    {-# OPTIONS_HADDOCK hide #-}
    {-# LANGUAGE ExistentialQuantification #-}
    -- |
    -- Module      : Network.TLS.Compression
    -- License     : BSD-style
    -- Maintainer  : Vincent Hanquez <vincent@snarc.org>
    -- Stability   : experimental
    -- Portability : unknown
    --
    module Network.TLS.Compression
        ( CompressionC(..)
        , Compression(..)
        , CompressionID
        , nullCompression
        , NullCompression

        -- * member redefined for the class abstraction
        , compressionID
        , compressionDeflate
        , compressionInflate

        -- * helper
        , compressionIntersectID
        ) where

    import Data.Word
    import Network.TLS.Types (CompressionID)
    import Data.ByteString (ByteString)
    import Control.Arrow (first)

    -- | supported compression algorithms need to be part of this class
    class CompressionC a where
        compressionCID      :: a -> CompressionID
        compressionCDeflate :: a -> ByteString -> (a, ByteString)
        compressionCInflate :: a -> ByteString -> (a, ByteString)

    -- | every compression need to be wrapped in this, to fit in structure
    data Compression = forall a . CompressionC a => Compression a

    -- | return the associated ID for this algorithm
    compressionID :: Compression -> CompressionID
    compressionID (Compression c) = compressionCID c

    -- | deflate (compress) a bytestring using a compression context and return the result
    -- along with the new compression context.
    compressionDeflate :: ByteString -> Compression -> (Compression, ByteString)
    compressionDeflate bytes (Compression c) = first Compression $ compressionCDeflate c bytes

    -- | inflate (decompress) a bytestring using a compression context and return the result
    -- along the new compression context.
    compressionInflate :: ByteString -> Compression -> (Compression, ByteString)
    compressionInflate bytes (Compression c) = first Compression $ compressionCInflate c bytes

    instance Show Compression where
        show = show . compressionID
    instance Eq Compression where
        (==) c1 c2 = compressionID c1 == compressionID c2

    -- | intersect a list of ids commonly given by the other side with a list of compression
    -- the function keeps the list of compression in order, to be able to find quickly the prefered
    -- compression.
    compressionIntersectID :: [Compression] -> [Word8] -> [Compression]
    compressionIntersectID l ids = filter (\c -> elem (compressionID c) ids) l

    -- | This is the default compression which is a NOOP.
    data NullCompression = NullCompression

    instance CompressionC NullCompression where
        compressionCID _        = 0
        compressionCDeflate s b = (s, b)
        compressionCInflate s b = (s, b)

    -- | default null compression
    nullCompression :: Compression
    nullCompression = Compression NullCompression