{-# 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 Control.Monad
import Control.Monad.Trans.Reader
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 :: forall name a. (Ord name, DataId name, NamedThing name)
            => Data a
            => [(name, HsType name)] -> a -> a
specialize specs = go
  where
    go :: forall x. Data x => x -> x
    go = everywhereButType @name $ mkT $ sugar . specialize_ty_var
    specialize_ty_var (HsTyVar _ (L _ name'))
      | Just t <- Map.lookup name' spec_map = t
    specialize_ty_var typ = typ
    -- This is a tricky recursive definition that is guaranteed to terminate
    -- because a type binder cannot be instantiated with a type that depends
    -- on that binder. i.e. @a -> Maybe a@ is invalid
    spec_map = Map.fromList [ (n, go t) | (n, t) <- specs]


-- | 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 :: (Ord name, DataId name, NamedThing name)
                     => Data a
                     => LHsQTyVars name -> [HsType name]
                     -> a -> a
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


specializePseudoFamilyDecl :: (Ord name, DataId name, NamedThing name)
                           => LHsQTyVars name -> [HsType name]
                           -> PseudoFamilyDecl name
                           -> PseudoFamilyDecl name
specializePseudoFamilyDecl bndrs typs decl =
  decl {pfdTyVars = map (specializeTyVarBndrs bndrs typs) (pfdTyVars decl)}

specializeSig :: forall name . (Ord name, DataId name, SetName name, NamedThing name)
              => LHsQTyVars name -> [HsType name]
              -> Sig name
              -> Sig name
specializeSig bndrs typs (TypeSig lnames typ) =
  TypeSig lnames (typ {hswc_body = (hswc_body typ) {hsib_body = noLoc typ'}})
  where
    true_type :: HsType name
    true_type = unLoc (hsSigWcType typ)
    typ' :: HsType name
    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 :: (Ord name, DataId name, SetName name, NamedThing name)
                   => InstHead name -> InstHead name
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 :: forall name. (NamedThing name, DataId name)
      => HsType name -> HsType name
sugar = sugarOperators . sugarTuples . sugarLists

sugarLists :: NamedThing name => HsType name -> HsType name
sugarLists (HsAppTy (L _ (HsTyVar _ (L _ name))) ltyp)
    | isBuiltInSyntax name' && strName == "[]" = HsListTy ltyp
  where
    name' = getName name
    strName = occNameString . nameOccName $ name'
sugarLists typ = typ


sugarTuples :: NamedThing name => HsType name -> HsType name
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 HsBoxedTuple apps
      where
        name' = getName name
        strName = occNameString . nameOccName $ name'
        suitable = case parseTupleArity strName of
            Just arity -> arity == length apps
            Nothing -> False
    aux _ _ = typ


sugarOperators :: NamedThing name => HsType name -> HsType name
sugarOperators (HsAppTy (L _ (HsAppTy (L _ (HsTyVar _ (L l name))) la)) lb)
    | isSymOcc $ getOccName name' = mkHsOpTy la (L l name) lb
    | isBuiltInSyntax name' && getOccString name == "(->)" = HsFunTy 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 = occNameFS . getOccName

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 :: forall name. (NamedThing name, DataId name)
              => HsType name -> Set NameRep
freeVariables =
    everythingWithState Set.empty Set.union query
  where
    query term ctx = case cast term :: Maybe (HsType name) 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 $ getNameRep 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 -> c) -> b@).
rename :: SetName name => Set NameRep -> HsType name -> HsType name
rename fv typ = runReader (renameType typ) $ RenameEnv
    { rneFV = fv
    , rneCtx = Map.empty
    }


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

-- | Binding generation monad.
type Rebind name = State (RenameEnv name)

