
 Copyright ( C ) 2006 - 2010   <  > 

 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 

Copyright (C) 2006-2010 John MacFarlane <>

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       : Text . Pandoc . Readers . HTML 
    Copyright    : Copyright ( C ) 2006 - 2010   
    License      : GNU GPL , version 2 or above 

    Maintainer   :   <  > 
    Stability    : alpha 
    Portability : portable 

 Conversion of HTML to ' Pandoc ' document . 

   Module      : Text.Pandoc.Readers.HTML
   Copyright   : Copyright (C) 2006-2010 John MacFarlane
   License     : GNU GPL, version 2 or above 

   Maintainer  : John MacFarlane <>
   Stability   : alpha 
   Portability : portable

Conversion of HTML to 'Pandoc' document.
-}


 module Text . Pandoc . Readers . HTML ( readHtml 
                                 , htmlTag 
                                 , htmlInBalanced 
                                 , isInlineTag 
                                 , isBlockTag 
                                 , isTextTag 
                                 , isCommentTag 
                                 ) where 

module Text.Pandoc.Readers.HTML ( readHtml
                                , htmlTag
                                , htmlInBalanced
                                , isInlineTag
                                , isBlockTag
                                , isTextTag
                                , isCommentTag
                                ) where
-}

module Pandoc.Readers.HTML where

import Text.ParserCombinators.Parsec
import Text.ParserCombinators.Parsec.Pos
import Text.HTML.TagSoup
import Text.HTML.TagSoup.Match
import Text.Pandoc.Definition
import Text.Pandoc.Builder (text, toList)
import Text.Pandoc.Shared
import Text.Pandoc.Parsing
import Data.Maybe ( fromMaybe, isJust )
import Data.List ( intercalate )
import Data.Char ( isSpace, isDigit, toLower )
import Control.Monad ( liftM, guard, when )

  | Convert HTML - formatted string to ' Pandoc ' document .
readHtml :: ParserState   -- ^ Parser state
         -> String        -- ^ String to parse (assumes @'\n'@ line endings)
         -> Pandoc
readHtml st inp = Pandoc meta blocks
  where blocks  = readWith parseBody st rest
        tags    = canonicalizeTags $
                   parseTagsOptions parseOptions{ optTagPosition = True } inp
        hasHeader = any (~== TagOpen "head" []) tags
        (meta, rest) = if hasHeader
                          then parseHeader tags
                          else (Meta [] [] [], tags)

type TagParser = GenParser (Tag String) ParserState

-- TODO - fix this - not every header has a title tag
parseHeader :: [Tag String] -> (Meta, [Tag String])
parseHeader tags = (Meta{docTitle = tit'', docAuthors = [], docDate = []}, rest)
  where (tit,_) = break (~== TagClose "title") $ drop 1 $
                   dropWhile (\t -> not $ t ~== TagOpen "title" []) tags
        tit' = concatMap fromTagText $ filter isTagText tit
        tit'' = normalizeSpaces $ toList $ text tit'
        rest  = drop 1 $ dropWhile (\t -> not $ t ~== TagClose "head" ||
                                                t ~== TagOpen "body" []) tags

parseBody :: TagParser [Block]
parseBody = liftM (fixPlains False . concat) $ manyTill block eof

block :: TagParser [Block]
block = choice
            [ pPara
            , pHeader
            , pBlockQuote
            , pCodeBlock
            , pList
            , pHrule
            , pSimpleTable
            , pPlain
            , pRawHtmlBlock
            ]

  repeated in SelfContained -- consolidate eventually
renderTags' :: [Tag String] -> String
renderTags' = renderTagsOptions
               renderOptions{ optMinimize = \x ->
                                    let y = map toLower x
                                    in  y == "hr" || y == "br" ||
                                        y == "img" || y == "meta" ||
                                        y == "link"
                            , optRawTag = \x ->
                                    let y = map toLower x
                                    in  y == "script" || y == "style" }

pList :: TagParser [Block]
pList = pBulletList <|> pOrderedList <|> pDefinitionList

pBulletList :: TagParser [Block]
pBulletList = try $ do
  pSatisfy (~== TagOpen "ul" [])
  let nonItem = pSatisfy (\t ->
                  not (tagOpen (`elem` ["li","ol","ul","dl"]) (const True) t) &&
                  not (t ~== TagClose "ul"))
  -- note: if they have an <ol> or <ul> not in scope of a <li>,
  treat it as a list item , though it 's not valid  ...
  skipMany nonItem
  items <- manyTill (pInTags "li" block >>~ skipMany nonItem) (pCloses "ul")
  return [BulletList $ map (fixPlains True) items]

pOrderedList :: TagParser [Block]
pOrderedList = try $ do
  TagOpen _ attribs <- pSatisfy (~== TagOpen "ol" [])
  st <- getState
  let (start, style) =  if stateStrict st
                           then (1, DefaultStyle) 
                           else (sta', sty')
                              where sta = fromMaybe "1" $
                                          lookup "start" attribs
                                    sta' = if all isDigit sta
                                              then read sta
                                              else 1
                                    sty = fromMaybe (fromMaybe "" $
                                          lookup "style" attribs) $
                                          lookup "class" attribs
                                    sty' = case sty of
                                            "lower-roman"  -> LowerRoman
                                            "upper-roman"  -> UpperRoman
                                            "lower-alpha"  -> LowerAlpha
                                            "upper-alpha"  -> UpperAlpha
                                            "decimal"      -> Decimal
                                            _              -> DefaultStyle
  let nonItem = pSatisfy (\t ->
                  not (tagOpen (`elem` ["li","ol","ul","dl"]) (const True) t) &&
                  not (t ~== TagClose "ol"))
  -- note: if they have an <ol> or <ul> not in scope of a <li>,
  treat it as a list item , though it 's not valid  ...
  skipMany nonItem
  items <- manyTill (pInTags "li" block >>~ skipMany nonItem) (pCloses "ol")
  return [OrderedList (start, style, DefaultDelim) $ map (fixPlains True) items]

pDefinitionList :: TagParser [Block]
pDefinitionList = try $ do
  pSatisfy (~== TagOpen "dl" [])
  items <- manyTill pDefListItem (pCloses "dl")
  return [DefinitionList items]

