    {-# LANGUAGE OverloadedStrings #-}
    -----------------------------------------------------------------------------
    -- |
    -- Module      :  HSP.XML.PCDATA
    -- Copyright   :  (c) Niklas Broberg 2008-2012
    -- License     :  BSD-style (see the file LICENSE.txt)
    --
    -- Maintainer  :  Niklas Broberg, nibro@cs.chalmers.se
    -- Stability   :  experimental
    -- Portability :  Haskell 98
    --
    -- Escaping between CDATA <=> PCDATA
    -----------------------------------------------------------------------------
    module HSP.XML.PCDATA (
              escape
    --	, unescape
            , escaper
    --        , unescaper
            , xmlEscapeChars
            ) where

    import Data.Monoid              ((<>), mempty)
    import Data.Text.Lazy           (Text, uncons)
    import qualified Data.Text.Lazy as Text
    import Data.Text.Lazy.Builder   (Builder, fromLazyText, singleton)

    -- | Take a normal string and transform it to PCDATA by escaping special characters.
    -- calls 'escaper' with 'xmlEscapeChars'
    -- See also: 'escaper'
    escape :: Text -> Builder
    escape = escaper xmlEscapeChars

    -- | Take a normal string and transform it to PCDATA by escaping special characters.
    -- See also: 'escape', 'xmlEscapeChars'
    escaper :: [(Char, Builder)] -- ^ table of escape characters
            -> Text -- ^ String to escape
            -> Builder -- ^ Escaped String
    escaper escapeTable = go
        where
          escapeChars = map fst escapeTable
          go txt | Text.null txt = mempty
          go txt =
              case Text.break (`elem` escapeChars) txt of
                (hd,tl) ->
                    case uncons tl of
                      Nothing -> fromLazyText hd
                      (Just (c, tl')) -> fromLazyText hd <> pChar escapeTable c <> go tl'

    pChar :: [(Char, Builder)] -- ^ table of escape characters
          -> Char              -- ^ character to escape
          -> Builder           -- ^ escaped character
    pChar escapeChars c =
        case lookup c escapeChars of
          Nothing -> singleton c
          Just s  -> singleton '&' <> s <> singleton ';'

    -- This list should be extended.
    xmlEscapeChars :: [(Char, Builder)]
    xmlEscapeChars = [
            ('&',   "amp"   ),
            ('\"',  "quot"  ),
            ('\'',  "apos"  ),
            ('<',   "lt"    ),
            ('>',   "gt"    )
            ]
    {-
    -- | Take a PCDATA string and translate all escaped characters in it to the normal
    -- characters they represent.
    -- Does no error checking of input string, will fail if input is not valid PCDATA.
    -- calls 'unescaper' with 'xmlEscapeChars'
    -- See also: 'unescaper'
    unescape :: String -> String
    unescape = unescaper xmlEscapeChars

    -- | Take a PCDATA string and translate all escaped characters in it to the normal
    -- characters they represent.
    -- Does no error checking of input string, will fail if input is not valid PCDATA.
    -- See also: 'unescape', 'xmlEscapeChars'
    unescaper :: [(Char, Builder)] -- ^ table of escape characters
              -> Text -- ^ String to unescape
              -> Builder -- ^ unescaped String
    unescaper escapeChars = reverse . unE ""
      where unE acc "" = acc
      	unE acc (c:cs) =
      	  case c of
      	    '&' -> let (esc, ';':rest) = break (==';') cs
      	               Just ec = revLookup esc escapeChars
      	            in unE (ec:acc) rest
      	    _ -> unE (c:acc) cs

      	revLookup e = lookup e . map (\(a,b) -> (b,a))
    -}