{-# LANGUAGE Arrows       #-}
{-# LANGUAGE ViewPatterns #-}
module Hasura.GraphQL.Schema
  ( buildGQLContext
  ) where

import           Hasura.Prelude

import qualified Data.Aeson.Ordered                    as JO
import qualified Data.HashMap.Strict                   as Map
import qualified Data.HashMap.Strict.InsOrd            as OMap
import qualified Data.HashSet                          as Set
import qualified Language.GraphQL.Draft.Syntax         as G

import           Control.Arrow.Extended
import           Control.Lens.Extended
import           Control.Monad.Unique
import           Data.Has
import           Data.List.Extended                    (duplicates)
import           Data.Text.Extended

import qualified Hasura.GraphQL.Parser                 as P
import qualified Hasura.SQL.AnyBackend                 as AB

import           Hasura.Base.Error
import           Hasura.GraphQL.Context
import           Hasura.GraphQL.Execute.Types
import           Hasura.GraphQL.Parser                 (Kind (..), Parser, Schema (..),
                                                        UnpreparedValue (..))
import           Hasura.GraphQL.Parser.Class
import           Hasura.GraphQL.Parser.Directives      (directivesInfo)
import           Hasura.GraphQL.Parser.Internal.Parser (FieldParser (..))
import           Hasura.GraphQL.Schema.Backend
import           Hasura.GraphQL.Schema.Common
import           Hasura.GraphQL.Schema.Instances       ()
import           Hasura.GraphQL.Schema.Introspect
import           Hasura.GraphQL.Schema.Postgres
import           Hasura.GraphQL.Schema.Remote          (buildRemoteParser)
import           Hasura.GraphQL.Schema.Select
import           Hasura.GraphQL.Schema.Table
import           Hasura.RQL.DDL.Schema.Cache.Common
import           Hasura.RQL.IR
import           Hasura.RQL.Types
import           Hasura.Session


----------------------------------------------------------------
-- Building contexts

buildGQLContext
  :: forall arr m
   . ( ArrowChoice arr
     , ArrowWriter (Seq InconsistentMetadata) arr
     , ArrowKleisli m arr
     , MonadError QErr m
     , MonadIO m
     , MonadUnique m
     , HasServerConfigCtx m
     )
  => ( GraphQLQueryType
     , SourceCache
     , RemoteSchemaCache
     , ActionCache
     , NonObjectTypeMap
     )
     `arr`
     ( HashMap RoleName (RoleContext GQLContext)
     , GQLContext
     )
buildGQLContext =
  proc (queryType, sources, allRemoteSchemas, allActions, nonObjectCustomTypes) -> do
    ServerConfigCtx functionPermsCtx remoteSchemaPermsCtx sqlGenCtx@(SQLGenCtx stringifyNum boolCollapse) _maintenanceMode _experimentalFeatures <-
      bindA -< askServerConfigCtx
    let remoteSchemasRoles = concatMap (Map.keys . _rscPermissions . fst . snd) $ Map.toList allRemoteSchemas

    let nonTableRoles =
          Set.insert adminRoleName $
          (allActionInfos ^.. folded.aiPermissions.to Map.keys.folded)
          <> Set.fromList (bool mempty remoteSchemasRoles $ remoteSchemaPermsCtx == RemoteSchemaPermsEnabled)
        allActionInfos = Map.elems allActions

        allTableRoles = Set.fromList $ getTableRoles =<< Map.elems sources
        adminRemoteRelationshipQueryCtx =
          allRemoteSchemas
          <&> (\(remoteSchemaCtx, _metadataObj) ->
                 (_rscIntro remoteSchemaCtx, _rscParsed remoteSchemaCtx))
        allRoles :: Set.HashSet RoleName
        allRoles = nonTableRoles <> allTableRoles
        -- The function permissions context doesn't actually matter because the
        -- admin will have access to the function anyway
        adminQueryContext = QueryContext
          stringifyNum
          boolCollapse
          queryType
          adminRemoteRelationshipQueryCtx
          FunctionPermissionsInferred

    -- build the admin DB-only context so that we can check against name clashes with remotes
    -- TODO: Is there a better way to check for conflicts without actually building the admin schema?
    adminHasuraDBContext <- bindA -<
      buildFullestDBSchema adminQueryContext sources allActionInfos nonObjectCustomTypes

