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|
{-# LANGUAGE OverloadedStrings #-}
-- | This module provides a representation of a @GraphQL@ Schema in addition to
-- functions for defining and manipulating schemas.
module Language.GraphQL.Schema
( Resolver
, Subs
, object
, objectA
, scalar
, scalarA
, resolve
, wrappedObject
, wrappedObjectA
, wrappedScalar
, wrappedScalarA
-- * AST Reexports
, Field
, Argument(..)
, Value(..)
) where
import Control.Monad.IO.Class (MonadIO(..))
import Control.Monad.Trans.Class (lift)
import Control.Monad.Trans.Except (runExceptT)
import Data.Foldable (find, fold)
import Data.Maybe (fromMaybe)
import qualified Data.Aeson as Aeson
import Data.HashMap.Strict (HashMap)
import qualified Data.HashMap.Strict as HashMap
import Data.Text (Text)
import qualified Data.Text as T
import Language.GraphQL.Error
import Language.GraphQL.Trans
import Language.GraphQL.Type
import Language.GraphQL.AST.Core
-- | Resolves a 'Field' into an @Aeson.@'Data.Aeson.Types.Object' with error
-- information (if an error has occurred). @m@ is usually expected to be an
-- instance of 'MonadIO'.
data Resolver m = Resolver
Text -- ^ Name
(Field -> CollectErrsT m Aeson.Object) -- ^ Resolver
-- | Variable substitution function.
type Subs = Name -> Maybe Value
-- | Create a new 'Resolver' with the given 'Name' from the given 'Resolver's.
object :: MonadIO m => Name -> ActionT m [Resolver m] -> Resolver m
object name = objectA name . const
-- | Like 'object' but also taking 'Argument's.
objectA :: MonadIO m
=> Name -> ([Argument] -> ActionT m [Resolver m]) -> Resolver m
objectA name f = Resolver name $ resolveFieldValue f resolveRight
where
resolveRight fld@(Field _ _ _ flds) resolver = withField (resolve resolver flds) fld
-- | Like 'object' but also taking 'Argument's and can be null or a list of objects.
wrappedObjectA :: MonadIO m
=> Name -> ([Argument] -> ActionT m (Wrapping [Resolver m])) -> Resolver m
wrappedObjectA name f = Resolver name $ resolveFieldValue f resolveRight
where
resolveRight fld@(Field _ _ _ sels) resolver
= withField (traverse (`resolve` sels) resolver) fld
-- | Like 'object' but can be null or a list of objects.
wrappedObject :: MonadIO m
=> Name -> ActionT m (Wrapping [Resolver m]) -> Resolver m
wrappedObject name = wrappedObjectA name . const
-- | A scalar represents a primitive value, like a string or an integer.
scalar :: (MonadIO m, Aeson.ToJSON a) => Name -> ActionT m a -> Resolver m
scalar name = scalarA name . const
-- | Like 'scalar' but also taking 'Argument's.
scalarA :: (MonadIO m, Aeson.ToJSON a)
=> Name -> ([Argument] -> ActionT m a) -> Resolver m
scalarA name f = Resolver name $ resolveFieldValue f resolveRight
where
resolveRight fld result = withField (return result) fld
-- | Lika 'scalar' but also taking 'Argument's and can be null or a list of scalars.
wrappedScalarA :: (MonadIO m, Aeson.ToJSON a)
=> Name -> ([Argument] -> ActionT m (Wrapping a)) -> Resolver m
wrappedScalarA name f = Resolver name $ resolveFieldValue f resolveRight
where
resolveRight fld (Named result) = withField (return result) fld
resolveRight fld Null
= return $ HashMap.singleton (aliasOrName fld) Aeson.Null
resolveRight fld (List result) = withField (return result) fld
-- | Like 'scalar' but can be null or a list of scalars.
wrappedScalar :: (MonadIO m, Aeson.ToJSON a)
=> Name -> ActionT m (Wrapping a) -> Resolver m
wrappedScalar name = wrappedScalarA name . const
resolveFieldValue :: MonadIO m
=> ([Argument] -> ActionT m a)
-> (Field -> a -> CollectErrsT m (HashMap Text Aeson.Value))
-> Field
-> CollectErrsT m (HashMap Text Aeson.Value)
resolveFieldValue f resolveRight fld@(Field _ _ args _) = do
result <- lift $ runExceptT . runActionT $ f args
either resolveLeft (resolveRight fld) result
where
resolveLeft err = do
_ <- addErrMsg err
return $ HashMap.singleton (aliasOrName fld) Aeson.Null
-- | Helper function to facilitate 'Argument' handling.
withField :: (MonadIO m, Aeson.ToJSON a)
=> CollectErrsT m a -> Field -> CollectErrsT m (HashMap Text Aeson.Value)
withField v fld
= HashMap.singleton (aliasOrName fld) . Aeson.toJSON <$> runAppendErrs v
-- | Takes a list of 'Resolver's and a list of 'Field's and applies each
-- 'Resolver' to each 'Field'. Resolves into a value containing the
-- resolved 'Field', or a null value and error information.
resolve :: MonadIO m
=> [Resolver m] -> [Selection] -> CollectErrsT m Aeson.Value
resolve resolvers = fmap (Aeson.toJSON . fold) . traverse tryResolvers
where
resolveTypeName (Resolver "__typename" f) = do
value <- f $ Field Nothing "__typename" mempty mempty
return $ HashMap.lookupDefault "" "__typename" value
resolveTypeName _ = return ""
tryResolvers (SelectionField fld@(Field _ name _ _))
= maybe (errmsg fld) (tryResolver fld) $ find (compareResolvers name) resolvers
tryResolvers (SelectionFragment (Fragment typeCondition selections')) = do
that <- maybe (return "") resolveTypeName (find (compareResolvers "__typename") resolvers)
if Aeson.String typeCondition == that
then fmap fold . traverse tryResolvers $ selections'
else return mempty
compareResolvers name (Resolver name' _) = name == name'
tryResolver fld (Resolver _ resolver) = resolver fld
errmsg fld@(Field _ name _ _) = do
addErrMsg $ T.unwords ["field", name, "not resolved."]
return $ HashMap.singleton (aliasOrName fld) Aeson.Null
aliasOrName :: Field -> Text
aliasOrName (Field alias name _ _) = fromMaybe name alias
|
