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{-# LANGUAGE OverloadedStrings, CPP, ViewPatterns, ScopedTypeVariables #-}
{-
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.Writers.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 'Pandoc' documents to HTML.
-}
module Text.Pandoc.Writers.HTML ( writeHtml , writeHtmlString ) where
import Text.Pandoc.Definition
import Data.Monoid ((<>))
import Text.Pandoc.Shared
import Text.Pandoc.Writers.Shared
import Text.Pandoc.Options
import Text.Pandoc.ImageSize
import Text.Pandoc.Templates
import Text.Pandoc.Readers.TeXMath
import Text.Pandoc.Slides
import Text.Pandoc.Highlighting ( highlight, styleToCss,
                                  formatHtmlInline, formatHtmlBlock )
import Text.Pandoc.XML (fromEntities, escapeStringForXML)
import Network.URI ( parseURIReference, URI(..), unEscapeString )
import Network.HTTP ( urlEncode )
import Numeric ( showHex )
import Data.Char ( ord, toLower )
import Data.List ( isPrefixOf, intersperse )
import Data.String ( fromString )
import Data.Maybe ( catMaybes, fromMaybe, isJust )
import Control.Monad.State
import Text.Blaze.Html hiding(contents)
#if MIN_VERSION_blaze_markup(0,6,3)
#else
import Text.Blaze.Internal(preEscapedString)
#endif
#if MIN_VERSION_blaze_html(0,5,1)
import qualified Text.Blaze.XHtml5 as H5
#else
import qualified Text.Blaze.Html5 as H5
#endif
import qualified Text.Blaze.XHtml1.Transitional as H
import qualified Text.Blaze.XHtml1.Transitional.Attributes as A
import Text.Blaze.Html.Renderer.String (renderHtml)
import Text.TeXMath
import Text.XML.Light.Output
import Text.XML.Light (unode, elChildren, unqual)
import qualified Text.XML.Light as XML
import System.FilePath (takeExtension)
import Data.Aeson (Value)
import Control.Monad.Except (throwError)
import Text.Pandoc.Class (PandocMonad, PandocExecutionError(..))

data WriterState = WriterState
    { stNotes            :: [Html]  -- ^ List of notes
    , stMath             :: Bool    -- ^ Math is used in document
    , stQuotes           :: Bool    -- ^ <q> tag is used
    , stHighlighting     :: Bool    -- ^ Syntax highlighting is used
    , stSecNum           :: [Int]   -- ^ Number of current section
    , stElement          :: Bool    -- ^ Processing an Element
    }

defaultWriterState :: WriterState
defaultWriterState = WriterState {stNotes= [], stMath = False, stQuotes = False,
                                  stHighlighting = False, stSecNum = [],
                                  stElement = False}

-- Helpers to render HTML with the appropriate function.

strToHtml :: String -> Html
strToHtml ('\'':xs) = preEscapedString "\'" `mappend` strToHtml xs
strToHtml xs@(_:_)  = case break (=='\'') xs of
                           (_ ,[]) -> toHtml xs
                           (ys,zs) -> toHtml ys `mappend` strToHtml zs
strToHtml [] = ""

-- | Hard linebreak.
nl :: WriterOptions -> Html
nl opts = if writerWrapText opts == WrapNone
             then mempty
             else preEscapedString "\n"

-- | Convert Pandoc document to Html string.
writeHtmlString :: PandocMonad m => WriterOptions -> Pandoc -> m String
writeHtmlString opts d = do
  (body, context) <- evalStateT (pandocToHtml opts d) defaultWriterState
  return $ case writerTemplate opts of
             Nothing  -> renderHtml body
             Just tpl -> renderTemplate' tpl $
                           defField "body" (renderHtml body) context

-- | Convert Pandoc document to Html structure.
writeHtml :: PandocMonad m => WriterOptions -> Pandoc -> m Html
writeHtml opts d = do
  (body, context) <- evalStateT (pandocToHtml opts d) defaultWriterState
  return $ case writerTemplate opts of
             Nothing  -> renderHtml body
             Just tpl -> renderTemplate' tpl $
                           defField "body" (renderHtml body) context