    -- TODO factor out the common function; throw500 in both cases:
    queryFieldNames :: [G.Name] <- bindA -<
      case P.discardNullability $ P.parserType $ fst adminHasuraDBContext of
        -- It really ought to be this case; anything else is a programming error.
        P.TNamed (P.Definition _ _ _ (P.TIObject (P.ObjectInfo rootFields _interfaces))) ->
          pure $ fmap P.dName rootFields
        _ -> throw500 "We encountered an root query of unexpected GraphQL type.  It should be an object type."
    let mutationFieldNames :: [G.Name]
        mutationFieldNames =
          case P.discardNullability . P.parserType <$> snd adminHasuraDBContext of
            Just (P.TNamed def) ->
              case P.dInfo def of
                -- It really ought to be this case; anything else is a programming error.
                P.TIObject (P.ObjectInfo rootFields _interfaces) -> fmap P.dName rootFields
                _                                                -> []
            _ -> []

    -- This block of code checks that there are no conflicting root field names between remotes.
    remotes <- remoteSchemaFields -< (queryFieldNames, mutationFieldNames, allRemoteSchemas)

    let adminQueryRemotes = concatMap (piQuery . snd . snd) remotes
        adminMutationRemotes = concatMap (concat . piMutation . snd . snd) remotes

    roleContexts <- bindA -<
      ( Set.toMap allRoles & Map.traverseWithKey \role () ->
          case queryType of
            QueryHasura ->
              buildRoleContext (sqlGenCtx, queryType, functionPermsCtx) sources allRemoteSchemas allActionInfos
              nonObjectCustomTypes remotes role remoteSchemaPermsCtx
            QueryRelay ->
              buildRelayRoleContext (sqlGenCtx, queryType, functionPermsCtx) sources allActionInfos
              nonObjectCustomTypes role
      )
    unauthenticated <- bindA -< unauthenticatedContext adminQueryRemotes adminMutationRemotes remoteSchemaPermsCtx
    returnA -< (roleContexts, unauthenticated)

buildRoleContext
  :: forall m. (MonadError QErr m, MonadIO m, MonadUnique m)
  => (SQLGenCtx, GraphQLQueryType, FunctionPermissionsCtx)
  -> SourceCache
  -> RemoteSchemaCache
  -> [ActionInfo]
  -> NonObjectTypeMap
  -> [( RemoteSchemaName , (IntrospectionResult, ParsedIntrospection))]
  -> RoleName
  -> RemoteSchemaPermsCtx
  -> m (RoleContext GQLContext)
buildRoleContext
  (SQLGenCtx stringifyNum boolCollapse, queryType, functionPermsCtx)
  sources
  allRemoteSchemas
  allActionInfos
  nonObjectCustomTypes
  remotes
  role
  remoteSchemaPermsCtx
  = do
    roleBasedRemoteSchemas <-
      if | role == adminRoleName                            -> pure remotes
         | remoteSchemaPermsCtx == RemoteSchemaPermsEnabled -> buildRoleBasedRemoteSchemaParser role allRemoteSchemas
         -- when remote schema permissions are not enabled, then remote schemas
         -- are a public entity which is accesible to all the roles
         | otherwise                                        -> pure remotes
    let queryRemotes    = getQueryRemotes    $ snd . snd <$> roleBasedRemoteSchemas
        mutationRemotes = getMutationRemotes $ snd . snd <$> roleBasedRemoteSchemas
        remoteRelationshipQueryContext = Map.fromList roleBasedRemoteSchemas
        roleQueryContext = QueryContext
          stringifyNum
          boolCollapse
          queryType
          remoteRelationshipQueryContext
          functionPermsCtx
    runMonadSchema role roleQueryContext sources $ do
      fieldsList <- traverse (buildBackendSource buildSource) $ toList sources
      let (queryFields, mutationFrontendFields, mutationBackendFields) = mconcat fieldsList

      mutationParserFrontend <-
        buildMutationParser mutationRemotes allActionInfos nonObjectCustomTypes mutationFrontendFields
      mutationParserBackend <-
        buildMutationParser mutationRemotes allActionInfos nonObjectCustomTypes mutationBackendFields
      subscriptionParser <-
        buildSubscriptionParser queryFields allActionInfos
      queryParserFrontend <-
        buildQueryParser queryFields queryRemotes allActionInfos nonObjectCustomTypes mutationParserFrontend subscriptionParser
      queryParserBackend <-
        buildQueryParser queryFields queryRemotes allActionInfos nonObjectCustomTypes mutationParserBackend  subscriptionParser

      let frontendContext =
            GQLContext (finalizeParser queryParserFrontend) (finalizeParser <$> mutationParserFrontend)
          backendContext =
            GQLContext (finalizeParser queryParserBackend)  (finalizeParser <$> mutationParserBackend)

