{-# LANGUAGE CPP #-}
#ifdef TRUSTWORTHY
{-# LANGUAGE Trustworthy #-}
#endif

#ifndef MIN_VERSION_template_haskell
#define MIN_VERSION_template_haskell(x,y,z) 1
#endif
-----------------------------------------------------------------------------
-- |
-- Module      :  Control.Lens.Internal.PrismTH
-- Copyright   :  (C) 2014-2016 Edward Kmett and Eric Mertens
-- License     :  BSD-style (see the file LICENSE)
-- Maintainer  :  Edward Kmett <ekmett@gmail.com>
-- Stability   :  experimental
-- Portability :  non-portable
--
-----------------------------------------------------------------------------

module Control.Lens.Internal.PrismTH
  ( makePrisms
  , makeClassyPrisms
  , makeDecPrisms
  ) where

import Control.Applicative
import Control.Lens.Fold
import Control.Lens.Getter
import Control.Lens.Internal.TH
import Control.Lens.Lens
import Control.Lens.Setter
import Control.Monad
import Data.Char (isUpper)
import Data.List
import Data.Set.Lens
import Data.Traversable
import Language.Haskell.TH
import qualified Language.Haskell.TH.Datatype as D
import Language.Haskell.TH.Lens
import qualified Data.Map as Map
import qualified Data.Set as Set
import Prelude

-- | Generate a 'Prism' for each constructor of a data type.
-- Isos generated when possible.
-- Reviews are created for constructors with existentially
-- quantified constructors and GADTs.
--
-- /e.g./
--
-- @
-- data FooBarBaz a
--   = Foo Int
--   | Bar a
--   | Baz Int Char
-- makePrisms ''FooBarBaz
-- @
--
-- will create
--
-- @
-- _Foo :: Prism' (FooBarBaz a) Int
-- _Bar :: Prism (FooBarBaz a) (FooBarBaz b) a b
-- _Baz :: Prism' (FooBarBaz a) (Int, Char)
-- @
makePrisms :: Name {- ^ Type constructor name -} -> DecsQ
makePrisms = makePrisms' True


-- | Generate a 'Prism' for each constructor of a data type
-- and combine them into a single class. No Isos are created.
-- Reviews are created for constructors with existentially
-- quantified constructors and GADTs.
--
-- /e.g./
--
-- @
-- data FooBarBaz a
--   = Foo Int
--   | Bar a
--   | Baz Int Char
-- makeClassyPrisms ''FooBarBaz
-- @
--
-- will create
--
-- @
-- class AsFooBarBaz s a | s -> a where
--   _FooBarBaz :: Prism' s (FooBarBaz a)
--   _Foo :: Prism' s Int
--   _Bar :: Prism' s a
--   _Baz :: Prism' s (Int,Char)
--
--   _Foo = _FooBarBaz . _Foo
--   _Bar = _FooBarBaz . _Bar
--   _Baz = _FooBarBaz . _Baz
--
-- instance AsFooBarBaz (FooBarBaz a) a
-- @
--
-- Generate an "As" class of prisms. Names are selected by prefixing the constructor
-- name with an underscore.  Constructors with multiple fields will
-- construct Prisms to tuples of those fields.
makeClassyPrisms :: Name {- ^ Type constructor name -} -> DecsQ
makeClassyPrisms = makePrisms' False


-- | Main entry point into Prism generation for a given type constructor name.
makePrisms' :: Bool -> Name -> DecsQ
makePrisms' normal typeName =
  do info <- D.reifyDatatype typeName
     let cls | normal    = Nothing
             | otherwise = Just (D.datatypeName info)
         cons = D.datatypeCons info
     makeConsPrisms (D.datatypeType info) (map normalizeCon cons) cls


-- | Generate prisms for the given 'Dec'
makeDecPrisms :: Bool {- ^ generate top-level definitions -} -> Dec -> DecsQ
makeDecPrisms normal dec =
  do info <- D.normalizeDec dec
     let cls | normal    = Nothing
             | otherwise = Just (D.datatypeName info)
         cons = D.datatypeCons info
     makeConsPrisms (D.datatypeType info) (map normalizeCon cons) cls