-- result is (title, authors, date, toc, body, new variables)
pandocToHtml :: PandocMonad m
             => WriterOptions
             -> Pandoc
             -> StateT WriterState m (Html, Value)
pandocToHtml opts (Pandoc meta blocks) = do
  metadata <- metaToJSON opts
              (fmap renderHtml . blockListToHtml opts)
              (fmap renderHtml . inlineListToHtml opts)
              meta
  let stringifyHTML = escapeStringForXML . stringify
  let authsMeta = map stringifyHTML $ docAuthors meta
  let dateMeta  = stringifyHTML $ docDate meta
  let slideLevel = fromMaybe (getSlideLevel blocks) $ writerSlideLevel opts
  let sects = hierarchicalize $
              if writerSlideVariant opts == NoSlides
                 then blocks
                 else prepSlides slideLevel blocks
  toc <- if writerTableOfContents opts
            then tableOfContents opts sects
            else return Nothing
  blocks' <- liftM (mconcat . intersperse (nl opts)) $
                 mapM (elementToHtml slideLevel opts) sects
  st <- get
  let notes = reverse (stNotes st)
  let thebody = blocks' >> footnoteSection opts notes
  let  math = case writerHTMLMathMethod opts of
                      LaTeXMathML (Just url) ->
                         H.script ! A.src (toValue url)
                                  ! A.type_ "text/javascript"
                                  $ mempty
                      MathML (Just url) ->
                         H.script ! A.src (toValue url)
                                  ! A.type_ "text/javascript"
                                  $ mempty
                      MathJax url ->
                         H.script ! A.src (toValue url)
                                  ! A.type_ "text/javascript"
                                  $ case writerSlideVariant opts of
                                         SlideousSlides ->
                                            preEscapedString
                                            "MathJax.Hub.Queue([\"Typeset\",MathJax.Hub]);"
                                         _ -> mempty
                      JsMath (Just url) ->
                         H.script ! A.src (toValue url)
                                  ! A.type_ "text/javascript"
                                  $ mempty
                      KaTeX js css ->
                         (H.script ! A.src (toValue js) $ mempty) <>
                         (H.link ! A.rel "stylesheet" ! A.href (toValue css)) <>
                         (H.script ! A.type_ "text/javascript" $ toHtml renderKaTeX)
                      _ -> case lookup "mathml-script" (writerVariables opts) of
                                 Just s | not (writerHtml5 opts) ->
                                   H.script ! A.type_ "text/javascript"
                                      $ preEscapedString
                                       ("/*<![CDATA[*/\n" ++ s ++ "/*]]>*/\n")
                                        | otherwise -> mempty
                                 Nothing -> mempty
  let context =   (if stHighlighting st
                      then defField "highlighting-css"
                             (styleToCss $ writerHighlightStyle opts)
                      else id) $
                  (if stMath st
                      then defField "math" (renderHtml math)
                      else id) $
                  defField "quotes" (stQuotes st) $
                  maybe id (defField "toc" . renderHtml) toc $
                  defField "author-meta" authsMeta $
                  maybe id (defField "date-meta") (normalizeDate dateMeta) $
                  defField "pagetitle" (stringifyHTML $ docTitle meta) $
                  defField "idprefix" (writerIdentifierPrefix opts) $
                  -- these should maybe be set in pandoc.hs
                  defField "slidy-url"
                    ("http://www.w3.org/Talks/Tools/Slidy2" :: String) $
                  defField "slideous-url" ("slideous" :: String) $
                  defField "revealjs-url" ("reveal.js" :: String) $
                  defField "s5-url" ("s5/default" :: String) $
                  defField "html5" (writerHtml5 opts) $
                  metadata
  return (thebody, context)

-- | Like Text.XHtml's identifier, but adds the writerIdentifierPrefix
prefixedId :: WriterOptions -> String -> Attribute
prefixedId opts s =
  case s of
    ""       -> mempty
    _        -> A.id $ toValue $ writerIdentifierPrefix opts ++ s

toList :: (Html -> Html) -> WriterOptions -> ([Html] -> Html)
toList listop opts items = do
    if (writerIncremental opts)
       then if (writerSlideVariant opts /= RevealJsSlides)
               then (listop $ mconcat items) ! A.class_ "incremental"
               else listop $ mconcat $ map (! A.class_ "fragment") items
       else listop $ mconcat items

unordList :: WriterOptions -> [Html] -> Html
unordList opts = toList H.ul opts . toListItems opts

ordList :: WriterOptions -> [Html] -> Html
ordList opts = toList H.ol opts . toListItems opts

defList :: WriterOptions -> [Html] -> Html
defList opts items = toList H.dl opts (items ++ [nl opts])

-- | Construct table of contents from list of elements.
tableOfContents :: PandocMonad m => WriterOptions -> [Element] -> StateT WriterState m (Maybe Html)
tableOfContents _ [] = return Nothing
tableOfContents opts sects = do
  let opts'        = opts { writerIgnoreNotes = True }
  contents  <- mapM (elementToListItem opts') sects
  let tocList = catMaybes contents
  return $ if null tocList
              then Nothing
              else Just $ unordList opts tocList

-- | Convert section number to string
showSecNum :: [Int] -> String
showSecNum = concat . intersperse "." . map show

-- | Converts an Element to a list item for a table of contents,
-- retrieving the appropriate identifier from state.
elementToListItem :: PandocMonad m => WriterOptions -> Element -> StateT WriterState m (Maybe Html)
-- Don't include the empty headers created in slide shows
-- shows when an hrule is used to separate slides without a new title:
elementToListItem _ (Sec _ _ _ [Str "\0"] _) = return Nothing
elementToListItem opts (Sec lev num (id',classes,_) headerText subsecs)
  | lev <= writerTOCDepth opts = do
  let num' = zipWith (+) num (writerNumberOffset opts ++ repeat 0)
  let sectnum = if writerNumberSections opts && not (null num) &&
                   "unnumbered" `notElem` classes
                   then (H.span ! A.class_ "toc-section-number"
                        $ toHtml $ showSecNum num') >> preEscapedString " "
                   else mempty
  txt <- liftM (sectnum >>) $ inlineListToHtml opts headerText
  subHeads <- mapM (elementToListItem opts) subsecs >>= return . catMaybes
  let subList = if null subHeads
                   then mempty
                   else unordList opts subHeads
  -- in reveal.js, we need #/apples, not #apples:
  let revealSlash = ['/' | writerSlideVariant opts == RevealJsSlides]
  return $ Just
         $ if null id'
              then (H.a $ toHtml txt) >> subList
              else (H.a ! A.href (toValue $ "#" ++ revealSlash ++
                    writerIdentifierPrefix opts ++ id')
                       $ toHtml txt) >> subList
elementToListItem _ _ = return Nothing