      pure $ RoleContext frontendContext $ Just backendContext

  where
    getQueryRemotes
      :: [ParsedIntrospection]
      -> [P.FieldParser (P.ParseT Identity) RemoteField]
    getQueryRemotes = concatMap piQuery

    getMutationRemotes
      :: [ParsedIntrospection]
      -> [P.FieldParser (P.ParseT Identity) RemoteField]
    getMutationRemotes = concatMap (concat . piMutation)

    buildSource :: forall b. BackendSchema b => SourceInfo b ->
      ConcreteSchemaT m ( [FieldParser (P.ParseT Identity) (QueryRootField    UnpreparedValue)]
                        , [FieldParser (P.ParseT Identity) (MutationRootField UnpreparedValue)]
                        , [FieldParser (P.ParseT Identity) (MutationRootField UnpreparedValue)]
                        )
    buildSource (SourceInfo sourceName tables functions sourceConfig) = do
      let validFunctions = takeValidFunctions functions
          validTables    = takeValidTables tables

      (,,)
        <$> buildQueryFields             sourceName sourceConfig validTables validFunctions
        <*> buildMutationFields Frontend sourceName sourceConfig validTables validFunctions
        <*> buildMutationFields Backend  sourceName sourceConfig validTables validFunctions


buildRelayRoleContext
  :: forall m. (MonadError QErr m, MonadIO m, MonadUnique m)
  => (SQLGenCtx, GraphQLQueryType, FunctionPermissionsCtx)
  -> SourceCache
  -> [ActionInfo]
  -> NonObjectTypeMap
  -> RoleName
  -> m (RoleContext GQLContext)
buildRelayRoleContext
  (SQLGenCtx stringifyNum boolCollapse, queryType, functionPermsCtx)
  sources
  allActionInfos
  nonObjectCustomTypes
  role = do
  -- TODO: At the time of writing this, remote schema queries are not supported in relay.
  -- When they are supported, we should get do what `buildRoleContext` does. Since, they
  -- are not supported yet, we use `mempty` below for `RemoteRelationshipQueryContext`.
  let roleQueryContext = QueryContext
        stringifyNum
        boolCollapse
        queryType
        mempty
        functionPermsCtx
  runMonadSchema role roleQueryContext sources do
    fieldsList <- traverse (buildBackendSource buildSource) $ toList sources

    -- Add node root field.
    -- FIXME: for now this is PG-only. This isn't a problem yet since for now only PG supports relay.
    -- To fix this, we'd need to first generalize `nodeField`.
    nodeField_ <- nodeField
    let (queryPGFields', mutationFrontendFields, mutationBackendFields) = mconcat fieldsList
        queryPGFields = nodeField_:queryPGFields'

    -- Remote schema mutations aren't exposed in relay because many times it throws
    -- the conflicting definitions error between the relay types like `Node`, `PageInfo` etc
    mutationParserFrontend <-
      buildMutationParser mempty allActionInfos nonObjectCustomTypes mutationFrontendFields
    mutationParserBackend <-
      buildMutationParser mempty allActionInfos nonObjectCustomTypes mutationBackendFields
    subscriptionParser <-
      P.safeSelectionSet subscriptionRoot Nothing queryPGFields <&> fmap (fmap typenameToRawRF)
    queryParserFrontend <-
      queryWithIntrospectionHelper queryPGFields mutationParserFrontend subscriptionParser
    queryParserBackend <-
      queryWithIntrospectionHelper queryPGFields mutationParserBackend  subscriptionParser

    let frontendContext =
          GQLContext (finalizeParser queryParserFrontend) (finalizeParser <$> mutationParserFrontend)
        backendContext =
          GQLContext (finalizeParser queryParserBackend)  (finalizeParser <$> mutationParserBackend)

    pure $ RoleContext frontendContext $ Just backendContext

  where
    buildSource :: forall b. BackendSchema b => SourceInfo b ->
        ConcreteSchemaT m ( [FieldParser (P.ParseT Identity) (QueryRootField    UnpreparedValue)]
                          , [FieldParser (P.ParseT Identity) (MutationRootField UnpreparedValue)]
                          , [FieldParser (P.ParseT Identity) (MutationRootField UnpreparedValue)]
                          )
    buildSource (SourceInfo sourceName tables functions sourceConfig) = do
      let validFunctions = takeValidFunctions functions
          validTables    = takeValidTables tables