pDefListItem :: TagParser ([Inline],[[Block]])
pDefListItem = try $ do
  let nonItem = pSatisfy (\t -> not (t ~== TagOpen "dt" []) &&
                  not (t ~== TagOpen "dd" []) && not (t ~== TagClose "dl"))
  terms <- many1 (try $ skipMany nonItem >> pInTags "dt" inline)
  defs  <- many1 (try $ skipMany nonItem >> pInTags "dd" block)
  skipMany nonItem
  let term = intercalate [LineBreak] terms
  return (term, map (fixPlains True) defs)

fixPlains :: Bool -> [Block] -> [Block]
fixPlains inList bs = if any isParaish bs
                         then map plainToPara bs
                         else bs
  where isParaish (Para _) = True
        isParaish (CodeBlock _ _) = True
        isParaish (Header _ _) = True
        isParaish (BlockQuote _) = True
        isParaish (BulletList _) = not inList
        isParaish (OrderedList _ _) = not inList
        isParaish (DefinitionList _) = not inList
        isParaish _        = False
        plainToPara (Plain xs) = Para xs
        plainToPara x = x

pRawTag :: TagParser String
pRawTag = do
  tag <- pAnyTag
  let ignorable x = x `elem` ["html","head","body"]
  if tagOpen ignorable (const True) tag || tagClose ignorable tag
     then return []
     else return $ renderTags' [tag]

pRawHtmlBlock :: TagParser [Block]
pRawHtmlBlock = do
  raw <- pHtmlBlock "script" <|> pHtmlBlock "style" <|> pRawTag
  state <- getState
  if stateParseRaw state && not (null raw)
     then return [RawBlock "html" raw]
     else return []

pHtmlBlock :: String -> TagParser String
pHtmlBlock t = try $ do
  open <- pSatisfy (~== TagOpen t [])
  contents <- manyTill pAnyTag (pSatisfy (~== TagClose t))
  return $ renderTags' $ [open] ++ contents ++ [TagClose t]

pHeader :: TagParser [Block]
pHeader = try $ do
  TagOpen tagtype attr <- pSatisfy $
                           tagOpen (`elem` ["h1","h2","h3","h4","h5","h6"])
                           (const True)
  let bodyTitle = TagOpen tagtype attr ~== TagOpen "h1" [("class","title")]
  let level = read (drop 1 tagtype)
  contents <- liftM concat $ manyTill inline (pCloses tagtype <|> eof)
  return $ if bodyTitle
              then []  -- skip a representation of the title in the body
              else [Header level $ normalizeSpaces contents]

pHrule :: TagParser [Block]
pHrule = do
  pSelfClosing (=="hr") (const True)
  return [HorizontalRule]

pSimpleTable :: TagParser [Block]
pSimpleTable = try $ do
  TagOpen _ _ <- pSatisfy (~== TagOpen "table" [])
  skipMany pBlank
  head' <- option [] $ pOptInTag "thead" $ pInTags "tr" (pCell "th")
  skipMany pBlank
  rows <- pOptInTag "tbody"
          $ many1 $ try $ skipMany pBlank >> pInTags "tr" (pCell "td")
  skipMany pBlank
  TagClose _ <- pSatisfy (~== TagClose "table") 
  let cols = maximum $ map length rows
  let aligns = replicate cols AlignLeft
  let widths = replicate cols 0
  return [Table [] aligns widths head' rows]

pCell :: String -> TagParser [TableCell]
pCell celltype = try $ do
  skipMany pBlank
  res <- pInTags celltype pPlain
  skipMany pBlank
  return [res]

pBlockQuote :: TagParser [Block]
pBlockQuote = do
  contents <- pInTags "blockquote" block
  return [BlockQuote $ fixPlains False contents]

pPlain :: TagParser [Block]
pPlain = do
  contents <- liftM (normalizeSpaces . concat) $ many1 inline
  if null contents
     then return []
     else return [Plain contents]

pPara :: TagParser [Block]
pPara = do
  contents <- pInTags "p" inline
  return [Para $ normalizeSpaces contents]

pCodeBlock :: TagParser [Block]
pCodeBlock = try $ do
  TagOpen _ attr <- pSatisfy (~== TagOpen "pre" [])
  contents <- manyTill pAnyTag (pCloses "pre" <|> eof)
  let rawText = concatMap fromTagText $ filter isTagText contents
  -- drop leading newline if any
  let result' = case rawText of
                     '\n':xs  -> xs
                     _        -> rawText
  -- drop trailing newline if any
  let result = case reverse result' of
                    '\n':_   -> init result'
                    _        -> result'
  let attribsId = fromMaybe "" $ lookup "id" attr
  let attribsClasses = words $ fromMaybe "" $ lookup "class" attr
  let attribsKV = filter (\(k,_) -> k /= "class" && k /= "id") attr
  st <- getState
  let attribs = if stateStrict st
                   then ("",[],[])
                   else (attribsId, attribsClasses, attribsKV)
  return [CodeBlock attribs result]

inline :: TagParser [Inline]
inline = choice
           [ pTagText
           , pEmph
           , pStrong
           , pSuperscript
           , pSubscript
           , pStrikeout
           , pLineBreak
           , pLink
           , pImage
           , pCode
           , pRawHtmlInline
           ]

pLocation :: TagParser ()
pLocation = do
  (TagPosition r c) <- pSat isTagPosition
  setPosition $ newPos "input" r c

pSat :: (Tag String -> Bool) -> TagParser (Tag String)
pSat f = do
  pos <- getPosition
  token show (const pos) (\x -> if f x then Just x else Nothing) 

pSatisfy :: (Tag String -> Bool) -> TagParser (Tag String)
pSatisfy f = try $ optional pLocation >> pSat f

pAnyTag :: TagParser (Tag String)
pAnyTag = pSatisfy (const True)

pSelfClosing :: (String -> Bool) -> ([Attribute String] -> Bool)
             -> TagParser (Tag String)
pSelfClosing f g = do
  open <- pSatisfy (tagOpen f g)
  optional $ pSatisfy (tagClose f)
  return open