-- | Convert an Element to Html.
elementToHtml :: PandocMonad m => Int -> WriterOptions -> Element -> StateT WriterState m Html
elementToHtml _slideLevel opts (Blk block) = blockToHtml opts block
elementToHtml slideLevel opts (Sec level num (id',classes,keyvals) title' elements) = do
  let slide = writerSlideVariant opts /= NoSlides && level <= slideLevel
  let num' = zipWith (+) num (writerNumberOffset opts ++ repeat 0)
  modify $ \st -> st{stSecNum = num'}  -- update section number
  let titleSlide = slide && level < slideLevel
  header' <- if title' == [Str "\0"]  -- marker for hrule
                then return mempty
                else do
                  modify (\st -> st{ stElement = True})
                  res <- blockToHtml opts
                           (Header level (id',classes,keyvals) title')
                  modify (\st -> st{ stElement = False})
                  return res

  let isSec (Sec _ _ _ _ _) = True
      isSec (Blk _)         = False
  let isPause (Blk x) = x == Para [Str ".",Space,Str ".",Space,Str "."]
      isPause _       = False
  let fragmentClass = case writerSlideVariant opts of
                           RevealJsSlides  -> "fragment"
                           _               -> "incremental"
  let inDiv xs = Blk (RawBlock (Format "html") ("<div class=\""
                       ++ fragmentClass ++ "\">")) :
                   (xs ++ [Blk (RawBlock (Format "html") "</div>")])
  innerContents <- mapM (elementToHtml slideLevel opts)
                   $ if titleSlide
                        -- title slides have no content of their own
                        then filter isSec elements
                        else case splitBy isPause elements of
                                  []     -> []
                                  (x:xs) -> x ++ concatMap inDiv xs
  let inNl x = mconcat $ nl opts : intersperse (nl opts) x ++ [nl opts]
  let classes' = ["titleslide" | titleSlide] ++ ["slide" | slide] ++
                  ["section" | (slide || writerSectionDivs opts) &&
                               not (writerHtml5 opts) ] ++
                  ["level" ++ show level | slide || writerSectionDivs opts ]
                  ++ classes
  let secttag  = if writerHtml5 opts
                    then H5.section
                    else H.div
  let attr = (id',classes',keyvals)
  return $ if titleSlide
              then (if writerSlideVariant opts == RevealJsSlides
                       then H5.section
                       else id) $ mconcat $
                       (addAttrs opts attr $ secttag $ header') : innerContents
              else if writerSectionDivs opts || slide
                   then addAttrs opts attr
                        $ secttag $ inNl $ header' : innerContents
                   else mconcat $ intersperse (nl opts)
                        $ addAttrs opts attr header' : innerContents

-- | Convert list of Note blocks to a footnote <div>.
-- Assumes notes are sorted.
footnoteSection :: WriterOptions -> [Html] -> Html
footnoteSection opts notes =
  if null notes
     then mempty
     else nl opts >> (container
          $ nl opts >> hrtag >> nl opts >>
            H.ol (mconcat notes >> nl opts) >> nl opts)
   where container x = if writerHtml5 opts
                          then H5.section ! A.class_ "footnotes" $ x
                          else if writerSlideVariant opts /= NoSlides
                               then H.div ! A.class_ "footnotes slide" $ x
                               else H.div ! A.class_ "footnotes" $ x
         hrtag = if writerHtml5 opts then H5.hr else H.hr

-- | Parse a mailto link; return Just (name, domain) or Nothing.
parseMailto :: String -> Maybe (String, String)
parseMailto s = do
  case break (==':') s of
       (xs,':':addr) | map toLower xs == "mailto" -> do
         let (name', rest) = span (/='@') addr
         let domain = drop 1 rest
         return (name', domain)
       _ -> fail "not a mailto: URL"

-- | Obfuscate a "mailto:" link.
obfuscateLink :: PandocMonad m => WriterOptions -> Attr -> Html -> String -> m Html
obfuscateLink opts attr txt s | writerEmailObfuscation opts == NoObfuscation =
  return $ addAttrs opts attr $ H.a ! A.href (toValue s) $ txt
obfuscateLink opts attr (renderHtml -> txt) s =
  let meth = writerEmailObfuscation opts
      s' = map toLower (take 7 s) ++ drop 7 s
  in  case parseMailto s' of
        (Just (name', domain)) ->
          let domain'  = substitute "." " dot " domain
              at'      = obfuscateChar '@'
              (linkText, altText) =
                 if txt == drop 7 s' -- autolink
                    then ("e", name' ++ " at " ++ domain')
                    else ("'" ++ obfuscateString txt ++ "'",
                          txt ++ " (" ++ name' ++ " at " ++ domain' ++ ")")
          in  case meth of
                ReferenceObfuscation ->
                     -- need to use preEscapedString or &'s are escaped to &amp; in URL
                     return $
                     preEscapedString $ "<a href=\"" ++ (obfuscateString s')
                     ++ "\" class=\"email\">" ++ (obfuscateString txt) ++ "</a>"
                JavascriptObfuscation ->
                     return $
                     (H.script ! A.type_ "text/javascript" $
                     preEscapedString ("\n<!--\nh='" ++
                     obfuscateString domain ++ "';a='" ++ at' ++ "';n='" ++
                     obfuscateString name' ++ "';e=n+a+h;\n" ++
                     "document.write('<a h'+'ref'+'=\"ma'+'ilto'+':'+e+'\" clas'+'s=\"em' + 'ail\">'+" ++
                     linkText  ++ "+'<\\/'+'a'+'>');\n// -->\n")) >>
                     H.noscript (preEscapedString $ obfuscateString altText)
                _ -> throwError $ PandocSomeError $ "Unknown obfuscation method: " ++ show meth
        _ -> return $ addAttrs opts attr $ H.a ! A.href (toValue s) $ toHtml txt  -- malformed email