      (,,)
        <$> buildRelayQueryFields        sourceName sourceConfig validTables validFunctions
        <*> buildMutationFields Frontend sourceName sourceConfig validTables validFunctions
        <*> buildMutationFields Backend  sourceName sourceConfig validTables validFunctions


buildFullestDBSchema
  :: forall m. (MonadError QErr m, MonadIO m, MonadUnique m)
  => QueryContext
  -> SourceCache
  -> [ActionInfo]
  -> NonObjectTypeMap
  -> m (        Parser 'Output (P.ParseT Identity) (OMap.InsOrdHashMap G.Name (QueryRootField    UnpreparedValue))
       , Maybe (Parser 'Output (P.ParseT Identity) (OMap.InsOrdHashMap G.Name (MutationRootField UnpreparedValue)))
       )
buildFullestDBSchema queryContext sources allActionInfos nonObjectCustomTypes =
  runMonadSchema adminRoleName queryContext sources do
    fieldsList <- traverse (buildBackendSource buildSource) $ toList sources
    let (queryFields, mutationFrontendFields) = mconcat fieldsList

    mutationParserFrontend <-
      -- NOTE: we omit remotes here on purpose since we're trying to check name
      -- clashes with remotes:
      buildMutationParser mempty allActionInfos nonObjectCustomTypes mutationFrontendFields
    subscriptionParser <-
      buildSubscriptionParser queryFields allActionInfos
    queryParserFrontend <-
      buildQueryParser queryFields mempty allActionInfos nonObjectCustomTypes mutationParserFrontend subscriptionParser

    pure (queryParserFrontend, mutationParserFrontend)

  where
    buildSource :: forall b. BackendSchema b => SourceInfo b ->
        ConcreteSchemaT m ( [FieldParser (P.ParseT Identity) (QueryRootField    UnpreparedValue)]
                          , [FieldParser (P.ParseT Identity) (MutationRootField UnpreparedValue)]
                          )
    buildSource (SourceInfo sourceName tables functions sourceConfig) = do
      let validFunctions = takeValidFunctions functions
          validTables    = takeValidTables tables

      (,)
        <$> buildQueryFields sourceName sourceConfig validTables validFunctions
        <*> buildMutationFields Frontend sourceName sourceConfig validTables validFunctions


-- The `unauthenticatedContext` is used when the user queries the graphql-engine
-- with a role that it's unaware of. Before remote schema permissions, remotes
-- were considered to be a public entity, hence, we allowed an unknown role also
-- to query the remotes. To maintain backwards compatibility, we check if the
-- remote schema permissions are enabled, and if it's we don't expose the remote
-- schema fields in the unauthenticatedContext, otherwise we expose them.
unauthenticatedContext
  :: forall m
   . ( MonadError QErr m
     , MonadIO m
     , MonadUnique m
     )
  => [P.FieldParser (P.ParseT Identity) RemoteField]
  -> [P.FieldParser (P.ParseT Identity) RemoteField]
  -> RemoteSchemaPermsCtx
  -> m GQLContext
unauthenticatedContext adminQueryRemotes adminMutationRemotes remoteSchemaPermsCtx = P.runSchemaT $ do
  let isRemoteSchemaPermsEnabled = remoteSchemaPermsCtx == RemoteSchemaPermsEnabled
      queryFields    = bool (fmap (fmap RFRemote) adminQueryRemotes)    [] isRemoteSchemaPermsEnabled
      mutationFields = bool (fmap (fmap RFRemote) adminMutationRemotes) [] isRemoteSchemaPermsEnabled
  mutationParser <-
    if null adminMutationRemotes
    then pure Nothing
    else P.safeSelectionSet mutationRoot Nothing mutationFields <&> Just . fmap (fmap typenameToRawRF)
  subscriptionParser <-
    P.safeSelectionSet subscriptionRoot Nothing [] <&> fmap (fmap typenameToRawRF)
  queryParser <- queryWithIntrospectionHelper queryFields mutationParser subscriptionParser
  pure $ GQLContext (finalizeParser queryParser) (finalizeParser <$> mutationParser)


