{-# LANGUAGE CApiFFI #-}
{-# LANGUAGE ForeignFunctionInterface #-}

module StrictEq
  ( StrictEq (..),
    (/==),
  )
where

import Data.ByteString (ByteString)
import Data.Int (Int64)
import Data.Text (Text)
import Foreign.C
import Foreign.Marshal.Alloc
import Foreign.Ptr
import Foreign.Storable
import Sqlite
import System.IO.Unsafe (unsafePerformIO)

foreign import capi unsafe "string.h memcmp"
  c_memcmp :: Ptr a -> Ptr a -> CSize -> IO CInt

-- | Variant of Eq that compares Double based on raw representation,
-- rather than applying IEEE 754 coercion rules.
class StrictEq a where
  (===) :: a -> a -> Bool

(/==) :: (StrictEq a) => a -> a -> Bool
(/==) a b = not (a === b)

instance StrictEq Double where
  a === b = unsafePerformIO $
    alloca $ \aptr ->
      alloca $ \bptr -> do
        poke aptr a
        poke bptr b
        rc <- c_memcmp aptr bptr (fromIntegral $ sizeOf a)
        return (rc == 0)

instance StrictEq Int64 where
  a === b = a == b

instance StrictEq Text where
  a === b = a == b

instance StrictEq ByteString where
  a === b = a == b

instance (StrictEq a) => StrictEq [a] where
  [] === [] = True
  (x : xs) === (y : ys) = x === y && xs === ys
  _ === _ = False

instance StrictEq SqlData where
  SqlInteger a === SqlInteger b = a === b
  SqlFloat a === SqlFloat b = a === b
  SqlText a === SqlText b = a === b
  SqlBlob a === SqlBlob b = a === b
  SqlNull === SqlNull = True
  _ === _ = False