-- | Extract docs from the renamer output so they can be be serialized.
{-# language LambdaCase #-}
{-# language TypeFamilies #-}
module ExtractDocs (extractDocs) where

import GhcPrelude
import Bag
import HsBinds
import HsDoc
import HsDecls
import HsExtension
import HsTypes
import HsUtils
import Name
import NameSet
import SrcLoc
import TcRnTypes

import Control.Applicative
import Data.List
import Data.Map (Map)
import qualified Data.Map as M
import Data.Maybe
import Data.Semigroup

-- | Extract docs from renamer output.
extractDocs :: TcGblEnv
            -> (Maybe HsDocString, DeclDocMap, ArgDocMap)
            -- ^
            -- 1. Module header
            -- 2. Docs on top level declarations
            -- 3. Docs on arguments
extractDocs TcGblEnv { tcg_semantic_mod = mod
                     , tcg_rn_decls = mb_rn_decls
                     , tcg_insts = insts
                     , tcg_fam_insts = fam_insts
                     , tcg_doc_hdr = mb_doc_hdr
                     } =
    (unLoc <$> mb_doc_hdr, DeclDocMap doc_map, ArgDocMap arg_map)
  where
    (doc_map, arg_map) = maybe (M.empty, M.empty)
                               (mkMaps local_insts)
                               mb_decls_with_docs
    mb_decls_with_docs = topDecls <$> mb_rn_decls
    local_insts = filter (nameIsLocalOrFrom mod)
                         $ map getName insts ++ map getName fam_insts

-- | Create decl and arg doc-maps by looping through the declarations.
-- For each declaration, find its names, its subordinates, and its doc strings.
mkMaps :: [Name]
       -> [(LHsDecl GhcRn, [HsDocString])]
       -> (Map Name (HsDocString), Map Name (Map Int (HsDocString)))
mkMaps instances decls =
    ( f' (map (nubByName fst) decls')
    , f  (filterMapping (not . M.null) args)
    )
  where
    (decls', args) = unzip (map mappings decls)

    f :: (Ord a, Semigroup b) => [[(a, b)]] -> Map a b
    f = M.fromListWith (<>) . concat

    f' :: Ord a => [[(a, HsDocString)]] -> Map a HsDocString
    f' = M.fromListWith appendDocs . concat

    filterMapping :: (b -> Bool) ->  [[(a, b)]] -> [[(a, b)]]
    filterMapping p = map (filter (p . snd))

    mappings :: (LHsDecl GhcRn, [HsDocString])
             -> ( [(Name, HsDocString)]
                , [(Name, Map Int (HsDocString))]
                )
    mappings (L l decl, docStrs) =
           (dm, am)
      where
        doc = concatDocs docStrs
        args = declTypeDocs decl

        subs :: [(Name, [(HsDocString)], Map Int (HsDocString))]
        subs = subordinates instanceMap decl

        (subDocs, subArgs) =
          unzip (map (\(_, strs, m) -> (concatDocs strs, m)) subs)

        ns = names l decl
        subNs = [ n | (n, _, _) <- subs ]
        dm = [(n, d) | (n, Just d) <- zip ns (repeat doc) ++ zip subNs subDocs]
        am = [(n, args) | n <- ns] ++ zip subNs subArgs

    instanceMap :: Map SrcSpan Name
    instanceMap = M.fromList [(getSrcSpan n, n) | n <- instances]

    names :: SrcSpan -> HsDecl GhcRn -> [Name]
    names l (InstD _ d) = maybeToList (M.lookup loc instanceMap) -- See
                                                                 -- Note [1].
      where loc = case d of
              TyFamInstD _ _ -> l -- The CoAx's loc is the whole line, but only
                                  -- for TFs
              _ -> getInstLoc d
    names l (DerivD {}) = maybeToList (M.lookup l instanceMap) -- See Note [1].
    names _ decl = getMainDeclBinder decl