-- | Obfuscate character as entity.
obfuscateChar :: Char -> String
obfuscateChar char =
  let num    = ord char
      numstr = if even num then show num else "x" ++ showHex num ""
  in  "&#" ++ numstr ++ ";"

-- | Obfuscate string using entities.
obfuscateString :: String -> String
obfuscateString = concatMap obfuscateChar . fromEntities

addAttrs :: WriterOptions -> Attr -> Html -> Html
addAttrs opts attr h = foldl (!) h (attrsToHtml opts attr)

toAttrs :: [(String, String)] -> [Attribute]
toAttrs kvs = map (\(x,y) -> customAttribute (fromString x) (toValue y)) kvs

attrsToHtml :: WriterOptions -> Attr -> [Attribute]
attrsToHtml opts (id',classes',keyvals) =
  [prefixedId opts id' | not (null id')] ++
  [A.class_ (toValue $ unwords classes') | not (null classes')] ++ toAttrs keyvals

imgAttrsToHtml :: WriterOptions -> Attr -> [Attribute]
imgAttrsToHtml opts attr =
    attrsToHtml opts (ident,cls,kvs') ++
    toAttrs (dimensionsToAttrList opts attr)
  where
    (ident,cls,kvs) = attr
    kvs' = filter isNotDim kvs
    isNotDim ("width", _)  = False
    isNotDim ("height", _) = False
    isNotDim _ = True

dimensionsToAttrList :: WriterOptions -> Attr -> [(String, String)]
dimensionsToAttrList opts attr = (go Width) ++ (go Height)
  where
    go dir = case (dimension dir attr) of
               (Just (Percent a)) -> [("style", show dir ++ ":" ++ show (Percent a))]
               (Just dim)         -> [(show dir, showInPixel opts dim)]
               _ -> []


imageExts :: [String]
imageExts = [ "art", "bmp", "cdr", "cdt", "cpt", "cr2", "crw", "djvu", "erf",
              "gif", "ico", "ief", "jng", "jpg", "jpeg", "nef", "orf", "pat", "pbm",
              "pcx", "pgm", "png", "pnm", "ppm", "psd", "ras", "rgb", "svg", "tiff",
              "wbmp", "xbm", "xpm", "xwd" ]

treatAsImage :: FilePath -> Bool
treatAsImage fp =
  let path = case uriPath `fmap` parseURIReference fp of
                  Nothing -> fp
                  Just up -> up
      ext  = map toLower $ drop 1 $ takeExtension path
  in  null ext || ext `elem` imageExts