----------------------------------------------------------------
-- Building parser fields

buildRoleBasedRemoteSchemaParser
  :: forall m
   . (MonadError QErr m, MonadUnique m, MonadIO m)
  => RoleName
  -> RemoteSchemaCache
  -> m [(RemoteSchemaName, (IntrospectionResult, ParsedIntrospection))]
buildRoleBasedRemoteSchemaParser roleName remoteSchemaCache = do
  let remoteSchemaIntroInfos = map fst $ toList remoteSchemaCache
  remoteSchemaPerms <-
    for remoteSchemaIntroInfos $ \(RemoteSchemaCtx remoteSchemaName _ remoteSchemaInfo _ _ permissions) ->
      for (Map.lookup roleName permissions) $ \introspectRes -> do
        (queryParsers, mutationParsers, subscriptionParsers) <-
             P.runSchemaT @m @(P.ParseT Identity) $ buildRemoteParser introspectRes remoteSchemaInfo
        let parsedIntrospection = ParsedIntrospection queryParsers mutationParsers subscriptionParsers
        return (remoteSchemaName, (introspectRes, parsedIntrospection))
  return $ catMaybes remoteSchemaPerms

-- checks that there are no conflicting root field names between remotes and
-- hasura fields
remoteSchemaFields
  :: forall arr m
   . ( ArrowChoice arr
     , ArrowWriter (Seq InconsistentMetadata) arr
     , ArrowKleisli m arr
     , MonadError QErr m
     )
  => ([G.Name], [G.Name], HashMap RemoteSchemaName (RemoteSchemaCtx, MetadataObject))
     `arr`
     [( RemoteSchemaName , (IntrospectionResult, ParsedIntrospection))]
remoteSchemaFields = proc (queryFieldNames, mutationFieldNames, allRemoteSchemas) -> do
  (| foldlA' (\okSchemas (newSchemaName, (newSchemaContext, newMetadataObject)) -> do
       checkedDuplicates <- (| withRecordInconsistency (do
         let (queryOld, mutationOld) =
               unzip $ fmap ((\case ParsedIntrospection q m _ -> (q,m)) . snd . snd) okSchemas
         let ParsedIntrospection queryNew mutationNew _subscriptionNew
               = _rscParsed newSchemaContext
         -- Check for conflicts between remotes
         bindErrorA -<
           for_ (duplicates (fmap (P.getName . fDefinition) (queryNew ++ concat queryOld))) $
           \name -> throw400 Unexpected $ "Duplicate remote field " <> squote name
         -- Check for conflicts between this remote and the tables
         bindErrorA -<
           for_ (duplicates (fmap (P.getName . fDefinition) queryNew ++ queryFieldNames)) $
           \name -> throw400 RemoteSchemaConflicts $ "Field cannot be overwritten by remote field " <> squote name
         -- Ditto, but for mutations
         case mutationNew of
           Nothing -> returnA -< ()
           Just ms -> do
             bindErrorA -<
               for_ (duplicates (fmap (P.getName . fDefinition) (ms ++ concat (catMaybes mutationOld)))) $
               \name -> throw400 Unexpected $ "Duplicate remote field " <> squote name
             -- Ditto, but for mutations
             bindErrorA -<
               for_ (duplicates (fmap (P.getName . fDefinition) ms ++ mutationFieldNames)) $
               \name -> throw400 Unexpected $ "Field cannot be overwritten by remote field " <> squote name
         -- No need to check subscriptions as these are not supported
         returnA -< ()
         ) |) newMetadataObject
       case checkedDuplicates of
         Nothing -> returnA -< okSchemas
         Just _  -> returnA -< (newSchemaName, ( _rscIntro newSchemaContext,_rscParsed newSchemaContext)):okSchemas
     ) |) [] (Map.toList allRemoteSchemas)

buildQueryFields
  :: forall b r m n
   . MonadBuildSchema b r m n
  => SourceName
  -> SourceConfig b
  -> TableCache b
  -> FunctionCache b
  -> m [P.FieldParser n (QueryRootField UnpreparedValue)]
buildQueryFields sourceName sourceConfig tables (takeExposedAs FEAQuery -> functions) = do
  roleName <- askRoleName
  functionPermsCtx <- asks $ qcFunctionPermsContext . getter
  tableSelectExpParsers <- for (Map.toList tables) \(tableName, tableInfo) -> do
    tableGQLName <- getTableGQLName @b tableInfo
    -- FIXME: retrieve permissions directly from tableInfo to avoid a sourceCache lookup
    selectPerms  <- tableSelectPermissions tableInfo
    for selectPerms $ buildTableQueryFields sourceName sourceConfig tableName tableInfo tableGQLName
  functionSelectExpParsers <- for (Map.toList functions) \(functionName, functionInfo) -> runMaybeT $ do
    guard
      $ roleName == adminRoleName
      || roleName `elem` _fiPermissions functionInfo
      || functionPermsCtx == FunctionPermissionsInferred
    let targetTableName = _fiReturnType functionInfo
    targetTableInfo <- askTableInfo sourceName targetTableName
    selectPerms <- MaybeT $ tableSelectPermissions targetTableInfo
    lift $ buildFunctionQueryFields sourceName sourceConfig functionName functionInfo targetTableName selectPerms
  pure $ concat $ catMaybes $ tableSelectExpParsers <> functionSelectExpParsers

