{-# LANGUAGE QuasiQuotes #-}
{-# LANGUAGE ViewPatterns #-}
{-# LANGUAGE NoMonomorphismRestriction #-}

module Hasura.GraphQL.Schema
  ( buildGQLContext,
  )
where

import Control.Concurrent.Extended (concurrentlyEIO, forConcurrentlyEIO)
import Control.Lens hiding (contexts)
import Control.Monad.Memoize
import Data.Aeson.Ordered qualified as JO
import Data.Has
import Data.HashMap.Strict qualified as Map
import Data.HashMap.Strict.InsOrd qualified as OMap
import Data.HashSet qualified as Set
import Data.List.Extended (duplicates)
import Data.Text.Extended
import Data.Text.NonEmpty qualified as NT
import Hasura.Base.Error
import Hasura.Base.ErrorMessage
import Hasura.Base.ToErrorValue
import Hasura.GraphQL.ApolloFederation
import Hasura.GraphQL.Context
import Hasura.GraphQL.Namespace
import Hasura.GraphQL.Parser.Schema.Convert (convertToSchemaIntrospection)
import Hasura.GraphQL.Schema.Backend
import Hasura.GraphQL.Schema.Common
import Hasura.GraphQL.Schema.Instances ()
import Hasura.GraphQL.Schema.Introspect
import Hasura.GraphQL.Schema.NamingCase
import Hasura.GraphQL.Schema.Options (SchemaOptions (..))
import Hasura.GraphQL.Schema.Options qualified as Options
import Hasura.GraphQL.Schema.Parser
  ( FieldParser,
    Kind (..),
    MonadParse,
    Parser,
    Schema,
  )
import Hasura.GraphQL.Schema.Parser qualified as P
import Hasura.GraphQL.Schema.Postgres
import Hasura.GraphQL.Schema.Relay
import Hasura.GraphQL.Schema.Remote (buildRemoteParser)
import Hasura.GraphQL.Schema.RemoteRelationship
import Hasura.GraphQL.Schema.Table
import Hasura.GraphQL.Schema.Typename (MkTypename (..))
import Hasura.Name qualified as Name
import Hasura.Prelude
import Hasura.RQL.IR
import Hasura.RQL.Types.Action
import Hasura.RQL.Types.Backend
import Hasura.RQL.Types.Common
import Hasura.RQL.Types.CustomTypes
import Hasura.RQL.Types.Function
import Hasura.RQL.Types.Metadata.Object
import Hasura.RQL.Types.Permission
import Hasura.RQL.Types.QueryTags
import Hasura.RQL.Types.SchemaCache hiding (askTableInfo)
import Hasura.RQL.Types.Source
import Hasura.RQL.Types.SourceCustomization
import Hasura.RQL.Types.Table
import Hasura.RemoteSchema.Metadata
import Hasura.RemoteSchema.SchemaCache
import Hasura.SQL.AnyBackend qualified as AB
import Hasura.SQL.Tag (HasTag)
import Hasura.Server.Types
import Hasura.Session
import Language.GraphQL.Draft.Syntax qualified as G

-------------------------------------------------------------------------------

-- Building contexts

-- | Builds the full GraphQL context for a given query type.
--
-- A 'GQLContext' stores how an incoming request should be processed: how to
-- translate each incoming field of a request into a corresponding semantic
-- representation. There is a different one per 'Role', as each role might have
-- different permissions, and therefore not access to the same set of objects in
-- the schema.
--
-- This function takes all necessary information from the metadata, and the
-- 'GraphQLQueryType', and builds all relevant contexts: a hash map from
-- 'RoleName' to their 'GQLContext' and the "default" context for
-- unauthenticated users.
--
-- When building the schema for each role, we treat the remote schemas as
-- "second-class citizens" compared to sources; more specifically, we attempt to
-- detect whether the inclusion of a given remote schema would result in root
-- fields conflict, and only keep schemas that don't generate any. This results
-- in a partial schema being available to the users, and a better error message
-- than would arise from 'safeSelectionSet'.
buildGQLContext ::
  forall m.
  ( MonadError QErr m,
    MonadIO m
  ) =>
  ServerConfigCtx ->
  SourceCache ->
  HashMap RemoteSchemaName (RemoteSchemaCtx, MetadataObject) ->
  ActionCache ->
  AnnotatedCustomTypes ->
  m
    ( -- Hasura schema
      ( G.SchemaIntrospection,
        HashMap RoleName (RoleContext GQLContext),
        GQLContext,
        HashSet InconsistentMetadata
      ),
      -- Relay schema
      ( HashMap RoleName (RoleContext GQLContext),
        GQLContext
      )
    )
buildGQLContext ServerConfigCtx {..} sources allRemoteSchemas allActions customTypes = do
  let remoteSchemasRoles = concatMap (Map.keys . _rscPermissions . fst . snd) $ Map.toList allRemoteSchemas
      nonTableRoles =
        Set.insert adminRoleName $
          Set.fromList (allActionInfos ^.. folded . aiPermissions . to Map.keys . folded)
            <> Set.fromList (bool mempty remoteSchemasRoles $ _sccRemoteSchemaPermsCtx == Options.EnableRemoteSchemaPermissions)
      allActionInfos = Map.elems allActions
      allTableRoles = Set.fromList $ getTableRoles =<< Map.elems sources
      allRoles = nonTableRoles <> allTableRoles