-- | Convert Pandoc block element to HTML.
blockToHtml :: PandocMonad m => WriterOptions -> Block -> StateT WriterState m Html
blockToHtml _ Null = return mempty
blockToHtml opts (Plain lst) = inlineListToHtml opts lst
-- title beginning with fig: indicates that the image is a figure
blockToHtml opts (Para [Image attr txt (s,'f':'i':'g':':':tit)]) = do
  img <- inlineToHtml opts (Image attr txt (s,tit))
  let tocapt = if writerHtml5 opts
                  then H5.figcaption
                  else H.p ! A.class_ "caption"
  capt <- if null txt
             then return mempty
             else tocapt `fmap` inlineListToHtml opts txt
  return $ if writerHtml5 opts
              then H5.figure $ mconcat
                    [nl opts, img, capt, nl opts]
              else H.div ! A.class_ "figure" $ mconcat
                    [nl opts, img, nl opts, capt, nl opts]
blockToHtml opts (Para lst)
  | isEmptyRaw lst = return mempty
  | otherwise = do
      contents <- inlineListToHtml opts lst
      return $ H.p contents
  where
    isEmptyRaw [RawInline f _] = f /= (Format "html")
    isEmptyRaw _                 = False
blockToHtml opts (LineBlock lns) =
  if writerWrapText opts == WrapNone
  then blockToHtml opts $ linesToPara lns
  else do
    let lf = preEscapedString "\n"
    htmlLines <- mconcat . intersperse lf <$> mapM (inlineListToHtml opts) lns
    return $ H.div ! A.style "white-space: pre-line;" $ htmlLines
blockToHtml opts (Div attr@(ident, classes, kvs) bs) = do
  let speakerNotes = "notes" `elem` classes
  -- we don't want incremental output inside speaker notes, see #1394
  let opts' = if speakerNotes then opts{ writerIncremental = False } else opts
  contents <- blockListToHtml opts' bs
  let contents' = nl opts >> contents >> nl opts
  let (divtag, classes') = if writerHtml5 opts && "section" `elem` classes
                              then (H5.section, filter (/= "section") classes)
                              else (H.div, classes)
  return $
     if speakerNotes
        then case writerSlideVariant opts of
                  RevealJsSlides -> addAttrs opts' attr $ H5.aside $ contents'
                  DZSlides       -> (addAttrs opts' attr $ H5.div $ contents')
                                      ! (H5.customAttribute "role" "note")
                  NoSlides       -> addAttrs opts' attr $ H.div $ contents'
                  _              -> mempty
        else addAttrs opts (ident, classes', kvs) $ divtag $ contents'
blockToHtml opts (RawBlock f str)
  | f == Format "html" = return $ preEscapedString str
  | (f == Format "latex" || f == Format "tex") &&
     allowsMathEnvironments (writerHTMLMathMethod opts) &&
     isMathEnvironment str = blockToHtml opts $ Plain [Math DisplayMath str]
  | otherwise          = return mempty
blockToHtml opts (HorizontalRule) = return $ if writerHtml5 opts then H5.hr else H.hr
blockToHtml opts (CodeBlock (id',classes,keyvals) rawCode) = do
  let tolhs = isEnabled Ext_literate_haskell opts &&
                any (\c -> map toLower c == "haskell") classes &&
                any (\c -> map toLower c == "literate") classes
      classes' = if tolhs
                    then map (\c -> if map toLower c == "haskell"
                                       then "literatehaskell"
                                       else c) classes
                    else classes
      adjCode  = if tolhs
                    then unlines . map ("> " ++) . lines $ rawCode
                    else rawCode
      hlCode   = if writerHighlight opts -- check highlighting options
                    then highlight formatHtmlBlock (id',classes',keyvals) adjCode
                    else Nothing
  case hlCode of
         Nothing -> return $ addAttrs opts (id',classes,keyvals)
                           $ H.pre $ H.code $ toHtml adjCode
         Just  h -> modify (\st -> st{ stHighlighting = True }) >>
                    return (addAttrs opts (id',[],keyvals) h)
blockToHtml opts (BlockQuote blocks) =
  -- in S5, treat list in blockquote specially
  -- if default is incremental, make it nonincremental;
  -- otherwise incremental
  if writerSlideVariant opts /= NoSlides
     then let inc = not (writerIncremental opts) in
          case blocks of
             [BulletList lst]  -> blockToHtml (opts {writerIncremental = inc})
                                  (BulletList lst)
             [OrderedList attribs lst] ->
                                  blockToHtml (opts {writerIncremental = inc})
                                  (OrderedList attribs lst)
             [DefinitionList lst] ->
                                  blockToHtml (opts {writerIncremental = inc})
                                  (DefinitionList lst)
             _                 -> do contents <- blockListToHtml opts blocks
                                     return $ H.blockquote
                                            $ nl opts >> contents >> nl opts
     else do
       contents <- blockListToHtml opts blocks
       return $ H.blockquote $ nl opts >> contents >> nl opts
blockToHtml opts (Header level attr@(_,classes,_) lst) = do
  contents <- inlineListToHtml opts lst
  secnum <- liftM stSecNum get
  let contents' = if writerNumberSections opts && not (null secnum)
                     && "unnumbered" `notElem` classes
                     then (H.span ! A.class_ "header-section-number" $ toHtml
                          $ showSecNum secnum) >> strToHtml " " >> contents
                     else contents
  inElement <- gets stElement
  return $ (if inElement then id else addAttrs opts attr)
         $ case level of
              1 -> H.h1 contents'
              2 -> H.h2 contents'
              3 -> H.h3 contents'
              4 -> H.h4 contents'
              5 -> H.h5 contents'
              6 -> H.h6 contents'
              _ -> H.p contents'
blockToHtml opts (BulletList lst) = do
  contents <- mapM (blockListToHtml opts) lst
  return $ unordList opts contents
blockToHtml opts (OrderedList (startnum, numstyle, _) lst) = do
  contents <- mapM (blockListToHtml opts) lst
  let numstyle' = case numstyle of
                       Example -> "decimal"
                       _       -> camelCaseToHyphenated $ show numstyle
  let attribs = (if startnum /= 1
                   then [A.start $ toValue startnum]
                   else []) ++
                (if numstyle == Example
                    then [A.class_ "example"]
                    else []) ++
                (if numstyle /= DefaultStyle
                   then if writerHtml5 opts
                           then [A.type_ $
                                 case numstyle of
                                      Decimal    -> "1"
                                      LowerAlpha -> "a"
                                      UpperAlpha -> "A"
                                      LowerRoman -> "i"
                                      UpperRoman -> "I"
                                      _          -> "1"]
                           else [A.style $ toValue $ "list-style-type: " ++
                                   numstyle']
                   else [])
  return $ foldl (!) (ordList opts contents) attribs
blockToHtml opts (DefinitionList lst) = do
  contents <- mapM (\(term, defs) ->
                  do term' <- if null term
                                 then return mempty
                                 else liftM H.dt $ inlineListToHtml opts term
                     defs' <- mapM ((liftM (\x -> H.dd $ (x >> nl opts))) .
                                    blockListToHtml opts) defs
                     return $ mconcat $ nl opts : term' : nl opts :
                                        intersperse (nl opts) defs') lst
  return $ defList opts contents
blockToHtml opts (Table capt aligns widths headers rows') = do
  captionDoc <- if null capt
                   then return mempty
                   else do
                     cs <- inlineListToHtml opts capt
                     return $ H.caption cs >> nl opts
  let percent w = show (truncate (100*w) :: Integer) ++ "%"
  let coltags = if all (== 0.0) widths
                   then mempty
                   else do
                     H.colgroup $ do
                       nl opts
                       mapM_ (\w -> do
                            if writerHtml5 opts
                               then H.col ! A.style (toValue $ "width: " ++
                                                      percent w)
                               else H.col ! A.width (toValue $ percent w)
                            nl opts) widths
                     nl opts
  head' <- if all null headers
              then return mempty
              else do
                contents <- tableRowToHtml opts aligns 0 headers
                return $ H.thead (nl opts >> contents) >> nl opts
  body' <- liftM (\x -> H.tbody (nl opts >> mconcat x)) $
               zipWithM (tableRowToHtml opts aligns) [1..] rows'
  let tbl = H.table $
              nl opts >> captionDoc >> coltags >> head' >> body' >> nl opts
  let totalWidth = sum widths
  -- When widths of columns are < 100%, we need to set width for the whole
  -- table, or some browsers give us skinny columns with lots of space between:
  return $ if totalWidth == 0 || totalWidth == 1
              then tbl
              else tbl ! A.style (toValue $ "width:" ++
                              show (round (totalWidth * 100) :: Int) ++ "%;")

