
parseTupleArity ('(':commas) = do
    n <- parseCommas commas
    guard $ n /= 0
    return $ n + 1
  where
    parseCommas (',':rest) = (+ 1) <$> parseCommas rest
    parseCommas ")" = Just 0
    parseCommas _ = Nothing
parseTupleArity _ = Nothing


-- | Haskell AST type representation.
--
-- This type is used for renaming (more below), essentially the ambiguous (!)
-- version of 'Name'. So, why is this 'FastString' instead of 'OccName'? Well,
-- it was 'OccName' before, but turned out that 'OccName' sometimes also
-- contains namespace information, differentiating visually same types.
--
-- And 'FastString' is used because it is /visual/ part of 'OccName' - it is
-- not converted to 'String' or alike to avoid new allocations. Additionally,
-- since it is stored mostly in 'Set', fast comparison of 'FastString' is also
-- quite nice.
type NameRep = FastString

getNameRep :: NamedThing name => name -> NameRep
getNameRep = getOccFS

nameRepString :: NameRep -> String
nameRepString = unpackFS

stringNameRep :: String -> NameRep
stringNameRep = mkFastString

setInternalNameRep :: SetName name => NameRep -> name -> name
setInternalNameRep = setInternalOccName . mkVarOccFS

setInternalOccName :: SetName name => OccName -> name -> name
setInternalOccName occ name =
    setName nname' name
  where
    nname = getName name
    nname' = mkInternalName (nameUnique nname) occ (nameSrcSpan nname)


-- | Compute set of free variables of given type.
freeVariables :: HsType GhcRn -> Set Name
freeVariables =
    everythingWithState Set.empty Set.union query
  where
    query term ctx = case cast term :: Maybe (HsType GhcRn) of
        Just (HsForAllTy _ bndrs _) ->
            (Set.empty, Set.union ctx (bndrsNames bndrs))
        Just (HsTyVar _ _ (L _ name))
            | getName name `Set.member` ctx -> (Set.empty, ctx)
            | otherwise -> (Set.singleton $ getName name, ctx)
        _ -> (Set.empty, ctx)
    bndrsNames = Set.fromList . map (getName . tyVarName . unLoc)


-- | Make given type visually unambiguous.
--
-- After applying 'specialize' method, some free type variables may become
-- visually ambiguous - for example, having @a -> b@ and specializing @a@ to
-- @(a -> b)@ we get @(a -> b) -> b@ where first occurrence of @b@ refers to
-- different type variable than latter one. Applying 'rename' function
-- will fix that type to be visually unambiguous again (making it something
-- like @(a -> b0) -> b@).
rename :: Set Name -> HsType GhcRn -> HsType GhcRn
rename fv typ = evalState (renameType typ) env
  where
    env = RenameEnv
      { rneHeadFVs = Map.fromList . map mkPair . Set.toList $ fv
      , rneSigFVs = Set.map getNameRep $ freeVariables typ
      , rneCtx = Map.empty
      }
    mkPair name = (getNameRep name, name)

-- | Renaming monad.
type Rename name = State (RenameEnv name)

data RenameEnv name = RenameEnv
  { rneHeadFVs :: Map NameRep Name
  , rneSigFVs :: Set NameRep
  , rneCtx :: Map Name name
  }


