    {- arch-tag: HVIO main file
    Copyright (C) 2004-2006 John Goerzen <jgoerzen@complete.org>

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
    -}

    {- |
       Module     : System.IO.HVIO
       Copyright  : Copyright (C) 2004-2006 John Goerzen
       License    : GNU GPL, version 2 or above

       Maintainer : John Goerzen <jgoerzen@complete.org>
       Stability  : provisional
       Portability: portable

    Haskell Virtual I\/O -- a system to increase the flexibility of input and
    output in Haskell

    Copyright (c) 2004-2005 John Goerzen, jgoerzen\@complete.org

    HVIO provides the following general features:

     * The ability to use a single set of functions on various different
       types of objects, including standard Handles, in-memory buffers,
       compressed files, network data streams, etc.

     * The ability to transparently add filters to the I\/O process.
       These filters could include things such as character set conversions,
       compression or decompression of a data stream, and more.

     * The ability to define new objects that have the properties
       of I\/O objects and can be used interchangably with them.

     * Specification compatibility with, and complete support for,
       existing I\/O on Handles.

     * Provide easier unit testing capabilities for I\/O actions

    HVIO defines several basic type classes that you can use.  You will mostly
    be interested in 'HVIO'.

    It's trivial to adapt old code to work with HVIO.  For instance, consider
    this example of old and new code:

    >printMsg :: Handle -> String -> IO ()
    >printMsg h msg = hPutStr h ("msg: " ++ msg)

    And now, the new way:

    >printMsg :: HVIO h => h -> String -> IO ()
    >printMsg h msg = vPutStr h ("msg: " ++ msg)

    There are several points to note about this conversion:

     * The new method can still accept a Handle in exactly the same way as
       the old method.  Changing your functions to use HVIO will require no
       changes from functions that call them with Handles.

     * Most \"h\" functions have equivolent \"v\" functions that operate
       on HVIO classes instead of the more specific Handle.  The \"v\" functions
       behave identically to the \"h\" functions whenever possible.

     * There is no equivolent of \"openFile\" in any HVIO class.  You must
       create your Handle (or other HVIO object) using normal means.
       This is because the creation is so different that it cannot be standardized.

    In addition to Handle, there are several pre-defined classes for your use.
    'StreamReader' is a particularly interesting one.  At creation time, you pass
    it a String.  Its contents are read lazily whenever a read call is made.  It
    can be used, therefore, to implement filters (simply initialize it with the
    result from, say, a map over hGetContents from another HVIO object), codecs,
    and simple I\/O testing.  Because it is lazy, it need not hold the entire
    string in memory.  You can create a 'StreamReader' with a call to
    'newStreamReader'.

    'MemoryBuffer' is a similar class, but with a different purpose.  It provides
    a full interface like Handle (it implements 'HVIOReader', 'HVIOWriter',
    and 'HVIOSeeker').  However, it maintains an in-memory buffer with the
    contents of the file, rather than an actual on-disk file.  You can access
    the entire contents of this buffer at any time.  This can be quite useful
    for testing I\/O code, or for cases where existing APIs use I\/O, but you
    prefer a String representation.  You can create a 'MemoryBuffer' with a call
    to 'newMemoryBuffer'.

    Finally, there are pipes.  These pipes are analogous to the Unix
    pipes that are available from System.Posix, but don't require Unix and work
    only in Haskell.  When you create a pipe, you actually get two HVIO objects:
    a 'PipeReader' and a 'PipeWriter'.  You must use the 'PipeWriter' in one
    thread and the 'PipeReader' in another thread.  Data that's written to the
    'PipeWriter' will then be available for reading with the 'PipeReader'.  The
    pipes are implemented completely with existing Haskell threading primitives,
    and require no special operating system support.  Unlike Unix pipes, these
    pipes cannot be used across a fork().  Also unlike Unix pipes, these pipes
    are portable and interact well with Haskell threads.  A new pipe can be created
    with a call to 'newHVIOPipe'.

