path: root/src/Text/Pandoc/Readers/HTML.hs

{-# LANGUAGE FlexibleContexts, FlexibleInstances, MultiParamTypeClasses,
ViewPatterns#-}
{-
Copyright (C) 2006-2015 John MacFarlane <jgm@berkeley.edu>

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) 2006-2015 John MacFarlane
   License     : GNU GPL, version 2 or above

   Maintainer  : John MacFarlane <jgm@berkeley.edu>
   Stability   : alpha
   Portability : portable

Conversion of HTML to 'Pandoc' document.
-}
module Text.Pandoc.Readers.HTML ( readHtml
                                , htmlTag
                                , htmlInBalanced
                                , isInlineTag
                                , isBlockTag
                                , isTextTag
                                , isCommentTag
                                ) where

import Text.HTML.TagSoup
import Text.HTML.TagSoup.Match
import Text.Pandoc.Definition
import qualified Text.Pandoc.Builder as B
import Text.Pandoc.Builder (Blocks, Inlines, trimInlines, HasMeta(..))
import Text.Pandoc.Shared ( extractSpaces, renderTags', addMetaField
                          , escapeURI, safeRead )
import Text.Pandoc.Options (ReaderOptions(readerExtensions), extensionEnabled,
                               Verbosity(..), Extension (Ext_epub_html_exts,
                               Ext_raw_html, Ext_native_divs, Ext_native_spans))
import Text.Pandoc.Parsing hiding ((<|>))
import Text.Pandoc.Walk
import qualified Data.Map as M
import Data.Maybe ( fromMaybe, isJust)
import Data.List ( intercalate, isInfixOf, isPrefixOf )
import Data.Char ( isDigit )
import Control.Monad ( guard, mzero, void, unless )
import Control.Arrow ((***))
import Control.Applicative ( (<|>) )
import Data.Monoid (First (..))
import Text.Printf (printf)
import Text.TeXMath (readMathML, writeTeX)
import Data.Default (Default (..), def)
import Control.Monad.Reader (ask, asks, local, ReaderT, runReaderT, lift)
import Network.URI (URI, parseURIReference, nonStrictRelativeTo)
import Text.Pandoc.CSS (foldOrElse, pickStyleAttrProps)
import Data.Monoid ((<>))
import Text.Parsec.Error
import qualified Data.Set as Set
import Text.Pandoc.Error
import Text.Pandoc.Class (PandocMonad, report)
import Control.Monad.Except (throwError)


-- | Convert HTML-formatted string to 'Pandoc' document.
readHtml :: PandocMonad m
         => ReaderOptions -- ^ Reader options
         -> String        -- ^ String to parse (assumes @'\n'@ line endings)
         -> m Pandoc
readHtml opts inp = do
  let tags = stripPrefixes . canonicalizeTags $
             parseTagsOptions parseOptions{ optTagPosition = True } inp
      parseDoc = do
        blocks <- (fixPlains False) . mconcat <$> manyTill block eof
        meta <- stateMeta . parserState <$> getState
        bs' <- replaceNotes (B.toList blocks)
        return $ Pandoc meta bs'
      getError (errorMessages -> ms) = case ms of
                                         []    -> ""
                                         (m:_) -> messageString m
  result <- flip runReaderT def $
         runParserT parseDoc
         (HTMLState def{ stateOptions = opts } [] Nothing Set.empty M.empty)
         "source" tags
  case result of
    Right doc -> return doc
    Left  err -> throwError $ PandocParseError $ getError err

replaceNotes :: PandocMonad m => [Block] -> TagParser m [Block]
replaceNotes = walkM replaceNotes'

replaceNotes' :: PandocMonad m => Inline -> TagParser m Inline
replaceNotes' (RawInline (Format "noteref") ref) = maybe (Str "") (Note . B.toList) . lookup ref <$> getNotes
  where
    getNotes = noteTable <$> getState
replaceNotes' x = return x

data HTMLState =
  HTMLState
  {  parserState :: ParserState,
     noteTable   :: [(String, Blocks)],
     baseHref    :: Maybe URI,
     identifiers :: Set.Set String,
     headerMap   :: M.Map Inlines String
  }

data HTMLLocal = HTMLLocal { quoteContext :: QuoteContext
                           , inChapter :: Bool -- ^ Set if in chapter section
                           , inPlain :: Bool -- ^ Set if in pPlain
                           }

setInChapter :: PandocMonad m => HTMLParser m s a -> HTMLParser m s a
setInChapter = local (\s -> s {inChapter = True})

setInPlain :: PandocMonad m => HTMLParser m s a -> HTMLParser m s a
setInPlain = local (\s -> s {inPlain = True})

type HTMLParser m s = ParserT s HTMLState (ReaderT HTMLLocal m)