  contexts <-
    -- Buld role contexts in parallel. We'd prefer deterministic parallelism
    -- but that isn't really acheivable (see mono #3829). NOTE: the admin role
    -- will still be a bottleneck here, even on huge_schema which has many
    -- roles.
    fmap Map.fromList $
      forConcurrentlyEIO 10 (Set.toList allRoles) $ \role -> do
        (role,)
          <$> concurrentlyEIO
            ( buildRoleContext
                (_sccSQLGenCtx, _sccFunctionPermsCtx)
                sources
                allRemoteSchemas
                allActionInfos
                customTypes
                role
                _sccRemoteSchemaPermsCtx
                _sccExperimentalFeatures
            )
            ( buildRelayRoleContext
                (_sccSQLGenCtx, _sccFunctionPermsCtx)
                sources
                allActionInfos
                customTypes
                role
                _sccExperimentalFeatures
            )
  let hasuraContexts = fst <$> contexts
      relayContexts = snd <$> contexts

  adminIntrospection <-
    case Map.lookup adminRoleName hasuraContexts of
      Just (_context, _errors, introspection) -> pure introspection
      Nothing -> throw500 "buildGQLContext failed to build for the admin role"
  (unauthenticated, unauthenticatedRemotesErrors) <- unauthenticatedContext allRemoteSchemas _sccRemoteSchemaPermsCtx
  pure
    ( ( adminIntrospection,
        view _1 <$> hasuraContexts,
        unauthenticated,
        Set.unions $ unauthenticatedRemotesErrors : (view _2 <$> Map.elems hasuraContexts)
      ),
      ( relayContexts,
        -- Currently, remote schemas are exposed through Relay, but ONLY through
        -- the unauthenticated role.  This is probably an oversight.  See
        -- hasura/graphql-engine-mono#3883.
        unauthenticated
      )
    )

buildSchemaOptions ::
  (SQLGenCtx, Options.InferFunctionPermissions) ->
  HashSet ExperimentalFeature ->
  SchemaOptions
buildSchemaOptions
  ( SQLGenCtx stringifyNum dangerousBooleanCollapse optimizePermissionFilters bigqueryStringNumericInput,
    functionPermsCtx
    )
  expFeatures =
    SchemaOptions
      { soStringifyNumbers = stringifyNum,
        soDangerousBooleanCollapse = dangerousBooleanCollapse,
        soInferFunctionPermissions = functionPermsCtx,
        soOptimizePermissionFilters = optimizePermissionFilters,
        soIncludeUpdateManyFields =
          if EFHideUpdateManyFields `Set.member` expFeatures
            then Options.Don'tIncludeUpdateManyFields
            else Options.IncludeUpdateManyFields,
        soIncludeAggregationPredicates =
          if EFHideAggregationPredicates `Set.member` expFeatures
            then Options.Don'tIncludeAggregationPredicates
            else Options.IncludeAggregationPredicates,
        soIncludeStreamFields =
          if EFHideStreamFields `Set.member` expFeatures
            then Options.Don'tIncludeStreamFields
            else Options.IncludeStreamFields,
        soBigQueryStringNumericInput = bigqueryStringNumericInput
      }

-- | Build the @QueryHasura@ context for a given role.
buildRoleContext ::
  forall m.
  (MonadError QErr m, MonadIO m) =>
  (SQLGenCtx, Options.InferFunctionPermissions) ->
  SourceCache ->
  HashMap RemoteSchemaName (RemoteSchemaCtx, MetadataObject) ->
  [ActionInfo] ->
  AnnotatedCustomTypes ->
  RoleName ->
  Options.RemoteSchemaPermissions ->
  Set.HashSet ExperimentalFeature ->
  m
    ( RoleContext GQLContext,
      HashSet InconsistentMetadata,
      G.SchemaIntrospection
    )
buildRoleContext options sources remotes actions customTypes role remoteSchemaPermsCtx expFeatures = do
  let schemaOptions = buildSchemaOptions options expFeatures
      schemaContext =
        SchemaContext
          HasuraSchema
          ( remoteRelationshipField
              schemaContext
              schemaOptions
              sources
              (fst <$> remotes)
              remoteSchemaPermsCtx
          )
          role
  runMemoizeT $ do
    -- build all sources (`apolloFedTableParsers` contains all the parsers and
    -- type names, which are eligible for the `_Entity` Union)
    (sourcesQueryFields, sourcesMutationFrontendFields, sourcesMutationBackendFields, sourcesSubscriptionFields, apolloFedTableParsers) <-
      runSourceSchema schemaContext schemaOptions $
        fmap mconcat $ for (toList sources) \sourceInfo ->
          AB.dispatchAnyBackend @BackendSchema sourceInfo buildSource

    -- build all remote schemas
    -- we only keep the ones that don't result in a name conflict
    (remoteSchemaFields, !remoteSchemaErrors) <-
      runRemoteSchema schemaContext $
        buildAndValidateRemoteSchemas remotes sourcesQueryFields sourcesMutationBackendFields role remoteSchemaPermsCtx
    let remotesQueryFields = concatMap piQuery remoteSchemaFields
        remotesMutationFields = concat $ mapMaybe piMutation remoteSchemaFields
        remotesSubscriptionFields = concat $ mapMaybe piSubscription remoteSchemaFields
        apolloQueryFields = apolloRootFields expFeatures apolloFedTableParsers

    -- build all actions
    -- we use the source context due to how async query relationships are implemented
    (actionsQueryFields, actionsMutationFields, actionsSubscriptionFields) <-
      runSourceSchema schemaContext schemaOptions $
        fmap mconcat $ for actions \action -> do
          queryFields <- buildActionQueryFields customTypes action
          mutationFields <- buildActionMutationFields customTypes action
          subscriptionFields <- buildActionSubscriptionFields customTypes action
          pure (queryFields, mutationFields, subscriptionFields)

    mutationParserFrontend <-
      buildMutationParser sourcesMutationFrontendFields remotesMutationFields actionsMutationFields
    mutationParserBackend <-
      buildMutationParser sourcesMutationBackendFields remotesMutationFields actionsMutationFields
    subscriptionParser <-
      buildSubscriptionParser sourcesSubscriptionFields remotesSubscriptionFields actionsSubscriptionFields
    queryParserFrontend <-
      buildQueryParser sourcesQueryFields apolloQueryFields remotesQueryFields actionsQueryFields mutationParserFrontend subscriptionParser
    queryParserBackend <-
      buildQueryParser sourcesQueryFields apolloQueryFields remotesQueryFields actionsQueryFields mutationParserBackend subscriptionParser