-- | Generate prisms for the given type, normalized constructors, and
-- an optional name to be used for generating a prism class.
-- This function dispatches between Iso generation, normal top-level
-- prisms, and classy prisms.
makeConsPrisms :: Type -> [NCon] -> Maybe Name -> DecsQ

-- special case: single constructor, not classy -> make iso
makeConsPrisms t [con@(NCon _ [] [] _)] Nothing = makeConIso t con

-- top-level definitions
makeConsPrisms t cons Nothing =
  fmap concat $ for cons $ \con ->
    do let conName = view nconName con
       stab <- computeOpticType t cons con
       let n = prismName conName
       sequenceA
         [ sigD n (close (stabToType stab))
         , valD (varP n) (normalB (makeConOpticExp stab cons con)) []
         ]


-- classy prism class and instance
makeConsPrisms t cons (Just typeName) =
  sequenceA
    [ makeClassyPrismClass t className methodName cons
    , makeClassyPrismInstance t className methodName cons
    ]
  where
  className = mkName ("As" ++ nameBase typeName)
  methodName = prismName typeName


data OpticType = PrismType | ReviewType
data Stab  = Stab Cxt OpticType Type Type Type Type

simplifyStab :: Stab -> Stab
simplifyStab (Stab cx ty _ t _ b) = Stab cx ty t t b b
  -- simplification uses t and b because those types
  -- are interesting in the Review case

stabSimple :: Stab -> Bool
stabSimple (Stab _ _ s t a b) = s == t && a == b

stabToType :: Stab -> Type
stabToType stab@(Stab cx ty s t a b) = ForallT vs cx $
  case ty of
    PrismType  | stabSimple stab -> prism'TypeName  `conAppsT` [t,b]
               | otherwise       -> prismTypeName   `conAppsT` [s,t,a,b]
    ReviewType                   -> reviewTypeName  `conAppsT` [t,b]

  where
  vs = map PlainTV
     $ nub -- stable order
     $ toListOf typeVars cx

stabType :: Stab -> OpticType
stabType (Stab _ o _ _ _ _) = o

computeOpticType :: Type -> [NCon] -> NCon -> Q Stab
computeOpticType t cons con =
  do let cons' = delete con cons
     if null (_nconVars con)
         then computePrismType t (view nconCxt con) cons' con
         else computeReviewType t (view nconCxt con) (view nconTypes con)


computeReviewType :: Type -> Cxt -> [Type] -> Q Stab
computeReviewType s' cx tys =
  do let t = s'
     s <- fmap VarT (newName "s")
     a <- fmap VarT (newName "a")
     b <- toTupleT (map return tys)
     return (Stab cx ReviewType s t a b)


-- | Compute the full type-changing Prism type given an outer type,
-- list of constructors, and target constructor name. Additionally
-- return 'True' if the resulting type is a "simple" prism.
computePrismType :: Type -> Cxt -> [NCon] -> NCon -> Q Stab
computePrismType t cx cons con =
  do let ts      = view nconTypes con
         unbound = setOf typeVars t Set.\\ setOf typeVars cons
     sub <- sequenceA (fromSet (newName . nameBase) unbound)
     b   <- toTupleT (map return ts)
     a   <- toTupleT (map return (substTypeVars sub ts))
     let s = substTypeVars sub t
     return (Stab cx PrismType s t a b)


computeIsoType :: Type -> [Type] -> TypeQ
computeIsoType t' fields =
  do sub <- sequenceA (fromSet (newName . nameBase) (setOf typeVars t'))
     let t = return                    t'
         s = return (substTypeVars sub t')
         b = toTupleT (map return                    fields)
         a = toTupleT (map return (substTypeVars sub fields))

#ifndef HLINT
         ty | Map.null sub = appsT (conT iso'TypeName) [t,b]
            | otherwise    = appsT (conT isoTypeName) [s,t,a,b]
#endif

     close =<< ty



-- | Construct either a Review or Prism as appropriate
makeConOpticExp :: Stab -> [NCon] -> NCon -> ExpQ
makeConOpticExp stab cons con =
  case stabType stab of
    PrismType  -> makeConPrismExp stab cons con
    ReviewType -> makeConReviewExp con