type TagParser m = HTMLParser m [Tag String]

pBody :: PandocMonad m => TagParser m Blocks
pBody = pInTags "body" block

pHead :: PandocMonad m => TagParser m Blocks
pHead = pInTags "head" $ pTitle <|> pMetaTag <|> pBaseTag <|> (mempty <$ pAnyTag)
  where pTitle = pInTags "title" inline >>= setTitle . trimInlines
        setTitle t = mempty <$ (updateState $ B.setMeta "title" t)
        pMetaTag = do
          mt <- pSatisfy (~== TagOpen "meta" [])
          let name = fromAttrib "name" mt
          if null name
             then return mempty
             else do
               let content = fromAttrib "content" mt
               updateState $ \s ->
                 let ps = parserState s in
                 s{ parserState = ps{
                      stateMeta = addMetaField name (B.text content)
                                   (stateMeta ps) } }
               return mempty
        pBaseTag = do
          bt <- pSatisfy (~== TagOpen "base" [])
          updateState $ \st -> st{ baseHref =
               parseURIReference $ fromAttrib "href" bt }
          return mempty

block :: PandocMonad m => TagParser m Blocks
block = do
  pos <- getPosition
  res <- choice
            [ eSection
            , eSwitch B.para block
            , mempty <$ eFootnote
            , mempty <$ eTOC
            , mempty <$ eTitlePage
            , pPara
            , pHeader
            , pBlockQuote
            , pCodeBlock
            , pList
            , pHrule
            , pTable
            , pHead
            , pBody
            , pDiv
            , pPlain
            , pRawHtmlBlock
            ]
  report DEBUG $ printf "line %d: %s"
                  (sourceLine pos) (take 60 $ show $ B.toList res)
  return res

namespaces :: PandocMonad m => [(String, TagParser m Inlines)]
namespaces = [(mathMLNamespace, pMath True)]

mathMLNamespace :: String
mathMLNamespace = "http://www.w3.org/1998/Math/MathML"

eSwitch :: (PandocMonad m, Monoid a)
        => (Inlines -> a)
        -> TagParser m a
        -> TagParser m a
eSwitch constructor parser = try $ do
  guardEnabled Ext_epub_html_exts
  pSatisfy (~== TagOpen "switch" [])
  cases <- getFirst . mconcat <$>
            manyTill (First <$> (eCase <* skipMany pBlank) )
              (lookAhead $ try $ pSatisfy (~== TagOpen "default" []))
  skipMany pBlank
  fallback <- pInTags "default" (skipMany pBlank *> parser <* skipMany pBlank)
  skipMany pBlank
  pSatisfy (~== TagClose "switch")
  return $ maybe fallback constructor cases

eCase :: PandocMonad m => TagParser m (Maybe Inlines)
eCase = do
  skipMany pBlank
  TagOpen _ attr <- lookAhead $ pSatisfy $ (~== TagOpen "case" [])
  case (flip lookup namespaces) =<< lookup "required-namespace" attr of
    Just p -> Just <$> (pInTags "case" (skipMany pBlank *> p <* skipMany pBlank))
    Nothing -> Nothing <$ manyTill pAnyTag (pSatisfy (~== TagClose "case"))

eFootnote :: PandocMonad m => TagParser m ()
eFootnote = try $ do
  let notes = ["footnote", "rearnote"]
  guardEnabled Ext_epub_html_exts
  (TagOpen tag attr) <- lookAhead $ pAnyTag
  guard (maybe False (flip elem notes) (lookup "type" attr))
  let ident = fromMaybe "" (lookup "id" attr)
  content <- pInTags tag block
  addNote ident content

addNote :: PandocMonad m => String -> Blocks -> TagParser m ()
addNote uid cont = updateState (\s -> s {noteTable = (uid, cont) : (noteTable s)})

eNoteref :: PandocMonad m => TagParser m Inlines
eNoteref = try $ do
  guardEnabled Ext_epub_html_exts
  TagOpen tag attr <- lookAhead $ pAnyTag
  guard (maybe False (== "noteref") (lookup "type" attr))
  let ident = maybe "" (dropWhile (== '#')) (lookup "href" attr)
  guard (not (null ident))
  pInTags tag block
  return $ B.rawInline "noteref" ident