    Together with "System.IO.HVFS", this module is part of a complete
    virtual filesystem solution.
    -}

    module System.IO.HVIO(-- * Implementation Classes
                         HVIO(..),
                         -- * Standard HVIO Implementations

                         -- ** Handle
                         -- | Handle is a member of 'HVIO'.

                         -- ** Stream Reader
                         StreamReader, newStreamReader,

                         -- ** Memory Buffer
                         MemoryBuffer, newMemoryBuffer,
                         mbDefaultCloseFunc, getMemoryBuffer,

                         -- ** Haskell Pipe
                         PipeReader, PipeWriter, newHVIOPipe
                        )
    where

    import System.IO
    import System.IO.Error
    import Control.Concurrent.MVar
    import Data.IORef
    import Foreign.Ptr
    import Foreign.C
    import Foreign.Storable

    {- | This is the generic I\/O support class.  All objects that are to be used
    in the HVIO system must provide an instance of 'HVIO'.

    Functions in this class provide an interface with the same specification as
    the similar functions in System.IO.  Please refer to that documentation
    for a more complete specification than is provided here.

    Instances of 'HVIO' must provide 'vClose', 'vIsEOF', and either
    'vIsOpen' or 'vIsClosed'.

    Implementators of readable objects must provide at least 'vGetChar'
    and 'vIsReadable'.
    An implementation of 'vGetContents' is also highly suggested, since
    the default cannot implement proper partial closing semantics.

    Implementators of writable objects must provide at least 'vPutChar' and
    'vIsWritable'.

    Implementators of seekable objects must provide at least
    'vIsSeekable', 'vTell', and 'vSeek'.
    -}
    class (Show a) => HVIO a where
        -- | Close a file
        vClose :: a -> IO ()
        -- | Test if a file is open
        vIsOpen :: a -> IO Bool
        -- | Test if a file is closed
        vIsClosed :: a -> IO Bool
        -- | Raise an error if the file is not open.
        -- This is a new HVIO function and is implemented in terms of
        -- 'vIsOpen'.
        vTestOpen :: a -> IO ()
        -- | Whether or not we're at EOF.  This may raise on exception
        -- on some items, most notably write-only Handles such as stdout.
        -- In general, this is most reliable on items opened for reading.
        -- vIsEOF implementations must implicitly call vTestOpen.
        vIsEOF :: a -> IO Bool
        -- | Detailed show output.
        vShow :: a -> IO String
        -- | Make an IOError.
        vMkIOError :: a -> IOErrorType -> String -> Maybe FilePath -> IOError
        -- | Throw an IOError.
        vThrow :: a -> IOErrorType -> IO b
        -- | Get the filename\/object\/whatever that this corresponds to.
        -- May be Nothing.
        vGetFP :: a -> IO (Maybe FilePath)
        -- | Throw an isEOFError if we're at EOF; returns nothing otherwise.
        -- If an implementation overrides the default, make sure that it
        -- calls vTestOpen at some point.  The default implementation is
        -- a wrapper around a call to 'vIsEOF'.
        vTestEOF :: a -> IO ()

        -- | Read one character
        vGetChar :: a -> IO Char
        -- | Read one line
        vGetLine :: a -> IO String
        {- | Get the remaining contents.  Please note that as a user of this
           function, the same partial-closing semantics as are used in the
           standard 'hGetContents' are /encouraged/ from implementators,
           but are not /required/.  That means that, for instance,
           a 'vGetChar' after a 'vGetContents' may return some undefined
           result instead of the error you would normally get.  You should
           use caution to make sure your code doesn't fall into that trap,
           or make sure to test your code with Handle or one of the
           default instances defined in this module.  Also, some implementations
           may essentially provide a complete close after a call to 'vGetContents'.
           The bottom line: after a call to 'vGetContents', you should do nothing
           else with the object save closing it with 'vClose'.