    -- In order to catch errors early, we attempt to generate the data
    -- required for introspection, which ends up doing a few correctness
    -- checks in the GraphQL schema. Furthermore, we want to persist this
    -- information in the case of the admin role.
    !introspectionSchema <- do
      result <-
        throwOnConflictingDefinitions $
          convertToSchemaIntrospection
            <$> buildIntrospectionSchema
              (P.parserType queryParserBackend)
              (P.parserType <$> mutationParserBackend)
              (P.parserType <$> subscriptionParser)
      pure $
        -- We don't need to persist the introspection schema for all the roles here.
        -- TODO(nicuveo): we treat the admin role differently in this function,
        -- which is a bit inelegant; we might want to refactor this function and
        -- split it into several steps, so that we can make a separate function for
        -- the admin role that reuses the common parts and avoid such tests.
        if role == adminRoleName
          then result
          else G.SchemaIntrospection mempty

    void . throwOnConflictingDefinitions $
      buildIntrospectionSchema
        (P.parserType queryParserFrontend)
        (P.parserType <$> mutationParserFrontend)
        (P.parserType <$> subscriptionParser)

    -- (since we're running this in parallel in caller, be strict)
    let !frontendContext =
          GQLContext
            (finalizeParser queryParserFrontend)
            (finalizeParser <$> mutationParserFrontend)
            (finalizeParser <$> subscriptionParser)
        !backendContext =
          GQLContext
            (finalizeParser queryParserBackend)
            (finalizeParser <$> mutationParserBackend)
            (finalizeParser <$> subscriptionParser)

    pure
      ( RoleContext frontendContext $ Just backendContext,
        remoteSchemaErrors,
        introspectionSchema
      )
  where
    buildSource ::
      forall b.
      BackendSchema b =>
      SourceInfo b ->
      SchemaT
        ( SchemaContext,
          SchemaOptions,
          MkTypename,
          NamingCase
        )
        (MemoizeT m)
        ( [FieldParser P.Parse (NamespacedField (QueryRootField UnpreparedValue))],
          [FieldParser P.Parse (NamespacedField (MutationRootField UnpreparedValue))],
          [FieldParser P.Parse (NamespacedField (MutationRootField UnpreparedValue))],
          [FieldParser P.Parse (NamespacedField (QueryRootField UnpreparedValue))],
          [(G.Name, Parser 'Output P.Parse (ApolloFederationParserFunction P.Parse))]
        )
    buildSource sourceInfo@(SourceInfo _ tables functions _ _ sourceCustomization) =
      withSourceCustomization sourceCustomization do
        let validFunctions = takeValidFunctions functions
            validTables = takeValidTables tables
            mkRootFieldName = _rscRootFields sourceCustomization
        makeTypename <- asks getter
        (uncustomizedQueryRootFields, uncustomizedSubscriptionRootFields, apolloFedTableParsers) <-
          buildQueryAndSubscriptionFields mkRootFieldName sourceInfo validTables validFunctions
        (,,,,apolloFedTableParsers)
          <$> customizeFields
            sourceCustomization
            (makeTypename <> MkTypename (<> Name.__query))
            (pure uncustomizedQueryRootFields)
          <*> customizeFields
            sourceCustomization
            (makeTypename <> MkTypename (<> Name.__mutation_frontend))
            (buildMutationFields mkRootFieldName Frontend sourceInfo validTables validFunctions)
          <*> customizeFields
            sourceCustomization
            (makeTypename <> MkTypename (<> Name.__mutation_backend))
            (buildMutationFields mkRootFieldName Backend sourceInfo validTables validFunctions)
          <*> customizeFields
            sourceCustomization
            (makeTypename <> MkTypename (<> Name.__subscription))
            (pure uncustomizedSubscriptionRootFields)

buildRelayRoleContext ::
  forall m.
  (MonadError QErr m, MonadIO m) =>
  (SQLGenCtx, Options.InferFunctionPermissions) ->
  SourceCache ->
  [ActionInfo] ->
  AnnotatedCustomTypes ->
  RoleName ->
  Set.HashSet ExperimentalFeature ->
  m (RoleContext GQLContext)
buildRelayRoleContext options sources actions customTypes role expFeatures = do
  let schemaOptions = buildSchemaOptions options expFeatures
      -- 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 `RemoteSchemaMap`.
      schemaContext =
        SchemaContext
          (RelaySchema $ nodeInterface sources)
          ( remoteRelationshipField
              schemaContext
              schemaOptions
              sources
              mempty
              Options.DisableRemoteSchemaPermissions
          )
          role
  runMemoizeT do
    -- build all sources, and the node root
    (node, fieldsList) <-
      runSourceSchema schemaContext schemaOptions do
        node <- fmap NotNamespaced <$> nodeField sources
        fieldsList <-
          for (toList sources) \sourceInfo ->
            AB.dispatchAnyBackend @BackendSchema sourceInfo buildSource
        pure (node, fieldsList)

    let (queryFields, mutationFrontendFields, mutationBackendFields, subscriptionFields) = mconcat fieldsList
        allQueryFields = node : queryFields
        allSubscriptionFields = node : subscriptionFields

    -- build all actions
    -- we only build mutations in the relay schema
    actionsMutationFields <-
      runSourceSchema schemaContext schemaOptions $
        fmap concat $
          traverse (buildActionMutationFields customTypes) actions

