-- {-# LANGUAGE FlexibleInstances #-}

-- |
-- Module      : Crypto.Saltine.Class
-- Copyright   : (c) Joseph Abrahamson 2013
-- License     : MIT
--
-- Maintainer  : me@jspha.com
-- Stability   : experimental
-- Portability : non-portable
--
-- Saltine type classes
module Crypto.Saltine.Class (
  IsEncoding (..),
  IsNonce (..)
  ) where

import Data.Profunctor
import Data.ByteString (ByteString)

-- | Class for all keys and nonces in Saltine which have a
-- representation as ByteString. 'encoded' is a 'Prism' of
-- type @Prism' ByteString a@ compatible with "Control.Lens" and
-- is automatically deduced.
class IsEncoding a where
  encode  :: a -> ByteString
  decode  :: ByteString -> Maybe a
  encoded :: (Choice p, Applicative f)
             => p a (f a) -> p ByteString (f ByteString)
  encoded = prism' encode decode
  {-# INLINE encoded #-}

-- | A generic class for interacting with nonces.
class IsNonce n where
  zero  :: n
  -- ^ Some privileged nonce value.
  nudge :: n -> n
  -- ^ Some perturbation on nonces such that @n /= nudge n@ with high
  -- probability. Since nonces are finite, repeats may happen in
  -- particularly small cases, but no nonces in Saltine are so
  -- small. This is not guaranteed to be difficult to predict---if a
  -- nonce had an `Enum` instance `succ` would be a good
  -- implementation excepting that `succ` is partial.

-- Copied over from Control.Lens

prism' :: (Applicative f, Choice p) =>
          (a1 -> a) -> (a -> Maybe a2) -> p a2 (f a1) -> p a (f a)
prism' bs sma = prism bs (\s -> maybe (Left s) Right (sma s))
{-# INLINE prism' #-}

prism :: (Applicative f, Choice p) =>
         (a2 -> a1) -> (a -> Either a1 a3) -> p a3 (f a2) -> p a (f a1)
prism bt seta = dimap seta (either pure (fmap bt)) . right'
{-# INLINE prism #-}