buildRelayQueryFields
  :: forall b r m n
   . MonadBuildSchema b r m n
  => SourceName
  -> SourceConfig b
  -> TableCache b
  -> FunctionCache b
  -> m [P.FieldParser n (QueryRootField UnpreparedValue)]
buildRelayQueryFields sourceName sourceConfig tables (takeExposedAs FEAQuery -> functions) = do
  tableConnectionFields <- for (Map.toList tables) \(tableName, tableInfo) -> runMaybeT do
    tableGQLName <- getTableGQLName @b tableInfo
    pkeyColumns  <- hoistMaybe $ tableInfo ^? tiCoreInfo.tciPrimaryKey._Just.pkColumns
    -- FIXME: retrieve permissions directly from tableInfo to avoid a sourceCache lookup
    selectPerms  <- MaybeT $ tableSelectPermissions tableInfo
    MaybeT $ buildTableRelayQueryFields sourceName sourceConfig tableName tableInfo tableGQLName pkeyColumns selectPerms
  functionConnectionFields <- for (Map.toList functions) $ \(functionName, functionInfo) -> runMaybeT do
    let returnTableName = _fiReturnType functionInfo
    -- FIXME: only extract the TableInfo once to avoid redundant cache lookups
    returnTableInfo <- lift $ askTableInfo sourceName returnTableName
    pkeyColumns <- MaybeT $ (^? tiCoreInfo.tciPrimaryKey._Just.pkColumns) <$> pure returnTableInfo
    selectPerms <- MaybeT $ tableSelectPermissions returnTableInfo
    MaybeT $ buildFunctionRelayQueryFields sourceName sourceConfig functionName functionInfo returnTableName pkeyColumns selectPerms
  pure $ catMaybes $ tableConnectionFields <> functionConnectionFields

buildMutationFields
  :: forall b r m n
   . MonadBuildSchema b r m n
  => Scenario
  -> SourceName
  -> SourceConfig b
  -> TableCache b
  -> FunctionCache b
  -> m [P.FieldParser n (MutationRootField UnpreparedValue)]
buildMutationFields scenario sourceName sourceConfig tables (takeExposedAs FEAMutation -> functions) = do
  roleName <- askRoleName
  tableMutations <- for (Map.toList tables) \(tableName, tableInfo) -> do
    tableGQLName  <- getTableGQLName @b tableInfo
    -- FIXME: retrieve permissions directly from tableInfo to avoid a sourceCache lookup
    tablePerms    <- tablePermissions tableInfo
    for tablePerms \RolePermInfo{..} -> do
      let viewInfo = _tciViewInfo $ _tiCoreInfo tableInfo
      inserts <- runMaybeT $ do
        guard $ isMutable viIsInsertable viewInfo
        insertPerms <- hoistMaybe $ do
          -- If we're in a frontend scenario, we should not include backend_only inserts
          insertPerms <- _permIns
          if scenario == Frontend && ipiBackendOnly insertPerms
            then Nothing
            else Just insertPerms
        lift $
          buildTableInsertMutationFields sourceName sourceConfig tableName tableInfo
                                 tableGQLName insertPerms _permSel _permUpd
      updates <- runMaybeT $ do
        guard $ isMutable viIsUpdatable viewInfo
        updatePerms <- hoistMaybe _permUpd
        lift $ buildTableUpdateMutationFields sourceName sourceConfig tableName tableInfo tableGQLName updatePerms _permSel
      deletes <- runMaybeT $ do
        guard $ isMutable viIsDeletable viewInfo
        deletePerms <- hoistMaybe _permDel
        lift $ buildTableDeleteMutationFields sourceName sourceConfig tableName tableInfo tableGQLName deletePerms _permSel
      pure $ concat $ catMaybes [inserts, updates, deletes]
  functionMutations <- for (Map.toList functions) \(functionName, functionInfo) -> runMaybeT $ do
    let targetTableName = _fiReturnType functionInfo
    targetTableInfo <- askTableInfo sourceName targetTableName
    selectPerms <- MaybeT $ tableSelectPermissions targetTableInfo
    -- A function exposed as mutation must have a function permission
    -- configured for the role. See Note [Function Permissions]
    guard $
      -- when function permissions are inferred, we don't expose the
      -- mutation functions for non-admin roles. See Note [Function Permissions]
      roleName == adminRoleName || roleName `elem` (_fiPermissions functionInfo)
    lift $ buildFunctionMutationFields sourceName sourceConfig functionName functionInfo targetTableName selectPerms
  pure $ concat $ catMaybes $ tableMutations <> functionMutations



