content: {-# LANGUAGE CPP #-}
  {-# LANGUAGE PatternGuards #-}
  #ifdef TRUSTWORTHY
  # if MIN_VERSION_template_haskell(2,12,0)
  # else
  {-# LANGUAGE Trustworthy #-}
  # endif
  #endif
  
  -----------------------------------------------------------------------------
  -- |
  -- Module      :  Silica.Internal.FieldTH
  -- Copyright   :  (C) 2014-2016 Edward Kmett, (C) 2014 Eric Mertens
  -- License     :  BSD-style (see the file LICENSE)
  -- Maintainer  :  Edward Kmett <ekmett@gmail.com>
  -- Stability   :  experimental
  -- Portability :  non-portable
  --
  -----------------------------------------------------------------------------
  
  module Silica.Internal.FieldTH
    ( LensRules(..)
    , FieldNamer
    , DefName(..)
    , ClassyNamer
    , makeFieldSilica
    , makeFieldSilicaForDec
    , makeFieldSilicaForDec'
    , HasFieldClasses
    ) where
  
  import Silica.At
  import Silica.Fold
  import Silica.Internal.TH
  import Silica.Plated
  import Silica.Prism
  import Silica.Setter
  import Silica.Getter
  import Silica.Tuple
  import Silica.Traversal
  import Control.Applicative
  import Control.Monad
  import Control.Monad.State
  import Language.Haskell.TH.Lens
  import Language.Haskell.TH
  import qualified Language.Haskell.TH.Datatype as D
  import Data.Maybe (isJust,maybeToList)
  import Data.List (nub, findIndices)
  import Data.Either (partitionEithers)
  import Data.Set.Lens
  import           Data.Map ( Map )
  import           Data.Set ( Set )
  import qualified Data.Set as Set
  import qualified Data.Map as Map
  import qualified Data.Traversable as T
  import Prelude
  
  ------------------------------------------------------------------------
  -- Field generation entry point
  ------------------------------------------------------------------------
  
  
  -- | Compute the field optics for the type identified by the given type name.
  -- Lenses will be computed when possible, Traversals otherwise.
  makeFieldSilica :: LensRules -> Name -> DecsQ
  makeFieldSilica rules = (`evalStateT` Set.empty) . makeFieldSilicaForDatatype rules <=< D.reifyDatatype
  
  makeFieldSilicaForDec :: LensRules -> Dec -> DecsQ
  makeFieldSilicaForDec rules = (`evalStateT` Set.empty) . makeFieldSilicaForDec' rules
  
  makeFieldSilicaForDec' :: LensRules -> Dec -> HasFieldClasses [Dec]
  makeFieldSilicaForDec' rules = makeFieldSilicaForDatatype rules <=< lift . D.normalizeDec
  
  -- | Compute the field optics for a deconstructed datatype Dec
  -- When possible build an Iso otherwise build one optic per field.
  makeFieldSilicaForDatatype :: LensRules -> D.DatatypeInfo -> HasFieldClasses [Dec]
  makeFieldSilicaForDatatype rules info =
    do perDef <- lift $ do
         fieldCons <- traverse normalizeConstructor cons
         let allFields  = toListOf (folded . _2 . folded . _1 . folded) fieldCons
         let defCons    = over normFieldLabels (expandName allFields) fieldCons
             allDefs    = setOf (normFieldLabels . folded) defCons
         T.sequenceA (fromSet (buildScaffold rules s defCons) allDefs)
  
       let defs = Map.toList perDef
       case _classyLenses rules tyName of
         Just (className, methodName) ->
           makeClassyDriver rules className methodName s defs
         Nothing -> do decss <- traverse (makeFieldOptic rules) defs
                       return (concat decss)
  
    where
    tyName = D.datatypeName info
    s      = D.datatypeType info
    cons   = D.datatypeCons info
  
    -- Traverse the field labels of a normalized constructor
    normFieldLabels :: Traversal [(Name,[(a,Type)])] [(Name,[(b,Type)])] a b
    normFieldLabels = traverse . _2 . traverse . _1
  
    -- Map a (possibly missing) field's name to zero-to-many optic definitions
    expandName :: [Name] -> Maybe Name -> [DefName]
    expandName allFields = concatMap (_fieldToDef rules tyName allFields) . maybeToList
  
