{-# LANGUAGE FlexibleContexts  #-}
{-# LANGUAGE NoImplicitPrelude #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE TemplateHaskell   #-}

module Hasura.GraphQL.Validate.Field
  ( ArgsMap
  , Field(..)
  , SelSet
  , denormSelSet
  ) where

import           Hasura.Prelude

import qualified Data.Aeson                         as J
import qualified Data.Aeson.Casing                  as J
import qualified Data.Aeson.TH                      as J
import qualified Data.HashMap.Strict                as Map
import qualified Data.List                          as L
import qualified Data.Sequence                      as Seq
import qualified Data.Text                          as T
import qualified Hasura.GraphQL.NonEmptySeq         as NE
import qualified Hasura.GraphQL.OrderedMap          as OMap
import qualified Language.GraphQL.Draft.Syntax      as G

import           Hasura.GraphQL.Validate.Context
import           Hasura.GraphQL.Validate.InputValue
import           Hasura.GraphQL.Validate.Types
import           Hasura.RQL.Types

-- data ScalarInfo
--   = SIBuiltin !GBuiltin
--   | SICustom !PGColType
--   deriving (Show, Eq)

-- data GBuiltin
--   = GInt
--   | GFloat
--   | GBoolean
--   | GString
--   deriving (Show, Eq)

data TypedOperation
  = TypedOperation
  { _toType         :: !G.OperationType
  , _toName         :: !(Maybe G.Name)
  , _toSelectionSet :: ![Field]
  } deriving (Show, Eq)

type ArgsMap = Map.HashMap G.Name AnnGValue

type SelSet = Seq.Seq Field

data Field
  = Field
  { _fAlias     :: !G.Alias
  , _fName      :: !G.Name
  , _fType      :: !G.NamedType
  , _fArguments :: !ArgsMap
  , _fSelSet    :: !SelSet
  } deriving (Eq, Show)

$(J.deriveToJSON (J.aesonDrop 2 J.camelCase){J.omitNothingFields=True}
  ''Field
 )

-- newtype FieldMapAlias
--   = FieldMapAlias
--   { unFieldMapAlias :: Map.HashMap G.Alias (FieldG FieldMapAlias)
--   } deriving (Show, Eq)

-- newtype FieldMapName
--   = FieldMapName
--   { unFieldMapName :: Map.HashMap G.Name (NE.NonEmpty (FieldG FieldMapName))
--   } deriving (Show, Eq)

-- type Field = FieldG FieldMapAlias

-- type FieldGrouped = FieldG FieldMapName

-- toFieldGrouped :: Field -> FieldGrouped
-- toFieldGrouped =
--   fmap groupFields
--   where
--     groupFields m =
--       FieldMapName $ groupTuples $
--       flip map (Map.elems $ unFieldMapAlias m) $ \fld ->
--       (_fName fld, toFieldGrouped fld)

data FieldGroupSrc
  = FGSFragSprd !G.Name
  | FGSInlnFrag
  deriving (Show, Eq)

data FieldGroup
  = FieldGroup
  { _fgSource :: !FieldGroupSrc
  , _fgFields :: !(Seq.Seq Field)
  } deriving (Show, Eq)

-- data GLoc
--   = GLoc
--   { _glLine   :: !Int
--   , _glColumn :: !Int
--   } deriving (Show, Eq)

-- data GErr
--   = GErr
--   { _geMessage   :: !Text
--   , _geLocations :: ![GLoc]
--   } deriving (Show, Eq)

-- throwGE :: (MonadError QErr m) => Text -> m a
-- throwGE msg = throwError $ QErr msg []

withDirectives
  :: ( MonadReader ValidationCtx m
     , MonadError QErr m)
  => [G.Directive]
  -> m a
  -> m (Maybe a)
withDirectives dirs act =
  -- TODO, use the directives
  Just <$> act

denormSel
  :: ( MonadReader ValidationCtx m
     , MonadError QErr m)
  => [G.Name] -- visited fragments
  -> ObjTyInfo -- parent type info
  -> G.Selection
  -> m (Maybe (Either Field FieldGroup))
denormSel visFrags parObjTyInfo sel = case sel of
  G.SelectionField fld -> do
    fldInfo <- getFieldInfo parObjTyInfo $ G._fName fld
    fmap Left <$> denormFld visFrags fldInfo fld
  G.SelectionFragmentSpread fragSprd ->
    fmap Right <$> denormFrag visFrags parTy fragSprd
  G.SelectionInlineFragment inlnFrag ->
    fmap Right <$> denormInlnFrag visFrags parObjTyInfo inlnFrag
  where
    parTy = _otiName parObjTyInfo

processArgs
  :: ( MonadReader ValidationCtx m
     , MonadError QErr m)
  => ObjFldInfo
  -> [G.Argument]
  -> m (Map.HashMap G.Name AnnGValue)
processArgs (ObjFldInfo _ fldName fldParams fldTy) argsL = do

  args <- onLeft (mkMapWith G._aName argsL) $ \dups ->
    throwVE $ "the following arguments are defined more than once: " <>
    showNames dups

  let requiredParams = Map.filter (G.isNotNull . _iviType) fldParams

  inpArgs <- forM args $ \(G.Argument argName argVal) -> do
    argTy <- getArgTy argName
    validateInputValue valueParser argTy argVal

  forM_ requiredParams $ \argDef -> do
    let param = _iviName argDef
    onNothing (Map.lookup param inpArgs) $ throwVE $ mconcat
      [ "the required argument ", showName param
      , " is missing on field ", showName fldName
      ]

