139 lines
5.1 KiB
Haskell
139 lines
5.1 KiB
Haskell
{-# 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
|
|
, resolve
|
|
, resolversToMap
|
|
, scalar
|
|
, wrappedObject
|
|
, wrappedScalar
|
|
-- * AST Reexports
|
|
, Field
|
|
, Value(..)
|
|
) where
|
|
|
|
import Control.Monad.Trans.Class (lift)
|
|
import Control.Monad.Trans.Except (runExceptT)
|
|
import Control.Monad.Trans.Reader (runReaderT)
|
|
import Data.Foldable (fold, toList)
|
|
import Data.Maybe (fromMaybe)
|
|
import qualified Data.Aeson as Aeson
|
|
import Data.HashMap.Strict (HashMap)
|
|
import qualified Data.HashMap.Strict as HashMap
|
|
import Data.Sequence (Seq)
|
|
import Data.Text (Text)
|
|
import qualified Data.Text as T
|
|
import Language.GraphQL.AST.Core
|
|
import Language.GraphQL.Error
|
|
import Language.GraphQL.Trans
|
|
import qualified Language.GraphQL.Type as Type
|
|
|
|
-- | Resolves a 'Field' into an @Aeson.@'Data.Aeson.Types.Object' with error
|
|
-- information (if an error has occurred). @m@ is an arbitrary monad, usually
|
|
-- 'IO'.
|
|
data Resolver m = Resolver
|
|
Text -- ^ Name
|
|
(Field -> CollectErrsT m Aeson.Object) -- ^ Resolver
|
|
|
|
-- | Converts resolvers to a map.
|
|
resolversToMap
|
|
:: (Foldable f, Functor f)
|
|
=> f (Resolver m)
|
|
-> HashMap Text (Field -> CollectErrsT m Aeson.Object)
|
|
resolversToMap = HashMap.fromList . toList . fmap toKV
|
|
where
|
|
toKV (Resolver name f) = (name, f)
|
|
|
|
-- | Contains variables for the query. The key of the map is a variable name,
|
|
-- and the value is the variable value.
|
|
type Subs = HashMap Name Value
|
|
|
|
-- | Create a new 'Resolver' with the given 'Name' from the given 'Resolver's.
|
|
object :: Monad m => Name -> ActionT m [Resolver m] -> Resolver m
|
|
object name f = Resolver name $ resolveFieldValue f resolveRight
|
|
where
|
|
resolveRight fld@(Field _ _ _ flds) resolver
|
|
= withField (resolve (resolversToMap resolver) flds) fld
|
|
|
|
-- | Like 'object' but can be null or a list of objects.
|
|
wrappedObject ::
|
|
Monad m =>
|
|
Name ->
|
|
ActionT m (Type.Wrapping [Resolver m]) ->
|
|
Resolver m
|
|
wrappedObject name f = Resolver name $ resolveFieldValue f resolveRight
|
|
where
|
|
resolveRight fld@(Field _ _ _ sels) resolver
|
|
= withField (traverse (resolveMap sels) resolver) fld
|
|
resolveMap = flip (resolve . resolversToMap)
|
|
|
|
-- | A scalar represents a primitive value, like a string or an integer.
|
|
scalar :: (Monad m, Aeson.ToJSON a) => Name -> ActionT m a -> Resolver m
|
|
scalar name f = Resolver name $ resolveFieldValue f resolveRight
|
|
where
|
|
resolveRight fld result = withField (return result) fld
|
|
|
|
-- | Like 'scalar' but can be null or a list of scalars.
|
|
wrappedScalar ::
|
|
(Monad m, Aeson.ToJSON a) =>
|
|
Name ->
|
|
ActionT m (Type.Wrapping a) ->
|
|
Resolver m
|
|
wrappedScalar name f = Resolver name $ resolveFieldValue f resolveRight
|
|
where
|
|
resolveRight fld (Type.Named result) = withField (return result) fld
|
|
resolveRight fld Type.Null
|
|
= return $ HashMap.singleton (aliasOrName fld) Aeson.Null
|
|
resolveRight fld (Type.List result) = withField (return result) fld
|
|
|
|
resolveFieldValue ::
|
|
Monad m =>
|
|
ActionT m a ->
|
|
(Field -> a -> CollectErrsT m Aeson.Object) ->
|
|
Field ->
|
|
CollectErrsT m (HashMap Text Aeson.Value)
|
|
resolveFieldValue f resolveRight fld@(Field _ _ args _) = do
|
|
result <- lift $ reader . runExceptT . runActionT $ f
|
|
either resolveLeft (resolveRight fld) result
|
|
where
|
|
reader = flip runReaderT $ Context {arguments=args}
|
|
resolveLeft err = do
|
|
_ <- addErrMsg err
|
|
return $ HashMap.singleton (aliasOrName fld) Aeson.Null
|
|
|
|
-- | Helper function to facilitate error handling and result emitting.
|
|
withField :: (Monad 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 :: Monad m
|
|
=> HashMap Text (Field -> CollectErrsT m Aeson.Object)
|
|
-> Seq Selection
|
|
-> CollectErrsT m Aeson.Value
|
|
resolve resolvers = fmap (Aeson.toJSON . fold) . traverse tryResolvers
|
|
where
|
|
resolveTypeName f = do
|
|
value <- f $ Field Nothing "__typename" mempty mempty
|
|
return $ HashMap.lookupDefault "" "__typename" value
|
|
tryResolvers (SelectionField fld@(Field _ name _ _))
|
|
= fromMaybe (errmsg fld) $ HashMap.lookup name resolvers <*> Just fld
|
|
tryResolvers (SelectionFragment (Fragment typeCondition selections')) = do
|
|
that <- traverse resolveTypeName $ HashMap.lookup "__typename" resolvers
|
|
if maybe True (Aeson.String typeCondition ==) that
|
|
then fmap fold . traverse tryResolvers $ selections'
|
|
else return mempty
|
|
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
|