----------------------------------------------------------------
-- Building root parser from fields

-- | Prepare the parser for query-type GraphQL requests, but with introspection
--   for queries, mutations and subscriptions built in.
buildQueryParser
  :: forall m n r
   . ( MonadSchema n m
     , MonadTableInfo r m
     , MonadRole r m
     , Has QueryContext r
     )
  => [P.FieldParser n (QueryRootField UnpreparedValue)]
  -> [P.FieldParser n RemoteField]
  -> [ActionInfo]
  -> NonObjectTypeMap
  -> Maybe (Parser 'Output n (OMap.InsOrdHashMap G.Name (MutationRootField UnpreparedValue)))
  -> Parser 'Output n (OMap.InsOrdHashMap G.Name (QueryRootField UnpreparedValue))
  -> m (Parser 'Output n (OMap.InsOrdHashMap G.Name (QueryRootField UnpreparedValue)))
buildQueryParser pgQueryFields remoteFields allActions nonObjectCustomTypes mutationParser subscriptionParser = do
  actionQueryFields <- concat <$> traverse (buildActionQueryFields nonObjectCustomTypes) allActions
  let allQueryFields = pgQueryFields <> actionQueryFields <> map (fmap RFRemote) remoteFields
  queryWithIntrospectionHelper allQueryFields mutationParser subscriptionParser

queryWithIntrospectionHelper
  :: forall n m. (MonadSchema n m, MonadError QErr m)
  => [P.FieldParser n (QueryRootField UnpreparedValue)]
  -> Maybe (Parser 'Output n (OMap.InsOrdHashMap G.Name (MutationRootField UnpreparedValue)))
  -> Parser 'Output n (OMap.InsOrdHashMap G.Name (QueryRootField UnpreparedValue))
  -> m (Parser 'Output n (OMap.InsOrdHashMap G.Name (QueryRootField UnpreparedValue)))
queryWithIntrospectionHelper basicQueryFP mutationP subscriptionP = do
  basicQueryP <- queryRootFromFields basicQueryFP
  emptyIntro  <- emptyIntrospection
  let directives = directivesInfo @n
  allBasicTypes <- collectTypes $
    [ P.TypeDefinitionsWrapper $ P.parserType basicQueryP
    , P.TypeDefinitionsWrapper $ P.parserType subscriptionP
    , P.TypeDefinitionsWrapper $ P.diArguments =<< directives
    ]
    ++ maybeToList (P.TypeDefinitionsWrapper . P.parserType <$> mutationP)
  allIntrospectionTypes <- collectTypes . P.parserType =<< queryRootFromFields emptyIntro
  let allTypes = Map.unions
        [ allBasicTypes
        , Map.filterWithKey (\name _info -> name /= queryRoot) allIntrospectionTypes
        ]
      partialSchema = Schema
        { sDescription = Nothing
        , sTypes = allTypes
        , sQueryType = P.parserType basicQueryP
        , sMutationType = P.parserType <$> mutationP
        , sSubscriptionType = Just $ P.parserType subscriptionP
        , sDirectives = directives
        }
  let partialQueryFields =
        basicQueryFP ++ (fmap RFRaw <$> [schema partialSchema, typeIntrospection partialSchema])
  P.safeSelectionSet queryRoot Nothing partialQueryFields <&> fmap (fmap typenameToRawRF)

queryRootFromFields
  :: forall n m
   . (MonadError QErr m, MonadParse n)
  => [P.FieldParser n (QueryRootField UnpreparedValue)]
  -> m (Parser 'Output n (OMap.InsOrdHashMap G.Name (QueryRootField UnpreparedValue)))
queryRootFromFields fps =
  P.safeSelectionSet queryRoot Nothing fps <&> fmap (fmap typenameToRawRF)

emptyIntrospection
  :: forall m n
   . (MonadSchema n m, MonadError QErr m)
  => m [P.FieldParser n (QueryRootField UnpreparedValue)]
emptyIntrospection = do
  emptyQueryP <- queryRootFromFields @n []
  introspectionTypes <- collectTypes (P.parserType emptyQueryP)
  let introspectionSchema = Schema
        { sDescription = Nothing
        , sTypes = introspectionTypes
        , sQueryType = P.parserType emptyQueryP
        , sMutationType = Nothing
        , sSubscriptionType = Nothing
        , sDirectives = mempty
        }
  return $ fmap (fmap RFRaw) [schema introspectionSchema, typeIntrospection introspectionSchema]

