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|
{-# LANGUAGE OverloadedStrings #-}
-- | Types and functions used for input and result coercion.
module Language.GraphQL.Execute.Coerce
( VariableValue(..)
) where
import qualified Data.Aeson as Aeson
import qualified Data.HashMap.Strict as HashMap
import Data.Scientific (toBoundedInteger, toRealFloat)
import Language.GraphQL.AST.Core
import Language.GraphQL.Type.Definition
-- | Since variables are passed separately from the query, in an independent
-- format, they should be first coerced to the internal representation used by
-- this implementation.
class VariableValue a where
-- | Only a basic, format-specific, coercion must be done here. Type
-- correctness or nullability shouldn't be validated here, they will be
-- validated later. The type information is provided only as a hint.
--
-- For example @GraphQL@ prohibits the coercion from a 't:Float' to an
-- 't:Int', but @JSON@ doesn't have integers, so whole numbers should be
-- coerced to 't:Int` when receiving variables as a JSON object. The same
-- holds for 't:Enum'. There are formats that support enumerations, @JSON@
-- doesn't, so the type information is given and 'coerceVariableValue' can
-- check that an 't:Enum' is expected and treat the given value
-- appropriately. Even checking whether this value is a proper member of the
-- corresponding 't:Enum' type isn't required here, since this can be
-- checked independently.
--
-- Another example is an @ID@. @GraphQL@ explicitly allows to coerce
-- integers and strings to @ID@s, so if an @ID@ is received as an integer,
-- it can be left as is and will be coerced later.
--
-- If a value cannot be coerced without losing information, 'Nothing' should
-- be returned, the coercion will fail then and the query won't be executed.
coerceVariableValue
:: InputType -- ^ Expected type (variable type given in the query).
-> a -- ^ Variable value being coerced.
-> Maybe Value -- ^ Coerced value on success, 'Nothing' otherwise.
instance VariableValue Aeson.Value where
coerceVariableValue _ Aeson.Null = Just Null
coerceVariableValue (ScalarInputTypeDefinition scalarType) value
| (Aeson.String stringValue) <- value = Just $ String stringValue
| (Aeson.Bool booleanValue) <- value = Just $ Boolean booleanValue
| (Aeson.Number numberValue) <- value
, (ScalarType "Float" _) <- scalarType =
Just $ Float $ toRealFloat numberValue
| (Aeson.Number numberValue) <- value = -- ID or Int
Int <$> toBoundedInteger numberValue
coerceVariableValue (EnumInputTypeDefinition _) (Aeson.String stringValue) =
Just $ Enum stringValue
coerceVariableValue (ObjectInputTypeDefinition objectType) value
| (Aeson.Object objectValue) <- value = do
let (InputObjectType _ _ inputFields) = objectType
(newObjectValue, resultMap) <- foldWithKey objectValue inputFields
if HashMap.null newObjectValue
then Just $ Object resultMap
else Nothing
where
foldWithKey objectValue = HashMap.foldrWithKey matchFieldValues
$ Just (objectValue, HashMap.empty)
matchFieldValues _ _ Nothing = Nothing
matchFieldValues fieldName inputField (Just (objectValue, resultMap)) =
let (InputField _ fieldType _) = inputField
insert = flip (HashMap.insert fieldName) resultMap
newObjectValue = HashMap.delete fieldName objectValue
in case HashMap.lookup fieldName objectValue of
Just variableValue -> do
coerced <- coerceVariableValue fieldType variableValue
pure (newObjectValue, insert coerced)
Nothing -> Just (objectValue, resultMap)
coerceVariableValue (ListInputTypeDefinition listType) value
| (Aeson.Array arrayValue) <- value = List
<$> foldr foldVector (Just []) arrayValue
| otherwise = coerceVariableValue listType value
where
foldVector _ Nothing = Nothing
foldVector variableValue (Just list) = do
coerced <- coerceVariableValue listType variableValue
pure $ coerced : list
coerceVariableValue _ _ = Nothing
|