  -- | Normalized the Con type into a uniform positional representation,
  -- eliminating the variance between records, infix constructors, and normal
  -- constructors.
  normalizeConstructor ::
    D.ConstructorInfo ->
    Q (Name, [(Maybe Name, Type)]) -- ^ constructor name, field name, field type
  
  normalizeConstructor con =
    return (D.constructorName con,
            zipWith checkForExistentials fieldNames (D.constructorFields con))
    where
      fieldNames =
        case D.constructorVariant con of
          D.RecordConstructor xs -> fmap Just xs
          D.NormalConstructor    -> repeat Nothing
          D.InfixConstructor     -> repeat Nothing
  
      -- Fields mentioning existentially quantified types are not
      -- elligible for TH generated optics.
      checkForExistentials _ fieldtype
        | any (\tv -> D.tvName tv `Set.member` used) unallowable
        = (Nothing, fieldtype)
        where
          used        = setOf typeVars fieldtype
          unallowable = D.constructorVars con
      checkForExistentials fieldname fieldtype = (fieldname, fieldtype)
  
  data OpticType = GetterType | LensType | IsoType
  
  -- | Compute the positional location of the fields involved in
  -- each constructor for a given optic definition as well as the
  -- type of clauses to generate and the type to annotate the declaration
  -- with.
  buildScaffold ::
    LensRules                                                                  ->
    Type                              {- ^ outer type                       -} ->
    [(Name, [([DefName], Type)])]     {- ^ normalized constructors          -} ->
    DefName                           {- ^ target definition                -} ->
    Q (OpticType, OpticStab, [(Name, Int, [Int])])
                {- ^ optic type, definition type, field count, target fields -}
  buildScaffold rules s cons defName =
  
    do (s',t,a,b) <- buildStab s (concatMap snd consForDef)
  
       let defType
             | Just (_,cx,a') <- preview _ForallT a =
                 let optic | lensCase  = getterTypeName
                           | otherwise = foldTypeName
                 in OpticSa cx optic s' a'
  
             -- Getter and Fold are always simple
             | not (_allowUpdates rules) =
                 let optic | lensCase  = getterTypeName
                           | otherwise = foldTypeName
                 in OpticSa [] optic s' a
  
             -- Generate simple Lens and Traversal where possible
             | _simpleLenses rules || s' == t && a == b =
                 let optic | isoCase && _allowIsos rules = iso'TypeName
                           | lensCase                    = lens'TypeName
                           | otherwise                   = traversal'TypeName
                 in OpticSa [] optic s' a
  
             -- Generate type-changing Lens and Traversal otherwise
             | otherwise =
                 let optic | isoCase && _allowIsos rules = isoTypeName
                           | lensCase                    = lensTypeName
                           | otherwise                   = traversalTypeName
                 in OpticStab optic s' t a b
  
           opticType | has _ForallT a            = GetterType
                     | not (_allowUpdates rules) = GetterType
                     | isoCase                   = IsoType
                     | otherwise                 = LensType
  
       return (opticType, defType, scaffolds)
    where
    consForDef :: [(Name, [Either Type Type])]
    consForDef = over (mapped . _2 . mapped) categorize cons
  
    scaffolds :: [(Name, Int, [Int])]
    scaffolds = [ (n, length ts, rightIndices ts) | (n,ts) <- consForDef ]
  
    rightIndices :: [Either Type Type] -> [Int]
    rightIndices = findIndices (has _Right)
  
    -- Right: types for this definition
    -- Left : other types
    categorize :: ([DefName], Type) -> Either Type Type
    categorize (defNames, t)
      | defName `elem` defNames = Right t
      | otherwise               = Left  t
  
    lensCase :: Bool
    lensCase = all (\x -> lengthOf (_2 . folded . _Right) x == 1) consForDef
  
    isoCase :: Bool
    isoCase = case scaffolds of
                [(_,1,[0])] -> True
                _           -> False
  
  
  data OpticStab = OpticStab     Name Type Type Type Type
                 | OpticSa   Cxt Name Type Type
  