           For implementators, you are highly encouraged to provide a correct
           implementation. -}
        vGetContents :: a -> IO String
        -- | Indicate whether at least one item is ready for reading.
        -- This will always be True for a great many implementations.
        vReady :: a -> IO Bool
        -- | Indicate whether a particular item is available for reading.
        vIsReadable :: a -> IO Bool

        -- | Write one character
        vPutChar :: a -> Char -> IO ()
        -- | Write a string
        vPutStr :: a -> String -> IO ()
        -- | Write a string with newline character after it
        vPutStrLn :: a -> String -> IO ()
        -- | Write a string representation of the argument, plus a newline.
        vPrint :: Show b => a -> b -> IO ()
        -- | Flush any output buffers.
        -- Note: implementations should assure that a vFlush is automatically
        -- performed
        -- on file close, if necessary to ensure all data sent is written.
        vFlush :: a -> IO ()
        -- | Indicate whether or not this particular object supports writing.
        vIsWritable :: a -> IO Bool

        -- | Seek to a specific location.
        vSeek :: a -> SeekMode -> Integer -> IO ()

        -- | Get the current position.
        vTell :: a -> IO Integer

        -- | Convenience function to reset the file pointer to the beginning
        -- of the file.  A call to @vRewind h@ is the
        -- same as @'vSeek' h AbsoluteSeek 0@.
        vRewind :: a -> IO ()

        -- | Indicate whether this instance supports seeking.
        vIsSeekable :: a -> IO Bool

        -- | Set buffering; the default action is a no-op.
        vSetBuffering :: a -> BufferMode -> IO ()

        -- | Get buffering; the default action always returns NoBuffering.
        vGetBuffering :: a -> IO BufferMode

        -- | Binary output: write the specified number of octets from the specified
        -- buffer location.
        vPutBuf :: a -> Ptr b -> Int -> IO ()

        -- | Binary input: read the specified number of octets from the
        -- specified buffer location, continuing to read
        -- until it either consumes that much data or EOF is encountered.
        -- Returns the number of octets actually read.  EOF errors are never
        -- raised; fewer bytes than requested are returned on EOF.
        vGetBuf :: a -> Ptr b -> Int -> IO Int

        vSetBuffering _ _ = return ()
        vGetBuffering _ = return NoBuffering

        vShow x = return (show x)

        vMkIOError _ et desc mfp =
            mkIOError et desc Nothing mfp

        vGetFP _ = return Nothing

        vThrow h et = do
                      fp <- vGetFP h
                      ioError (vMkIOError h et "" fp)

        vTestEOF h = do e <- vIsEOF h
                        if e then vThrow h eofErrorType
                           else return ()

        vIsOpen h = vIsClosed h >>= return . not
        vIsClosed h = vIsOpen h >>= return . not
        vTestOpen h = do e <- vIsClosed h
                         if e then vThrow h illegalOperationErrorType
                            else return ()

        vIsReadable _ = return False

        vGetLine h =
            let loop accum =
                    let func = do c <- vGetChar h
                                  case c of
                                         '\n' -> return accum
                                         x -> accum `seq` loop (accum ++ [x])
                        handler e = if isEOFError e then return accum
                                    else ioError e
                        in catch func handler
                in
                do firstchar <- vGetChar h
                   case firstchar of
                       '\n' -> return []
                       x -> loop [x]

        vGetContents h =
            let loop =
                    let func = do c <- vGetChar h
                                  next <- loop
                                  c `seq` return (c : next)
                        handler e = if isEOFError e then return []
                                    else ioError e
                        in catch func handler
                in
                do loop

        vReady h = do vTestEOF h
                      return True

        vIsWritable _ = return False

        vPutStr _ [] = return ()
        vPutStr h (x:xs) = do vPutChar h x
                              vPutStr h xs

        vPutStrLn h s = vPutStr h (s ++ "\n")

        vPrint h s = vPutStrLn h (show s)

        vFlush = vTestOpen

        vIsSeekable _ = return False

        vRewind h = vSeek h AbsoluteSeek 0

        vPutChar h _ = vThrow h illegalOperationErrorType
        vSeek h _ _ = vThrow h illegalOperationErrorType
        vTell h = vThrow h illegalOperationErrorType
        vGetChar h = vThrow h illegalOperationErrorType

        vPutBuf h buf len =
            do str <- peekCStringLen (castPtr buf, len)
               vPutStr h str

        vGetBuf h b l =
            worker b l 0
            where worker _ 0 accum = return accum
                  worker buf len accum =
                      do iseof <- vIsEOF h
                         if iseof
                            then return accum
                            else do c <- vGetChar h
                                    let cc = castCharToCChar c
                                    poke (castPtr buf) cc
                                    let newptr = plusPtr buf 1
                                    worker newptr (len - 1) (accum + 1)

