Parser.hs

{-

 Copyright (c) 2005 Lemmih <lemmih@gmail.com>

 Permission to use, copy, modify, and distribute this software for any
 purpose with or without fee is hereby granted, provided that the above
 copyright notice and this permission notice appear in all copies.

 THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

-}
-----------------------------------------------------------------------------
-- |
-- Module      :  BParser
-- Copyright   :  (c) Lemmih, 2005
-- License     :  BSD-style (see the file libraries/base/LICENSE)
-- 
-- Maintainer  :  lemmih@gmail.com
-- Stability   :  stable
-- Portability :  portable
-- 
-- A parsec style parser for BEncoded data
-----------------------------------------------------------------------------
module Data.BEncode.Parser
    ( BParser
    , runParser
    , token
    , dict
    , list
    , optional
    , bstring
    , bfaststring
    , bint
    , setInput
    , (<|>)
    ) where


import Data.BEncode
import qualified Data.Map as Map
import qualified Data.ByteString.Char8 as BS
import Control.Monad

data BParser a
    = BParser (BEncode -> Reply a)

runB :: BParser a -> BEncode -> Reply a
runB (BParser b) = b

data Reply a
    = Ok a BEncode
    | Error String

instance Monad BParser where
    (BParser p) >>= f = BParser $ \b -> case p b of
                                          Ok a b' -> runB (f a) b'
                                          Error str -> Error str
    return val = BParser $ Ok val
    fail str = BParser $ \_ -> Error str

(<|>) :: BParser a -> BParser a -> BParser a
(BParser b1) <|> (BParser b2)
        = BParser $ \b -> case b1 b of
                            Ok a b' -> Ok a b'
                            _ -> b2 b

runParser :: BParser a -> BEncode -> Either String a
runParser parser b = case runB parser b of
                       Ok a _ -> Right a
                       Error str -> Left str

token :: BParser BEncode
token = BParser $ \b -> Ok b b

dict :: String -> BParser BEncode
dict name = BParser $ \b -> case b of
                              BDict bmap | Just code <- Map.lookup name bmap
                                   -> Ok code b
                              BDict _ -> Error $ "Name not found in dictionary: " ++ name
                              _ -> Error $ "Not a dictionary: " ++ name

list :: String -> BParser a -> BParser [a]
list name p
    = dict name >>= \lst ->
      BParser $ \b -> case lst of
                      BList bs -> foldr cat (Ok [] b) (map (runB p) bs)
                      _ -> Error $ "Not a list: " ++ name
    where cat (Ok v _) (Ok vs b) = Ok (v:vs) b
          cat (Ok _ _) (Error str) = Error str
          cat (Error str) _ = Error str

optional :: BParser a -> BParser (Maybe a)
optional p = liftM Just p <|> return Nothing

bstring :: BParser BEncode -> BParser String
bstring p = do b <- p
               case b of
                 BString str -> return (BS.unpack str)
                 _ -> fail $ "Expected BString, found: " ++ show b

bfaststring :: BParser BEncode -> BParser BS.ByteString
bfaststring p = do b <- p
                   case b of
                     BString str -> return str
                     _ -> fail $ "Expected BString, found: " ++ show b

bint :: BParser BEncode -> BParser Int
bint p = do b <- p
            case b of
              BInt int -> return int
              _ -> fail $ "Expected BInt, found: " ++ show b

setInput :: BEncode -> BParser ()
setInput b = BParser $ \_ -> Ok () b