    -- 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 mutationFrontendFields mempty actionsMutationFields
    mutationParserBackend <-
      buildMutationParser mutationBackendFields mempty actionsMutationFields
    subscriptionParser <-
      buildSubscriptionParser allSubscriptionFields [] []
    queryParserFrontend <-
      queryWithIntrospectionHelper allQueryFields mutationParserFrontend subscriptionParser
    queryParserBackend <-
      queryWithIntrospectionHelper allQueryFields mutationParserBackend subscriptionParser

    -- In order to catch errors early, we attempt to generate the data
    -- required for introspection, which ends up doing a few correctness
    -- checks in the GraphQL schema.
    void . throwOnConflictingDefinitions $
      buildIntrospectionSchema
        (P.parserType queryParserBackend)
        (P.parserType <$> mutationParserBackend)
        (P.parserType <$> subscriptionParser)
    void . throwOnConflictingDefinitions $
      buildIntrospectionSchema
        (P.parserType queryParserFrontend)
        (P.parserType <$> mutationParserFrontend)
        (P.parserType <$> subscriptionParser)

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

    pure $ RoleContext frontendContext $ Just backendContext
  where
    buildSource ::
      forall b.
      BackendSchema b =>
      SourceInfo b ->
      SchemaT
        ( SchemaContext,
          SchemaOptions,
          MkTypename,
          NamingCase
        )
        (MemoizeT m)
        ( [FieldParser P.Parse (NamespacedField (QueryRootField UnpreparedValue))],
          [FieldParser P.Parse (NamespacedField (MutationRootField UnpreparedValue))],
          [FieldParser P.Parse (NamespacedField (MutationRootField UnpreparedValue))],
          [FieldParser P.Parse (NamespacedField (QueryRootField UnpreparedValue))]
        )
    buildSource sourceInfo@(SourceInfo _ tables functions _ _ sourceCustomization) = do
      withSourceCustomization sourceCustomization do
        let validFunctions = takeValidFunctions functions
            validTables = takeValidTables tables
            mkRootFieldName = _rscRootFields sourceCustomization
        (uncustomizedQueryRootFields, uncustomizedSubscriptionRootFields) <-
          buildRelayQueryAndSubscriptionFields mkRootFieldName sourceInfo validTables validFunctions
        makeTypename <- asks getter
        (,,,)
          <$> customizeFields
            sourceCustomization
            (makeTypename <> MkTypename (<> Name.__query))
            (pure uncustomizedQueryRootFields)
          <*> customizeFields
            sourceCustomization
            (makeTypename <> MkTypename (<> Name.__mutation_frontend))
            (buildMutationFields mkRootFieldName Frontend sourceInfo validTables validFunctions)
          <*> customizeFields
            sourceCustomization
            (makeTypename <> MkTypename (<> Name.__mutation_backend))
            (buildMutationFields mkRootFieldName Backend sourceInfo validTables validFunctions)
          <*> customizeFields
            sourceCustomization
            (makeTypename <> MkTypename (<> Name.__subscription))
            (pure uncustomizedSubscriptionRootFields)

-- | Builds the schema context for unauthenticated users.
--
-- This context is used whenever the user queries the engine with a role that is
-- unknown, and therefore not present in the context map. Before remote schema
-- permissions were introduced, remotes were considered to be a public entity,
-- and we therefore allowed an unknown role also to query the remotes. To
-- maintain backwards compatibility, we check if remote schema permissions are
-- enabled; remote schemas will only be available to unauthenticated users if
-- permissions aren't enabled.
unauthenticatedContext ::
  forall m.
  ( MonadError QErr m,
    MonadIO m
  ) =>
  HashMap RemoteSchemaName (RemoteSchemaCtx, MetadataObject) ->
  Options.RemoteSchemaPermissions ->
  m (GQLContext, HashSet InconsistentMetadata)
unauthenticatedContext allRemotes remoteSchemaPermsCtx = do
  let fakeSchemaContext =
        SchemaContext
          HasuraSchema
          ignoreRemoteRelationship
          fakeRole
      -- chosen arbitrarily to be as improbable as possible
      fakeRole = mkRoleNameSafe [NT.nonEmptyTextQQ|MyNameIsOzymandiasKingOfKingsLookOnMyWorksYeMightyAndDespair|]
      -- we delete all references to remote joins
      alteredRemoteSchemas =
        allRemotes <&> first \context ->
          context {_rscRemoteRelationships = mempty}

  runMemoizeT do
    (queryFields, mutationFields, subscriptionFields, remoteErrors) <- case remoteSchemaPermsCtx of
      Options.EnableRemoteSchemaPermissions ->
        -- Permissions are enabled, unauthenticated users have access to nothing.
        pure ([], [], [], mempty)
      Options.DisableRemoteSchemaPermissions -> do
        -- Permissions are disabled, unauthenticated users have access to remote schemas.
        (remoteFields, remoteSchemaErrors) <-
          runRemoteSchema fakeSchemaContext $
            buildAndValidateRemoteSchemas alteredRemoteSchemas [] [] fakeRole remoteSchemaPermsCtx
        pure
          ( fmap (fmap RFRemote) <$> concatMap piQuery remoteFields,
            fmap (fmap RFRemote) <$> concat (mapMaybe piMutation remoteFields),
            fmap (fmap RFRemote) <$> concat (mapMaybe piSubscription remoteFields),
            remoteSchemaErrors
          )
    mutationParser <-
      whenMaybe (not $ null mutationFields) $
        safeSelectionSet mutationRoot (Just $ G.Description "mutation root") mutationFields
          <&> fmap (flattenNamespaces . fmap typenameToNamespacedRawRF)
    subscriptionParser <-
      whenMaybe (not $ null subscriptionFields) $
        safeSelectionSet subscriptionRoot (Just $ G.Description "subscription root") subscriptionFields
          <&> fmap (flattenNamespaces . fmap typenameToNamespacedRawRF)
    queryParser <- queryWithIntrospectionHelper queryFields mutationParser Nothing
    void . throwOnConflictingDefinitions $
      buildIntrospectionSchema
        (P.parserType queryParser)
        (P.parserType <$> mutationParser)
        (P.parserType <$> subscriptionParser)
    pure (GQLContext (finalizeParser queryParser) (finalizeParser <$> mutationParser) (finalizeParser <$> subscriptionParser), remoteErrors)