{-
Note [1]:
---------
We relate ClsInsts to InstDecls and DerivDecls using the SrcSpans buried
inside them. That should work for normal user-written instances (from
looking at GHC sources). We can assume that commented instances are
user-written. This lets us relate Names (from ClsInsts) to comments
(associated with InstDecls and DerivDecls).
-}

getMainDeclBinder :: HsDecl pass -> [IdP pass]
getMainDeclBinder (TyClD _ d) = [tcdName d]
getMainDeclBinder (ValD _ d) =
  case collectHsBindBinders d of
    []       -> []
    (name:_) -> [name]
getMainDeclBinder (SigD _ d) = sigNameNoLoc d
getMainDeclBinder (ForD _ (ForeignImport _ name _ _)) = [unLoc name]
getMainDeclBinder (ForD _ (ForeignExport _ _ _ _)) = []
getMainDeclBinder _ = []

sigNameNoLoc :: Sig pass -> [IdP pass]
sigNameNoLoc (TypeSig    _   ns _)         = map unLoc ns
sigNameNoLoc (ClassOpSig _ _ ns _)         = map unLoc ns
sigNameNoLoc (PatSynSig  _   ns _)         = map unLoc ns
sigNameNoLoc (SpecSig    _   n _ _)        = [unLoc n]
sigNameNoLoc (InlineSig  _   n _)          = [unLoc n]
sigNameNoLoc (FixSig _ (FixitySig _ ns _)) = map unLoc ns
sigNameNoLoc _                             = []

-- Extract the source location where an instance is defined. This is used
-- to correlate InstDecls with their Instance/CoAxiom Names, via the
-- instanceMap.
getInstLoc :: InstDecl name -> SrcSpan
getInstLoc = \case
  ClsInstD _ (ClsInstDecl { cid_poly_ty = ty }) -> getLoc (hsSigType ty)
  DataFamInstD _ (DataFamInstDecl
    { dfid_eqn = HsIB { hsib_body = FamEqn { feqn_tycon = L l _ }}}) -> l
  TyFamInstD _ (TyFamInstDecl
    -- Since CoAxioms' Names refer to the whole line for type family instances
    -- in particular, we need to dig a bit deeper to pull out the entire
    -- equation. This does not happen for data family instances, for some
    -- reason.
    { tfid_eqn = HsIB { hsib_body = FamEqn { feqn_rhs = L l _ }}}) -> l
  ClsInstD _ (XClsInstDecl _) -> error "getInstLoc"
  DataFamInstD _ (DataFamInstDecl (HsIB _ (XFamEqn _))) -> error "getInstLoc"
  TyFamInstD _ (TyFamInstDecl (HsIB _ (XFamEqn _))) -> error "getInstLoc"
  XInstDecl _ -> error "getInstLoc"
  DataFamInstD _ (DataFamInstDecl (XHsImplicitBndrs _)) -> error "getInstLoc"
  TyFamInstD _ (TyFamInstDecl (XHsImplicitBndrs _)) -> error "getInstLoc"

-- | Get all subordinate declarations inside a declaration, and their docs.
-- A subordinate declaration is something like the associate type or data
-- family of a type class.
subordinates :: Map SrcSpan Name
             -> HsDecl GhcRn
             -> [(Name, [(HsDocString)], Map Int (HsDocString))]
subordinates instMap decl = case decl of
  InstD _ (ClsInstD _ d) -> do
    DataFamInstDecl { dfid_eqn = HsIB { hsib_body =
      FamEqn { feqn_tycon = L l _
             , feqn_rhs   = defn }}} <- unLoc <$> cid_datafam_insts d
    [ (n, [], M.empty) | Just n <- [M.lookup l instMap] ] ++ dataSubs defn