-- Strip TOC if there is one, better to generate again
eTOC :: PandocMonad m => TagParser m ()
eTOC = try $ do
  guardEnabled Ext_epub_html_exts
  (TagOpen tag attr) <- lookAhead $ pAnyTag
  guard (maybe False (== "toc") (lookup "type" attr))
  void (pInTags tag block)

pList :: PandocMonad m => TagParser m Blocks
pList = pBulletList <|> pOrderedList <|> pDefinitionList

pBulletList :: PandocMonad m => TagParser m Blocks
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 xhtml...
  skipMany nonItem
  items <- manyTill (pListItem nonItem) (pCloses "ul")
  return $ B.bulletList $ map (fixPlains True) items

pListItem :: PandocMonad m => TagParser m a -> TagParser m Blocks
pListItem nonItem = do
  TagOpen _ attr <- lookAhead $ pSatisfy (~== TagOpen "li" [])
  let liDiv = maybe mempty (\x -> B.divWith (x, [], []) mempty) (lookup "id" attr)
  (liDiv <>) <$> pInTags "li" block <* skipMany nonItem

parseListStyleType :: String -> ListNumberStyle
parseListStyleType "lower-roman" = LowerRoman
parseListStyleType "upper-roman" = UpperRoman
parseListStyleType "lower-alpha" = LowerAlpha
parseListStyleType "upper-alpha" = UpperAlpha
parseListStyleType "decimal"     = Decimal
parseListStyleType _             = DefaultStyle

parseTypeAttr :: String -> ListNumberStyle
parseTypeAttr "i" = LowerRoman
parseTypeAttr "I" = UpperRoman
parseTypeAttr "a" = LowerAlpha
parseTypeAttr "A" = UpperAlpha
parseTypeAttr "1" = Decimal
parseTypeAttr _   = DefaultStyle

pOrderedList :: PandocMonad m => TagParser m Blocks
pOrderedList = try $ do
  TagOpen _ attribs <- pSatisfy (~== TagOpen "ol" [])
  let (start, style) = (sta', sty')
                       where sta = fromMaybe "1" $
                                   lookup "start" attribs
                             sta' = if all isDigit sta
                                       then read sta
                                       else 1

                             pickListStyle = pickStyleAttrProps ["list-style-type", "list-style"]

                             typeAttr  = fromMaybe "" $ lookup "type"  attribs
                             classAttr = fromMaybe "" $ lookup "class" attribs
                             styleAttr = fromMaybe "" $ lookup "style" attribs
                             listStyle = fromMaybe "" $ pickListStyle styleAttr

                             sty' = foldOrElse DefaultStyle
                                      [ parseTypeAttr      typeAttr
                                      , parseListStyleType classAttr
                                      , parseListStyleType listStyle
                                      ]
  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 xhtml...
  skipMany nonItem
  items <- manyTill (pListItem nonItem) (pCloses "ol")
  return $ B.orderedListWith (start, style, DefaultDelim) $ map (fixPlains True) items

pDefinitionList :: PandocMonad m => TagParser m Blocks
pDefinitionList = try $ do
  pSatisfy (~== TagOpen "dl" [])
  items <- manyTill pDefListItem (pCloses "dl")
  return $ B.definitionList items

pDefListItem :: PandocMonad m => TagParser m (Inlines, [Blocks])
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 = foldl1 (\x y ->  x <> B.linebreak <> y) terms
  return (term, map (fixPlains True) defs)

fixPlains :: Bool -> Blocks -> Blocks
fixPlains inList bs = if any isParaish bs'
                         then B.fromList $ 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
        bs' = B.toList bs

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

pDiv :: PandocMonad m => TagParser m Blocks
pDiv = try $ do
  guardEnabled Ext_native_divs
  let isDivLike "div" = True
      isDivLike "section" = True
      isDivLike _ = False
  TagOpen tag attr <- lookAhead $ pSatisfy $ tagOpen isDivLike (const True)
  contents <- pInTags tag block
  let (ident, classes, kvs) = mkAttr attr
  let classes' = if tag == "section"
                    then "section":classes
                    else classes
  return $ B.divWith (ident, classes', kvs) contents

pRawHtmlBlock :: PandocMonad m => TagParser m Blocks
pRawHtmlBlock = do
  raw <- pHtmlBlock "script" <|> pHtmlBlock "style" <|> pRawTag
  exts <- getOption readerExtensions
  if extensionEnabled Ext_raw_html exts && not (null raw)
     then return $ B.rawBlock "html" raw
     else return mempty