pEmph :: TagParser [Inline]
pEmph = pInlinesInTags "em" Emph <|> pInlinesInTags "i" Emph

pStrong :: TagParser [Inline]
pStrong = pInlinesInTags "strong" Strong <|> pInlinesInTags "b" Strong

pSuperscript :: TagParser [Inline]
pSuperscript = failIfStrict >> pInlinesInTags "sup" Superscript

pSubscript :: TagParser [Inline]
pSubscript = failIfStrict >> pInlinesInTags "sub" Subscript

pStrikeout :: TagParser [Inline]
pStrikeout = do
  failIfStrict
  pInlinesInTags "s" Strikeout <|>
    pInlinesInTags "strike" Strikeout <|>
    pInlinesInTags "del" Strikeout <|>
    try (do pSatisfy (~== TagOpen "span" [("class","strikeout")])
            contents <- liftM concat $ manyTill inline (pCloses "span")
            return [Strikeout contents])

pLineBreak :: TagParser [Inline]
pLineBreak = do
  pSelfClosing (=="br") (const True)
  return [LineBreak]

pLink :: TagParser [Inline]
pLink = try $ do
  tag <- pSatisfy (tagOpenLit "a" (isJust . lookup "href"))
  let url = fromAttrib "href" tag
  let title = fromAttrib "title" tag
  lab <- liftM concat $ manyTill inline (pCloses "a")
  return [Link (normalizeSpaces lab) (escapeURI url, title)]

pImage :: TagParser [Inline]
pImage = do
  tag <- pSelfClosing (=="img") (isJust . lookup "src")
  let url = fromAttrib "src" tag
  let title = fromAttrib "title" tag
  let alt = fromAttrib "alt" tag
  return [Image (toList $ text alt) (escapeURI url, title)]

pCode :: TagParser [Inline]
pCode = try $ do
  (TagOpen open attr) <- pSatisfy $ tagOpen (`elem` ["code","tt"]) (const True)
  result <- manyTill pAnyTag (pCloses open)
  let ident = fromMaybe "" $ lookup "id" attr
  let classes = words $ fromMaybe [] $ lookup "class" attr
  let rest = filter (\(x,_) -> x /= "id" && x /= "class") attr
  return [Code (ident,classes,rest)
         $ intercalate " " $ lines $ innerText result]

pRawHtmlInline :: TagParser [Inline]
pRawHtmlInline = do
  result <- pSatisfy (tagComment (const True)) <|> pSatisfy isInlineTag
  state <- getState
  if stateParseRaw state
     then return [RawInline "html" $ renderTags' [result]]
     else return []

pInlinesInTags :: String -> ([Inline] -> Inline)
               -> TagParser [Inline]
pInlinesInTags tagtype f = do
  contents <- pInTags tagtype inline
  return [f $ normalizeSpaces contents]

pInTags :: String -> TagParser [a]
        -> TagParser [a]
pInTags tagtype parser = try $ do
  pSatisfy (~== TagOpen tagtype [])
  liftM concat $ manyTill parser (pCloses tagtype <|> eof)

pOptInTag :: String -> TagParser a
          -> TagParser a
pOptInTag tagtype parser = try $ do
  open <- option False (pSatisfy (~== TagOpen tagtype []) >> return True)
  skipMany pBlank
  x <- parser
  skipMany pBlank
  when open $ pCloses tagtype
  return x

pCloses :: String -> TagParser ()
pCloses tagtype = try $ do
  t <- lookAhead $ pSatisfy $ \tag -> isTagClose tag || isTagOpen tag
  case t of
       (TagClose t')  | t' == tagtype -> pAnyTag >> return ()
       (TagOpen t' _) | t' `closes` tagtype -> return ()
       (TagClose "ul") | tagtype == "li" -> return ()
       (TagClose "ol") | tagtype == "li" -> return ()
       (TagClose "dl") | tagtype == "li" -> return ()
       _ -> pzero

pTagText :: TagParser [Inline]
pTagText = try $ do
  (TagText str) <- pSatisfy isTagText
  st <- getState
  case runParser (many pTagContents) st "text" str of
       Left _        -> fail $ "Could not parse `" ++ str ++ "'"
       Right result  -> return result

pBlank :: TagParser ()
pBlank = try $ do
  (TagText str) <- pSatisfy isTagText
  guard $ all isSpace str

pTagContents :: GenParser Char ParserState Inline
pTagContents =
  pStr <|> pSpace <|> smartPunctuation pTagContents <|> pSymbol <|> pBad

pStr :: GenParser Char ParserState Inline
pStr = do
  result <- many1 $ satisfy $ \c ->
                     not (isSpace c) && not (isSpecial c) && not (isBad c)
  pos <- getPosition
  updateState $ \s -> s{ stateLastStrPos = Just pos }
  return $ Str result

isSpecial :: Char -> Bool
isSpecial '"' = True
isSpecial '\'' = True
isSpecial '.' = True
isSpecial '-' = True
isSpecial '\8216' = True
isSpecial '\8217' = True
isSpecial '\8220' = True
isSpecial '\8221' = True
isSpecial _ = False

pSymbol :: GenParser Char ParserState Inline
pSymbol = satisfy isSpecial >>= return . Str . (:[])

isBad :: Char -> Bool
isBad c = c >= '\128' && c <= '\159' -- not allowed in HTML

pBad :: GenParser Char ParserState Inline
pBad = do
  c <- satisfy isBad
  let c' = case c of
                '\128' -> '\8364'
                '\130' -> '\8218'
                '\131' -> '\402'
                '\132' -> '\8222'
                '\133' -> '\8230'
                '\134' -> '\8224'
                '\135' -> '\8225'
                '\136' -> '\710'
                '\137' -> '\8240'
                '\138' -> '\352'
                '\139' -> '\8249'
                '\140' -> '\338'
                '\142' -> '\381'
                '\145' -> '\8216'
                '\146' -> '\8217'
                '\147' -> '\8220'
                '\148' -> '\8221'
                '\149' -> '\8226'
                '\150' -> '\8211'
                '\151' -> '\8212'
                '\152' -> '\732'
                '\153' -> '\8482'
                '\154' -> '\353'
                '\155' -> '\8250'
                '\156' -> '\339'
                '\158' -> '\382'
                '\159' -> '\376'
                _      -> '?'
  return $ Str [c']

pSpace :: GenParser Char ParserState Inline
pSpace = many1 (satisfy isSpace) >> return Space