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

buildAndValidateRemoteSchemas ::
  forall m.
  ( MonadError QErr m,
    MonadIO m
  ) =>
  HashMap RemoteSchemaName (RemoteSchemaCtx, MetadataObject) ->
  [FieldParser P.Parse (NamespacedField (QueryRootField UnpreparedValue))] ->
  [FieldParser P.Parse (NamespacedField (MutationRootField UnpreparedValue))] ->
  RoleName ->
  Options.RemoteSchemaPermissions ->
  SchemaT
    ( SchemaContext,
      MkTypename,
      CustomizeRemoteFieldName
    )
    (MemoizeT m)
    ([RemoteSchemaParser P.Parse], HashSet InconsistentMetadata)
buildAndValidateRemoteSchemas remotes sourcesQueryFields sourcesMutationFields role remoteSchemaPermsCtx =
  runWriterT $ foldlM step [] (Map.elems remotes)
  where
    getFieldName = P.getName . P.fDefinition

    sourcesQueryFieldNames = getFieldName <$> sourcesQueryFields
    sourcesMutationFieldNames = getFieldName <$> sourcesMutationFields

    step validatedSchemas (remoteSchemaContext, metadataId) = do
      let previousSchemasQueryFieldNames = map getFieldName $ concatMap piQuery validatedSchemas
          previousSchemasMutationFieldNames = map getFieldName $ concat $ mapMaybe piMutation validatedSchemas
          reportInconsistency reason = tell $ Set.singleton $ InconsistentObject reason Nothing metadataId
      maybeParser <- lift $ buildRemoteSchemaParser remoteSchemaPermsCtx role remoteSchemaContext
      case maybeParser of
        Nothing -> pure validatedSchemas
        Just remoteSchemaParser -> do
          (_, inconsistencies) <- listen $ do
            let newSchemaQueryFieldNames = map getFieldName $ piQuery remoteSchemaParser
                newSchemaMutationFieldNames = foldMap (map getFieldName) $ piMutation remoteSchemaParser
            -- First we check for conflicts in query_root:
            --   - between this remote and the previous ones:
            for_
              (duplicates $ newSchemaQueryFieldNames <> previousSchemasQueryFieldNames)
              \name -> reportInconsistency $ "Duplicate remote field " <> squote name
            --   - between this remote and the sources:
            for_ (duplicates $ newSchemaQueryFieldNames <> sourcesQueryFieldNames) $
              \name -> reportInconsistency $ "Field cannot be overwritten by remote field " <> squote name
            -- Ditto, but for mutations - i.e. with mutation_root:
            unless (null newSchemaMutationFieldNames) do
              --   - between this remote and the previous ones:
              for_ (duplicates $ newSchemaMutationFieldNames <> previousSchemasMutationFieldNames) $
                \name -> reportInconsistency $ "Duplicate remote field " <> squote name
              --   - between this remote and the sources:
              for_ (duplicates $ newSchemaMutationFieldNames <> sourcesMutationFieldNames) $
                \name -> reportInconsistency $ "Field cannot be overwritten by remote field " <> squote name
          -- No need to check for conflicts between subscription fields, since
          -- remote subscriptions aren't supported yet.

          -- Only add this new remote to the list if there was no error
          pure $
            if Set.null inconsistencies
              then remoteSchemaParser : validatedSchemas
              else validatedSchemas

buildRemoteSchemaParser ::
  forall m.
  (MonadError QErr m, MonadIO m) =>
  Options.RemoteSchemaPermissions ->
  RoleName ->
  RemoteSchemaCtx ->
  SchemaT
    ( SchemaContext,
      MkTypename,
      CustomizeRemoteFieldName
    )
    (MemoizeT m)
    (Maybe (RemoteSchemaParser P.Parse))
buildRemoteSchemaParser remoteSchemaPermsCtx roleName context = do
  let maybeIntrospection = getIntrospectionResult remoteSchemaPermsCtx roleName context
  for maybeIntrospection \introspection -> do
    RemoteSchemaParser {..} <- buildRemoteParser introspection (_rscRemoteRelationships context) (_rscInfo context)
    pure $ RemoteSchemaParser (setOrigin piQuery) (setOrigin <$> piMutation) (setOrigin <$> piSubscription)
  where
    setOrigin = fmap (P.setFieldParserOrigin (MORemoteSchema (_rscName context)))

-- | `buildQueryAndSubscriptionFields` builds the query and the subscription
--   fields of the tables tracked in the source. The query root fields and
--   the subscription root fields may not be equal because a root field may be
--   enabled in the `query_root_field` and not in the `subscription_root_field`,
--   so a tuple of array of field parsers corresponding to query field parsers and
--   subscription field parsers.
buildQueryAndSubscriptionFields ::
  forall b r m n.
  MonadBuildSchema b r m n =>
  MkRootFieldName ->
  SourceInfo b ->
  TableCache b ->
  FunctionCache b ->
  SchemaT r m ([P.FieldParser n (QueryRootField UnpreparedValue)], [P.FieldParser n (SubscriptionRootField UnpreparedValue)], [(G.Name, Parser 'Output n (ApolloFederationParserFunction n))])
buildQueryAndSubscriptionFields mkRootFieldName sourceInfo tables (takeExposedAs FEAQuery -> functions) = do
  roleName <- retrieve scRole
  functionPermsCtx <- retrieve Options.soInferFunctionPermissions
  functionSelectExpParsers <-
    concat . catMaybes
      <$> for (Map.toList functions) \(functionName, functionInfo) -> runMaybeT $ do
        guard $
          roleName == adminRoleName
            || roleName `Map.member` _fiPermissions functionInfo
            || functionPermsCtx == Options.InferFunctionPermissions
        let targetTableName = _fiReturnType functionInfo
        lift $ mkRFs $ buildFunctionQueryFields mkRootFieldName sourceInfo functionName functionInfo targetTableName

