module Data.Bson.Generic
( ToBSON(..)
, FromBSON(..)
, ObjectKey(..)
, keyLabel
, constructorLabel
) where
import GHC.Generics
import qualified Data.Bson as BSON (lookup)
import Data.Bson
import Data.UString (u)
import Data.Typeable
import Control.Monad
keyLabel :: Label
keyLabel = u "_id"
constructorLabel :: Label
constructorLabel = u "_co"
class GConstructorCount f where
gconstructorCount :: f a -> Int
instance GConstructorCount V1 where
gconstructorCount _ = 0
instance (GConstructorCount a) => GConstructorCount (D1 d a) where
gconstructorCount (M1 x) = gconstructorCount x
instance (Constructor c) => GConstructorCount (C1 c a) where
gconstructorCount c = 1
instance (GConstructorCount a, GConstructorCount b) => GConstructorCount (a :+: b) where
gconstructorCount (_ :: (a :+: b) r) = gconstructorCount (undefined :: a r) +
gconstructorCount (undefined :: b r)
constructorCount :: (Generic a, GConstructorCount (Rep a)) => a -> Int
constructorCount x = gconstructorCount $ from x
newtype ObjectKey = ObjectKey { unObjectKey :: Maybe ObjectId } deriving (Generic, Typeable, Show, Eq)
instance FromBSON ObjectKey
instance ToBSON ObjectKey
instance (FromBSON a, ToBSON a, Typeable a, Show a, Eq a) => Val a where
val x = Doc $ toBSON x
cast' (Doc x) = fromBSON x
cast' _ = Nothing
class ToBSON a where
toBSON :: a -> Document
default toBSON :: (Generic a, GConstructorCount (Rep a), GToBSON (Rep a)) => a -> Document
toBSON a = genericToBSON (constructorCount a) (from a)
class GToBSON f where
genericToBSON :: Int -> f a -> Document
instance GToBSON U1 where
genericToBSON _ U1 = []
instance (GToBSON a, GToBSON b) => GToBSON (a :*: b) where
genericToBSON n (x :*: y) = genericToBSON n x ++ genericToBSON n y
instance (GToBSON a, GToBSON b) => GToBSON (a :+: b) where
genericToBSON n (L1 x) = genericToBSON n x
genericToBSON n (R1 x) = genericToBSON n x
instance (GToBSON a) => GToBSON (D1 c a) where
genericToBSON n (M1 x) = genericToBSON n x
instance (GToBSON a, Constructor c) => GToBSON (C1 c a) where
genericToBSON 0 (M1 x) = genericToBSON 0 x
genericToBSON 1 (M1 x) = genericToBSON 1 x
genericToBSON n c@(M1 x) = genericToBSON n x ++ [ constructorLabel =: conName c ]
instance (Val a, Selector s) => GToBSON (S1 s (K1 i a)) where
genericToBSON _ s@(M1 (K1 x)) = [u (selName s) =: x]
instance (Selector s) => GToBSON (S1 s (K1 i ObjectKey)) where
genericToBSON _ (M1 (K1 (ObjectKey (Just key)))) = [ keyLabel =: key ]
genericToBSON _ _ = []
instance (ToBSON a) => GToBSON (K1 i a) where
genericToBSON _ (K1 x) = toBSON x
class FromBSON a where
fromBSON :: Document -> Maybe a
default fromBSON :: (Generic a, GConstructorCount (Rep a), GFromBSON (Rep a)) => Document -> Maybe a
fromBSON doc = maybe Nothing (Just . to) (genericFromBSON (constructorCount (undefined :: a)) doc)
class GFromBSON f where
genericFromBSON :: Int -> Document -> Maybe (f a)
instance GFromBSON U1 where
genericFromBSON _ doc = Just U1
instance (GFromBSON a, GFromBSON b) => GFromBSON (a :*: b) where
genericFromBSON n doc = do
x <- (genericFromBSON n doc)
y <- (genericFromBSON n doc)
return (x :*: y)
instance (GFromBSON a, GFromBSON b) => GFromBSON (a :+: b) where
genericFromBSON n doc = left `mplus` right
where left = maybe Nothing (Just . L1) (genericFromBSON n doc)
right = maybe Nothing (Just . R1) (genericFromBSON n doc)
instance (GFromBSON a, Constructor c) => GFromBSON (C1 c a) where
genericFromBSON 0 doc = maybe Nothing (Just . M1) (genericFromBSON 0 doc)
genericFromBSON 1 doc = maybe Nothing (Just . M1) (genericFromBSON 0 doc)
genericFromBSON n doc = do
cname <- BSON.lookup constructorLabel doc
if (cname == (conName (undefined :: M1 C c a r)))
then maybe Nothing (Just . M1) (genericFromBSON n doc)
else Nothing
instance (GFromBSON a) => GFromBSON (M1 D c a) where
genericFromBSON n doc = genericFromBSON n doc >>= return . M1
instance (Val a, Selector s) => GFromBSON (S1 s (K1 i a)) where
genericFromBSON n doc = (BSON.lookup sname doc) >>= return . M1 . K1
where sname = u . selName $ (undefined :: S1 s (K1 i a) r)
instance (Selector s) => GFromBSON (S1 s (K1 i ObjectKey)) where
genericFromBSON n doc = Just . M1 . K1 $ ObjectKey (BSON.lookup keyLabel doc)