  stabToType :: OpticStab -> Type
  stabToType (OpticStab  c s t a b) = quantifyType [] (c `conAppsT` [s,t,a,b])
  stabToType (OpticSa cx c s   a  ) = quantifyType cx (c `conAppsT` [s,a])
  
  stabToContext :: OpticStab -> Cxt
  stabToContext OpticStab{}        = []
  stabToContext (OpticSa cx _ _ _) = cx
  
  stabToOptic :: OpticStab -> Name
  stabToOptic (OpticStab c _ _ _ _) = c
  stabToOptic (OpticSa _ c _ _) = c
  
  stabToS :: OpticStab -> Type
  stabToS (OpticStab _ s _ _ _) = s
  stabToS (OpticSa _ _ s _) = s
  
  stabToA :: OpticStab -> Type
  stabToA (OpticStab _ _ _ a _) = a
  stabToA (OpticSa _ _ _ a) = a
  
  -- | Compute the s t a b types given the outer type 's' and the
  -- categorized field types. Left for fixed and Right for visited.
  -- These types are "raw" and will be packaged into an 'OpticStab'
  -- shortly after creation.
  buildStab :: Type -> [Either Type Type] -> Q (Type,Type,Type,Type)
  buildStab s categorizedFields =
    do (subA,a) <- unifyTypes targetFields
       let s' = applyTypeSubst subA s
  
       -- compute possible type changes
       sub <- T.sequenceA (fromSet (newName . nameBase) unfixedTypeVars)
       let (t,b) = over both (substTypeVars sub) (s',a)
  
       return (s',t,a,b)
  
    where
    (fixedFields, targetFields) = partitionEithers categorizedFields
    fixedTypeVars               = setOf typeVars fixedFields
    unfixedTypeVars             = setOf typeVars s Set.\\ fixedTypeVars
  
  
  -- | Build the signature and definition for a single field optic.
  -- In the case of a singleton constructor irrefutable matches are
  -- used to enable the resulting lenses to be used on a bottom value.
  makeFieldOptic ::
    LensRules ->
    (DefName, (OpticType, OpticStab, [(Name, Int, [Int])])) ->
    HasFieldClasses [Dec]
  makeFieldOptic rules (defName, (opticType, defType, cons)) = do
    locals <- get
    addName
    lift $ do cls <- mkCls locals
              T.sequenceA (cls ++ sig ++ def)
    where
    mkCls locals = case defName of
                   MethodName c n | _generateClasses rules ->
                    do classExists <- isJust <$> lookupTypeName (show c)
                       return (if classExists || Set.member c locals then [] else [makeFieldClass defType c n])
                   _ -> return []
  
    addName = case defName of
              MethodName c _ -> addFieldClassName c
              _              -> return ()
  
    sig = case defName of
            _ | not (_generateSigs rules) -> []
            TopName n -> [sigD n (return (stabToType defType))]
            MethodName{} -> []
  
    fun n = funD n clauses : inlinePragma n
  
    def = case defName of
            TopName n      -> fun n
            MethodName c n -> [makeFieldInstance defType c (fun n)]
  
    clauses = makeFieldClauses rules opticType cons
  
  ------------------------------------------------------------------------
  -- Classy class generator
  ------------------------------------------------------------------------
  
  
  makeClassyDriver ::
    LensRules ->
    Name ->
    Name ->
    Type {- ^ Outer 's' type -} ->
    [(DefName, (OpticType, OpticStab, [(Name, Int, [Int])]))] ->
    HasFieldClasses [Dec]
  makeClassyDriver rules className methodName s defs = T.sequenceA (cls ++ inst)
  
    where
    cls | _generateClasses rules = [lift $ makeClassyClass className methodName s defs]
        | otherwise = []
  
    inst = [makeClassyInstance rules className methodName s defs]
  
  
  makeClassyClass ::
    Name ->
    Name ->
    Type {- ^ Outer 's' type -} ->
    [(DefName, (OpticType, OpticStab, [(Name, Int, [Int])]))] ->
    DecQ
  makeClassyClass className methodName s defs = do
    let ss   = map (stabToS . view (_2 . _2)) defs
    (sub,s') <- unifyTypes (s : ss)
    c <- newName "c"
    let vars = toListOf typeVars s'
        fd   | null vars = []
             | otherwise = [FunDep [c] vars]
  