  (tableQueryFields, tableSubscriptionFields, apolloFedTableParsers) <-
    unzip3 . catMaybes
      <$> for (Map.toList tables) \(tableName, tableInfo) -> runMaybeT $ do
        tableIdentifierName <- getTableIdentifierName @b tableInfo
        lift $ buildTableQueryAndSubscriptionFields mkRootFieldName sourceInfo tableName tableInfo tableIdentifierName

  let tableQueryRootFields = fmap mkRF $ concat tableQueryFields
      tableSubscriptionRootFields = fmap mkRF $ concat tableSubscriptionFields

  pure
    ( tableQueryRootFields <> functionSelectExpParsers,
      tableSubscriptionRootFields <> functionSelectExpParsers,
      catMaybes apolloFedTableParsers
    )
  where
    mkRFs = mkRootFields sourceName sourceConfig queryTagsConfig QDBR
    mkRF = mkRootField sourceName sourceConfig queryTagsConfig QDBR
    sourceName = _siName sourceInfo
    sourceConfig = _siConfiguration sourceInfo
    queryTagsConfig = _siQueryTagsConfig sourceInfo

buildRelayQueryAndSubscriptionFields ::
  forall b r m n.
  MonadBuildSchema b r m n =>
  MkRootFieldName ->
  SourceInfo b ->
  TableCache b ->
  FunctionCache b ->
  SchemaT r m ([P.FieldParser n (QueryRootField UnpreparedValue)], [P.FieldParser n (SubscriptionRootField UnpreparedValue)])
buildRelayQueryAndSubscriptionFields mkRootFieldName sourceInfo tables (takeExposedAs FEAQuery -> functions) = do
  roleName <- retrieve scRole
  (tableConnectionQueryFields, tableConnectionSubscriptionFields) <-
    unzip . catMaybes
      <$> for (Map.toList tables) \(tableName, tableInfo) -> runMaybeT do
        tableIdentifierName <- getTableIdentifierName @b tableInfo
        SelPermInfo {..} <- hoistMaybe $ tableSelectPermissions roleName tableInfo
        pkeyColumns <- hoistMaybe $ tableInfo ^? tiCoreInfo . tciPrimaryKey . _Just . pkColumns
        relayRootFields <- lift $ mkRFs $ buildTableRelayQueryFields mkRootFieldName sourceInfo tableName tableInfo tableIdentifierName pkeyColumns
        let includeRelayWhen True = Just relayRootFields
            includeRelayWhen False = Nothing
        pure
          ( includeRelayWhen (isRootFieldAllowed QRFTSelect spiAllowedQueryRootFields),
            includeRelayWhen (isRootFieldAllowed SRFTSelect spiAllowedSubscriptionRootFields)
          )

  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 sourceInfo returnTableName
    pkeyColumns <- MaybeT $ (^? tiCoreInfo . tciPrimaryKey . _Just . pkColumns) <$> pure returnTableInfo
    lift $ mkRFs $ buildFunctionRelayQueryFields mkRootFieldName sourceInfo functionName functionInfo returnTableName pkeyColumns
  pure $
    ( concat $ catMaybes $ tableConnectionQueryFields <> functionConnectionFields,
      concat $ catMaybes $ tableConnectionSubscriptionFields <> functionConnectionFields
    )
  where
    mkRFs = mkRootFields sourceName sourceConfig queryTagsConfig QDBR
    sourceName = _siName sourceInfo
    sourceConfig = _siConfiguration sourceInfo
    queryTagsConfig = _siQueryTagsConfig sourceInfo

buildMutationFields ::
  forall b r m n.
  MonadBuildSchema b r m n =>
  MkRootFieldName ->
  Scenario ->
  SourceInfo b ->
  TableCache b ->
  FunctionCache b ->
  SchemaT r m [P.FieldParser n (MutationRootField UnpreparedValue)]
buildMutationFields mkRootFieldName scenario sourceInfo tables (takeExposedAs FEAMutation -> functions) = do
  roleName <- retrieve scRole
  tableMutations <- for (Map.toList tables) \(tableName, tableInfo) -> do
    tableIdentifierName <- getTableIdentifierName @b tableInfo
    inserts <-
      mkRFs (MDBR . MDBInsert) $ buildTableInsertMutationFields mkRootFieldName scenario sourceInfo tableName tableInfo tableIdentifierName
    updates <-
      mkRFs (MDBR . MDBUpdate) $ buildTableUpdateMutationFields mkRootFieldName scenario sourceInfo tableName tableInfo tableIdentifierName
    deletes <-
      mkRFs (MDBR . MDBDelete) $ buildTableDeleteMutationFields mkRootFieldName scenario sourceInfo tableName tableInfo tableIdentifierName
    pure $ concat [inserts, updates, deletes]
  functionMutations <- for (Map.toList functions) \(functionName, functionInfo) -> runMaybeT $ do
    let targetTableName = _fiReturnType functionInfo
    -- 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 `Map.member` _fiPermissions functionInfo
    lift $ mkRFs MDBR $ buildFunctionMutationFields mkRootFieldName sourceInfo functionName functionInfo targetTableName
  pure $ concat $ tableMutations <> catMaybes functionMutations
  where
    mkRFs :: forall a db remote action raw. (a -> db b) -> SchemaT r m [FieldParser n a] -> SchemaT r m [FieldParser n (RootField db remote action raw)]
    mkRFs = mkRootFields sourceName sourceConfig queryTagsConfig
    sourceName = _siName sourceInfo
    sourceConfig = _siConfiguration sourceInfo
    queryTagsConfig = _siQueryTagsConfig sourceInfo

