{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE TemplateHaskell #-}
module Yesod.Internal.Cache
    ( Cache
    , CacheKey
    , mkCacheKey
    , lookup
    , insert
    , delete
    ) where

import Prelude hiding (lookup)
import qualified Data.IntMap as Map
import Language.Haskell.TH.Syntax (Q, Exp, runIO, Exp (LitE), Lit (IntegerL))
import Language.Haskell.TH (appE)
import Data.Unique (hashUnique, newUnique)
import Unsafe.Coerce (unsafeCoerce)
import Control.Applicative ((<$>))
import Yesod.Core.Types

-- | Generate a new 'CacheKey'. Be sure to give a full type signature.
mkCacheKey :: Q Exp
mkCacheKey = [|CacheKey|] `appE` (LitE . IntegerL . fromIntegral . hashUnique <$> runIO newUnique)

lookup :: CacheKey a -> Cache -> Maybe a
lookup (CacheKey i) (Cache m) = unsafeCoerce <$> Map.lookup i m

insert :: CacheKey a -> a -> Cache -> Cache
insert (CacheKey k) v (Cache m) = Cache (Map.insert k (unsafeCoerce v) m)

delete :: CacheKey a -> Cache -> Cache
delete (CacheKey k) (Cache m) = Cache (Map.delete k m)