--
-- Constants
--

eitherBlockOrInline :: [String]
eitherBlockOrInline = ["applet", "button", "del", "iframe", "ins",
                  "map", "area", "object"]


 inlineHtmlTags : : [ [  ] ] 
 inlineHtmlTags = [ " a " , " abbr " , " acronym " , " b " , " basefont " , " bdo " , " big " , 
                   " br " , " cite " , " code " , " dfn " , " em " , " font " , " i " , " img " , 
                   " input " , "  " , " label " , " q " , " s " , " samp " , " select " , 
                   " small " , " span " , " strike " , " strong " , " sub " , " sup " , 
                   " textarea " , " tt " , " u " , " var " ] 

inlineHtmlTags :: [[Char]]
inlineHtmlTags = ["a", "abbr", "acronym", "b", "basefont", "bdo", "big",
                  "br", "cite", "code", "dfn", "em", "font", "i", "img",
                  "input", "kbd", "label", "q", "s", "samp", "select",
                  "small", "span", "strike", "strong", "sub", "sup",
                  "textarea", "tt", "u", "var"]
-}

blockHtmlTags :: [String]
blockHtmlTags = ["address", "blockquote", "body", "center", "dir", "div",
                 "dl", "fieldset", "form", "h1", "h2", "h3", "h4",
                 "h5", "h6", "head", "hr", "html", "isindex", "menu",
                 "noframes", "noscript", "ol", "p", "pre", "table", "ul", "dd",
                 "dt", "frameset", "li", "tbody", "td", "tfoot",
                 "th", "thead", "tr", "script", "style"]

-- We want to allow raw docbook in markdown documents, so we
-- include docbook block tags here too.
blockDocBookTags :: [String]
blockDocBookTags = ["calloutlist", "bibliolist", "glosslist", "itemizedlist",
                    "orderedlist", "segmentedlist", "simplelist",
                    "variablelist", "caution", "important", "note", "tip",
                    "warning", "address", "literallayout", "programlisting",
                    "programlistingco", "screen", "screenco", "screenshot",
                    "synopsis", "example", "informalexample", "figure",
                    "informalfigure", "table", "informaltable", "para",
                    "simpara", "formalpara", "equation", "informalequation",
                    "figure", "screenshot", "mediaobject", "qandaset",
                    "procedure", "task", "cmdsynopsis", "funcsynopsis",
                    "classsynopsis", "blockquote", "epigraph", "msgset",
                    "sidebar", "title"]

blockTags :: [String]
blockTags = blockHtmlTags ++ blockDocBookTags

isInlineTag :: Tag String -> Bool
isInlineTag t = tagOpen (`notElem` blockTags) (const True) t ||
                tagClose (`notElem` blockTags) t ||
                tagComment (const True) t

isBlockTag :: Tag String -> Bool
isBlockTag t = tagOpen (`elem` blocktags) (const True) t ||
               tagClose (`elem` blocktags) t ||
               tagComment (const True) t
                 where blocktags = blockTags ++ eitherBlockOrInline

isTextTag :: Tag String -> Bool
isTextTag = tagText (const True)

isCommentTag :: Tag String -> Bool
isCommentTag = tagComment (const True)

  taken from HXT and extended

closes :: String -> String -> Bool
_ `closes` "body" = False
_ `closes` "html" = False
"a" `closes` "a" = True
"li" `closes` "li" = True
"th" `closes` t | t `elem` ["th","td"] = True
"tr" `closes` t | t `elem` ["th","td","tr"] = True
"dt" `closes` t | t `elem` ["dt","dd"] = True
"hr" `closes` "p" = True
"p" `closes` "p" = True
"meta" `closes` "meta" = True
"colgroup" `closes` "colgroup" = True
"form" `closes` "form" = True
"label" `closes` "label" = True
"map" `closes` "map" = True
"object" `closes` "object" = True
_ `closes` t | t `elem` ["option","style","script","textarea","title"] = True
t `closes` "select" | t /= "option" = True
"thead" `closes` t | t `elem` ["colgroup"] = True
"tfoot" `closes` t | t `elem` ["thead","colgroup"] = True
"tbody" `closes` t | t `elem` ["tbody","tfoot","thead","colgroup"] = True
t `closes` t2 |
   t `elem` ["h1","h2","h3","h4","h5","h6","dl","ol","ul","table","div","p"] &&
   t2 `elem` ["h1","h2","h3","h4","h5","h6","p" ] = True -- not "div"
t1 `closes` t2 |
   t1 `elem` blockTags &&
   t2 `notElem` (blockTags ++ eitherBlockOrInline) = True
_ `closes` _ = False

--- parsers for use in markdown, textile readers

-- | Matches a stretch of HTML in balanced tags.
htmlInBalanced :: (Tag String -> Bool) -> GenParser Char ParserState String
htmlInBalanced f = try $ do
  (TagOpen t _, tag) <- htmlTag f
  guard $ '/' `notElem` tag      -- not a self-closing tag
  let nonTagChunk = many1 $ satisfy (/= '<')
  let stopper = htmlTag (~== TagClose t)
  let anytag = liftM snd $ htmlTag (const True)
  contents <- many $ notFollowedBy' stopper >>
                     (nonTagChunk <|> htmlInBalanced (const True) <|> anytag)
  endtag <- liftM snd stopper
  return $ tag ++ concat contents ++ endtag