    ----------------------------------------------------------------------
    -- Handle instances
    ----------------------------------------------------------------------
    instance HVIO Handle where
        vClose = hClose
        vIsEOF = hIsEOF
    #ifdef __GLASGOW_HASKELL__
        vShow = hShow
    #endif
        vMkIOError h et desc mfp =
            mkIOError et desc (Just h) mfp
        vGetChar = hGetChar
        vGetLine = hGetLine
        vGetContents = hGetContents
        vReady = hReady
        vIsReadable = hIsReadable
        vPutChar = hPutChar
        vPutStr = hPutStr
        vPutStrLn = hPutStrLn
        vPrint = hPrint
        vFlush = hFlush
        vIsWritable = hIsWritable
        vSeek = hSeek
        vTell = hTell
        vIsSeekable = hIsSeekable
        vSetBuffering = hSetBuffering
        vGetBuffering = hGetBuffering
        vGetBuf = hGetBuf
        vPutBuf = hPutBuf
        vIsOpen = hIsOpen
        vIsClosed = hIsClosed

    ----------------------------------------------------------------------
    -- VIO Support
    ----------------------------------------------------------------------
    type VIOCloseSupport a = IORef (Bool, a)

    vioc_isopen :: VIOCloseSupport a -> IO Bool
    vioc_isopen x = readIORef x >>= return . fst

    vioc_get :: VIOCloseSupport a -> IO a
    vioc_get x = readIORef x >>= return . snd

    vioc_close :: VIOCloseSupport a -> IO ()
    vioc_close x = modifyIORef x (\ (_, dat) -> (False, dat))

    vioc_set :: VIOCloseSupport a -> a -> IO ()
    vioc_set x newdat = modifyIORef x (\ (stat, _) -> (stat, newdat))

    ----------------------------------------------------------------------
    -- Stream Readers
    ----------------------------------------------------------------------
    {- | Simulate I\/O based on a string buffer.

    When a 'StreamReader' is created, it is initialized based on the contents of
    a 'String'.  Its contents are read lazily whenever a request is made to read
    something from the 'StreamReader'.    It
    can be used, therefore, to implement filters (simply initialize it with the
    result from, say, a map over hGetContents from another HVIO object), codecs,
    and simple I\/O testing.  Because it is lazy, it need not hold the entire
    string in memory.  You can create a 'StreamReader' with a call to
    'newStreamReader'.
     -}
    newtype StreamReader = StreamReader (VIOCloseSupport String)

    {- | Create a new 'StreamReader' object. -}
    newStreamReader :: String            -- ^ Initial contents of the 'StreamReader'
                    -> IO StreamReader
    newStreamReader s = do ref <- newIORef (True, s)
                           return (StreamReader ref)

    srv :: StreamReader -> VIOCloseSupport String
    srv (StreamReader x) = x

    instance Show StreamReader where
        show _ = "<StreamReader>"

    instance HVIO StreamReader where
        vClose = vioc_close . srv
        vIsEOF h = do vTestOpen h
                      d <- vioc_get (srv h)
                      return $ case d of
                                      [] -> True
                                      _ -> False
        vIsOpen = vioc_isopen . srv
        vGetChar h = do vTestEOF h
                        c <- vioc_get (srv h)
                        let retval = head c
                        vioc_set (srv h) (tail c)
                        return retval

        vGetContents h = do vTestEOF h
                            c <- vioc_get (srv h)
                            vClose h
                            return c
        vIsReadable _ = return True

    ----------------------------------------------------------------------
    -- Buffers
    ----------------------------------------------------------------------
    {- | A 'MemoryBuffer' simulates true I\/O, but uses an in-memory buffer instead
    of on-disk storage.