----------------------------------------------------------------
-- 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 n m.
  (MonadMemoize m, MonadError QErr m, MonadParse n) =>
  [P.FieldParser n (NamespacedField (QueryRootField UnpreparedValue))] ->
  [P.FieldParser n (G.SchemaIntrospection -> QueryRootField UnpreparedValue)] ->
  [P.FieldParser n (NamespacedField (RemoteSchemaRootField (RemoteRelationshipField UnpreparedValue) RemoteSchemaVariable))] ->
  [P.FieldParser n (QueryRootField UnpreparedValue)] ->
  Maybe (Parser 'Output n (RootFieldMap (MutationRootField UnpreparedValue))) ->
  Maybe (Parser 'Output n (RootFieldMap (QueryRootField UnpreparedValue))) ->
  m (Parser 'Output n (RootFieldMap (QueryRootField UnpreparedValue)))
buildQueryParser sourceQueryFields apolloFederationFields remoteQueryFields actionQueryFields mutationParser subscriptionParser = do
  -- This method is aware of our rudimentary support for Apollo federation.
  -- Apollo federation adds two fields, `_service` and `_entities`. The
  -- `_service` field parser is a selection set that contains an `sdl` field.
  -- The `sdl` field, exposes a _serialized_ introspection of the schema. So in
  -- that sense it is similar to the `__type` and `__schema` introspection
  -- fields. However, a few things must be excluded from this introspection
  -- data, notably the Apollo federation fields `_service` and `_entities`
  -- themselves. So in this method we build a version of the introspection for
  -- Apollo federation purposes.
  let partialApolloQueryFP = sourceQueryFields <> fmap (fmap NotNamespaced) actionQueryFields <> fmap (fmap $ fmap RFRemote) remoteQueryFields
  basicQueryPForApollo <- queryRootFromFields partialApolloQueryFP
  let buildApolloIntrospection buildQRF = do
        partialSchema <-
          parseBuildIntrospectionSchema
            (P.parserType basicQueryPForApollo)
            (P.parserType <$> mutationParser)
            (P.parserType <$> subscriptionParser)
        pure $ NotNamespaced $ buildQRF $ convertToSchemaIntrospection partialSchema
      apolloFederationFieldsWithIntrospection :: [P.FieldParser n (NamespacedField (QueryRootField UnpreparedValue))]
      apolloFederationFieldsWithIntrospection = apolloFederationFields <&> (`P.bindField` buildApolloIntrospection)
      allQueryFields = partialApolloQueryFP <> apolloFederationFieldsWithIntrospection
  queryWithIntrospectionHelper allQueryFields mutationParser subscriptionParser

-- | Builds a @Schema@ at query parsing time
parseBuildIntrospectionSchema ::
  MonadParse m =>
  P.Type 'Output ->
  Maybe (P.Type 'Output) ->
  Maybe (P.Type 'Output) ->
  m Schema
parseBuildIntrospectionSchema q m s =
  buildIntrospectionSchema q m s `onLeft` (P.parseErrorWith P.ConflictingDefinitionsError . toErrorValue)

queryWithIntrospectionHelper ::
  forall n m.
  (MonadMemoize m, MonadParse n, MonadError QErr m) =>
  [P.FieldParser n (NamespacedField (QueryRootField UnpreparedValue))] ->
  Maybe (Parser 'Output n (RootFieldMap (MutationRootField UnpreparedValue))) ->
  Maybe (Parser 'Output n (RootFieldMap (QueryRootField UnpreparedValue))) ->
  m (Parser 'Output n (RootFieldMap (QueryRootField UnpreparedValue)))
queryWithIntrospectionHelper basicQueryFP mutationP subscriptionP = do
  let -- Per the GraphQL spec:
      --  * "The query root operation type must be provided and must be an Object type." (§3.2.1)
      --  * "An Object type must define one or more fields." (§3.6, type validation)
      -- Those two requirements cannot both be met when a service is mutations-only, and does not
      -- provide any query. In such a case, to meet both of those, we introduce a placeholder query
      -- in the schema.
      placeholderText = "There are no queries available to the current role. Either there are no sources or remote schemas configured, or the current role doesn't have the required permissions."
      placeholderField = NotNamespaced (RFRaw $ JO.String placeholderText) <$ P.selection_ Name._no_queries_available (Just $ G.Description placeholderText) P.string
      fixedQueryFP = if null basicQueryFP then [placeholderField] else basicQueryFP
  basicQueryP <- queryRootFromFields fixedQueryFP
  let buildIntrospectionResponse printResponseFromSchema =
        NotNamespaced . RFRaw . printResponseFromSchema
          <$> parseBuildIntrospectionSchema
            (P.parserType basicQueryP)
            (P.parserType <$> mutationP)
            (P.parserType <$> subscriptionP)
      introspection = [schema, typeIntrospection] <&> (`P.bindField` buildIntrospectionResponse)
      {-# INLINE introspection #-}
      partialQueryFields = fixedQueryFP ++ introspection
  safeSelectionSet queryRoot Nothing partialQueryFields <&> fmap (flattenNamespaces . fmap typenameToNamespacedRawRF)