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

-- Sets chapter context
eSection :: PandocMonad m => TagParser m Blocks
eSection = try $ do
  let matchChapter as = maybe False (isInfixOf "chapter") (lookup "type" as)
  let sectTag = tagOpen (`elem` sectioningContent) matchChapter
  TagOpen tag _ <- lookAhead $ pSatisfy sectTag
  setInChapter (pInTags tag block)

headerLevel :: PandocMonad m => String -> TagParser m Int
headerLevel tagtype = do
  let level = read (drop 1 tagtype)
  (try $ do
    guardEnabled Ext_epub_html_exts
    asks inChapter >>= guard
    return (level - 1))
    <|>
      return level

eTitlePage :: PandocMonad m => TagParser m ()
eTitlePage = try $ do
  let isTitlePage as = maybe False (isInfixOf "titlepage") (lookup "type" as)
  let groupTag = tagOpen (\x -> x `elem` groupingContent || x == "section")
                          isTitlePage
  TagOpen tag _ <- lookAhead $ pSatisfy groupTag
  () <$ pInTags tag block

pHeader :: PandocMonad m => TagParser m Blocks
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")]
  level <- headerLevel tagtype
  contents <- trimInlines . mconcat <$> manyTill inline (pCloses tagtype <|> eof)
  let ident = fromMaybe "" $ lookup "id" attr
  let classes = maybe [] words $ lookup "class" attr
  let keyvals = [(k,v) | (k,v) <- attr, k /= "class", k /= "id"]
  attr' <- registerHeader (ident, classes, keyvals) contents
  return $ if bodyTitle
              then mempty  -- skip a representation of the title in the body
              else B.headerWith attr' level contents

pHrule :: PandocMonad m => TagParser m Blocks
pHrule = do
  pSelfClosing (=="hr") (const True)
  return B.horizontalRule

pTable :: PandocMonad m => TagParser m Blocks
pTable = try $ do
  TagOpen _ _ <- pSatisfy (~== TagOpen "table" [])
  skipMany pBlank
  caption <- option mempty $ pInTags "caption" inline <* skipMany pBlank
  widths' <- (mconcat <$> many1 pColgroup) <|> many pCol
  let pTh = option [] $ pInTags "tr" (pCell "th")
      pTr = try $ skipMany pBlank >> pInTags "tr" (pCell "td" <|> pCell "th")
      pTBody = do pOptInTag "tbody" $ many1 pTr
  head'' <- pOptInTag "thead" pTh
  head'  <- pOptInTag "tbody" $ do
              if null head''
                 then pTh
                 else return head''
  rowsLs <- many pTBody
  rows'  <- pOptInTag "tfoot" $ many pTr
  TagClose _ <- pSatisfy (~== TagClose "table")
  let rows'' = (concat rowsLs) ++ rows'
  -- fail on empty table
  guard $ not $ null head' && null rows''
  let isSinglePlain x = case B.toList x of
                             []        -> True
                             [Plain _] -> True
                             _         -> False
  let isSimple = all isSinglePlain $ concat (head':rows'')
  let cols = length $ if null head' then head rows'' else head'
  -- add empty cells to short rows
  let addEmpties r = case cols - length r of
                           n | n > 0 -> r ++ replicate n mempty
                             | otherwise -> r
  let rows = map addEmpties rows''
  let aligns = replicate cols AlignDefault
  let widths = if null widths'
                  then if isSimple
                       then replicate cols 0
                       else replicate cols (1.0 / fromIntegral cols)
                  else widths'
  return $ B.table caption (zip aligns widths) head' rows

pCol :: PandocMonad m => TagParser m Double
pCol = try $ do
  TagOpen _ attribs <- pSatisfy (~== TagOpen "col" [])
  skipMany pBlank
  optional $ pSatisfy (~== TagClose "col")
  skipMany pBlank
  return $ case lookup "width" attribs of
           Nothing -> case lookup "style" attribs of
               Just ('w':'i':'d':'t':'h':':':xs) | '%' `elem` xs ->
                 fromMaybe 0.0 $ safeRead ('0':'.':filter
                   (`notElem` " \t\r\n%'\";") xs)
               _ -> 0.0
           Just x | not (null x) && last x == '%' ->
             fromMaybe 0.0 $ safeRead ('0':'.':init x)
           _ -> 0.0

pColgroup :: PandocMonad m => TagParser m [Double]
pColgroup = try $ do
  pSatisfy (~== TagOpen "colgroup" [])
  skipMany pBlank
  manyTill pCol (pCloses "colgroup" <|> eof) <* skipMany pBlank

noColOrRowSpans :: Tag String -> Bool
noColOrRowSpans t = isNullOrOne "colspan" && isNullOrOne "rowspan"
  where isNullOrOne x = case fromAttrib x t of
                              ""  -> True
                              "1" -> True
                              _   -> False

pCell :: PandocMonad m => String -> TagParser m [Blocks]
pCell celltype = try $ do
  skipMany pBlank
  res <- pInTags' celltype noColOrRowSpans block
  skipMany pBlank
  return [res]

pBlockQuote :: PandocMonad m => TagParser m Blocks
pBlockQuote = do
  contents <- pInTags "blockquote" block
  return $ B.blockQuote $ fixPlains False contents

pPlain :: PandocMonad m => TagParser m Blocks
pPlain = do
  contents <- setInPlain $ trimInlines . mconcat <$> many1 inline
  if B.isNull contents
     then return mempty
     else return $ B.plain contents