    It provides
    a full interface like Handle (it implements 'HVIOReader', 'HVIOWriter',
    and 'HVIOSeeker').  However, it maintains an in-memory buffer with the
    contents of the file, rather than an actual on-disk file.  You can access
    the entire contents of this buffer at any time.  This can be quite useful
    for testing I\/O code, or for cases where existing APIs use I\/O, but you
    prefer a String representation.  You can create a 'MemoryBuffer' with a call
    to 'newMemoryBuffer'.

    The present 'MemoryBuffer' implementation is rather inefficient, particularly
    when reading towards the end of large files.  It's best used for smallish
    data storage.  This problem will be fixed eventually.
    -}
    data MemoryBuffer = MemoryBuffer (String -> IO ()) (VIOCloseSupport (Int, String))

    {- | Create a new 'MemoryBuffer' instance.  The buffer is initialized
    to the value passed, and the pointer is placed at the beginning of the file.

    You can put things in it by using the normal 'vPutStr' calls, and reset to
    the beginning by using the normal 'vRewind' call.

    The function is called when 'vClose' is called, and is passed the contents of
    the buffer at close time.  You can use 'mbDefaultCloseFunc' if you don't want to
    do anything.

    To create an empty buffer, pass the initial value @\"\"@. -}
    newMemoryBuffer :: String               -- ^ Initial Contents
                    -> (String -> IO ())    -- ^ close func
                    -> IO MemoryBuffer
    newMemoryBuffer initval closefunc = do ref <- newIORef (True, (0, initval))
                                           return (MemoryBuffer closefunc ref)

    {- | Default (no-op) memory buf close function. -}
    mbDefaultCloseFunc :: String -> IO ()
    mbDefaultCloseFunc _ = return ()

    vrv :: MemoryBuffer -> VIOCloseSupport (Int, String)
    vrv (MemoryBuffer _ x) = x

    {- | Grab the entire contents of the buffer as a string.
    Unlike 'vGetContents', this has no effect on the open status of the
    item, the EOF status, or the current position of the file pointer. -}
    getMemoryBuffer :: MemoryBuffer -> IO String
    getMemoryBuffer h = do c <- vioc_get (vrv h)
                           return (snd c)

    instance Show MemoryBuffer where
        show _ = "<MemoryBuffer>"

    instance HVIO MemoryBuffer where
        vClose x = do wasopen <- vIsOpen x
                      vioc_close (vrv x)
                      if wasopen
                         then do c <- getMemoryBuffer x
                                 case x of
                                     MemoryBuffer cf _ -> cf c
                         else return ()
        vIsEOF h = do vTestOpen h
                      c <- vioc_get (vrv h)
                      return ((length (snd c)) == (fst c))
        vIsOpen = vioc_isopen . vrv
        vGetChar h = do vTestEOF h
                        c <- vioc_get (vrv h)
                        let retval = (snd c) !! (fst c)
                        vioc_set (vrv h) (succ (fst c), snd c)
                        return retval
        vGetContents h = do vTestEOF h
                            v <- vioc_get (vrv h)
                            let retval = drop (fst v) (snd v)
                            vioc_set (vrv h) (-1, "")
                            vClose h
                            return retval
        vIsReadable _ = return True

        vPutStr h s = do (pos, buf) <- vioc_get (vrv h)
                         let (pre, post) = splitAt pos buf
                         let newbuf = pre ++ s ++ (drop (length s) post)
                         vioc_set (vrv h) (pos + (length s), newbuf)
        vPutChar h c = vPutStr h [c]
        vIsWritable _ = return True
        vTell h = do v <- vioc_get (vrv h)
                     return . fromIntegral $ (fst v)
        vSeek h seekmode seekposp =
            do (pos, buf) <- vioc_get (vrv h)
               let seekpos = fromInteger seekposp
               let newpos = case seekmode of
                                 AbsoluteSeek -> seekpos
                                 RelativeSeek -> pos + seekpos
                                 SeekFromEnd -> (length buf) + seekpos
               let buf2 = buf ++ if newpos > (length buf)
                                    then replicate (newpos - (length buf)) '\0'
                                    else []
               vioc_set (vrv h) (newpos, buf2)
        vIsSeekable _ = return True

    ----------------------------------------------------------------------
    -- Pipes
    ----------------------------------------------------------------------
    {- | Create a Haskell pipe.

