Use.hs

{-----------------------------------------------------------------
 
  (c) 2008-2009 Markus Dittrich 
 
  This program is free software; you can redistribute it 
  and/or modify it under the terms of the GNU General Public 
  License Version 3 as published by the Free Software Foundation. 
 
  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 Version 3 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.

--------------------------------------------------------------------}


-- | this module parses the USE info of a package
module Parsers.Use ( get_USE_flags 
                   , get_IUSE_flags
                   , try_get_USE_flags
                   , try_get_IUSE_flags
                   ) where 


-- imports
import qualified Data.ByteString as B(ByteString, head, tail)
import Prelude
import System.FilePath.Posix((</>))


-- local imports
import Helpers.ByteString(tokenize_BS, plusW, dashW)
import Helpers.FileIO(read_file, try_read_file)



-- | parses the USE flags active during the emerge of the current 
-- package and returns them as a raw ByteString
get_IUSE_flags :: FilePath -> IO [B.ByteString]
get_IUSE_flags path = (get_USE_flags_generic "IUSE" path)
                      >>= \flags ->
                        let
                          filteredFlags = filter_prefix flags
                        in
                          return filteredFlags



-- | parses the USE flags active during the emerge of the current 
-- package and returns the content in tokenized form.
get_USE_flags :: FilePath -> IO [B.ByteString]
get_USE_flags = get_USE_flags_generic "USE"
                
         

-- | same as get_useFlags_raw but uses try_read so we can handle
-- failure in opening a USE file during execution
try_get_IUSE_flags :: FilePath -> IO (Maybe [B.ByteString])
try_get_IUSE_flags path = 
 
  (try_get_USE_flags_generic "IUSE" path)
  >>= \flags ->
    case flags of
      Nothing -> return Nothing
      Just f  -> let
                   filteredFlags = filter_prefix f
                 in       
                   return $ Just filteredFlags

              

-- | same as get_useFlags but uses try_read so we can handle
-- failure in opening a USE file during execution
try_get_USE_flags :: FilePath -> IO (Maybe [B.ByteString])
try_get_USE_flags = try_get_USE_flags_generic "USE"



-- | generic function to parse USE/IUSE flags active during the 
-- emerge of the current package and returns them as a 
-- tokenized ByteString
get_USE_flags_generic :: String -> FilePath -> IO [B.ByteString]
get_USE_flags_generic name path = (read_file $ path </> name)
                                  >>= return . tokenize_BS


-- | same as get_USE_flags_generic but uses try_read so we can handle
-- failure in opening a USE/IUSE file during execution
try_get_USE_flags_generic :: String -> FilePath 
                          -> IO (Maybe [B.ByteString])
try_get_USE_flags_generic name path = 

  try_read_file (path </> name)
  >>= \useContent -> 
    case useContent of
      Just v -> return . Just $ tokenize_BS v
      _      -> return Nothing



-- | according to EAPI=1 use flags in IUSE can have a prefix
-- of +/- that we throw out for the moment in order to be able
-- to match it against plain use flag requests.
-- NOTE: We might be able to use these prefixes for more detailed
-- queries in the future
filter_prefix :: [B.ByteString] -> [B.ByteString]
filter_prefix foo = map remove_prefix foo

  where
    remove_prefix x = if ( (B.head x) == plusW || (B.head x) == dashW)
                      then
                        B.tail x
                      else
                        x