pPara :: PandocMonad m => TagParser m Blocks
pPara = do
  contents <- trimInlines <$> pInTags "p" inline
  return $ B.para contents

pCodeBlock :: PandocMonad m => TagParser m Blocks
pCodeBlock = try $ do
  TagOpen _ attr <- pSatisfy (~== TagOpen "pre" [])
  contents <- manyTill pAnyTag (pCloses "pre" <|> eof)
  let rawText = concatMap tagToString 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'
  return $ B.codeBlockWith (mkAttr attr) result

tagToString :: Tag String -> String
tagToString (TagText s) = s
tagToString (TagOpen "br" _) = "\n"
tagToString _ = ""

inline :: PandocMonad m => TagParser m Inlines
inline = choice
           [ eNoteref
           , eSwitch id inline
           , pTagText
           , pQ
           , pEmph
           , pStrong
           , pSuperscript
           , pSubscript
           , pStrikeout
           , pLineBreak
           , pLink
           , pImage
           , pCode
           , pSpan
           , pMath False
           , pRawHtmlInline
           ]

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

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

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

pAnyTag :: PandocMonad m => TagParser m (Tag String)
pAnyTag = pSatisfy (const True)

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

pQ :: PandocMonad m => TagParser m Inlines
pQ = do
  context <- asks quoteContext
  let quoteType = case context of
                       InDoubleQuote -> SingleQuote
                       _             -> DoubleQuote
  let innerQuoteContext = if quoteType == SingleQuote
                             then InSingleQuote
                             else InDoubleQuote
  let constructor = case quoteType of
                            SingleQuote -> B.singleQuoted
                            DoubleQuote -> B.doubleQuoted
  withQuoteContext innerQuoteContext $
    pInlinesInTags "q" constructor

pEmph :: PandocMonad m => TagParser m Inlines
pEmph = pInlinesInTags "em" B.emph <|> pInlinesInTags "i" B.emph

pStrong :: PandocMonad m => TagParser m Inlines
pStrong = pInlinesInTags "strong" B.strong <|> pInlinesInTags "b" B.strong

pSuperscript :: PandocMonad m => TagParser m Inlines
pSuperscript = pInlinesInTags "sup" B.superscript

pSubscript :: PandocMonad m => TagParser m Inlines
pSubscript = pInlinesInTags "sub" B.subscript

pStrikeout :: PandocMonad m => TagParser m Inlines
pStrikeout = do
  pInlinesInTags "s" B.strikeout <|>
    pInlinesInTags "strike" B.strikeout <|>
    pInlinesInTags "del" B.strikeout <|>
    try (do pSatisfy (~== TagOpen "span" [("class","strikeout")])
            contents <- mconcat <$> manyTill inline (pCloses "span")
            return $ B.strikeout contents)

pLineBreak :: PandocMonad m => TagParser m Inlines
pLineBreak = do
  pSelfClosing (=="br") (const True)
  return B.linebreak

-- Unlike fromAttrib from tagsoup, this distinguishes
-- between a missing attribute and an attribute with empty content.
maybeFromAttrib :: String -> Tag String -> Maybe String
maybeFromAttrib name (TagOpen _ attrs) = lookup name attrs
maybeFromAttrib _ _ = Nothing

pLink :: PandocMonad m => TagParser m Inlines
pLink = try $ do
  tag <- pSatisfy $ tagOpenLit "a" (const True)
  let title = fromAttrib "title" tag
  -- take id from id attribute if present, otherwise name
  let uid = maybe (fromAttrib "name" tag) id $ maybeFromAttrib "id" tag
  let cls = words $ fromAttrib "class" tag
  lab <- trimInlines . mconcat <$> manyTill inline (pCloses "a")
  -- check for href; if href, then a link, otherwise a span
  case maybeFromAttrib "href" tag of
       Nothing   ->
         return $ B.spanWith (uid, cls, []) lab
       Just url' -> do
         mbBaseHref <- baseHref <$> getState
         let url = case (parseURIReference url', mbBaseHref) of
                        (Just rel, Just bs) ->
                          show (rel `nonStrictRelativeTo` bs)
                        _                   -> url'
         return $ B.linkWith (uid, cls, []) (escapeURI url) title lab

pImage :: PandocMonad m => TagParser m Inlines
pImage = do
  tag <- pSelfClosing (=="img") (isJust . lookup "src")
  mbBaseHref <- baseHref <$> getState
  let url' = fromAttrib "src" tag
  let url = case (parseURIReference url', mbBaseHref) of
                 (Just rel, Just bs) -> show (rel `nonStrictRelativeTo` bs)
                 _                   -> url'
  let title = fromAttrib "title" tag
  let alt = fromAttrib "alt" tag
  let uid = fromAttrib "id" tag
  let cls = words $ fromAttrib "class" tag
  let getAtt k = case fromAttrib k tag of
                   "" -> []
                   v  -> [(k, v)]
  let kvs = concat $ map getAtt ["width", "height", "sizes", "srcset"]
  return $ B.imageWith (uid, cls, kvs) (escapeURI url) title (B.text alt)

