{-# LANGUAGE RankNTypes, BangPatterns #-}
-- |

-- This module uses the stream decoding functions from the text-stream-decoding package
-- to define pipes decoding functions and lenses.

module Pipes.Text.Encoding
    ( Codec
    , utf8
    , utf8Pure
    , utf16LE
    , utf16BE
    , utf32LE
    , utf32BE
    , decodeUtf8
    , decodeUtf8Pure
    , decodeUtf16LE
    , decodeUtf16BE
    , decodeUtf32LE
    , decodeUtf32BE
    , encodeAscii
    , decodeAscii
    , encodeIso8859_1
    , decodeIso8859_1
    ) 
    where

import Data.Char (ord)
import Data.ByteString as B 
import Data.ByteString (ByteString)
import Data.ByteString.Char8 as B8
import Data.Text (Text)
import qualified Data.Text as T 
import qualified Data.Text.Encoding as TE 
import Data.Text.StreamDecoding
import Control.Monad (join)
import Data.Word (Word8)
import Pipes

type Lens' a b = forall f . Functor f => (b -> f b) -> (a -> f a)

{- | A 'Codec' is just an improper lens into a byte stream that is expected to contain text.
    They are named in accordance with the expected encoding, 'utf8', 'utf16LE' etc.
    The stream of text they 'see' in a bytestream ends by returning the original byte stream 
    beginning at the point of failure, or the empty bytestream with its return value.
   -}
type Codec
    =  forall m r
    .  Monad m
    => Lens' (Producer ByteString m r)
             (Producer Text m (Producer ByteString m r))

decodeStream :: Monad m 
       => (B.ByteString -> DecodeResult) 
       -> Producer ByteString m r -> Producer Text m (Producer ByteString m r)
decodeStream = loop where
  loop dec0 p = 
    do x <- lift (next p) 
       case x of Left r -> return (return r)
                 Right (chunk, p') -> case dec0 chunk of 
                    DecodeResultSuccess text dec -> do yield text
                                                       loop dec p'
                    DecodeResultFailure text bs -> do yield text 
                                                      return (do yield bs 
                                                                 p')
{-# INLINABLE decodeStream#-}

decodeUtf8 :: Monad m => Producer ByteString m r -> Producer Text m (Producer ByteString m r)
decodeUtf8 = decodeStream streamUtf8
{-# INLINE decodeUtf8 #-}

decodeUtf8Pure :: Monad m => Producer ByteString m r -> Producer Text m (Producer ByteString m r)
decodeUtf8Pure = decodeStream streamUtf8Pure
{-# INLINE decodeUtf8Pure #-}

decodeUtf16LE :: Monad m => Producer ByteString m r -> Producer Text m (Producer ByteString m r)
decodeUtf16LE = decodeStream streamUtf16LE
{-# INLINE decodeUtf16LE #-}

decodeUtf16BE :: Monad m => Producer ByteString m r -> Producer Text m (Producer ByteString m r)
decodeUtf16BE = decodeStream streamUtf16BE
{-# INLINE decodeUtf16BE #-}

decodeUtf32LE :: Monad m => Producer ByteString m r -> Producer Text m (Producer ByteString m r)
decodeUtf32LE = decodeStream streamUtf32LE
{-# INLINE decodeUtf32LE #-}

decodeUtf32BE :: Monad m => Producer ByteString m r -> Producer Text m (Producer ByteString m r)
decodeUtf32BE = decodeStream streamUtf32BE
{-# INLINE decodeUtf32BE #-}

mkCodec :: (forall r m . Monad m => 
           Producer ByteString m r -> Producer Text m (Producer ByteString m r ))
        -> (Text -> ByteString)
        -> Codec
mkCodec dec enc = \k p0 -> fmap (\p -> join (for p (yield . enc)))  (k (dec p0))


{- | An improper lens into a byte stream expected to be UTF-8 encoded; the associated
   text stream ends by returning the original bytestream beginning at the point of failure,
   or the empty bytestring for a well-encoded text. 
   -}

utf8 :: Codec
utf8 = mkCodec decodeUtf8 TE.encodeUtf8

utf8Pure :: Codec
utf8Pure = mkCodec decodeUtf8Pure TE.encodeUtf8

utf16LE :: Codec
utf16LE = mkCodec decodeUtf16LE TE.encodeUtf16LE

utf16BE :: Codec
utf16BE = mkCodec decodeUtf16BE TE.encodeUtf16BE

utf32LE :: Codec
utf32LE = mkCodec decodeUtf32LE TE.encodeUtf32LE

utf32BE :: Codec
utf32BE = mkCodec decodeUtf32BE TE.encodeUtf32BE


{- | ascii and latin encodings only use a small number of the characters 'Text'
     recognizes; thus we cannot use the pipes 'Lens' style to work with them. 
     Rather we simply define functions each way. 

     'encodeAscii' : Reduce as much of your stream of 'Text' actually is ascii to a byte stream,
     returning the rest of the 'Text' at the first non-ascii 'Char'
-}

encodeAscii :: Monad m => Producer Text m r -> Producer ByteString m (Producer Text m r)
encodeAscii = go where
  go p = do e <- lift (next p)
            case e of 
              Left r -> return (return r)
              Right (chunk, p') -> 
                 if T.null chunk 
                   then go p'
                   else let (safe, unsafe)  = T.span (\c -> ord c <= 0x7F) chunk
                        in do yield (B8.pack (T.unpack safe))
                              if T.null unsafe
                                then go p'
                                else return $ do yield unsafe 
                                                 p'
                                                 
{- | Reduce as much of your stream of 'Text' actually is iso8859 or latin1 to a byte stream,
     returning the rest of the 'Text' upon hitting any non-latin 'Char'
   -}
encodeIso8859_1 :: Monad m => Producer Text m r -> Producer ByteString m (Producer Text m r)
encodeIso8859_1 = go where
  go p = do e <- lift (next p)
            case e of 
              Left r -> return (return r)
              Right (txt, p') -> 
                 if T.null txt 
                   then go p'
                   else let (safe, unsafe)  = T.span (\c -> ord c <= 0xFF) txt
                        in do yield (B8.pack (T.unpack safe))
                              if T.null unsafe
                                then go p'
                                else return $ do yield unsafe 
                                                 p'

{- | Reduce a byte stream to a corresponding stream of ascii chars, returning the
     unused 'ByteString' upon hitting an un-ascii byte.
   -}
decodeAscii :: Monad m => Producer ByteString m r -> Producer Text m (Producer ByteString m r)
decodeAscii = go where
  go p = do e <- lift (next p)
            case e of 
              Left r -> return (return r)
              Right (chunk, p') -> 
                 if B.null chunk 
                   then go p'
                   else let (safe, unsafe) = B.span (<= 0x7F) chunk
                        in do yield (T.pack (B8.unpack safe))
                              if B.null unsafe
                                then go p'
                                else return (do yield unsafe 
                                                p')

{- | Reduce a byte stream to a corresponding stream of ascii chars, returning the
     unused 'ByteString' upon hitting the rare un-latinizable byte.
     -}
decodeIso8859_1 :: Monad m => Producer ByteString m r -> Producer Text m (Producer ByteString m r)
decodeIso8859_1 = go where
  go p = do e <- lift (next p)
            case e of 
              Left r -> return (return r)
              Right (chunk, p') -> 
                 if B.null chunk 
                    then go p'
                    else do let (safe, unsafe) = B.span (<= 0xFF) chunk
                            yield (T.pack (B8.unpack safe))
                            if B.null unsafe 
                               then go p'
                               else return (do yield unsafe 
                                               p')