tableRowToHtml :: PandocMonad m
               => WriterOptions
               -> [Alignment]
               -> Int
               -> [[Block]]
               -> StateT WriterState m Html
tableRowToHtml opts aligns rownum cols' = do
  let mkcell = if rownum == 0 then H.th else H.td
  let rowclass = case rownum of
                      0                  -> "header"
                      x | x `rem` 2 == 1 -> "odd"
                      _                  -> "even"
  cols'' <- sequence $ zipWith
            (\alignment item -> tableItemToHtml opts mkcell alignment item)
            aligns cols'
  return $ (H.tr ! A.class_ rowclass $ nl opts >> mconcat cols'')
          >> nl opts

alignmentToString :: Alignment -> [Char]
alignmentToString alignment = case alignment of
                                 AlignLeft    -> "left"
                                 AlignRight   -> "right"
                                 AlignCenter  -> "center"
                                 AlignDefault -> ""

tableItemToHtml :: PandocMonad m
                => WriterOptions
                -> (Html -> Html)
                -> Alignment
                -> [Block]
                -> StateT WriterState m Html
tableItemToHtml opts tag' align' item = do
  contents <- blockListToHtml opts item
  let alignStr = alignmentToString align'
  let attribs = if writerHtml5 opts
                   then A.style (toValue $ "text-align: " ++ alignStr ++ ";")
                   else A.align (toValue alignStr)
  let tag'' = if null alignStr
                 then tag'
                 else tag' ! attribs
  return $ (tag'' $ contents) >> nl opts

toListItems :: WriterOptions -> [Html] -> [Html]
toListItems opts items = map (toListItem opts) items ++ [nl opts]

toListItem :: WriterOptions -> Html -> Html
toListItem opts item = nl opts >> H.li item

blockListToHtml :: PandocMonad m => WriterOptions -> [Block] -> StateT WriterState m Html
blockListToHtml opts lst =
  fmap (mconcat . intersperse (nl opts)) $ mapM (blockToHtml opts) lst

-- | Convert list of Pandoc inline elements to HTML.
inlineListToHtml :: PandocMonad m => WriterOptions -> [Inline] -> StateT WriterState m Html
inlineListToHtml opts lst =
  mapM (inlineToHtml opts) lst >>= return . mconcat

-- | Annotates a MathML expression with the tex source
annotateMML :: XML.Element -> String -> XML.Element
annotateMML e tex = math (unode "semantics" [cs, unode "annotation" (annotAttrs, tex)])
  where
    cs = case elChildren e of
          [] -> unode "mrow" ()
          [x] -> x
          xs -> unode "mrow" xs
    math childs = XML.Element q as [XML.Elem childs] l
      where
        (XML.Element q as _ l) = e
    annotAttrs = [XML.Attr (unqual "encoding") "application/x-tex"]