  
    classD (cxt[]) className (map PlainTV (c:vars)) fd
      $ sigD methodName (return (lens'TypeName `conAppsT` [VarT c, s']))
      : concat
        [ [sigD defName (return ty)
          ,valD (varP defName) (normalB body) []
          ] ++
          inlinePragma defName
        | (TopName defName, (_, stab, _)) <- defs
        , let body = appsE [varE composeValName, varE methodName, varE defName]
        , let ty   = quantifyType' (Set.fromList (c:vars))
                                   (stabToContext stab)
                   $ stabToOptic stab `conAppsT`
                         [VarT c, applyTypeSubst sub (stabToA stab)]
        ]
  
  
  makeClassyInstance ::
    LensRules ->
    Name ->
    Name ->
    Type {- ^ Outer 's' type -} ->
    [(DefName, (OpticType, OpticStab, [(Name, Int, [Int])]))] ->
    HasFieldClasses Dec
  makeClassyInstance rules className methodName s defs = do
    methodss <- traverse (makeFieldOptic rules') defs
  
    lift $ instanceD (cxt[]) (return instanceHead)
             $ valD (varP methodName) (normalB (varE idValName)) []
             : map return (concat methodss)
  
    where
    instanceHead = className `conAppsT` (s : map VarT vars)
    vars         = toListOf typeVars s
    rules'       = rules { _generateSigs    = False
                         , _generateClasses = False
                         }
  
  ------------------------------------------------------------------------
  -- Field class generation
  ------------------------------------------------------------------------
  
  makeFieldClass :: OpticStab -> Name -> Name -> DecQ
  makeFieldClass defType className methodName =
    classD (cxt []) className [PlainTV s, PlainTV a] [FunDep [s] [a]]
           [sigD methodName (return methodType)]
    where
    methodType = quantifyType' (Set.fromList [s,a])
                               (stabToContext defType)
               $ stabToOptic defType `conAppsT` [VarT s,VarT a]
    s = mkName "s"
    a = mkName "a"
  
  -- | Build an instance for a field. If the field’s type contains any type
  -- families, will produce an equality constraint to avoid a type family
  -- application in the instance head.
  makeFieldInstance :: OpticStab -> Name -> [DecQ] -> DecQ
  makeFieldInstance defType className decs =
    containsTypeFamilies a >>= pickInstanceDec
    where
    s = stabToS defType
    a = stabToA defType
  
    containsTypeFamilies = go <=< D.resolveTypeSynonyms
      where
      go (ConT nm) = has _FamilyI <$> reify nm
      go ty = or <$> traverse go (ty ^.. plate)
  
    pickInstanceDec hasFamilies
      | hasFamilies = do
          placeholder <- VarT <$> newName "a"
          mkInstanceDec
            [return (D.equalPred placeholder a)]
            [s, placeholder]
      | otherwise = mkInstanceDec [] [s, a]
  
    mkInstanceDec context headTys =
      instanceD (cxt context) (return (className `conAppsT` headTys)) decs
  
  ------------------------------------------------------------------------
  -- Optic clause generators
  ------------------------------------------------------------------------
  
  
  makeFieldClauses :: LensRules -> OpticType -> [(Name, Int, [Int])] -> [ClauseQ]
  makeFieldClauses rules opticType cons =
    case opticType of
  
      IsoType    -> [ makeIsoClause conName | (conName, _, _) <- cons ]
  
      GetterType -> [ makeGetterClause conName fieldCount fields
                      | (conName, fieldCount, fields) <- cons ]
  
      LensType   -> [ makeFieldOpticClause conName fieldCount fields irref
                      | (conName, fieldCount, fields) <- cons ]
        where
        irref = _lazyPatterns rules
             && length cons == 1
  
  
  
  -- | Construct an optic clause that returns an unmodified value
  -- given a constructor name and the number of fields on that
  -- constructor.
  makePureClause :: Name -> Int -> ClauseQ
  makePureClause conName fieldCount =
    do xs <- newNames "x" fieldCount
       -- clause: _ (Con x1..xn) = pure (Con x1..xn)
       clause [wildP, conP conName (map varP xs)]
              (normalB (appE (varE pureValName) (appsE (conE conName : map varE xs))))
              []
  