-- | Construct an iso declaration
makeConIso :: Type -> NCon -> DecsQ
makeConIso s con =
  do let ty      = computeIsoType s (view nconTypes con)
         defName = prismName (view nconName con)
     sequenceA
       [ sigD       defName  ty
       , valD (varP defName) (normalB (makeConIsoExp con)) []
       ]


-- | Construct prism expression
--
-- prism <<reviewer>> <<remitter>>
makeConPrismExp ::
  Stab ->
  [NCon] {- ^ constructors       -} ->
  NCon   {- ^ target constructor -} ->
  ExpQ
makeConPrismExp stab cons con = appsE [varE prismValName, reviewer, remitter]
  where
  ts = view nconTypes con
  fields  = length ts
  conName = view nconName con

  reviewer                   = makeReviewer       conName fields
  remitter | stabSimple stab = makeSimpleRemitter conName fields
           | otherwise       = makeFullRemitter cons conName


-- | Construct an Iso expression
--
-- iso <<reviewer>> <<remitter>>
makeConIsoExp :: NCon -> ExpQ
makeConIsoExp con = appsE [varE isoValName, remitter, reviewer]
  where
  conName = view nconName con
  fields  = length (view nconTypes con)

  reviewer = makeReviewer    conName fields
  remitter = makeIsoRemitter conName fields


-- | Construct a Review expression
--
-- unto (\(x,y,z) -> Con x y z)
makeConReviewExp :: NCon -> ExpQ
makeConReviewExp con = appE (varE untoValName) reviewer
  where
  conName = view nconName con
  fields  = length (view nconTypes con)

  reviewer = makeReviewer conName fields


------------------------------------------------------------------------
-- Prism and Iso component builders
------------------------------------------------------------------------


-- | Construct the review portion of a prism.
--
-- (\(x,y,z) -> Con x y z) :: b -> t
makeReviewer :: Name -> Int -> ExpQ
makeReviewer conName fields =
  do xs <- newNames "x" fields
     lam1E (toTupleP (map varP xs))
           (conE conName `appsE1` map varE xs)


-- | Construct the remit portion of a prism.
-- Pattern match only target constructor, no type changing
--
-- (\x -> case s of
--          Con x y z -> Right (x,y,z)
--          _         -> Left x
-- ) :: s -> Either s a
makeSimpleRemitter :: Name -> Int -> ExpQ
makeSimpleRemitter conName fields =
  do x  <- newName "x"
     xs <- newNames "y" fields
     let matches =
           [ match (conP conName (map varP xs))
                   (normalB (appE (conE rightDataName) (toTupleE (map varE xs))))
                   []
           , match wildP (normalB (appE (conE leftDataName) (varE x))) []
           ]
     lam1E (varP x) (caseE (varE x) matches)


-- | Pattern match all constructors to enable type-changing
--
-- (\x -> case s of
--          Con x y z -> Right (x,y,z)
--          Other_n w   -> Left (Other_n w)
-- ) :: s -> Either t a
makeFullRemitter :: [NCon] -> Name -> ExpQ
makeFullRemitter cons target =
  do x <- newName "x"
     lam1E (varP x) (caseE (varE x) (map mkMatch cons))
  where
  mkMatch (NCon conName _ _ n) =
    do xs <- newNames "y" (length n)
       match (conP conName (map varP xs))
             (normalB
               (if conName == target
                  then appE (conE rightDataName) (toTupleE (map varE xs))
                  else appE (conE leftDataName) (conE conName `appsE1` map varE xs)))
             []


-- | Construct the remitter suitable for use in an 'Iso'
--
-- (\(Con x y z) -> (x,y,z)) :: s -> a
makeIsoRemitter :: Name -> Int -> ExpQ
makeIsoRemitter conName fields =
  do xs <- newNames "x" fields
     lam1E (conP conName (map varP xs))
           (toTupleE (map varE xs))


------------------------------------------------------------------------
-- Classy prisms
------------------------------------------------------------------------