-- | Convert Pandoc inline element to HTML.
inlineToHtml :: PandocMonad m => WriterOptions -> Inline -> StateT WriterState m Html
inlineToHtml opts inline =
  case inline of
    (Str str)        -> return $ strToHtml str
    (Space)          -> return $ strToHtml " "
    (SoftBreak)      -> return $ case writerWrapText opts of
                                       WrapNone     -> preEscapedString " "
                                       WrapAuto     -> preEscapedString " "
                                       WrapPreserve -> preEscapedString "\n"
    (LineBreak)      -> return $ (if writerHtml5 opts then H5.br else H.br)
                                 <> strToHtml "\n"
    (PageBreak)      -> return mempty
    (Span (id',classes,kvs) ils)
                     -> inlineListToHtml opts ils >>=
                           return . addAttrs opts attr' . H.span
                        where attr' = (id',classes',kvs')
                              classes' = filter (`notElem` ["csl-no-emph",
                                              "csl-no-strong",
                                              "csl-no-smallcaps"]) classes
                              kvs' = if null styles
                                        then kvs
                                        else (("style", concat styles) : kvs)
                              styles = ["font-style:normal;"
                                         | "csl-no-emph" `elem` classes]
                                    ++ ["font-weight:normal;"
                                         | "csl-no-strong" `elem` classes]
                                    ++ ["font-variant:normal;"
                                         | "csl-no-smallcaps" `elem` classes]
    (Emph lst)       -> inlineListToHtml opts lst >>= return . H.em
    (Strong lst)     -> inlineListToHtml opts lst >>= return . H.strong
    (Code attr str)  -> case hlCode of
                             Nothing -> return
                                        $ addAttrs opts attr
                                        $ H.code $ strToHtml str
                             Just  h -> do
                               modify $ \st -> st{ stHighlighting = True }
                               return $ addAttrs opts (id',[],keyvals) h
                        where (id',_,keyvals) = attr
                              hlCode = if writerHighlight opts
                                          then highlight formatHtmlInline attr str
                                          else Nothing
    (Strikeout lst)  -> inlineListToHtml opts lst >>=
                        return . H.del
    (SmallCaps lst)   -> inlineListToHtml opts lst >>=
                         return . (H.span ! A.style "font-variant: small-caps;")
    (Superscript lst) -> inlineListToHtml opts lst >>= return . H.sup
    (Subscript lst)   -> inlineListToHtml opts lst >>= return . H.sub
    (Quoted quoteType lst) ->
                        let (leftQuote, rightQuote) = case quoteType of
                              SingleQuote -> (strToHtml "‘",
                                              strToHtml "’")
                              DoubleQuote -> (strToHtml "“",
                                              strToHtml "”")
                        in  if writerHtmlQTags opts
                               then do
                                 modify $ \st -> st{ stQuotes = True }
                                 H.q `fmap` inlineListToHtml opts lst
                               else (\x -> leftQuote >> x >> rightQuote)
                                    `fmap` inlineListToHtml opts lst
    (Math t str) -> do
      modify (\st -> st {stMath = True})
      let mathClass = toValue $ ("math " :: String) ++
                      if t == InlineMath then "inline" else "display"
      case writerHTMLMathMethod opts of
           LaTeXMathML _ ->
              -- putting LaTeXMathML in container with class "LaTeX" prevents
              -- non-math elements on the page from being treated as math by
              -- the javascript
              return $ H.span ! A.class_ "LaTeX" $
                     case t of
                       InlineMath  -> toHtml ("$" ++ str ++ "$")
                       DisplayMath -> toHtml ("$$" ++ str ++ "$$")
           JsMath _ -> do
              let m = preEscapedString str
              return $ case t of
                       InlineMath -> H.span ! A.class_ mathClass $ m
                       DisplayMath -> H.div ! A.class_ mathClass $ m
           WebTeX url -> do
              let imtag = if writerHtml5 opts then H5.img else H.img
              let m = imtag ! A.style "vertical-align:middle"
                            ! A.src (toValue $ url ++ urlEncode str)
                            ! A.alt (toValue str)
                            ! A.title (toValue str)
              let brtag = if writerHtml5 opts then H5.br else H.br
              return $ case t of
                        InlineMath  -> m
                        DisplayMath -> brtag >> m >> brtag
           GladTeX ->
              return $ case t of
                         InlineMath -> preEscapedString $ "<EQ ENV=\"math\">" ++ str ++ "</EQ>"
                         DisplayMath -> preEscapedString $ "<EQ ENV=\"displaymath\">" ++ str ++ "</EQ>"
           MathML _ -> do
              let dt = if t == InlineMath
                          then DisplayInline
                          else DisplayBlock
              let conf = useShortEmptyTags (const False)
                           defaultConfigPP
              case writeMathML dt <$> readTeX str of
                    Right r  -> return $ preEscapedString $
                        ppcElement conf (annotateMML r str)
                    Left _   -> inlineListToHtml opts
                        (texMathToInlines t str) >>=
                        return .  (H.span ! A.class_ mathClass)
           MathJax _ -> return $ H.span ! A.class_ mathClass $ toHtml $
              case t of
                InlineMath  -> "\\(" ++ str ++ "\\)"
                DisplayMath -> "\\[" ++ str ++ "\\]"
           KaTeX _ _ -> return $ H.span ! A.class_ mathClass $
              toHtml (case t of
                        InlineMath -> str
                        DisplayMath -> "\\displaystyle " ++ str)
           PlainMath -> do
              x <- inlineListToHtml opts (texMathToInlines t str)
              let m = H.span ! A.class_ mathClass $ x
              let brtag = if writerHtml5 opts then H5.br else H.br
              return  $ case t of
                         InlineMath  -> m
                         DisplayMath -> brtag >> m >> brtag
    (RawInline f str)
      | f == Format "html" -> return $ preEscapedString str
      | otherwise          -> return mempty
    (Link attr txt (s,_)) | "mailto:" `isPrefixOf` s -> do
                        linkText <- inlineListToHtml opts txt
                        lift $ obfuscateLink opts attr linkText s
    (Link attr txt (s,tit)) -> do
                        linkText <- inlineListToHtml opts txt
                        let s' = case s of
                                      '#':xs | writerSlideVariant opts ==
                                            RevealJsSlides -> '#':'/':xs
                                      _ -> s
                        let link = H.a ! A.href (toValue s') $ linkText
                        let link' = if txt == [Str (unEscapeString s)]
                                       then link ! A.class_ "uri"
                                       else link
                        let link'' = addAttrs opts attr link'
                        return $ if null tit
                                    then link''
                                    else link'' ! A.title (toValue tit)
    (Image attr txt (s,tit)) | treatAsImage s -> do
                        let alternate' = stringify txt
                        let attributes = [A.src $ toValue s] ++
                                         [A.title $ toValue tit | not (null tit)] ++
                                         [A.alt $ toValue alternate' | not (null txt)] ++
                                         imgAttrsToHtml opts attr
                        let tag = if writerHtml5 opts then H5.img else H.img
                        return $ foldl (!) tag attributes
                        -- note:  null title included, as in Markdown.pl
    (Image attr _ (s,tit)) -> do
                        let attributes = [A.src $ toValue s] ++
                                         [A.title $ toValue tit | not (null tit)] ++
                                         imgAttrsToHtml opts attr
                        return $ foldl (!) H5.embed attributes
                        -- note:  null title included, as in Markdown.pl
    (Note contents)
      | writerIgnoreNotes opts -> return mempty
      | otherwise              -> do
                        notes <- gets stNotes
                        let number = (length notes) + 1
                        let ref = show number
                        htmlContents <- blockListToNote opts ref contents
                        -- push contents onto front of notes
                        modify $ \st -> st {stNotes = (htmlContents:notes)}
                        let revealSlash = ['/' | writerSlideVariant opts
                                                 == RevealJsSlides]
                        let link = H.a ! A.href (toValue $ "#" ++
                                         revealSlash ++
                                         writerIdentifierPrefix opts ++ "fn" ++ ref)
                                       ! A.class_ "footnoteRef"
                                       ! prefixedId opts ("fnref" ++ ref)
                                       $ (if isJust (writerEpubVersion opts)
                                             then id
                                             else H.sup)
                                       $ toHtml ref
                        return $ case writerEpubVersion opts of
                                      Just EPUB3 -> link ! customAttribute "epub:type" "noteref"
                                      _          -> link
    (Cite cits il)-> do contents <- inlineListToHtml opts il
                        let citationIds = unwords $ map citationId cits
                        let result = H.span ! A.class_ "citation" $ contents
                        return $ if writerHtml5 opts
                                    then result ! customAttribute "data-cites" (toValue citationIds)
                                    else result

