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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
, Schema
, Subs
, object
, objectA
, scalar
, scalarA
, enum
, enumA
, resolve
, wrappedEnum
, wrappedEnumA
, 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.List.NonEmpty (NonEmpty)
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
{-# DEPRECATED Schema "Use NonEmpty (Resolver m) instead" #-}
-- | A GraphQL schema.
-- @m@ is usually expected to be an instance of 'MonadIO'.
type Schema m = NonEmpty (Resolver m)
-- | 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
{-# DEPRECATED enum "Use scalar instead" #-}
enum :: MonadIO m => Name -> ActionT m [Text] -> Resolver m
enum name = enumA name . const
{-# DEPRECATED enumA "Use scalarA instead" #-}
enumA :: MonadIO m => Name -> ([Argument] -> ActionT m [Text]) -> Resolver m
enumA name f = Resolver name $ resolveFieldValue f resolveRight
where
resolveRight fld resolver = withField (return resolver) fld
{-# DEPRECATED wrappedEnumA "Use wrappedScalarA instead" #-}
wrappedEnumA :: MonadIO m
=> Name -> ([Argument] -> ActionT m (Wrapping [Text])) -> Resolver m
wrappedEnumA name f = Resolver name $ resolveFieldValue f resolveRight
where
resolveRight fld (Named resolver) = withField (return resolver) fld
resolveRight fld Null
= return $ HashMap.singleton (aliasOrName fld) Aeson.Null
resolveRight fld (List resolver) = withField (return resolver) fld
{-# DEPRECATED wrappedEnum "Use wrappedScalar instead" #-}
wrappedEnum :: MonadIO m => Name -> ActionT m (Wrapping [Text]) -> Resolver m
wrappedEnum name = wrappedEnumA 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] -> [Field] -> CollectErrsT m Aeson.Value
resolve resolvers = fmap (Aeson.toJSON . fold) . traverse tryResolvers
where
tryResolvers fld = maybe (errmsg fld) (tryResolver fld) $ find (compareResolvers fld) resolvers
compareResolvers (Field _ 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
|
