{-# language DataKinds #-}
{-# language FlexibleContexts #-}
{-# language FlexibleInstances #-}
{-# language MultiParamTypeClasses #-}
{-# language TypeFamilies #-}
{-# language StandaloneKindSignatures #-}
{-# language UndecidableInstances #-}

module Rel8.Type.Sum
  ( DBSum
  )
where

-- base
import Data.Int ( Int16, Int32, Int64 )
import Data.Kind ( Constraint, Type )
import Prelude

-- rel8
import Rel8.Schema.Nullability ( HasNullability, Unnullify, Sql )
import Rel8.Type ( DBType )

-- scientific
import Data.Scientific ( Scientific )

-- time
import Data.Time.Clock ( DiffTime, NominalDiffTime )


-- | The class of database types that support the @sum()@ aggregation function.
type DBSum :: Type -> Constraint
class DBType a => DBSum a
instance DBSum Int16
instance DBSum Int32
instance DBSum Int64
instance DBSum Float
instance DBSum Double
instance DBSum Scientific
instance DBSum DiffTime
instance DBSum NominalDiffTime


instance {-# INCOHERENT #-} (HasNullability a, DBSum (Unnullify a)) =>
  Sql DBSum a