    {-# LANGUAGE Trustworthy #-}
    {-# LANGUAGE CPP, NoImplicitPrelude #-}
    {-# OPTIONS_GHC -funbox-strict-fields #-}

    -----------------------------------------------------------------------------
    -- |
    -- Module      :  GHC.IO.Encoding
    -- Copyright   :  (c) The University of Glasgow, 2008-2009
    -- License     :  see libraries/base/LICENSE
    --
    -- Maintainer  :  libraries@haskell.org
    -- Stability   :  internal
    -- Portability :  non-portable
    --
    -- Text codecs for I/O
    --
    -----------------------------------------------------------------------------

    module GHC.IO.Encoding (
            BufferCodec(..), TextEncoding(..), TextEncoder, TextDecoder, CodingProgress(..),
            latin1, latin1_encode, latin1_decode,
            utf8, utf8_bom,
            utf16, utf16le, utf16be,
            utf32, utf32le, utf32be,
            initLocaleEncoding,
            getLocaleEncoding, getFileSystemEncoding, getForeignEncoding,
            setLocaleEncoding, setFileSystemEncoding, setForeignEncoding,
            char8,
            mkTextEncoding,
            argvEncoding
        ) where

    import GHC.Base
    import GHC.IO.Exception
    import GHC.IO.Buffer
    import GHC.IO.Encoding.Failure
    import GHC.IO.Encoding.Types
    #if !defined(mingw32_HOST_OS)
    import qualified GHC.IO.Encoding.Iconv as Iconv
    #else
    import qualified GHC.IO.Encoding.CodePage as CodePage
    import Text.Read (reads)
    #endif
    import qualified GHC.IO.Encoding.Latin1 as Latin1
    import qualified GHC.IO.Encoding.UTF8   as UTF8
    import qualified GHC.IO.Encoding.UTF16  as UTF16
    import qualified GHC.IO.Encoding.UTF32  as UTF32
    import GHC.List
    import GHC.Word

    import Data.IORef
    import Data.Char (toUpper)
    import System.IO.Unsafe (unsafePerformIO)

    -- -----------------------------------------------------------------------------

    -- | The Latin1 (ISO8859-1) encoding.  This encoding maps bytes
    -- directly to the first 256 Unicode code points, and is thus not a
    -- complete Unicode encoding.  An attempt to write a character greater than
    -- '\255' to a 'Handle' using the 'latin1' encoding will result in an error.
    latin1  :: TextEncoding
    latin1 = Latin1.latin1_checked

    -- | The UTF-8 Unicode encoding
    utf8  :: TextEncoding
    utf8 = UTF8.utf8

    -- | The UTF-8 Unicode encoding, with a byte-order-mark (BOM; the byte
    -- sequence 0xEF 0xBB 0xBF).  This encoding behaves like 'utf8',
    -- except that on input, the BOM sequence is ignored at the beginning
    -- of the stream, and on output, the BOM sequence is prepended.
    --
    -- The byte-order-mark is strictly unnecessary in UTF-8, but is
    -- sometimes used to identify the encoding of a file.
    --
    utf8_bom  :: TextEncoding
    utf8_bom = UTF8.utf8_bom

    -- | The UTF-16 Unicode encoding (a byte-order-mark should be used to
    -- indicate endianness).
    utf16  :: TextEncoding
    utf16 = UTF16.utf16

    -- | The UTF-16 Unicode encoding (litte-endian)
    utf16le  :: TextEncoding
    utf16le = UTF16.utf16le

    -- | The UTF-16 Unicode encoding (big-endian)
    utf16be  :: TextEncoding
    utf16be = UTF16.utf16be

    -- | The UTF-32 Unicode encoding (a byte-order-mark should be used to
    -- indicate endianness).
    utf32  :: TextEncoding
    utf32 = UTF32.utf32

    -- | The UTF-32 Unicode encoding (litte-endian)
    utf32le  :: TextEncoding
    utf32le = UTF32.utf32le

    -- | The UTF-32 Unicode encoding (big-endian)
    utf32be  :: TextEncoding
    utf32be = UTF32.utf32be

    -- | The Unicode encoding of the current locale
    --
    -- @since 4.5.0.0
    getLocaleEncoding :: IO TextEncoding

    -- | The Unicode encoding of the current locale, but allowing arbitrary
    -- undecodable bytes to be round-tripped through it.
    --
    -- This 'TextEncoding' is used to decode and encode command line arguments
    -- and environment variables on non-Windows platforms.
    --
    -- On Windows, this encoding *should not* be used if possible because
    -- the use of code pages is deprecated: Strings should be retrieved
    -- via the "wide" W-family of UTF-16 APIs instead
    --
    -- @since 4.5.0.0
    getFileSystemEncoding :: IO TextEncoding