    These pipes are analogous to the Unix
    pipes that are available from System.Posix, but don't require Unix and work
    only in Haskell.  When you create a pipe, you actually get two HVIO objects:
    a 'PipeReader' and a 'PipeWriter'.  You must use the 'PipeWriter' in one
    thread and the 'PipeReader' in another thread.  Data that's written to the
    'PipeWriter' will then be available for reading with the 'PipeReader'.  The
    pipes are implemented completely with existing Haskell threading primitives,
    and require no special operating system support.  Unlike Unix pipes, these
    pipes cannot be used across a fork().  Also unlike Unix pipes, these pipes
    are portable and interact well with Haskell threads. -}
    newHVIOPipe :: IO (PipeReader, PipeWriter)
    newHVIOPipe = do mv <- newEmptyMVar
                     readerref <- newIORef (True, mv)
                     let reader = PipeReader readerref
                     writerref <- newIORef (True, reader)
                     return (reader, PipeWriter writerref)

    data PipeBit = PipeBit Char
                 | PipeEOF
                   deriving (Eq, Show)

    {- | The reading side of a Haskell pipe.  Please see 'newHVIOPipe' for more
    details. -}
    newtype PipeReader = PipeReader (VIOCloseSupport (MVar PipeBit))

    {- | The writing side of a Haskell pipe.  Please see 'newHVIOPipe' for more
    details. -}
    newtype PipeWriter = PipeWriter (VIOCloseSupport PipeReader)

    ------------------------------
    -- Pipe Reader
    ------------------------------
    prv :: PipeReader -> VIOCloseSupport (MVar PipeBit)
    prv (PipeReader x) = x

    instance Show PipeReader where
        show _ = "<PipeReader>"

    pr_getc :: PipeReader -> IO PipeBit
    pr_getc h = do mv <- vioc_get (prv h)
                   takeMVar mv

    instance HVIO PipeReader where
        vClose = vioc_close . prv
        vIsOpen = vioc_isopen . prv
        vIsEOF h = do vTestOpen h
                      mv <- vioc_get (prv h)
                      dat <- readMVar mv
                      return (dat == PipeEOF)

        vGetChar h = do vTestEOF h
                        c <- pr_getc h
                        case c of
                            PipeBit x -> return x
                            -- vTestEOF should eliminate this case
                            _ -> fail "Internal error in HVIOReader vGetChar"
        vGetContents h =
            let loop = do c <- pr_getc h
                          case c of
                              PipeEOF -> return []
                              PipeBit x -> do next <- loop
                                              return (x : next)
            in do vTestEOF h
                  loop
        vIsReadable _ = return True

    ------------------------------
    -- Pipe Writer
    ------------------------------
    pwv :: PipeWriter -> VIOCloseSupport PipeReader
    pwv (PipeWriter x) = x

    pwmv :: PipeWriter -> IO (MVar PipeBit)
    pwmv (PipeWriter x) = do mv1 <- vioc_get x
                             vioc_get (prv mv1)

    instance Show PipeWriter where
        show _ = "<PipeWriter>"

    instance HVIO PipeWriter where
        vClose h = do o <- vIsOpen h
                      if o then do
                                mv <- pwmv h
                                putMVar mv PipeEOF
                                vioc_close (pwv h)
                         else return ()
        vIsOpen = vioc_isopen . pwv
        vIsEOF h = do vTestOpen h
                      return False

        -- FIXME: race condition below (could be closed after testing)
        vPutChar h c = do vTestOpen h
                          child <- vioc_get (pwv h)
                          copen <- vIsOpen child
                          if copen
                             then do mv <- pwmv h
                                     putMVar mv (PipeBit c)
                             else fail "PipeWriter: Couldn't write to pipe because child end is closed"
        vIsWritable _ = return True