  
  -- | Construct an optic clause suitable for a Getter or Fold
  -- by visited the fields identified by their 0 indexed positions
  makeGetterClause :: Name -> Int -> [Int] -> ClauseQ
  makeGetterClause conName fieldCount []     = makePureClause conName fieldCount
  makeGetterClause conName fieldCount fields =
    do f  <- newName "f"
       xs <- newNames "x" (length fields)
  
       let pats (i:is) (y:ys)
             | i `elem` fields = varP y : pats is ys
             | otherwise = wildP : pats is (y:ys)
           pats is     _  = map (const wildP) is
  
           fxs   = [ appE (varE f) (varE x) | x <- xs ]
           body  = foldl (\a b -> appsE [varE apValName, a, b])
                         (appE (varE phantomValName) (head fxs))
                         (tail fxs)
  
       -- clause f (Con x1..xn) = coerce (f x1) <*> ... <*> f xn
       clause [varP f, conP conName (pats [0..fieldCount - 1] xs)]
              (normalB body)
              []
  
  -- | Build a clause that updates the field at the given indexes
  -- When irref is 'True' the value with me matched with an irrefutable
  -- pattern. This is suitable for Lens and Traversal construction
  makeFieldOpticClause :: Name -> Int -> [Int] -> Bool -> ClauseQ
  makeFieldOpticClause conName fieldCount [] _ =
    makePureClause conName fieldCount
  makeFieldOpticClause conName fieldCount (field:fields) irref =
    do f  <- newName "f"
       xs <- newNames "x" fieldCount
       ys <- newNames "y" (1 + length fields)
  
       let xs' = foldr (\(i,x) -> set (ix i) x) xs (zip (field:fields) ys)
  
           mkFx i = appE (varE f) (varE (xs !! i))
  
           body0 = appsE [ varE fmapValName
                         , lamE (map varP ys) (appsE (conE conName : map varE xs'))
                         , mkFx field
                         ]
  
           body = foldl (\a b -> appsE [varE apValName, a, mkFx b]) body0 fields
  
       let wrap = if irref then tildeP else id
  
       clause [varP f, wrap (conP conName (map varP xs))]
              (normalB body)
              []
  
  
  -- | Build a clause that constructs an Iso
  makeIsoClause :: Name -> ClauseQ
  makeIsoClause conName = clause [] (normalB (appsE [varE isoValName, destruct, construct])) []
    where
    destruct  = do x <- newName "x"
                   lam1E (conP conName [varP x]) (varE x)
  
    construct = conE conName
  
  
  ------------------------------------------------------------------------
  -- Unification logic
  ------------------------------------------------------------------------
  
  -- The field-oriented optic generation supports incorporating fields
  -- with distinct but unifiable types into a single definition.
  
  
  
  -- | Unify the given list of types, if possible, and return the
  -- substitution used to unify the types for unifying the outer
  -- type when building a definition's type signature.
  unifyTypes :: [Type] -> Q (Map Name Type, Type)
  unifyTypes (x:xs) = foldM (uncurry unify1) (Map.empty, x) xs
  unifyTypes []     = fail "unifyTypes: Bug: Unexpected empty list"
  
  
  -- | Attempt to unify two given types using a running substitution
  unify1 :: Map Name Type -> Type -> Type -> Q (Map Name Type, Type)
  unify1 sub (VarT x) y
    | Just r <- Map.lookup x sub = unify1 sub r y
  unify1 sub x (VarT y)
    | Just r <- Map.lookup y sub = unify1 sub x r
  unify1 sub x y
    | x == y = return (sub, x)
  unify1 sub (AppT f1 x1) (AppT f2 x2) =
    do (sub1, f) <- unify1 sub  f1 f2
       (sub2, x) <- unify1 sub1 x1 x2
       return (sub2, AppT (applyTypeSubst sub2 f) x)
  unify1 sub x (VarT y)
    | elemOf typeVars y (applyTypeSubst sub x) =
        fail "Failed to unify types: occurs check"
    | otherwise = return (Map.insert y x sub, x)
  unify1 sub (VarT x) y = unify1 sub y (VarT x)
  
