-- Hoogle documentation, generated by Haddock
-- See Hoogle, http://www.haskell.org/hoogle/


-- | Type safe data migrations
--   
--   Please see the README on GitHub at
--   <a>https://github.com/agentultra/DataMigration#readme</a>
@package DataVersion
@version 0.1.0.0

module Data.Migration.Internal
type family RepToTree (a :: Type -> Type) :: [(Symbol, Type)]
type family (++) (xs :: [k]) (ys :: [k]) :: [k]
type family Sort (xs :: [(Symbol, k)])
type family Insert (x :: (Symbol, k)) (xs :: [(Symbol, k)])
type family Insert' (b :: Ordering) (x :: (Symbol, k)) (y :: (Symbol, k)) (ys :: [(Symbol, k)])
data DiffResult
NoChange :: Symbol -> Type -> DiffResult
Addition :: Symbol -> Type -> DiffResult
Change :: Symbol -> Type -> Type -> DiffResult
type family FieldDiff (a :: [(Symbol, Type)]) (b :: [(Symbol, Type)]) :: [DiffResult]
type family FieldDiffImpl (b :: Ordering) (x :: (Symbol, Type)) (y :: (Symbol, Type)) (xs :: [(Symbol, Type)]) (ys :: [(Symbol, Type)]) :: [DiffResult]
copyField :: forall name t from to. (HasField' name to t, HasField' name from t) => from -> to -> to
class GTransform (ts :: [DiffResult]) (src :: Type) (dst :: Type) where {
    type family Function ts src dst :: Type;
}
gTransform :: GTransform ts src dst => dst -> src -> Function ts src dst
class GUndefinedFields (o :: * -> *)
gUndefinedFields :: GUndefinedFields o => o x

-- | Don't use this, it's not meant to be useful
undefinedFields :: (Generic t, GUndefinedFields (Rep t)) => t
instance (GHC.Generics.Generic dst, Data.Migration.Internal.GUndefinedFields (GHC.Generics.Rep dst)) => Data.Migration.Internal.GTransform '[] src dst
instance Data.Migration.Internal.GUndefinedFields o => Data.Migration.Internal.GUndefinedFields (GHC.Generics.M1 _3 _4 o)
instance (Data.Migration.Internal.GUndefinedFields o1, Data.Migration.Internal.GUndefinedFields o2) => Data.Migration.Internal.GUndefinedFields (o1 GHC.Generics.:*: o2)
instance Data.Migration.Internal.GUndefinedFields (GHC.Generics.K1 _1 t)
instance (Data.Migration.Internal.GTransform ts src dst, Data.Generics.Product.Fields.HasField' name src t, Data.Generics.Product.Fields.HasField' name dst t) => Data.Migration.Internal.GTransform ('Data.Migration.Internal.NoChange name t : ts) src dst
instance (Data.Migration.Internal.GTransform ts src dst, Data.Generics.Product.Fields.HasField' name dst t) => Data.Migration.Internal.GTransform ('Data.Migration.Internal.Addition name t : ts) src dst
instance (Data.Migration.Internal.GTransform ts src dst, Data.Generics.Product.Fields.HasField' name src ti, Data.Generics.Product.Fields.HasField' name dst to) => Data.Migration.Internal.GTransform ('Data.Migration.Internal.Change name ti to : ts) src dst


-- | To begin migrating your data start with a type family for your record
--   and index it with a natural number
--   
--   <pre>
--   data family Foo (version :: Nat)
--   
--   newtype MyString = MyString { unMyString :: String }
--      deriving (IsString, Show, Eq)
--   
--   data instance Foo 0
--     = FooV0
--       { _fooId :: Int
--       , _fooName :: String
--       }
--     deriving (Generic, Show, Eq)
--   
--   data instance Foo 1
--     = FooV1
--     { _fooId        :: Int
--     , _fooName      :: MyString
--     , _fooHonorific :: String
--     }
--     deriving (Generic, Show, Eq)
--   
--   instance Transform Foo 0 where
--     up   v = genericUp   v (const "esquire") (const MyString)
--     down v = genericDown v (const unMyString)
--   </pre>
--   
--   You provide an instance of the Transform class for your type in order
--   to specify how to transform version <i>n</i> to version <i>n + 1</i>
--   and back.
--   
--   Presently only simple record types are supported. More to come in the
--   future.
module Data.Migration

-- | Implement this class on your type family instance to migrate values of
--   your type to the new version and back
class Transform (f :: Nat -> Type) (n :: Nat)
up :: Transform f n => f n -> f (n + 1)
down :: Transform f n => f (n + 1) -> f n

-- | Using this function in your <a>up</a> transformation ensures that you
--   only have to provide functions for fields that change or are added.
genericUp :: forall n src diff. (diff ~ FieldDiff (Sort (RepToTree (Rep (src n)))) (Sort (RepToTree (Rep (src (n + 1))))), GTransform diff (src n) (src (n + 1)), Generic (src (n + 1)), GUndefinedFields (Rep (src (n + 1)))) => src n -> Function diff (src n) (src (n + 1))

-- | This is the opposite of <a>genericUp</a>.
genericDown :: forall n src diff. (diff ~ FieldDiff (Sort (RepToTree (Rep (src (n + 1))))) (Sort (RepToTree (Rep (src n)))), GTransform diff (src (n + 1)) (src n), Generic (src n), GUndefinedFields (Rep (src n))) => src (n + 1) -> Function diff (src (n + 1)) (src n)