collectTypes
  :: forall m a
   . (MonadError QErr m, P.HasTypeDefinitions a)
  => a
  -> m (HashMap G.Name (P.Definition P.SomeTypeInfo))
collectTypes x = P.collectTypeDefinitions x
  `onLeft` \(P.ConflictingDefinitions (type1, origin1) (_type2, origins)) -> throw500 $
    "Found conflicting definitions for " <> P.getName type1 <<> ".  The definition at " <> origin1 <<>
    " differs from the the definition at " <> commaSeparated origins <<> "."

-- | Prepare the parser for subscriptions. Every postgres query field is
-- exposed as a subscription along with fields to get the status of
-- asynchronous actions.
buildSubscriptionParser
  :: forall m n r
   . ( MonadSchema n m
     , MonadTableInfo r m
     , MonadRole r m
     , Has QueryContext r
     )
  => [P.FieldParser n (QueryRootField UnpreparedValue)]
  -> [ActionInfo]
  -> m (Parser 'Output n (OMap.InsOrdHashMap G.Name (QueryRootField UnpreparedValue)))
buildSubscriptionParser queryFields allActions = do
  actionSubscriptionFields <- concat <$> traverse buildActionSubscriptionFields allActions
  let subscriptionFields = queryFields <> actionSubscriptionFields
  P.safeSelectionSet subscriptionRoot Nothing subscriptionFields <&> fmap (fmap typenameToRawRF)

buildMutationParser
  :: forall m n r
   . ( MonadSchema n m
     , MonadTableInfo r m
     , MonadRole r m
     , Has QueryContext r
     )
  => [P.FieldParser n RemoteField]
  -> [ActionInfo]
  -> NonObjectTypeMap
  -> [P.FieldParser n (MutationRootField UnpreparedValue)]
  -> m (Maybe (Parser 'Output n (OMap.InsOrdHashMap G.Name (MutationRootField UnpreparedValue))))
buildMutationParser allRemotes allActions nonObjectCustomTypes mutationFields = do
  actionParsers <- concat <$> traverse (buildActionMutationFields nonObjectCustomTypes) allActions
  let mutationFieldsParser =
        mutationFields <>
        actionParsers <>
        fmap (fmap RFRemote) allRemotes
  if null mutationFieldsParser
  then pure Nothing
  else P.safeSelectionSet mutationRoot (Just $ G.Description "mutation root") mutationFieldsParser
            <&> Just . fmap (fmap typenameToRawRF)



----------------------------------------------------------------
-- local helpers

takeExposedAs :: FunctionExposedAs -> FunctionCache b -> FunctionCache b
takeExposedAs x = Map.filter ((== x) . _fiExposedAs)

subscriptionRoot :: G.Name
subscriptionRoot = $$(G.litName "subscription_root")

mutationRoot :: G.Name
mutationRoot = $$(G.litName "mutation_root")

queryRoot :: G.Name
queryRoot = $$(G.litName "query_root")

finalizeParser :: Parser 'Output (P.ParseT Identity) a -> ParserFn a
finalizeParser parser = runIdentity . P.runParseT . P.runParser parser


type ConcreteSchemaT m a =
  P.SchemaT
    ( P.ParseT Identity )
    ( ReaderT ( RoleName
              , SourceCache
              , QueryContext
              ) m
    ) a

runMonadSchema
  :: forall m a
   . Monad m
  => RoleName
  -> QueryContext
  -> SourceCache
  -> ConcreteSchemaT m a
  -> m a
runMonadSchema roleName queryContext pgSources m =
  flip runReaderT (roleName, pgSources, queryContext) $ P.runSchemaT m

-- | Whether the request is sent with `x-hasura-use-backend-only-permissions` set to `true`.
data Scenario = Backend | Frontend deriving (Enum, Show, Eq)

type RemoteSchemaCache = HashMap RemoteSchemaName (RemoteSchemaCtx, MetadataObject)

buildBackendSource
  :: (forall b. BackendSchema b => SourceInfo b -> r)
  -> AB.AnyBackend SourceInfo
  -> r
buildBackendSource f e = AB.dispatchAnyBackend @BackendSchema e f

typenameToRawRF
  :: P.ParsedSelection (RootField db remote action JO.Value)
  -> RootField db remote action JO.Value
typenameToRawRF = P.handleTypename $ RFRaw . JO.String . G.unName