pCode :: PandocMonad m => TagParser m Inlines
pCode = try $ do
  (TagOpen open attr) <- pSatisfy $ tagOpen (`elem` ["code","tt"]) (const True)
  result <- manyTill pAnyTag (pCloses open)
  return $ B.codeWith (mkAttr attr) $ intercalate " " $ lines $ innerText result

pSpan :: PandocMonad m => TagParser m Inlines
pSpan = try $ do
  guardEnabled Ext_native_spans
  TagOpen _ attr <- lookAhead $ pSatisfy $ tagOpen (=="span") (const True)
  contents <- pInTags "span" inline
  let isSmallCaps = fontVariant == "small-caps"
                    where styleAttr   = fromMaybe "" $ lookup "style" attr
                          fontVariant = fromMaybe "" $ pickStyleAttrProps ["font-variant"] styleAttr
  let tag = if isSmallCaps then B.smallcaps else B.spanWith (mkAttr attr)
  return $ tag contents

pRawHtmlInline :: PandocMonad m => TagParser m Inlines
pRawHtmlInline = do
  inplain <- asks inPlain
  result <- pSatisfy (tagComment (const True))
            <|> if inplain
                   then pSatisfy (not . isBlockTag)
                   else pSatisfy isInlineTag
  exts <- getOption readerExtensions
  if extensionEnabled Ext_raw_html exts
     then return $ B.rawInline "html" $ renderTags' [result]
     else return mempty

mathMLToTeXMath :: String -> Either String String
mathMLToTeXMath s = writeTeX <$> readMathML s

pMath :: PandocMonad m => Bool -> TagParser m Inlines
pMath inCase = try $ do
  open@(TagOpen _ attr) <- pSatisfy $ tagOpen (=="math") (const True)
  -- we'll assume math tags are MathML unless specially marked
  -- otherwise...
  unless inCase $
    guard (maybe True (== mathMLNamespace) (lookup "xmlns" attr))
  contents <- manyTill pAnyTag (pSatisfy (~== TagClose "math"))
  case mathMLToTeXMath (renderTags $ [open] ++ contents ++ [TagClose "math"]) of
       Left _   -> return $ B.spanWith ("",["math"],attr) $ B.text $
                             innerText contents
       Right [] -> return mempty
       Right x  -> return $ case lookup "display" attr of
                                 Just "block" -> B.displayMath x
                                 _            -> B.math x

pInlinesInTags :: PandocMonad m => String -> (Inlines -> Inlines)
               -> TagParser m Inlines
pInlinesInTags tagtype f = extractSpaces f <$> pInTags tagtype inline

pInTags :: (PandocMonad m, Monoid a) => String -> TagParser m a -> TagParser m a
pInTags tagtype parser = pInTags' tagtype (const True) parser

pInTags' :: (PandocMonad m, Monoid a)
         => String
         -> (Tag String -> Bool)
         -> TagParser m a
         -> TagParser m a
pInTags' tagtype tagtest parser = try $ do
  pSatisfy (\t -> t ~== TagOpen tagtype [] && tagtest t)
  mconcat <$> manyTill parser (pCloses tagtype <|> eof)

-- parses p, preceeded by an optional opening tag
-- and followed by an optional closing tags
pOptInTag :: PandocMonad m => String -> TagParser m a -> TagParser m a
pOptInTag tagtype p = try $ do
  skipMany pBlank
  optional $ pSatisfy (~== TagOpen tagtype [])
  skipMany pBlank
  x <- p
  skipMany pBlank
  optional $ pSatisfy (~== TagClose tagtype)
  skipMany pBlank
  return x

pCloses :: PandocMonad m => String -> TagParser m ()
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 == "dd" -> return ()
       (TagClose "table") | tagtype == "td" -> return ()
       (TagClose "table") | tagtype == "tr" -> return ()
       _ -> mzero

pTagText :: PandocMonad m => TagParser m Inlines
pTagText = try $ do
  (TagText str) <- pSatisfy isTagText
  st <- getState
  qu <- ask
  parsed <- lift $ lift $
            flip runReaderT qu $ runParserT (many pTagContents) st "text" str
  case parsed of
       Left _        -> throwError $ PandocParseError $ "Could not parse `" ++ str ++ "'"
       Right result  -> return $ mconcat result

