{- 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
        _conversionError -> 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