    -- Copyright (C) 2003 David Roundy
    --
    -- 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, 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; see the file COPYING.  If not, write to
    -- the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
    -- Boston, MA 02110-1301, USA.

    module Darcs.Patch.RegChars ( regChars,
                    ) where

    (&&&) :: (a -> Bool) -> (a -> Bool) -> (a -> Bool)
    (&&&) a b c = a c && b c

    (|||) :: (a -> Bool) -> (a -> Bool) -> (a -> Bool)
    (|||) a b c = a c || b c

    {-# INLINE regChars #-}

    -- | 'regChars' returns a filter function that tells if a char is a member
    -- of the regChar expression or not. The regChar expression is basically a
    -- set of chars, but it can contain ranges with use of the '-' (dash), and
    -- it can also be specified as a complement set by prefixing with '^'
    -- (caret). The dash and caret, as well as the backslash, can all be
    -- escaped with a backslash to suppress their special meaning.
    --
    -- NOTE: The '.' (dot) is allowed to be escaped. It has no special meaning
    -- if it is not escaped, but the default 'filename_toks' in
    -- Darcs.Commands.Replace uses an escaped dot (WHY?).

    regChars :: String -> (Char -> Bool)
    regChars ('^':cs) = not . normalRegChars (unescapeChars cs)
    regChars ('\\':'^':cs) = normalRegChars $ unescapeChars $ '^':cs
    regChars cs = normalRegChars $ unescapeChars cs

    {-# INLINE unescapeChars #-}

    -- | 'unescapeChars' unescapes whitespace, which is escaped in the replace
    -- patch file format. It will also unescape escaped carets, which is useful
    -- for escaping a leading caret that should not invert the regChars. All
    -- other escapes are left for the unescaping in 'normalRegChars'.

    unescapeChars :: String -> String
    unescapeChars ('\\':'n':cs) = '\n' : unescapeChars cs
    unescapeChars ('\\':'t':cs) = '\t' : unescapeChars cs
    unescapeChars ('\\':'^':cs) = '^' : unescapeChars cs
    unescapeChars (c:cs) = c : unescapeChars cs
    unescapeChars [] = []

    {-# INLINE normalRegChars #-}

    -- | 'normalRegChars' assembles the filter function. It handles special
    -- chars, and also unescaping of escaped special chars. If a non-special
    -- char is still escaped by now we get a failure.

    normalRegChars :: String -> (Char -> Bool)
    normalRegChars ('\\':'.':cs) = (=='.') ||| normalRegChars cs
    normalRegChars ('\\':'-':cs) = (=='-') ||| normalRegChars cs
    normalRegChars ('\\':'\\':cs) = (=='\\') ||| normalRegChars cs
    normalRegChars ('\\':c:_) = error $ "'\\"++[c]++"' not supported."
    normalRegChars (c1:'-':c2:cs) = ((>= c1) &&& (<= c2)) ||| normalRegChars cs
    normalRegChars (c:cs) = (== c) ||| normalRegChars cs
    normalRegChars [] = \_ -> False