-- | Construct the classy prisms class for a given type and constructors.
--
-- class ClassName r <<vars in type>> | r -> <<vars in Type>> where
--   topMethodName   :: Prism' r Type
--   conMethodName_n :: Prism' r conTypes_n
--   conMethodName_n = topMethodName . conMethodName_n
makeClassyPrismClass ::
  Type   {- Outer type      -} ->
  Name   {- Class name      -} ->
  Name   {- Top method name -} ->
  [NCon] {- Constructors    -} ->
  DecQ
makeClassyPrismClass t className methodName cons =
  do r <- newName "r"
#ifndef HLINT
     let methodType = appsT (conT prism'TypeName) [varT r,return t]
#endif
     methodss <- traverse (mkMethod (VarT r)) cons'
     classD (cxt[]) className (map PlainTV (r : vs)) (fds r)
       ( sigD methodName methodType
       : map return (concat methodss)
       )

  where
  mkMethod r con =
    do Stab cx o _ _ _ b <- computeOpticType t cons con
       let stab' = Stab cx o r r b b
           defName = view nconName con
           body    = appsE [varE composeValName, varE methodName, varE defName]
       sequenceA
         [ sigD defName        (return (stabToType stab'))
         , valD (varP defName) (normalB body) []
         ]

  cons'         = map (over nconName prismName) cons
  vs            = Set.toList (setOf typeVars t)
  fds r
    | null vs   = []
    | otherwise = [FunDep [r] vs]



-- | Construct the classy prisms instance for a given type and constructors.
--
-- instance Classname OuterType where
--   topMethodName = id
--   conMethodName_n = <<prism>>
makeClassyPrismInstance ::
  Type ->
  Name     {- Class name      -} ->
  Name     {- Top method name -} ->
  [NCon] {- Constructors    -} ->
  DecQ
makeClassyPrismInstance s className methodName cons =
  do let vs = Set.toList (setOf typeVars s)
         cls = className `conAppsT` (s : map VarT vs)

     instanceD (cxt[]) (return cls)
       (   valD (varP methodName)
                (normalB (varE idValName)) []
       : [ do stab <- computeOpticType s cons con
              let stab' = simplifyStab stab
              valD (varP (prismName conName))
                (normalB (makeConOpticExp stab' cons con)) []
           | con <- cons
           , let conName = view nconName con
           ]
       )


------------------------------------------------------------------------
-- Utilities
------------------------------------------------------------------------


-- | Normalized constructor
data NCon = NCon
  { _nconName :: Name
  , _nconVars :: [Name]
  , _nconCxt  :: Cxt
  , _nconTypes :: [Type]
  }
  deriving (Eq)

instance HasTypeVars NCon where
  typeVarsEx s f (NCon x vars y z) = NCon x vars <$> typeVarsEx s' f y <*> typeVarsEx s' f z
    where s' = foldl' (flip Set.insert) s vars

nconName :: Lens' NCon Name
nconName f x = fmap (\y -> x {_nconName = y}) (f (_nconName x))

nconCxt :: Lens' NCon Cxt
nconCxt f x = fmap (\y -> x {_nconCxt = y}) (f (_nconCxt x))

nconTypes :: Lens' NCon [Type]
nconTypes f x = fmap (\y -> x {_nconTypes = y}) (f (_nconTypes x))


-- | Normalize a single 'Con' to its constructor name and field types.
-- Because GADT syntax allows multiple constructors to be defined at
-- the same time, this function can return multiple normalized results.
normalizeCon :: D.ConstructorInfo -> NCon
normalizeCon info = NCon (D.constructorName info)
                         (D.tvName <$> D.constructorVars info)
                         (D.constructorContext info)
                         (D.constructorFields info)


-- | Compute a prism's name by prefixing an underscore for normal
-- constructors and period for operators.
prismName :: Name -> Name
prismName n = case nameBase n of
                [] -> error "prismName: empty name base?"
                x:xs | isUpper x -> mkName ('_':x:xs)
                     | otherwise -> mkName ('.':x:xs) -- operator


-- | Quantify all the free variables in a type.
close :: Type -> TypeQ
close t = forallT (map PlainTV (Set.toList vs)) (cxt[]) (return t)
  where
  vs = setOf typeVars t