Add `ToGraphQL` and `FromGraphQL` typeclasses

With instances for basic types.

4 files changed, 161 insertions, 1 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8366c2e..e274b42 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,7 +6,13 @@ The format is based on
 and this project adheres to
 [Haskell Package Versioning Policy](https://pvp.haskell.org/).
 
+## [Unreleased]
+### Added
+- `ToGraphQL` and `FromGraphQL` typeclasses with instances for basic types.
+
 ## [1.0.0.0] - 2022-03-29
 ### Added
 - JSON serialization.
 - Test helpers.
+
+[Unreleased]: https://www.caraus.tech/projects/pub-graphql-spice/repository/28/diff?rev=master&rev_to=v1.0.0.0
diff --git a/graphql-spice.cabal b/graphql-spice.cabal
index abaf140..f774dcc 100644
--- a/graphql-spice.cabal
+++ b/graphql-spice.cabal
@@ -24,7 +24,8 @@ source-repository head
 
 library
     exposed-modules:
-      Language.GraphQL.JSON,
+      Language.GraphQL.Class
+      Language.GraphQL.JSON
       Test.Hspec.GraphQL
     other-modules:
     hs-source-dirs:   src
@@ -48,6 +49,7 @@ test-suite graphql-test
   type: exitcode-stdio-1.0
   main-is: Spec.hs
   other-modules:
+    Language.GraphQL.ClassSpec
     Language.GraphQL.CoerceSpec
     Language.GraphQL.DirectiveSpec
     Language.GraphQL.FragmentSpec
diff --git a/src/Language/GraphQL/Class.hs b/src/Language/GraphQL/Class.hs
new file mode 100644
index 0000000..66a0b2b
--- /dev/null
+++ b/src/Language/GraphQL/Class.hs
@@ -0,0 +1,105 @@
+{- This Source Code Form is subject to the terms of the Mozilla Public License,
+   v. 2.0. If a copy of the MPL was not distributed with this file, You can
+   obtain one at https://mozilla.org/MPL/2.0/. -}
+
+{-# LANGUAGE OverloadedStrings #-}
+
+-- | ToGraphQL and FromGraphQL typeclasses used for user-defined type
+-- conversion.
+module Language.GraphQL.Class
+    ( FromGraphQL(..)
+    , ToGraphQL(..)
+    ) where
+
+import Data.Foldable (toList)
+import Data.Int (Int8, Int16, Int32, Int64)
+import Data.Text (Text)
+import qualified Data.Text.Read as Text.Read
+import Data.Vector (Vector)
+import qualified Data.Vector as Vector
+import qualified Language.GraphQL.Type as Type
+
+fromGraphQLToIntegral :: Integral a => Type.Value -> Maybe a
+fromGraphQLToIntegral (Type.Int value) = Just $ fromIntegral value
+fromGraphQLToIntegral (Type.String value) =
+    case Text.Read.decimal value of
+        Right (converted, "") -> Just converted
+        _ -> Nothing
+fromGraphQLToIntegral _ = Nothing
+
+-- | Instances of this typeclass can be converted to GraphQL internal
+-- representation.
+class ToGraphQL a where
+    toGraphQL :: a -> Type.Value
+
+instance ToGraphQL Text where
+    toGraphQL = Type.String
+
+instance ToGraphQL Int where
+    toGraphQL = Type.Int . fromIntegral
+
+instance ToGraphQL Int8 where
+    toGraphQL = Type.Int . fromIntegral
+
+instance ToGraphQL Int16 where
+    toGraphQL = Type.Int . fromIntegral
+
+instance ToGraphQL Int32 where
+    toGraphQL = Type.Int
+
+instance ToGraphQL Int64 where
+    toGraphQL = Type.Int . fromIntegral
+
+instance ToGraphQL a => ToGraphQL [a] where
+    toGraphQL = Type.List . fmap toGraphQL
+
+instance ToGraphQL a => ToGraphQL (Vector a) where
+    toGraphQL = Type.List . toList . fmap toGraphQL
+
+instance ToGraphQL a => ToGraphQL (Maybe a) where
