    {-# LANGUAGE DeriveDataTypeable #-}
    -- |
    -- Module: Data.Conduit.Codec.Util
    -- Copyright: (c) 2014 Magnus Therning
    -- License: BSD3

    module Data.Conduit.Codec.Util
        ( CodecDecodeException(..)
        , encodeI
        , decodeI
        , decodeII
        , encodeII
        ) where

    import Data.Typeable (Typeable)
    import Control.Exception (Exception)
    import Data.ByteString as BS (ByteString, append, null)
    import Data.Conduit (ConduitT, await, yield)
    import Data.Maybe (fromJust)
    import Control.Monad (unless, void)
    import Control.Monad.Catch (MonadThrow, throwM)

    type EncFunc = ByteString -> ByteString
    type EncFuncPart = ByteString -> (ByteString, ByteString)
    type EncFuncFinal = ByteString -> Maybe ByteString
    type DecFunc = ByteString -> Either (ByteString, ByteString) (ByteString, ByteString)
    type DecFuncFinal = ByteString -> Maybe ByteString

    data CodecDecodeException = CodecDecodeException ByteString
        deriving (Typeable, Show)

    instance Exception CodecDecodeException

    encodeI :: (Monad m) => EncFuncPart -> EncFuncFinal -> ByteString -> ConduitT ByteString ByteString m ()
    encodeI enc_part enc_final i = do
        clear <- await
        case clear of
            Nothing -> void (yield $ fromJust $ enc_final i)
            Just s -> let
                    (a, b) = enc_part (i `append` s)
                in do
                    unless (BS.null a) $ yield a
                    encodeI enc_part enc_final b

    decodeI :: (Monad m, MonadThrow m) => DecFunc -> DecFuncFinal -> ByteString -> ConduitT ByteString ByteString m ()
    decodeI dec_part dec_final i = do
        enc <- await
        case enc of
            Nothing ->
                case dec_final i of
                    Nothing -> throwM (CodecDecodeException i)
                    Just s -> void (yield s)
            Just s ->
                case dec_part (i `append` s) of
                    Left (a, b) -> do
                        unless (BS.null a) $ yield a
                        throwM (CodecDecodeException b)
                    Right (a, b) -> do
                        unless (BS.null a) $ yield a
                        decodeI dec_part dec_final b

    encodeII :: (Monad m) => EncFunc -> ConduitT ByteString ByteString m ()
    encodeII enc = do
        clear <- await
        case clear of
            Nothing -> return ()
            Just s -> do
                yield $ enc s
                encodeII enc

    decodeII :: (Monad m, MonadThrow m) => DecFunc -> ByteString -> ConduitT ByteString ByteString m ()
    decodeII dec i = do
        enc <- await
        case enc of
            Nothing -> unless (BS.null i) (throwM $ CodecDecodeException i)
            Just s -> case dec $ i `append` s of
                Left (c, b) -> do
                    unless (BS.null c) $ yield c
                    throwM $ CodecDecodeException b
                Right (c, r) -> do
                    unless (BS.null c) $ yield c
                    decodeII dec r