    -- | The Unicode encoding of the current locale, but where undecodable
    -- bytes are replaced with their closest visual match. Used for
    -- the 'CString' marshalling functions in "Foreign.C.String"
    --
    -- @since 4.5.0.0
    getForeignEncoding :: IO TextEncoding

    -- | @since 4.5.0.0
    setLocaleEncoding, setFileSystemEncoding, setForeignEncoding :: TextEncoding -> IO ()

    (getLocaleEncoding, setLocaleEncoding)         = mkGlobal initLocaleEncoding
    (getFileSystemEncoding, setFileSystemEncoding) = mkGlobal initFileSystemEncoding
    (getForeignEncoding, setForeignEncoding)       = mkGlobal initForeignEncoding

    mkGlobal :: a -> (IO a, a -> IO ())
    mkGlobal x = unsafePerformIO $ do
        x_ref <- newIORef x
        return (readIORef x_ref, writeIORef x_ref)

    -- | @since 4.5.0.0
    initLocaleEncoding, initFileSystemEncoding, initForeignEncoding :: TextEncoding

    #if !defined(mingw32_HOST_OS)
    -- It is rather important that we don't just call Iconv.mkIconvEncoding here
    -- because some iconvs (in particular GNU iconv) will brokenly UTF-8 encode
    -- lone surrogates without complaint.
    --
    -- By going through our Haskell implementations of those encodings, we are
    -- guaranteed to catch such errors.
    --
    -- FIXME: this is not a complete solution because if the locale encoding is one
    -- which we don't have a Haskell-side decoder for, iconv might still ignore the
    -- lone surrogate in the input.
    initLocaleEncoding     = unsafePerformIO $ mkTextEncoding' ErrorOnCodingFailure Iconv.localeEncodingName
    initFileSystemEncoding = unsafePerformIO $ mkTextEncoding' RoundtripFailure     Iconv.localeEncodingName
    initForeignEncoding    = unsafePerformIO $ mkTextEncoding' IgnoreCodingFailure  Iconv.localeEncodingName
    #else
    initLocaleEncoding     = CodePage.localeEncoding
    initFileSystemEncoding = CodePage.mkLocaleEncoding RoundtripFailure
    initForeignEncoding    = CodePage.mkLocaleEncoding IgnoreCodingFailure
    #endif

    -- See Note [Windows Unicode Arguments] in rts/RtsFlags.c
    -- On Windows we assume hs_init argv is in utf8 encoding.

    -- | Internal encoding of argv
    argvEncoding :: IO TextEncoding
    #if defined(mingw32_HOST_OS)
    argvEncoding = return utf8
    #else
    argvEncoding = getFileSystemEncoding
    #endif

    -- | An encoding in which Unicode code points are translated to bytes
    -- by taking the code point modulo 256.  When decoding, bytes are
    -- translated directly into the equivalent code point.
    --
    -- This encoding never fails in either direction.  However, encoding
    -- discards information, so encode followed by decode is not the
    -- identity.
    --
    -- @since 4.4.0.0
    char8 :: TextEncoding
    char8 = Latin1.latin1

    -- | Look up the named Unicode encoding.  May fail with
    --
    --  * 'isDoesNotExistError' if the encoding is unknown
    --
    -- The set of known encodings is system-dependent, but includes at least:
    --
    --  * @UTF-8@
    --
    --  * @UTF-16@, @UTF-16BE@, @UTF-16LE@
    --
    --  * @UTF-32@, @UTF-32BE@, @UTF-32LE@
    --
    -- There is additional notation (borrowed from GNU iconv) for specifying
    -- how illegal characters are handled:
    --
    --  * a suffix of @\/\/IGNORE@, e.g. @UTF-8\/\/IGNORE@, will cause
    --    all illegal sequences on input to be ignored, and on output
    --    will drop all code points that have no representation in the
    --    target encoding.
    --
    --  * a suffix of @\/\/TRANSLIT@ will choose a replacement character
    --    for illegal sequences or code points.
    --
    --  * a suffix of @\/\/ROUNDTRIP@ will use a PEP383-style escape mechanism
    --    to represent any invalid bytes in the input as Unicode codepoints (specifically,
    --    as lone surrogates, which are normally invalid in UTF-32).
    --    Upon output, these special codepoints are detected and turned back into the
    --    corresponding original byte.
    --
    --    In theory, this mechanism allows arbitrary data to be roundtripped via
    --    a 'String' with no loss of data. In practice, there are two limitations
    --    to be aware of:
    --
    --      1. This only stands a chance of working for an encoding which is an ASCII
    --         superset, as for security reasons we refuse to escape any bytes smaller
    --         than 128. Many encodings of interest are ASCII supersets (in particular,
    --         you can assume that the locale encoding is an ASCII superset) but many
    --         (such as UTF-16) are not.
    --
    --      2. If the underlying encoding is not itself roundtrippable, this mechanism
    --         can fail. Roundtrippable encodings are those which have an injective mapping
    --         into Unicode. Almost all encodings meet this criteria, but some do not. Notably,
    --         Shift-JIS (CP932) and Big5 contain several different encodings of the same
    --         Unicode codepoint.
    --
    -- On Windows, you can access supported code pages with the prefix
    -- @CP@; for example, @\"CP1250\"@.
    --
    mkTextEncoding :: String -> IO TextEncoding
    mkTextEncoding e = case mb_coding_failure_mode of
        Nothing -> unknownEncodingErr e
        Just cfm -> mkTextEncoding' cfm enc
      where
        (enc, suffix) = span (/= '/') e
        mb_coding_failure_mode = case suffix of
            ""            -> Just ErrorOnCodingFailure
            "//IGNORE"    -> Just IgnoreCodingFailure
            "//TRANSLIT"  -> Just TransliterateCodingFailure
            "//ROUNDTRIP" -> Just RoundtripFailure
            _             -> Nothing