-- | Matches a tag meeting a certain condition.
htmlTag :: (Tag String -> Bool) -> GenParser Char ParserState (Tag String, String)
htmlTag f = try $ do
  lookAhead (char '<')
  (next : _) <- getInput >>= return . canonicalizeTags . parseTags
  guard $ f next
  -- advance the parser
  case next of
       TagComment s -> do
          count (length s + 4) anyChar
          skipMany (satisfy (/='>'))
          char '>'
          return (next, "<!--" ++ s ++ "-->") 
       _            -> do
          rendered <- manyTill anyChar (char '>')
          return (next, rendered ++ ">")
 ^ Parser state
 ^ String to parse (assumes @'\n'@ line endings)
 TODO - fix this - not every header has a title tag
 consolidate eventually
 note: if they have an <ol> or <ul> not in scope of a <li>,
 note: if they have an <ol> or <ul> not in scope of a <li>,
 skip a representation of the title in the body
 drop leading newline if any
 drop trailing newline if any
 not allowed in HTML

 Constants

 We want to allow raw docbook in markdown documents, so we
 include docbook block tags here too.
 not "div"
- parsers for use in markdown, textile readers
 | Matches a stretch of HTML in balanced tags.
 not a self-closing tag
 | Matches a tag meeting a certain condition.
 advance the parser

 Copyright ( C ) 2006 - 2010   <  > 

 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 

Copyright (C) 2006-2010 John MacFarlane <>

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       : Text . Pandoc . Readers . HTML 
    Copyright    : Copyright ( C ) 2006 - 2010   
    License      : GNU GPL , version 2 or above 

    Maintainer   :   <  > 
    Stability    : alpha 
    Portability : portable 

 Conversion of HTML to ' Pandoc ' document . 

   Module      : Text.Pandoc.Readers.HTML
   Copyright   : Copyright (C) 2006-2010 John MacFarlane
   License     : GNU GPL, version 2 or above 

   Maintainer  : John MacFarlane <>
   Stability   : alpha 
   Portability : portable

Conversion of HTML to 'Pandoc' document.
-}


 module Text . Pandoc . Readers . HTML ( readHtml 
                                 , htmlTag 
                                 , htmlInBalanced 
                                 , isInlineTag 
                                 , isBlockTag 
                                 , isTextTag 
                                 , isCommentTag 
                                 ) where 

module Text.Pandoc.Readers.HTML ( readHtml
                                , htmlTag
                                , htmlInBalanced
                                , isInlineTag
                                , isBlockTag
                                , isTextTag
                                , isCommentTag
                                ) where
-}

module Pandoc.Readers.HTML where

import Text.ParserCombinators.Parsec
import Text.ParserCombinators.Parsec.Pos
import Text.HTML.TagSoup
import Text.HTML.TagSoup.Match
import Text.Pandoc.Definition
import Text.Pandoc.Builder (text, toList)
import Text.Pandoc.Shared
import Text.Pandoc.Parsing
import Data.Maybe ( fromMaybe, isJust )
import Data.List ( intercalate )
import Data.Char ( isSpace, isDigit, toLower )
import Control.Monad ( liftM, guard, when )

  | Convert HTML - formatted string to ' Pandoc ' document .
         -> Pandoc
readHtml st inp = Pandoc meta blocks
  where blocks  = readWith parseBody st rest
        tags    = canonicalizeTags $
                   parseTagsOptions parseOptions{ optTagPosition = True } inp
        hasHeader = any (~== TagOpen "head" []) tags
        (meta, rest) = if hasHeader
                          then parseHeader tags
                          else (Meta [] [] [], tags)

type TagParser = GenParser (Tag String) ParserState

parseHeader :: [Tag String] -> (Meta, [Tag String])
parseHeader tags = (Meta{docTitle = tit'', docAuthors = [], docDate = []}, rest)
  where (tit,_) = break (~== TagClose "title") $ drop 1 $
                   dropWhile (\t -> not $ t ~== TagOpen "title" []) tags
        tit' = concatMap fromTagText $ filter isTagText tit
        tit'' = normalizeSpaces $ toList $ text tit'
        rest  = drop 1 $ dropWhile (\t -> not $ t ~== TagClose "head" ||
                                                t ~== TagOpen "body" []) tags

parseBody :: TagParser [Block]
parseBody = liftM (fixPlains False . concat) $ manyTill block eof

block :: TagParser [Block]
block = choice
            [ pPara
            , pHeader
            , pBlockQuote
            , pCodeBlock
            , pList
            , pHrule
            , pSimpleTable
            , pPlain
            , pRawHtmlBlock
            ]

renderTags' :: [Tag String] -> String
renderTags' = renderTagsOptions
               renderOptions{ optMinimize = \x ->
                                    let y = map toLower x
                                    in  y == "hr" || y == "br" ||
                                        y == "img" || y == "meta" ||
                                        y == "link"
                            , optRawTag = \x ->
                                    let y = map toLower x
                                    in  y == "script" || y == "style" }

pList :: TagParser [Block]
pList = pBulletList <|> pOrderedList <|> pDefinitionList

pBulletList :: TagParser [Block]
pBulletList = try $ do
  pSatisfy (~== TagOpen "ul" [])
  let nonItem = pSatisfy (\t ->
                  not (tagOpen (`elem` ["li","ol","ul","dl"]) (const True) t) &&
                  not (t ~== TagClose "ul"))
  treat it as a list item , though it 's not valid  ...
  skipMany nonItem
  items <- manyTill (pInTags "li" block >>~ skipMany nonItem) (pCloses "ul")
  return [BulletList $ map (fixPlains True) items]

pOrderedList :: TagParser [Block]
pOrderedList = try $ do
  TagOpen _ attribs <- pSatisfy (~== TagOpen "ol" [])
  st <- getState
  let (start, style) =  if stateStrict st
                           then (1, DefaultStyle) 
                           else (sta', sty')
                              where sta = fromMaybe "1" $
                                          lookup "start" attribs
                                    sta' = if all isDigit sta
                                              then read sta
                                              else 1
                                    sty = fromMaybe (fromMaybe "" $
                                          lookup "style" attribs) $
                                          lookup "class" attribs
                                    sty' = case sty of
                                            "lower-roman"  -> LowerRoman
                                            "upper-roman"  -> UpperRoman
                                            "lower-alpha"  -> LowerAlpha
                                            "upper-alpha"  -> UpperAlpha
                                            "decimal"      -> Decimal
                                            _              -> DefaultStyle
  let nonItem = pSatisfy (\t ->
                  not (tagOpen (`elem` ["li","ol","ul","dl"]) (const True) t) &&
                  not (t ~== TagClose "ol"))
  treat it as a list item , though it 's not valid  ...
  skipMany nonItem
  items <- manyTill (pInTags "li" block >>~ skipMany nonItem) (pCloses "ol")
  return [OrderedList (start, style, DefaultDelim) $ map (fixPlains True) items]

