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