blockListToNote :: PandocMonad m => WriterOptions -> String -> [Block] -> StateT WriterState m Html
blockListToNote opts ref blocks =
  -- If last block is Para or Plain, include the backlink at the end of
  -- that block. Otherwise, insert a new Plain block with the backlink.
  let backlink = [Link nullAttr [Str "↩"] ("#" ++ writerIdentifierPrefix opts ++ "fnref" ++ ref,[])]
      blocks'  = if null blocks
                    then []
                    else let lastBlock   = last blocks
                             otherBlocks = init blocks
                         in  case lastBlock of
                                  (Para lst)  -> otherBlocks ++
                                                 [Para (lst ++ backlink)]
                                  (Plain lst) -> otherBlocks ++
                                                 [Plain (lst ++ backlink)]
                                  _           -> otherBlocks ++ [lastBlock,
                                                 Plain backlink]
  in  do contents <- blockListToHtml opts blocks'
         let noteItem = H.li ! (prefixedId opts ("fn" ++ ref)) $ contents
         let noteItem' = case writerEpubVersion opts of
                              Just EPUB3 -> noteItem ! customAttribute "epub:type" "footnote"
                              _          -> noteItem
         return $ nl opts >> noteItem'

-- Javascript snippet to render all KaTeX elements
renderKaTeX :: String
renderKaTeX = unlines [
    "window.onload = function(){var mathElements = document.getElementsByClassName(\"math\");"
  , "for (var i=0; i < mathElements.length; i++)"
  , "{"
  , " var texText = mathElements[i].firstChild"
  , " katex.render(texText.data, mathElements[i])"
  , "}}"
  ]

isMathEnvironment :: String -> Bool
isMathEnvironment s = "\\begin{" `isPrefixOf` s &&
                         envName `elem` mathmlenvs
  where envName = takeWhile (/= '}') (drop 7 s)
        mathmlenvs = [ "align"
                     , "align*"
                     , "alignat"
                     , "alignat*"
                     , "aligned"
                     , "alignedat"
                     , "array"
                     , "Bmatrix"
                     , "bmatrix"
                     , "cases"
                     , "CD"
                     , "eqnarray"
                     , "eqnarray*"
                     , "equation"
                     , "equation*"
                     , "gather"
                     , "gather*"
                     , "gathered"
                     , "matrix"
                     , "multline"
                     , "multline*"
                     , "pmatrix"
                     , "smallmatrix"
                     , "split"
                     , "subarray"
                     , "Vmatrix"
                     , "vmatrix" ]

allowsMathEnvironments :: HTMLMathMethod -> Bool
allowsMathEnvironments (MathJax _) = True
allowsMathEnvironments (MathML _)  = True
allowsMathEnvironments (WebTeX _)  = True
allowsMathEnvironments _           = False