  return inpArgs

  where
    getArgTy argName =
      onNothing (_iviType <$> Map.lookup argName fldParams) $ throwVE $
      "no such argument " <> showName argName <> " defined on " <>
      "field " <> showName fldName

denormFld
  :: ( MonadReader ValidationCtx m
     , MonadError QErr m)
  => [G.Name] -- visited fragments
  -> ObjFldInfo
  -> G.Field
  -> m (Maybe Field)
denormFld visFrags fldInfo (G.Field aliasM name args dirs selSet) = do

  let fldTy = _fiTy fldInfo
      fldBaseTy = getBaseTy fldTy

  fldTyInfo <- getTyInfo fldBaseTy

  argMap <- processArgs fldInfo args

  fields <- case (fldTyInfo, selSet) of

    (TIObj _, [])  ->
      throwVE $ "field " <> showName name <> " of type "
      <> G.showGT fldTy <> " must have a selection of subfields"

    (TIObj fldObjTyInfo, _) ->
      denormSelSet visFrags fldObjTyInfo selSet

    (TIScalar _, []) -> return Seq.empty
    (TIEnum _, []) -> return Seq.empty

    (TIInpObj _, _) ->
      throwVE $ "internal error: unexpected input type for field: "
      <> showName name

    -- when scalar/enum and no empty set
    (_, _) ->
      throwVE $ "field " <> showName name <> " must not have a "
      <> "selection since type " <> G.showGT fldTy <> " has no subfields"

  withDirectives dirs $ return $
    Field (fromMaybe (G.Alias name) aliasM) name fldBaseTy argMap fields

denormInlnFrag
  :: ( MonadReader ValidationCtx m
     , MonadError QErr m)
  => [G.Name] -- visited fragments
  -> ObjTyInfo -- type information of the field
  -> G.InlineFragment
  -> m (Maybe FieldGroup)
denormInlnFrag visFrags fldTyInfo inlnFrag = do
  let fldTy  = _otiName fldTyInfo
  let fragTy = fromMaybe fldTy tyM
  when (fldTy /= fragTy) $
    throwVE $ "inline fragment is expected on type " <>
    showNamedTy fldTy <> " but found " <> showNamedTy fragTy
  withDirectives directives $ fmap (FieldGroup FGSInlnFrag) $
    denormSelSet visFrags fldTyInfo selSet
  where
    G.InlineFragment tyM directives selSet = inlnFrag

denormSelSet
  :: ( MonadReader ValidationCtx m
     , MonadError QErr m)
  => [G.Name] -- visited fragments
  -> ObjTyInfo
  -> G.SelectionSet
  -> m (Seq.Seq Field)
denormSelSet visFrags fldTyInfo selSet = do
  resFlds <- catMaybes <$> mapM (denormSel visFrags fldTyInfo) selSet
  mergeFields $ foldl' flatten Seq.empty resFlds
  where
    flatten s (Left fld) = s Seq.|> fld
    flatten s (Right (FieldGroup _ flds)) =
      s Seq.>< flds

mergeFields
  :: ( MonadReader ValidationCtx m
     , MonadError QErr m)
  => Seq.Seq Field
  -> m (Seq.Seq Field)
mergeFields flds =
  fmap Seq.fromList $ forM fldGroups $ \fieldGroup -> do
    newFld <- checkMergeability fieldGroup
    childFields <- mergeFields $ foldl' (\l f -> l Seq.>< _fSelSet f) Seq.empty $
                   NE.toSeq fieldGroup
    return $ newFld {_fSelSet = childFields}
  where
    fldGroups = OMap.elems $ OMap.groupListWith _fAlias flds
    -- can a group be merged?
    checkMergeability fldGroup = do
      let groupedFlds = toList $ NE.toSeq fldGroup
          fldNames = L.nub $ map _fName groupedFlds
          args = L.nub $ map _fArguments groupedFlds
          fld = NE.head fldGroup
          fldAl = _fAlias fld
      when (length fldNames > 1) $
        throwVE $ "cannot merge different fields under the same alias ("
        <> showName (G.unAlias fldAl) <> "): "
        <> showNames fldNames
      when (length args > 1) $
        throwVE $ "cannot merge fields with different arguments"
        <> " under the same alias: "
        <> showName (G.unAlias fldAl)
      return fld

onJust :: (Monad m) => Maybe a -> (a -> m ()) -> m ()
onJust m act = maybe (return ()) act m

denormFrag
  :: ( MonadReader ValidationCtx m
     , MonadError QErr m)
  => [G.Name] -- visited fragments
  -> G.NamedType -- parent type
  -> G.FragmentSpread
  -> m (Maybe FieldGroup)
denormFrag visFrags parTy (G.FragmentSpread name directives) = do

  -- check for cycles
  when (name `elem` visFrags) $
    throwVE $ "cannot spread fragment " <> showName name <> " within itself via "
    <> T.intercalate "," (map G.unName visFrags)

  (FragDef _ fragTyInfo selSet) <- getFragInfo

  let fragTy = _otiName fragTyInfo

  -- we don't have unions or interfaces so we can get away with equality
  when (fragTy /= parTy) $
    throwVE $ "cannot spread fragment " <> showName name <> " defined on " <>
    showNamedTy fragTy <> " when selecting fields of type " <> showNamedTy parTy

  resFlds <- withPathK "selset" $ denormSelSet (name:visFrags) fragTyInfo selSet

  withPathK "directives" $ withDirectives directives $
    return $ FieldGroup (FGSFragSprd  name) resFlds

  where
    getFragInfo = do
      dctx <- ask
      onNothing (Map.lookup name $ _vcFragDefMap dctx) $
        throwVE $ "fragment '" <> G.unName name <> "' not found"