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

type InlinesParser m = HTMLParser m String

pTagContents :: PandocMonad m => InlinesParser m Inlines
pTagContents =
      B.displayMath <$> mathDisplay
  <|> B.math        <$> mathInline
  <|> pStr
  <|> pSpace
  <|> smartPunctuation pTagContents
  <|> pSymbol
  <|> pBad

pStr :: PandocMonad m => InlinesParser m Inlines
pStr = do
  result <- many1 $ satisfy $ \c ->
                     not (isSpace c) && not (isSpecial c) && not (isBad c)
  updateLastStrPos
  return $ B.str result

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

pSymbol :: PandocMonad m => InlinesParser m Inlines
pSymbol = satisfy isSpecial >>= return . B.str . (:[])

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

pBad :: PandocMonad m => InlinesParser m Inlines
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 $ B.str [c']

pSpace :: PandocMonad m => InlinesParser m Inlines
pSpace = many1 (satisfy isSpace) >>= \xs ->
            if '\n' `elem` xs
               then return B.softbreak
               else return B.space

--
-- Constants
--

eitherBlockOrInline :: [String]
eitherBlockOrInline = ["audio", "applet", "button", "iframe", "embed",
                       "del", "ins",
                       "progress", "map", "area", "noscript", "script",
                       "object", "svg", "video", "source"]

{-
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 = ["?xml", "!DOCTYPE", "address", "article", "aside",
                 "blockquote", "body", "button", "canvas",
                 "caption", "center", "col", "colgroup", "dd", "dir", "div",
                 "dl", "dt", "fieldset", "figcaption", "figure",
                 "footer", "form", "h1", "h2", "h3", "h4",
                 "h5", "h6", "head", "header", "hgroup", "hr", "html",
                 "isindex", "menu", "noframes", "ol", "output", "p", "pre",
                 "section", "table", "tbody", "textarea",
                 "thead", "tfoot", "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"]

epubTags :: [String]
epubTags = ["case", "switch", "default"]

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

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

isBlockTag :: Tag String -> Bool
isBlockTag t = tagOpen isBlockTagName (const True) t ||
               tagClose isBlockTagName t ||
               tagComment (const True) t
                 where isBlockTagName ('?':_) = True
                       isBlockTagName ('!':_) = True
                       isBlockTagName x       = x `elem` blockTags
                                             || x `elem` eitherBlockOrInline

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

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

-- taken from HXT and extended
-- See http://www.w3.org/TR/html5/syntax.html sec 8.1.2.4 optional tags
closes :: String -> String -> Bool
_ `closes` "body" = False
_ `closes` "html" = False
"body" `closes` "head" = True
"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
"dd" `closes` t | t `elem` ["dt", "dd"] = True
"dt" `closes` t | t `elem` ["dt","dd"] = True
"rt" `closes` t | t `elem` ["rb", "rt", "rtc"] = True
"optgroup" `closes` "optgroup" = True
"optgroup" `closes` "option" = True
"option" `closes` "option" = True
-- http://www.w3.org/TR/html-markup/p.html
x `closes` "p" | x `elem` ["address", "article", "aside", "blockquote",
   "dir", "div", "dl", "fieldset", "footer", "form", "h1", "h2", "h3", "h4",
   "h5", "h6", "header", "hr", "menu", "nav", "ol", "p", "pre", "section",
   "table", "ul"] = True
"meta" `closes` "meta" = 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 :: (Monad m)
               => (Tag String -> Bool)
               -> ParserT String st m String
htmlInBalanced f = try $ do
  lookAhead (char '<')
  inp <- getInput
  let ts = canonicalizeTags $
        parseTagsOptions parseOptions{ optTagWarning = True,
                                       optTagPosition = True } inp
  case ts of
    (TagPosition sr sc : t@(TagOpen tn _) : rest) -> do
       guard $ f t
       guard $ not $ hasTagWarning (t : take 1 rest)
       case htmlInBalanced' tn (t:rest) of
            []  -> mzero
            xs  -> case reverse xs of
                        (TagClose _ : TagPosition er ec : _) -> do
                          let ls = er - sr
                          let cs = ec - sc
                          lscontents <- unlines <$> count ls anyLine
                          cscontents <- count cs anyChar
                          (_,closetag) <- htmlTag (~== TagClose tn)
                          return (lscontents ++ cscontents ++ closetag)
                        _ -> mzero
    _ -> mzero

htmlInBalanced' :: String
                -> [Tag String]
                -> [Tag String]
htmlInBalanced' tagname ts = fromMaybe [] $ go 0 ts
  where go :: Int -> [Tag String] -> Maybe [Tag String]
        go n (t@(TagOpen tn' _):rest) | tn' == tagname =
              (t :) <$> go (n + 1) rest
        go 1 (t@(TagClose tn'):_) | tn' == tagname =
              return [t]
        go n (t@(TagClose tn'):rest)  | tn' == tagname =
              (t :) <$> go (n - 1) rest
        go n (t:ts') = (t :) <$> go n ts'
        go _ [] = mzero

hasTagWarning :: [Tag String] -> Bool
hasTagWarning (TagWarning _:_) = True
hasTagWarning _ = False