pDefinitionList :: TagParser [Block]
pDefinitionList = try $ do
  pSatisfy (~== TagOpen "dl" [])
  items <- manyTill pDefListItem (pCloses "dl")
  return [DefinitionList items]

pDefListItem :: TagParser ([Inline],[[Block]])
pDefListItem = try $ do
  let nonItem = pSatisfy (\t -> not (t ~== TagOpen "dt" []) &&
                  not (t ~== TagOpen "dd" []) && not (t ~== TagClose "dl"))
  terms <- many1 (try $ skipMany nonItem >> pInTags "dt" inline)
  defs  <- many1 (try $ skipMany nonItem >> pInTags "dd" block)
  skipMany nonItem
  let term = intercalate [LineBreak] terms
  return (term, map (fixPlains True) defs)

fixPlains :: Bool -> [Block] -> [Block]
fixPlains inList bs = if any isParaish bs
                         then map plainToPara bs
                         else bs
  where isParaish (Para _) = True
        isParaish (CodeBlock _ _) = True
        isParaish (Header _ _) = True
        isParaish (BlockQuote _) = True
        isParaish (BulletList _) = not inList
        isParaish (OrderedList _ _) = not inList
        isParaish (DefinitionList _) = not inList
        isParaish _        = False
        plainToPara (Plain xs) = Para xs
        plainToPara x = x

pRawTag :: TagParser String
pRawTag = do
  tag <- pAnyTag
  let ignorable x = x `elem` ["html","head","body"]
  if tagOpen ignorable (const True) tag || tagClose ignorable tag
     then return []
     else return $ renderTags' [tag]

pRawHtmlBlock :: TagParser [Block]
pRawHtmlBlock = do
  raw <- pHtmlBlock "script" <|> pHtmlBlock "style" <|> pRawTag
  state <- getState
  if stateParseRaw state && not (null raw)
     then return [RawBlock "html" raw]
     else return []

pHtmlBlock :: String -> TagParser String
pHtmlBlock t = try $ do
  open <- pSatisfy (~== TagOpen t [])
  contents <- manyTill pAnyTag (pSatisfy (~== TagClose t))
  return $ renderTags' $ [open] ++ contents ++ [TagClose t]

pHeader :: TagParser [Block]
pHeader = try $ do
  TagOpen tagtype attr <- pSatisfy $
                           tagOpen (`elem` ["h1","h2","h3","h4","h5","h6"])
                           (const True)
  let bodyTitle = TagOpen tagtype attr ~== TagOpen "h1" [("class","title")]
  let level = read (drop 1 tagtype)
  contents <- liftM concat $ manyTill inline (pCloses tagtype <|> eof)
  return $ if bodyTitle
              else [Header level $ normalizeSpaces contents]

pHrule :: TagParser [Block]
pHrule = do
  pSelfClosing (=="hr") (const True)
  return [HorizontalRule]

pSimpleTable :: TagParser [Block]
pSimpleTable = try $ do
  TagOpen _ _ <- pSatisfy (~== TagOpen "table" [])
  skipMany pBlank
  head' <- option [] $ pOptInTag "thead" $ pInTags "tr" (pCell "th")
  skipMany pBlank
  rows <- pOptInTag "tbody"
          $ many1 $ try $ skipMany pBlank >> pInTags "tr" (pCell "td")
  skipMany pBlank
  TagClose _ <- pSatisfy (~== TagClose "table") 
  let cols = maximum $ map length rows
  let aligns = replicate cols AlignLeft
  let widths = replicate cols 0
  return [Table [] aligns widths head' rows]

pCell :: String -> TagParser [TableCell]
pCell celltype = try $ do
  skipMany pBlank
  res <- pInTags celltype pPlain
  skipMany pBlank
  return [res]

pBlockQuote :: TagParser [Block]
pBlockQuote = do
  contents <- pInTags "blockquote" block
  return [BlockQuote $ fixPlains False contents]

pPlain :: TagParser [Block]
pPlain = do
  contents <- liftM (normalizeSpaces . concat) $ many1 inline
  if null contents
     then return []
     else return [Plain contents]

pPara :: TagParser [Block]
pPara = do
  contents <- pInTags "p" inline
  return [Para $ normalizeSpaces contents]

pCodeBlock :: TagParser [Block]
pCodeBlock = try $ do
  TagOpen _ attr <- pSatisfy (~== TagOpen "pre" [])
  contents <- manyTill pAnyTag (pCloses "pre" <|> eof)
  let rawText = concatMap fromTagText $ filter isTagText contents
  let result' = case rawText of
                     '\n':xs  -> xs
                     _        -> rawText
  let result = case reverse result' of
                    '\n':_   -> init result'
                    _        -> result'
  let attribsId = fromMaybe "" $ lookup "id" attr
  let attribsClasses = words $ fromMaybe "" $ lookup "class" attr
  let attribsKV = filter (\(k,_) -> k /= "class" && k /= "id") attr
  st <- getState
  let attribs = if stateStrict st
                   then ("",[],[])
                   else (attribsId, attribsClasses, attribsKV)
  return [CodeBlock attribs result]

inline :: TagParser [Inline]
inline = choice
           [ pTagText
           , pEmph
           , pStrong
           , pSuperscript
           , pSubscript
           , pStrikeout
           , pLineBreak
           , pLink
           , pImage
           , pCode
           , pRawHtmlInline
           ]

pLocation :: TagParser ()
pLocation = do
  (TagPosition r c) <- pSat isTagPosition
  setPosition $ newPos "input" r c

pSat :: (Tag String -> Bool) -> TagParser (Tag String)
pSat f = do
  pos <- getPosition
  token show (const pos) (\x -> if f x then Just x else Nothing) 

pSatisfy :: (Tag String -> Bool) -> TagParser (Tag String)
pSatisfy f = try $ optional pLocation >> pSat f

