FakeCypher.hs

-- Wrapping a Reader Monad transformer (test environment)
newtype FakeCypher m a = FakeCypherT (ReaderT Cyphers m a)
  deriving (Functor, Applicative, Monad, MonadTrans)

-- MonadCypher instance for our test environment
instance Monad m => MonadCypher (FakeCypher m) where
  encryptJson json = do
    cyphers <- FakeCypherT ask
    pure (encryptMap cyphers M.! json)
  decryptJson str = do
    cyphers <- FakeCypherT ask
    pure (M.lookup str (decryptMap cyphers))

-- To run a `MonadCypher` computation in our test environment
runFakeCypher :: (Monad m) => FakeCypher m a -> Cyphers -> m a
runFakeCypher (FakeCypherT f) r = runReaderT f r