  InstD _ (DataFamInstD _ (DataFamInstDecl (HsIB { hsib_body = d })))
    -> dataSubs (feqn_rhs d)
  TyClD _ d | isClassDecl d -> classSubs d
            | isDataDecl  d -> dataSubs (tcdDataDefn d)
  _ -> []
  where
    classSubs dd = [ (name, doc, declTypeDocs d) | (L _ d, doc) <- classDecls dd
                   , name <- getMainDeclBinder d, not (isValD d)
                   ]
    dataSubs :: HsDataDefn GhcRn
             -> [(Name, [HsDocString], Map Int (HsDocString))]
    dataSubs dd = constrs ++ fields ++ derivs
      where
        cons = map unLoc $ (dd_cons dd)
        constrs = [ ( unLoc cname
                    , maybeToList $ fmap unLoc $ con_doc c
                    , conArgDocs c)
                  | c <- cons, cname <- getConNames c ]
        fields  = [ (extFieldOcc n, maybeToList $ fmap unLoc doc, M.empty)
                  | RecCon flds <- map getConArgs cons
                  , L _ (ConDeclField _ ns _ doc) <- (unLoc flds)
                  , L _ n <- ns ]
        derivs  = [ (instName, [unLoc doc], M.empty)
                  | HsIB { hsib_body = L l (HsDocTy _ _ doc) }
                      <- concatMap (unLoc . deriv_clause_tys . unLoc) $
                           unLoc $ dd_derivs dd
                  , Just instName <- [M.lookup l instMap] ]

-- | Extract constructor argument docs from inside constructor decls.
conArgDocs :: ConDecl GhcRn -> Map Int (HsDocString)
conArgDocs con = case getConArgs con of
                   PrefixCon args -> go 0 (map unLoc args ++ ret)
                   InfixCon arg1 arg2 -> go 0 ([unLoc arg1, unLoc arg2] ++ ret)
                   RecCon _ -> go 1 ret
  where
    go n (HsDocTy _ _ (L _ ds) : tys) = M.insert n ds $ go (n+1) tys
    go n (_ : tys) = go (n+1) tys
    go _ [] = M.empty

    ret = case con of
            ConDeclGADT { con_res_ty = res_ty } -> [ unLoc res_ty ]
            _ -> []

isValD :: HsDecl a -> Bool
isValD (ValD _ _) = True
isValD _ = False

-- | All the sub declarations of a class (that we handle), ordered by
-- source location, with documentation attached if it exists.
classDecls :: TyClDecl GhcRn -> [(LHsDecl GhcRn, [HsDocString])]
classDecls class_ = filterDecls . collectDocs . sortByLoc $ decls
  where
    decls = docs ++ defs ++ sigs ++ ats
    docs  = mkDecls tcdDocs (DocD noExt) class_
    defs  = mkDecls (bagToList . tcdMeths) (ValD noExt) class_
    sigs  = mkDecls tcdSigs (SigD noExt) class_
    ats   = mkDecls tcdATs (TyClD noExt . FamDecl noExt) class_

-- | Extract function argument docs from inside top-level decls.
declTypeDocs :: HsDecl GhcRn -> Map Int (HsDocString)
declTypeDocs = \case
  SigD  _ (TypeSig _ _ ty)          -> typeDocs (unLoc (hsSigWcType ty))
  SigD  _ (ClassOpSig _ _ _ ty)     -> typeDocs (unLoc (hsSigType ty))
  SigD  _ (PatSynSig _ _ ty)        -> typeDocs (unLoc (hsSigType ty))
  ForD  _ (ForeignImport _ _ ty _)  -> typeDocs (unLoc (hsSigType ty))
  TyClD _ (SynDecl { tcdRhs = ty }) -> typeDocs (unLoc ty)
  _                                 -> M.empty

nubByName :: (a -> Name) -> [a] -> [a]
nubByName f ns = go emptyNameSet ns
  where
    go _ [] = []
    go s (x:xs)
      | y `elemNameSet` s = go s xs
      | otherwise         = let s' = extendNameSet s y
                            in x : go s' xs
      where
        y = f x

-- | Extract function argument docs from inside types.
typeDocs :: HsType GhcRn -> Map Int (HsDocString)
typeDocs = go 0
  where
    go n (HsForAllTy { hst_body = ty }) = go n (unLoc ty)
    go n (HsQualTy   { hst_body = ty }) = go n (unLoc ty)
    go n (HsFunTy _ (L _ (HsDocTy _ _ (L _ x))) (L _ ty)) =
       M.insert n x $ go (n+1) ty
    go n (HsFunTy _ _ ty) = go (n+1) (unLoc ty)
    go n (HsDocTy _ _ (L _ doc)) = M.singleton n doc
    go _ _ = M.empty

