Add instances for UTCTime

src/Language/GraphQL/Class.hs

@@ -20,6 +20,17 @@ import Data.Vector (Vector)
 import qualified Data.Vector as Vector
 import qualified Language.GraphQL.Type as Type
 import Data.Scientific (Scientific, toRealFloat)
+import qualified Data.Text as Text
+import Data.Time
+    ( Day
+    , DiffTime
+    , NominalDiffTime
+    , UTCTime(..)
+    , showGregorian
+    , secondsToNominalDiffTime
+    , secondsToDiffTime
+    )
+import Data.Time.Format.ISO8601 (formatParseM, iso8601Format, iso8601Show)
 
 fromGraphQLToIntegral :: Integral a => Type.Value -> Maybe a
 fromGraphQLToIntegral (Type.Int value) = Just $ fromIntegral value
@@ -108,6 +119,22 @@ instance ToGraphQL Scientific
   where
     toGraphQL = Type.Float . toRealFloat
 
+instance ToGraphQL Day
+  where
+    toGraphQL = Type.String . Text.pack . showGregorian
+
+instance ToGraphQL DiffTime
+  where
+    toGraphQL = Type.Int . truncate . (realToFrac :: DiffTime -> Double)
+
+instance ToGraphQL NominalDiffTime
+  where
+    toGraphQL = Type.Int . truncate . (realToFrac :: NominalDiffTime -> Double)
+
+instance ToGraphQL UTCTime
+  where
+    toGraphQL = Type.String . Text.pack . iso8601Show
+
 -- | Instances of this typeclass can be used to convert GraphQL internal
 -- representation to user-defined type.
 class FromGraphQL a
@@ -194,3 +221,23 @@ instance FromGraphQL Scientific
   where
     fromGraphQL (Type.Float value) = Just $ realToFrac value
     fromGraphQL _ = Nothing
+
+instance FromGraphQL Day
+  where
+    fromGraphQL (Type.String value') = formatParseM iso8601Format $ Text.unpack value'
+    fromGraphQL _ = Nothing
+
+instance FromGraphQL DiffTime
+  where
+    fromGraphQL (Type.Int value') = Just $ secondsToDiffTime $ fromIntegral value'
+    fromGraphQL _ = Nothing
+
+instance FromGraphQL NominalDiffTime
+  where
+    fromGraphQL (Type.Int value') = Just $ secondsToNominalDiffTime $ fromIntegral value'
+    fromGraphQL _ = Nothing
+
+instance FromGraphQL UTCTime
+  where
+    fromGraphQL (Type.String value') = formatParseM iso8601Format $ Text.unpack value'
+    fromGraphQL _ = Nothing