pAnyTag :: TagParser (Tag String)
pAnyTag = pSatisfy (const True)

pSelfClosing :: (String -> Bool) -> ([Attribute String] -> Bool)
             -> TagParser (Tag String)
pSelfClosing f g = do
  open <- pSatisfy (tagOpen f g)
  optional $ pSatisfy (tagClose f)
  return open

pEmph :: TagParser [Inline]
pEmph = pInlinesInTags "em" Emph <|> pInlinesInTags "i" Emph

pStrong :: TagParser [Inline]
pStrong = pInlinesInTags "strong" Strong <|> pInlinesInTags "b" Strong

pSuperscript :: TagParser [Inline]
pSuperscript = failIfStrict >> pInlinesInTags "sup" Superscript

pSubscript :: TagParser [Inline]
pSubscript = failIfStrict >> pInlinesInTags "sub" Subscript

pStrikeout :: TagParser [Inline]
pStrikeout = do
  failIfStrict
  pInlinesInTags "s" Strikeout <|>
    pInlinesInTags "strike" Strikeout <|>
    pInlinesInTags "del" Strikeout <|>
    try (do pSatisfy (~== TagOpen "span" [("class","strikeout")])
            contents <- liftM concat $ manyTill inline (pCloses "span")
            return [Strikeout contents])

pLineBreak :: TagParser [Inline]
pLineBreak = do
  pSelfClosing (=="br") (const True)
  return [LineBreak]

pLink :: TagParser [Inline]
pLink = try $ do
  tag <- pSatisfy (tagOpenLit "a" (isJust . lookup "href"))
  let url = fromAttrib "href" tag
  let title = fromAttrib "title" tag
  lab <- liftM concat $ manyTill inline (pCloses "a")
  return [Link (normalizeSpaces lab) (escapeURI url, title)]

pImage :: TagParser [Inline]
pImage = do
  tag <- pSelfClosing (=="img") (isJust . lookup "src")
  let url = fromAttrib "src" tag
  let title = fromAttrib "title" tag
  let alt = fromAttrib "alt" tag
  return [Image (toList $ text alt) (escapeURI url, title)]

pCode :: TagParser [Inline]
pCode = try $ do
  (TagOpen open attr) <- pSatisfy $ tagOpen (`elem` ["code","tt"]) (const True)
  result <- manyTill pAnyTag (pCloses open)
  let ident = fromMaybe "" $ lookup "id" attr
  let classes = words $ fromMaybe [] $ lookup "class" attr
  let rest = filter (\(x,_) -> x /= "id" && x /= "class") attr
  return [Code (ident,classes,rest)
         $ intercalate " " $ lines $ innerText result]

pRawHtmlInline :: TagParser [Inline]
pRawHtmlInline = do
  result <- pSatisfy (tagComment (const True)) <|> pSatisfy isInlineTag
  state <- getState
  if stateParseRaw state
     then return [RawInline "html" $ renderTags' [result]]
     else return []

pInlinesInTags :: String -> ([Inline] -> Inline)
               -> TagParser [Inline]
pInlinesInTags tagtype f = do
  contents <- pInTags tagtype inline
  return [f $ normalizeSpaces contents]

pInTags :: String -> TagParser [a]
        -> TagParser [a]
pInTags tagtype parser = try $ do
  pSatisfy (~== TagOpen tagtype [])
  liftM concat $ manyTill parser (pCloses tagtype <|> eof)

pOptInTag :: String -> TagParser a
          -> TagParser a
pOptInTag tagtype parser = try $ do
  open <- option False (pSatisfy (~== TagOpen tagtype []) >> return True)
  skipMany pBlank
  x <- parser
  skipMany pBlank
  when open $ pCloses tagtype
  return x

pCloses :: String -> TagParser ()
pCloses tagtype = try $ do
  t <- lookAhead $ pSatisfy $ \tag -> isTagClose tag || isTagOpen tag
  case t of
       (TagClose t')  | t' == tagtype -> pAnyTag >> return ()
       (TagOpen t' _) | t' `closes` tagtype -> return ()
       (TagClose "ul") | tagtype == "li" -> return ()
       (TagClose "ol") | tagtype == "li" -> return ()
       (TagClose "dl") | tagtype == "li" -> return ()
       _ -> pzero

pTagText :: TagParser [Inline]
pTagText = try $ do
  (TagText str) <- pSatisfy isTagText
  st <- getState
  case runParser (many pTagContents) st "text" str of
       Left _        -> fail $ "Could not parse `" ++ str ++ "'"
       Right result  -> return result

pBlank :: TagParser ()
pBlank = try $ do
  (TagText str) <- pSatisfy isTagText
  guard $ all isSpace str

pTagContents :: GenParser Char ParserState Inline
pTagContents =
  pStr <|> pSpace <|> smartPunctuation pTagContents <|> pSymbol <|> pBad

pStr :: GenParser Char ParserState Inline
pStr = do
  result <- many1 $ satisfy $ \c ->
                     not (isSpace c) && not (isSpecial c) && not (isBad c)
  pos <- getPosition
  updateState $ \s -> s{ stateLastStrPos = Just pos }
  return $ Str result

isSpecial :: Char -> Bool
isSpecial '"' = True
isSpecial '\'' = True
isSpecial '.' = True
isSpecial '-' = True
isSpecial '\8216' = True
isSpecial '\8217' = True
isSpecial '\8220' = True
isSpecial '\8221' = True
isSpecial _ = False

pSymbol :: GenParser Char ParserState Inline
pSymbol = satisfy isSpecial >>= return . Str . (:[])

isBad :: Char -> Bool

pBad :: GenParser Char ParserState Inline
pBad = do
  c <- satisfy isBad
  let c' = case c of
                '\128' -> '\8364'
                '\130' -> '\8218'
                '\131' -> '\402'
                '\132' -> '\8222'
                '\133' -> '\8230'
                '\134' -> '\8224'
                '\135' -> '\8225'
                '\136' -> '\710'
                '\137' -> '\8240'
                '\138' -> '\352'
                '\139' -> '\8249'
                '\140' -> '\338'
                '\142' -> '\381'
                '\145' -> '\8216'
                '\146' -> '\8217'
                '\147' -> '\8220'
                '\148' -> '\8221'
                '\149' -> '\8226'
                '\150' -> '\8211'
                '\151' -> '\8212'
                '\152' -> '\732'
                '\153' -> '\8482'
                '\154' -> '\353'
                '\155' -> '\8250'
                '\156' -> '\339'
                '\158' -> '\382'
                '\159' -> '\376'
                _      -> '?'
  return $ Str [c']