  -- TODO: Unify contexts
  unify1 sub (ForallT v1 [] t1) (ForallT v2 [] t2) =
       -- This approach works out because by the time this code runs
       -- all of the type variables have been renamed. No risk of shadowing.
    do (sub1,t) <- unify1 sub t1 t2
       v <- fmap nub (traverse (limitedSubst sub1) (v1++v2))
       return (sub1, ForallT v [] t)
  
  unify1 _ x y = fail ("Failed to unify types: " ++ show (x,y))
  
  
  -- | Perform a limited substitution on type variables. This is used
  -- when unifying rank-2 fields when trying to achieve a Getter or Fold.
  limitedSubst :: Map Name Type -> TyVarBndr -> Q TyVarBndr
  limitedSubst sub (PlainTV n)
    | Just r <- Map.lookup n sub =
         case r of
           VarT m -> limitedSubst sub (PlainTV m)
           _ -> fail "Unable to unify exotic higher-rank type"
  limitedSubst sub (KindedTV n k)
    | Just r <- Map.lookup n sub =
         case r of
           VarT m -> limitedSubst sub (KindedTV m k)
           _ -> fail "Unable to unify exotic higher-rank type"
  limitedSubst _ tv = return tv
  
  
  -- | Apply a substitution to a type. This is used after unifying
  -- the types of the fields in unifyTypes.
  applyTypeSubst :: Map Name Type -> Type -> Type
  applyTypeSubst sub = rewrite aux
    where
    aux (VarT n) = Map.lookup n sub
    aux _        = Nothing
  
  
  ------------------------------------------------------------------------
  -- Field generation parameters
  ------------------------------------------------------------------------
  
  -- | Rules to construct lenses for data fields.
  data LensRules = LensRules
    { _simpleLenses    :: Bool
    , _generateSigs    :: Bool
    , _generateClasses :: Bool
    , _allowIsos       :: Bool
    , _allowUpdates    :: Bool -- ^ Allow Lens/Traversal (otherwise Getter/Fold)
    , _lazyPatterns    :: Bool
    , _fieldToDef      :: FieldNamer
         -- ^ Type Name -> Field Names -> Target Field Name -> Definition Names
    , _classyLenses    :: ClassyNamer
         -- type name to class name and top method
    }
  
  -- | The rule to create function names of lenses for data fields.
  --
  -- Although it's sometimes useful, you won't need the first two
  -- arguments most of the time.
  type FieldNamer = Name -- ^ Name of the data type that lenses are being generated for.
                    -> [Name] -- ^ Names of all fields (including the field being named) in the data type.
                    -> Name -- ^ Name of the field being named.
                    -> [DefName] -- ^ Name(s) of the lens functions. If empty, no lens is created for that field.
  
  -- | Name to give to generated field optics.
  data DefName
    = TopName Name -- ^ Simple top-level definiton name
    | MethodName Name Name -- ^ makeFields-style class name and method name
    deriving (Show, Eq, Ord)
  
  -- | The optional rule to create a class and method around a
  -- monomorphic data type. If this naming convention is provided, it
  -- generates a "classy" lens.
  type ClassyNamer = Name -- ^ Name of the data type that lenses are being generated for.
                     -> Maybe (Name, Name) -- ^ Names of the class and the main method it generates, respectively.
  
  -- | Tracks the field class 'Name's that have been created so far. We consult
  -- these so that we may avoid creating duplicate classes.
  
  -- See #643 for more information.
  type HasFieldClasses = StateT (Set Name) Q
  
  addFieldClassName :: Name -> HasFieldClasses ()
  addFieldClassName n = modify $ Set.insert n
  
  ------------------------------------------------------------------------
  -- Miscellaneous utility functions
  ------------------------------------------------------------------------
  
  
  -- | Template Haskell wants type variables declared in a forall, so
  -- we find all free type variables in a given type and declare them.
  quantifyType :: Cxt -> Type -> Type
  quantifyType = quantifyType' Set.empty
  
  -- | This function works like 'quantifyType' except that it takes
  -- a list of variables to exclude from quantification.
  quantifyType' :: Set Name -> Cxt -> Type -> Type
  quantifyType' exclude c t = ForallT vs c t
    where
    vs = map PlainTV
       $ filter (`Set.notMember` exclude)
       $ nub -- stable order
       $ toListOf typeVars t
  