    mkTextEncoding' :: CodingFailureMode -> String -> IO TextEncoding
    mkTextEncoding' cfm enc =
      case [toUpper c | c <- enc, c /= '-'] of
      -- UTF-8 and friends we can handle ourselves
        "UTF8"    -> return $ UTF8.mkUTF8 cfm
        "UTF16"   -> return $ UTF16.mkUTF16 cfm
        "UTF16LE" -> return $ UTF16.mkUTF16le cfm
        "UTF16BE" -> return $ UTF16.mkUTF16be cfm
        "UTF32"   -> return $ UTF32.mkUTF32 cfm
        "UTF32LE" -> return $ UTF32.mkUTF32le cfm
        "UTF32BE" -> return $ UTF32.mkUTF32be cfm
        -- On AIX, we want to avoid iconv, because it is either
        -- a) totally broken, or b) non-reentrant, or c) actually works.
        -- Detecting b) is difficult as you'd have to trigger the reentrancy
        -- corruption.
        -- Therefore, on AIX, we handle the popular ASCII and latin1 encodings
        -- ourselves. For consistency, we do the same on other platforms.
        -- We use `mkLatin1_checked` instead of `mkLatin1`, since the latter
        -- completely ignores the CodingFailureMode (TEST=encoding005).
        _ | isAscii -> return (Latin1.mkAscii cfm)
        _ | isLatin1 -> return (Latin1.mkLatin1_checked cfm)
    #if defined(mingw32_HOST_OS)
        'C':'P':n | [(cp,"")] <- reads n -> return $ CodePage.mkCodePageEncoding cfm cp
        _ -> unknownEncodingErr (enc ++ codingFailureModeSuffix cfm)
    #else
        -- Otherwise, handle other encoding needs via iconv.

        -- Unfortunately there is no good way to determine whether iconv is actually
        -- functional without telling it to do something.
        _ -> do res <- Iconv.mkIconvEncoding cfm enc
                case res of
                  Just e -> return e
                  Nothing -> unknownEncodingErr (enc ++ codingFailureModeSuffix cfm)
    #endif
      where
        isAscii = enc `elem` asciiEncNames
        isLatin1 = enc `elem` latin1EncNames
        asciiEncNames = -- ASCII aliases specified by RFC 1345 and RFC 3808.
          [ "ANSI_X3.4-1968", "iso-ir-6", "ANSI_X3.4-1986", "ISO_646.irv:1991"
          , "US-ASCII", "us", "IBM367", "cp367", "csASCII", "ASCII", "ISO646-US"
          ]
        latin1EncNames = -- latin1 aliases specified by RFC 1345 and RFC 3808.
          [ "ISO_8859-1:1987", "iso-ir-100", "ISO_8859-1", "ISO-8859-1", "latin1",
            "l1", "IBM819", "CP819", "csISOLatin1"
          ]

    latin1_encode :: CharBuffer -> Buffer Word8 -> IO (CharBuffer, Buffer Word8)
    latin1_encode input output = fmap (\(_why,input',output') -> (input',output')) $ Latin1.latin1_encode input output -- unchecked, used for char8
    --latin1_encode = unsafePerformIO $ do mkTextEncoder Iconv.latin1 >>= return.encode

    latin1_decode :: Buffer Word8 -> CharBuffer -> IO (Buffer Word8, CharBuffer)
    latin1_decode input output = fmap (\(_why,input',output') -> (input',output')) $ Latin1.latin1_decode input output
    --latin1_decode = unsafePerformIO $ do mkTextDecoder Iconv.latin1 >>= return.encode

    unknownEncodingErr :: String -> IO a
    unknownEncodingErr e = ioException (IOError Nothing NoSuchThing "mkTextEncoding"
                                                ("unknown encoding:" ++ e)  Nothing Nothing)