renameType :: HsType GhcRn -> Rename (IdP GhcRn) (HsType GhcRn)
renameType (HsForAllTy x bndrs lt) =
    HsForAllTy x
        <$> mapM (located renameBinder) bndrs
        <*> renameLType lt
renameType (HsQualTy x lctxt lt) =
    HsQualTy x
        <$> located renameContext lctxt
        <*> renameLType lt
renameType (HsTyVar x ip name) = HsTyVar x ip <$> located renameName name
renameType t@(HsStarTy _ _) = pure t
renameType (HsAppTy x lf la) = HsAppTy x <$> renameLType lf <*> renameLType la
renameType (HsFunTy x la lr) = HsFunTy x <$> renameLType la <*> renameLType lr
renameType (HsListTy x lt) = HsListTy x <$> renameLType lt
renameType (HsTupleTy x srt lt) = HsTupleTy x srt <$> mapM renameLType lt
renameType (HsSumTy x lt) = HsSumTy x <$> mapM renameLType lt
renameType (HsOpTy x la lop lb) =
    HsOpTy x <$> renameLType la <*> located renameName lop <*> renameLType lb
renameType (HsParTy x lt) = HsParTy x <$> renameLType lt
renameType (HsIParamTy x ip lt) = HsIParamTy x ip <$> renameLType lt
renameType (HsKindSig x lt lk) = HsKindSig x <$> renameLType lt <*> pure lk
renameType t@(HsSpliceTy _ _) = pure t
renameType (HsDocTy x lt doc) = HsDocTy x <$> renameLType lt <*> pure doc
renameType (HsBangTy x bang lt) = HsBangTy x bang <$> renameLType lt
renameType t@(HsRecTy _ _) = pure t
renameType t@(XHsType (NHsCoreTy _)) = pure t
renameType (HsExplicitListTy x ip ltys) =
    HsExplicitListTy x ip <$> renameLTypes ltys
renameType (HsExplicitTupleTy x ltys) =
    HsExplicitTupleTy x <$> renameLTypes ltys
renameType t@(HsTyLit _ _) = pure t
renameType (HsWildCardTy wc) = pure (HsWildCardTy wc)


renameLType :: LHsType GhcRn -> Rename (IdP GhcRn) (LHsType GhcRn)
renameLType = located renameType


renameLTypes :: [LHsType GhcRn] -> Rename (IdP GhcRn) [LHsType GhcRn]
renameLTypes = mapM renameLType


renameContext :: HsContext GhcRn -> Rename (IdP GhcRn) (HsContext GhcRn)
renameContext = renameLTypes

renameBinder :: HsTyVarBndr GhcRn -> Rename (IdP GhcRn) (HsTyVarBndr GhcRn)
renameBinder (UserTyVar x lname) = UserTyVar x <$> located renameName lname
renameBinder (KindedTyVar x lname lkind) =
  KindedTyVar x <$> located renameName lname <*> located renameType lkind
renameBinder (XTyVarBndr _) = error "haddock:renameBinder"

-- | Core renaming logic.
renameName :: (Eq name, SetName name) => name -> Rename name name
renameName name = do
    RenameEnv { .. } <- get
    case Map.lookup (getName name) rneCtx of
      Nothing
        | Just headTv <- Map.lookup (getNameRep name) rneHeadFVs
        , headTv /= getName name -> freshName name
      Just name' -> return name'
      _ -> return name


-- | Generate fresh occurrence name, put it into context and return.
freshName :: SetName name => name -> Rename name name
freshName name = do
    taken <- takenNames
    let name' = setInternalNameRep (findFreshName taken rep) name
    modify $ \rne -> rne
      { rneCtx = Map.insert (getName name) name' (rneCtx rne) }
    return name'
  where
    nname = getName name
    rep = getNameRep nname


takenNames :: NamedThing name => Rename name (Set NameRep)
takenNames = do
    RenameEnv { .. } <- get
    return $ Set.unions [headReps rneHeadFVs, rneSigFVs, ctxElems rneCtx]
  where
    headReps = Set.fromList . Map.keys
    ctxElems = Set.fromList . map getNameRep . Map.elems


findFreshName :: Set NameRep -> NameRep -> NameRep
findFreshName taken =
    fromJust . List.find isFresh . alternativeNames
  where
    isFresh = not . flip Set.member taken


alternativeNames :: NameRep -> [NameRep]
alternativeNames name =
    [ stringNameRep $ str ++ show i | i :: Int <- [0..] ]
  where
    str = nameRepString name


located :: Functor f => (a -> f b) -> Located a -> f (Located b)
located f (L loc e) = L loc <$> f e


tyVarName :: HsTyVarBndr name -> IdP name
tyVarName (UserTyVar _ name) = unLoc name
tyVarName (KindedTyVar _ (L _ name) _) = name
tyVarName (XTyVarBndr _ ) = error "haddock:tyVarName"