-- | Matches a tag meeting a certain condition.
htmlTag :: Monad m
        => (Tag String -> Bool)
        -> ParserT [Char] st m (Tag String, String)
htmlTag f = try $ do
  lookAhead (char '<')
  inp <- getInput
  let (next : _) = canonicalizeTags $ parseTagsOptions
                       parseOptions{ optTagWarning = False } inp
  guard $ f next
  let handleTag tagname = do
       -- <www.boe.es/buscar/act.php?id=BOE-A-1996-8930#a66>
       -- should NOT be parsed as an HTML tag, see #2277
       guard $ not ('.' `elem` tagname)
       -- <https://example.org> should NOT be a tag either.
       -- tagsoup will parse it as TagOpen "https:" [("example.org","")]
       guard $ not (null tagname)
       guard $ last tagname /= ':'
       rendered <- manyTill anyChar (char '>')
       return (next, rendered ++ ">")
  case next of
       TagComment s
         | "<!--" `isPrefixOf` inp -> do
          count (length s + 4) anyChar
          skipMany (satisfy (/='>'))
          char '>'
          return (next, "<!--" ++ s ++ "-->")
         | otherwise -> fail "bogus comment mode, HTML5 parse error"
       TagOpen tagname _attr -> handleTag tagname
       TagClose tagname -> handleTag tagname
       _ -> mzero

mkAttr :: [(String, String)] -> Attr
mkAttr attr = (attribsId, attribsClasses, attribsKV)
  where attribsId = fromMaybe "" $ lookup "id" attr
        attribsClasses = (words $ fromMaybe "" $ lookup "class" attr) ++ epubTypes
        attribsKV = filter (\(k,_) -> k /= "class" && k /= "id") attr
        epubTypes = words $ fromMaybe "" $ lookup "epub:type" attr

-- Strip namespace prefixes
stripPrefixes :: [Tag String] -> [Tag String]
stripPrefixes = map stripPrefix

stripPrefix :: Tag String -> Tag String
stripPrefix (TagOpen s as) =
    TagOpen (stripPrefix' s) (map (stripPrefix' *** id) as)
stripPrefix (TagClose s) = TagClose (stripPrefix' s)
stripPrefix x = x

stripPrefix' :: String -> String
stripPrefix' s =
  case span (/= ':') s of
    (_, "") -> s
    (_, (_:ts)) -> ts

isSpace :: Char -> Bool
isSpace ' '  = True
isSpace '\t' = True
isSpace '\n' = True
isSpace '\r' = True
isSpace _    = False

-- Instances

instance HasIdentifierList HTMLState where
  extractIdentifierList = identifiers
  updateIdentifierList f s = s{ identifiers = f (identifiers s) }

instance HasHeaderMap HTMLState where
  extractHeaderMap = headerMap
  updateHeaderMap  f s = s{ headerMap = f (headerMap s) }

-- This signature should be more general
-- MonadReader HTMLLocal m => HasQuoteContext st m
instance PandocMonad m => HasQuoteContext st (ReaderT HTMLLocal m) where
  getQuoteContext = asks quoteContext
  withQuoteContext q = local (\s -> s{quoteContext = q})

instance HasReaderOptions HTMLState where
    extractReaderOptions = extractReaderOptions . parserState

instance HasMeta HTMLState where
  setMeta s b st = st {parserState = setMeta s b $ parserState st}
  deleteMeta s st = st {parserState = deleteMeta s $ parserState st}

instance Default HTMLLocal where
  def = HTMLLocal NoQuote False False

instance HasLastStrPosition HTMLState where
  setLastStrPos s st = st {parserState = setLastStrPos s (parserState st)}
  getLastStrPos = getLastStrPos . parserState


-- EPUB Specific
--
--
sectioningContent :: [String]
sectioningContent = ["article", "aside", "nav", "section"]


groupingContent :: [String]
groupingContent = ["p", "hr", "pre", "blockquote", "ol"
                  , "ul", "li", "dl", "dt", "dt", "dd"
                  , "figure", "figcaption", "div", "main"]


{-

types :: [(String, ([String], Int))]
types =  -- Document divisions
   map (\s -> (s, (["section", "body"], 0)))
    ["volume", "part", "chapter", "division"]
  ++ -- Document section and components
  [
    ("abstract",  ([], 0))]
-}