-- | The top-level declarations of a module that we care about,
-- ordered by source location, with documentation attached if it exists.
topDecls :: HsGroup GhcRn -> [(LHsDecl GhcRn, [HsDocString])]
topDecls = filterClasses . filterDecls . collectDocs . sortByLoc . ungroup

-- | Take all declarations except pragmas, infix decls, rules from an 'HsGroup'.
ungroup :: HsGroup GhcRn -> [LHsDecl GhcRn]
ungroup group_ =
  mkDecls (tyClGroupTyClDecls . hs_tyclds) (TyClD noExt)  group_ ++
  mkDecls hs_derivds             (DerivD noExt) group_ ++
  mkDecls hs_defds               (DefD noExt)   group_ ++
  mkDecls hs_fords               (ForD noExt)   group_ ++
  mkDecls hs_docs                (DocD noExt)   group_ ++
  mkDecls (tyClGroupInstDecls . hs_tyclds) (InstD noExt)  group_ ++
  mkDecls (typesigs . hs_valds)  (SigD noExt)   group_ ++
  mkDecls (valbinds . hs_valds)  (ValD noExt)   group_
  where
    typesigs (XValBindsLR (NValBinds _ sigs)) = filter (isUserSig . unLoc) sigs
    typesigs _ = error "expected ValBindsOut"

    valbinds (XValBindsLR (NValBinds binds _)) =
      concatMap bagToList . snd . unzip $ binds
    valbinds _ = error "expected ValBindsOut"

-- | Sort by source location
sortByLoc :: [Located a] -> [Located a]
sortByLoc = sortOn getLoc

-- | Collect docs and attach them to the right declarations.
--
-- A declaration may have multiple doc strings attached to it.
collectDocs :: [LHsDecl pass] -> [(LHsDecl pass, [HsDocString])]
-- ^ This is an example.
collectDocs = go Nothing []
  where
    go Nothing _ [] = []
    go (Just prev) docs [] = finished prev docs []
    go prev docs (L _ (DocD _ (DocCommentNext str)) : ds)
      | Nothing <- prev = go Nothing (str:docs) ds
      | Just decl <- prev = finished decl docs (go Nothing [str] ds)
    go prev docs (L _ (DocD _ (DocCommentPrev str)) : ds) =
      go prev (str:docs) ds
    go Nothing docs (d:ds) = go (Just d) docs ds
    go (Just prev) docs (d:ds) = finished prev docs (go (Just d) [] ds)

    finished decl docs rest = (decl, reverse docs) : rest

-- | Filter out declarations that we don't handle in Haddock
filterDecls :: [(LHsDecl a, doc)] -> [(LHsDecl a, doc)]
filterDecls = filter (isHandled . unLoc . fst)
  where
    isHandled (ForD _ (ForeignImport {})) = True
    isHandled (TyClD {})  = True
    isHandled (InstD {})  = True
    isHandled (DerivD {}) = True
    isHandled (SigD _ d)  = isUserSig d
    isHandled (ValD {})   = True
    -- we keep doc declarations to be able to get at named docs
    isHandled (DocD {})   = True
    isHandled _ = False


-- | Go through all class declarations and filter their sub-declarations
filterClasses :: [(LHsDecl a, doc)] -> [(LHsDecl a, doc)]
filterClasses decls = [ if isClassD d then (L loc (filterClass d), doc) else x
                      | x@(L loc d, doc) <- decls ]
  where
    filterClass (TyClD x c) =
      TyClD x $ c { tcdSigs =
        filter (liftA2 (||) (isUserSig . unLoc) isMinimalLSig) (tcdSigs c) }
    filterClass _ = error "expected TyClD"

-- | Was this signature given by the user?
isUserSig :: Sig name -> Bool
isUserSig TypeSig {}    = True
isUserSig ClassOpSig {} = True
isUserSig PatSynSig {}  = True
isUserSig _             = False

isClassD :: HsDecl a -> Bool
isClassD (TyClD _ d) = isClassDecl d
isClassD _ = False

-- | Take a field of declarations from a data structure and create HsDecls
-- using the given constructor
mkDecls :: (a -> [Located b]) -> (b -> c) -> a -> [Located c]
mkDecls field con struct = [ L loc (con decl) | L loc decl <- field struct ]