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


renameType :: SetName name => HsType name -> Rename name (HsType name)
renameType (HsForAllTy bndrs lt) = rebind bndrs $ \bndrs' ->
    HsForAllTy
        <$> pure bndrs'
        <*> renameLType lt
renameType (HsQualTy lctxt lt) =
  HsQualTy
        <$> located renameContext lctxt
        <*> renameLType lt
renameType (HsTyVar ip name) = HsTyVar ip <$> located renameName name
renameType (HsAppTy lf la) = HsAppTy <$> renameLType lf <*> renameLType la
renameType (HsFunTy la lr) = HsFunTy <$> renameLType la <*> renameLType lr
renameType (HsListTy lt) = HsListTy <$> renameLType lt
renameType (HsPArrTy lt) = HsPArrTy <$> renameLType lt
renameType (HsTupleTy srt lt) = HsTupleTy srt <$> mapM renameLType lt
renameType (HsSumTy lt) = HsSumTy <$> mapM renameLType lt
renameType (HsOpTy la lop lb) =
    HsOpTy <$> renameLType la <*> located renameName lop <*> renameLType lb
renameType (HsParTy lt) = HsParTy <$> renameLType lt
renameType (HsIParamTy ip lt) = HsIParamTy ip <$> renameLType lt
renameType (HsEqTy la lb) = HsEqTy <$> renameLType la <*> renameLType lb
renameType (HsKindSig lt lk) = HsKindSig <$> renameLType lt <*> pure lk
renameType t@(HsSpliceTy _ _) = pure t
renameType (HsDocTy lt doc) = HsDocTy <$> renameLType lt <*> pure doc
renameType (HsBangTy bang lt) = HsBangTy bang <$> renameLType lt
renameType t@(HsRecTy _) = pure t
renameType t@(HsCoreTy _) = pure t
renameType (HsExplicitListTy ip ph ltys) =
    HsExplicitListTy ip ph <$> renameLTypes ltys
renameType (HsExplicitTupleTy phs ltys) =
    HsExplicitTupleTy phs <$> renameLTypes ltys
renameType t@(HsTyLit _) = pure t
renameType (HsWildCardTy wc) = pure (HsWildCardTy wc)
renameType (HsAppsTy _) = error "HsAppsTy: Only used before renaming"


renameLType :: SetName name => LHsType name -> Rename name (LHsType name)
renameLType = located renameType


renameLTypes :: SetName name => [LHsType name] -> Rename name [LHsType name]
renameLTypes = mapM renameLType


renameContext :: SetName name => HsContext name -> Rename name (HsContext name)
renameContext = renameLTypes

{-
renameLTyOp :: SetName name => LHsTyOp name -> Rename name (LHsTyOp name)
renameLTyOp (wrap, lname) = (,) wrap <$> located renameName lname
-}


renameName :: SetName name => name -> Rename name name
renameName name = do
    RenameEnv { rneCtx = ctx } <- ask
    pure $ fromMaybe name (Map.lookup (getName name) ctx)


rebind :: SetName name
       => [LHsTyVarBndr name] -> ([LHsTyVarBndr name] -> Rename name a)
       -> Rename name a
rebind lbndrs action = do
    (lbndrs', env') <- runState (rebindLTyVarBndrs lbndrs) <$> ask
    local (const env') (action lbndrs')


rebindLTyVarBndrs :: SetName name
                  => [LHsTyVarBndr name] -> Rebind name [LHsTyVarBndr name]
rebindLTyVarBndrs lbndrs = mapM (located rebindTyVarBndr) lbndrs


rebindTyVarBndr :: SetName name
                => HsTyVarBndr name -> Rebind name (HsTyVarBndr name)
rebindTyVarBndr (UserTyVar (L l name)) =
    UserTyVar . L l <$> rebindName name
rebindTyVarBndr (KindedTyVar name kinds) =
    KindedTyVar <$> located rebindName name <*> pure kinds


rebindName :: SetName name => name -> Rebind name name
rebindName name = do
    RenameEnv { .. } <- get
    taken <- takenNames
    case Map.lookup (getName name) rneCtx of
        Just name' -> pure name'
        Nothing | getNameRep name `Set.member` taken -> freshName name
        Nothing -> reuseName name


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


reuseName :: SetName name => name -> Rebind name name
reuseName name = do
    env@RenameEnv { .. } <- get
    put $ env { rneCtx = Map.insert (getName name) name rneCtx }
    return name


takenNames :: NamedThing name => Rebind name (Set NameRep)
takenNames = do
    RenameEnv { .. } <- get
    return $ Set.union rneFV (ctxElems rneCtx)
  where
    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
    | [_] <- nameRepString name = letterNames ++ alternativeNames' name
  where
    letterNames = map (stringNameRep . pure) ['a'..'z']
alternativeNames name = alternativeNames' name


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 -> name
tyVarName (UserTyVar name) = unLoc name
tyVarName (KindedTyVar (L _ name) _) = name