pSpace :: GenParser Char ParserState Inline
pSpace = many1 (satisfy isSpace) >> return Space


eitherBlockOrInline :: [String]
eitherBlockOrInline = ["applet", "button", "del", "iframe", "ins",
                  "map", "area", "object"]


 inlineHtmlTags : : [ [  ] ] 
 inlineHtmlTags = [ " a " , " abbr " , " acronym " , " b " , " basefont " , " bdo " , " big " , 
                   " br " , " cite " , " code " , " dfn " , " em " , " font " , " i " , " img " , 
                   " input " , "  " , " label " , " q " , " s " , " samp " , " select " , 
                   " small " , " span " , " strike " , " strong " , " sub " , " sup " , 
                   " textarea " , " tt " , " u " , " var " ] 

inlineHtmlTags :: [[Char]]
inlineHtmlTags = ["a", "abbr", "acronym", "b", "basefont", "bdo", "big",
                  "br", "cite", "code", "dfn", "em", "font", "i", "img",
                  "input", "kbd", "label", "q", "s", "samp", "select",
                  "small", "span", "strike", "strong", "sub", "sup",
                  "textarea", "tt", "u", "var"]
-}

blockHtmlTags :: [String]
blockHtmlTags = ["address", "blockquote", "body", "center", "dir", "div",
                 "dl", "fieldset", "form", "h1", "h2", "h3", "h4",
                 "h5", "h6", "head", "hr", "html", "isindex", "menu",
                 "noframes", "noscript", "ol", "p", "pre", "table", "ul", "dd",
                 "dt", "frameset", "li", "tbody", "td", "tfoot",
                 "th", "thead", "tr", "script", "style"]

blockDocBookTags :: [String]
blockDocBookTags = ["calloutlist", "bibliolist", "glosslist", "itemizedlist",
                    "orderedlist", "segmentedlist", "simplelist",
                    "variablelist", "caution", "important", "note", "tip",
                    "warning", "address", "literallayout", "programlisting",
                    "programlistingco", "screen", "screenco", "screenshot",
                    "synopsis", "example", "informalexample", "figure",
                    "informalfigure", "table", "informaltable", "para",
                    "simpara", "formalpara", "equation", "informalequation",
                    "figure", "screenshot", "mediaobject", "qandaset",
                    "procedure", "task", "cmdsynopsis", "funcsynopsis",
                    "classsynopsis", "blockquote", "epigraph", "msgset",
                    "sidebar", "title"]

blockTags :: [String]
blockTags = blockHtmlTags ++ blockDocBookTags

isInlineTag :: Tag String -> Bool
isInlineTag t = tagOpen (`notElem` blockTags) (const True) t ||
                tagClose (`notElem` blockTags) t ||
                tagComment (const True) t

isBlockTag :: Tag String -> Bool
isBlockTag t = tagOpen (`elem` blocktags) (const True) t ||
               tagClose (`elem` blocktags) t ||
               tagComment (const True) t
                 where blocktags = blockTags ++ eitherBlockOrInline

isTextTag :: Tag String -> Bool
isTextTag = tagText (const True)

isCommentTag :: Tag String -> Bool
isCommentTag = tagComment (const True)

  taken from HXT and extended

closes :: String -> String -> Bool
_ `closes` "body" = False
_ `closes` "html" = False
"a" `closes` "a" = True
"li" `closes` "li" = True
"th" `closes` t | t `elem` ["th","td"] = True
"tr" `closes` t | t `elem` ["th","td","tr"] = True
"dt" `closes` t | t `elem` ["dt","dd"] = True
"hr" `closes` "p" = True
"p" `closes` "p" = True
"meta" `closes` "meta" = True
"colgroup" `closes` "colgroup" = True
"form" `closes` "form" = True
"label" `closes` "label" = True
"map" `closes` "map" = True
"object" `closes` "object" = True
_ `closes` t | t `elem` ["option","style","script","textarea","title"] = True
t `closes` "select" | t /= "option" = True
"thead" `closes` t | t `elem` ["colgroup"] = True
"tfoot" `closes` t | t `elem` ["thead","colgroup"] = True
"tbody" `closes` t | t `elem` ["tbody","tfoot","thead","colgroup"] = True
t `closes` t2 |
   t `elem` ["h1","h2","h3","h4","h5","h6","dl","ol","ul","table","div","p"] &&
t1 `closes` t2 |
   t1 `elem` blockTags &&
   t2 `notElem` (blockTags ++ eitherBlockOrInline) = True
_ `closes` _ = False


htmlInBalanced :: (Tag String -> Bool) -> GenParser Char ParserState String
htmlInBalanced f = try $ do
  (TagOpen t _, tag) <- htmlTag f
  let nonTagChunk = many1 $ satisfy (/= '<')
  let stopper = htmlTag (~== TagClose t)
  let anytag = liftM snd $ htmlTag (const True)
  contents <- many $ notFollowedBy' stopper >>
                     (nonTagChunk <|> htmlInBalanced (const True) <|> anytag)
  endtag <- liftM snd stopper
  return $ tag ++ concat contents ++ endtag

htmlTag :: (Tag String -> Bool) -> GenParser Char ParserState (Tag String, String)
htmlTag f = try $ do
  lookAhead (char '<')
  (next : _) <- getInput >>= return . canonicalizeTags . parseTags
  guard $ f next
  case next of
       TagComment s -> do
          count (length s + 4) anyChar
          skipMany (satisfy (/='>'))
          char '>'
          return (next, "<!--" ++ s ++ "-->") 
       _            -> do
          rendered <- manyTill anyChar (char '>')
          return (next, rendered ++ ">")