+    toGraphQL (Just justValue) = toGraphQL justValue
+    toGraphQL Nothing = Type.Null
+
+instance ToGraphQL Bool where
+    toGraphQL = Type.Boolean
+
+-- | Instances of this typeclass can be used to convert GraphQL internal
+-- representation to user-defined type.
+class FromGraphQL a where
+    fromGraphQL :: Type.Value -> Maybe a
+
+instance FromGraphQL Text where
+    fromGraphQL (Type.String value) = Just value
+    fromGraphQL _ = Nothing
+
+instance FromGraphQL Int where
+    fromGraphQL = fromGraphQLToIntegral
+
+instance FromGraphQL Int8 where
+    fromGraphQL = fromGraphQLToIntegral
+
+instance FromGraphQL Int16 where
+    fromGraphQL = fromGraphQLToIntegral
+
+instance FromGraphQL Int32 where
+    fromGraphQL = fromGraphQLToIntegral
+
+instance FromGraphQL Int64 where
+    fromGraphQL = fromGraphQLToIntegral
+
+instance FromGraphQL a => FromGraphQL [a] where
+    fromGraphQL (Type.List value) = traverse fromGraphQL value
+    fromGraphQL _ = Nothing
+
+instance FromGraphQL a => FromGraphQL (Vector a) where
+    fromGraphQL (Type.List value) = Vector.fromList
+        <$> traverse fromGraphQL value
+    fromGraphQL _ = Nothing
+
+instance FromGraphQL a => FromGraphQL (Maybe a) where
+    fromGraphQL Type.Null = Just Nothing
+    fromGraphQL value = Just <$> fromGraphQL value
+
+instance FromGraphQL Bool where
+    fromGraphQL (Type.Boolean value) = Just value
+    fromGraphQL _ = Nothing
diff --git a/tests/Language/GraphQL/ClassSpec.hs b/tests/Language/GraphQL/ClassSpec.hs
new file mode 100644
index 0000000..087abd0
--- /dev/null
+++ b/tests/Language/GraphQL/ClassSpec.hs
@@ -0,0 +1,47 @@
+{- This Source Code Form is subject to the terms of the Mozilla Public License,
+   v. 2.0. If a copy of the MPL was not distributed with this file, You can
+   obtain one at https://mozilla.org/MPL/2.0/. -}
+
+{-# LANGUAGE OverloadedStrings #-}
+module Language.GraphQL.ClassSpec
+    ( spec
+    ) where
+
+import Data.Text (Text)
+import qualified Language.GraphQL.Type as Type
+import Language.GraphQL.Class (FromGraphQL(..), ToGraphQL(..))
+import Test.Hspec (Spec, describe, it, shouldBe)
+
+spec :: Spec
+spec = do
+    describe "ToGraphQL" $ do
+        it "converts integers" $
+            toGraphQL (5 :: Int) `shouldBe` Type.Int 5
+
+        it "converts text" $
+            toGraphQL ("String" :: Text) `shouldBe` Type.String "String"
+
+        it "converts booleans" $
+            toGraphQL True `shouldBe` Type.Boolean True
+
+        it "converts Nothing to Null" $
+            toGraphQL (Nothing :: Maybe Int) `shouldBe` Type.Null
+
+        it "converts singleton lists" $
+            toGraphQL [True] `shouldBe` Type.List [Type.Boolean True]
+
+    describe "FromGraphQL" $ do
+        it "converts integers" $
+            fromGraphQL (Type.Int 5) `shouldBe` Just (5 :: Int)
+
+        it "converts text" $
+            fromGraphQL (Type.String "String") `shouldBe` Just ("String" :: Text)
+
+        it "converts booleans" $
+            fromGraphQL (Type.Boolean True) `shouldBe` Just True
+
+        it "converts Null to Nothing" $
+            fromGraphQL Type.Null `shouldBe` Just (Nothing :: Maybe Int)
+
+        it "converts singleton lists" $
+            fromGraphQL (Type.List [Type.Boolean True]) `shouldBe` Just [True]