queryRootFromFields ::
  forall n m.
  (MonadError QErr m, MonadParse n) =>
  [P.FieldParser n (NamespacedField (QueryRootField UnpreparedValue))] ->
  m (Parser 'Output n (RootFieldMap (QueryRootField UnpreparedValue)))
queryRootFromFields fps =
  safeSelectionSet queryRoot Nothing fps <&> fmap (flattenNamespaces . fmap typenameToNamespacedRawRF)

buildMutationParser ::
  forall n m.
  (MonadMemoize m, MonadError QErr m, MonadParse n) =>
  [P.FieldParser n (NamespacedField (MutationRootField UnpreparedValue))] ->
  [P.FieldParser n (NamespacedField (RemoteSchemaRootField (RemoteRelationshipField UnpreparedValue) RemoteSchemaVariable))] ->
  [P.FieldParser n (MutationRootField UnpreparedValue)] ->
  m (Maybe (Parser 'Output n (RootFieldMap (MutationRootField UnpreparedValue))))
buildMutationParser mutationFields remoteFields actionFields = do
  let mutationFieldsParser =
        mutationFields
          <> (fmap (fmap RFRemote) <$> remoteFields)
          <> (fmap NotNamespaced <$> actionFields)
  whenMaybe (not $ null mutationFieldsParser) $
    safeSelectionSet mutationRoot (Just $ G.Description "mutation root") mutationFieldsParser
      <&> fmap (flattenNamespaces . fmap typenameToNamespacedRawRF)

-- | 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 n m.
  (MonadMemoize m, MonadError QErr m, MonadParse n) =>
  [P.FieldParser n (NamespacedField (QueryRootField UnpreparedValue))] ->
  [P.FieldParser n (NamespacedField (RemoteSchemaRootField (RemoteRelationshipField UnpreparedValue) RemoteSchemaVariable))] ->
  [P.FieldParser n (QueryRootField UnpreparedValue)] ->
  m (Maybe (Parser 'Output n (RootFieldMap (QueryRootField UnpreparedValue))))
buildSubscriptionParser sourceSubscriptionFields remoteSubscriptionFields actionFields = do
  let subscriptionFields =
        sourceSubscriptionFields
          <> fmap (fmap $ fmap RFRemote) remoteSubscriptionFields
          <> (fmap NotNamespaced <$> actionFields)
  whenMaybe (not $ null subscriptionFields) $
    safeSelectionSet subscriptionRoot Nothing subscriptionFields
      <&> fmap (flattenNamespaces . fmap typenameToNamespacedRawRF)

-------------------------------------------------------------------------------
-- Local helpers

-- | Calls 'P.safeSelectionSet', and rethrows any error as a 'QErr'.
safeSelectionSet ::
  forall n m a.
  (QErrM n, MonadParse m) =>
  G.Name ->
  Maybe G.Description ->
  [FieldParser m a] ->
  n (Parser 'Output m (OMap.InsOrdHashMap G.Name (P.ParsedSelection a)))
safeSelectionSet name description fields =
  P.safeSelectionSet name description fields `onLeft` (throw500 . fromErrorMessage)

-- | Apply a source's customization options to a list of its fields.
customizeFields ::
  forall f n db remote action.
  (Functor f, MonadParse n) =>
  ResolvedSourceCustomization ->
  MkTypename ->
  f [FieldParser n (RootField db remote action JO.Value)] ->
  f [FieldParser n (NamespacedField (RootField db remote action JO.Value))]
customizeFields ResolvedSourceCustomization {..} =
  fmap . customizeNamespace _rscRootNamespace (const typenameToRawRF)

-- | All the 'BackendSchema' methods produce something of the form @m
-- [FieldParser n a]@, where @a@ is something specific to what is being parsed
-- by the given method.
--
-- In order to build the complete schema these must be
-- homogenised and be annotated with query-tag data, which this function makes
-- easy.
-- This function converts a single field parser. @mkRootFields@ transforms a
-- list of field parsers.
mkRootField ::
  forall b n a db remote action raw.
  (HasTag b, Functor n) =>
  SourceName ->
  SourceConfig b ->
  Maybe QueryTagsConfig ->
  (a -> db b) ->
  FieldParser n a ->
  FieldParser n (RootField db remote action raw)
mkRootField sourceName sourceConfig queryTagsConfig inj =
  fmap
    ( RFDB sourceName
        . AB.mkAnyBackend @b
        . SourceConfigWith sourceConfig queryTagsConfig
        . inj
    )

-- | `mkRootFields` is `mkRootField` applied on a list of `FieldParser`.
mkRootFields ::
  forall b m n a db remote action raw.
  (HasTag b, Functor m, Functor n) =>
  SourceName ->
  SourceConfig b ->
  Maybe QueryTagsConfig ->
  (a -> db b) ->
  m [FieldParser n a] ->
  m [FieldParser n (RootField db remote action raw)]
mkRootFields sourceName sourceConfig queryTagsConfig inj =
  fmap
    ( map
        (mkRootField sourceName sourceConfig queryTagsConfig inj)
    )

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

subscriptionRoot :: G.Name
subscriptionRoot = Name._subscription_root

mutationRoot :: G.Name
mutationRoot = Name._mutation_root

queryRoot :: G.Name
queryRoot = Name._query_root

finalizeParser :: Parser 'Output P.Parse a -> ParserFn a
finalizeParser parser = P.toQErr . P.runParse . P.runParser parser

throwOnConflictingDefinitions :: QErrM m => Either P.ConflictingDefinitions a -> m a
throwOnConflictingDefinitions = either (throw500 . fromErrorMessage . toErrorValue) pure

typenameToNamespacedRawRF ::
  P.ParsedSelection (NamespacedField (RootField db remote action JO.Value)) ->
  NamespacedField (RootField db remote action JO.Value)
typenameToNamespacedRawRF = P.handleTypename $ NotNamespaced . RFRaw . JO.String . toTxt

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