aboutsummaryrefslogtreecommitdiff
path: root/src/Text/Pandoc/Writers/HTML.hs
blob: 19ec4692efc9e70d3d2b92c9b8a8f135480ff6ed (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
{-# LANGUAGE NoImplicitPrelude #-}
{-# LANGUAGE CPP                 #-}
{-# LANGUAGE OverloadedStrings   #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE ViewPatterns        #-}
{-# LANGUAGE MultiWayIf          #-}
{-
Copyright (C) 2006-2018 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) 2006-2018 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 (
  writeHtml4,
  writeHtml4String,
  writeHtml5,
  writeHtml5String,
  writeHtmlStringForEPUB,
  writeS5,
  writeSlidy,
  writeSlideous,
  writeDZSlides,
  writeRevealJs,
  tagWithAttributes
  ) where
import Prelude
import Control.Monad.State.Strict
import Data.Char (ord, toLower)
import Data.List (intercalate, intersperse, isPrefixOf, partition)
import Data.Maybe (catMaybes, fromMaybe, isJust, isNothing, mapMaybe)
import qualified Data.Set as Set
import Data.String (fromString)
import Data.Text (Text)
import qualified Data.Text.Lazy as TL
import Network.HTTP (urlEncode)
import Network.URI (URI (..), parseURIReference)
import Numeric (showHex)
import Text.Blaze.Internal (customLeaf, customParent, MarkupM(Empty))
#if MIN_VERSION_blaze_markup(0,6,3)
#else
import Text.Blaze.Internal (preEscapedString, preEscapedText)
#endif
import Text.Blaze.Html hiding (contents)
import Text.Pandoc.Definition
import Text.Pandoc.Highlighting (formatHtmlBlock, formatHtmlInline, highlight,
                                 styleToCss)
import Text.Pandoc.ImageSize
import Text.Pandoc.Options
import Text.Pandoc.Shared
import Text.Pandoc.Slides
import Text.Pandoc.Templates
import Text.Pandoc.Walk
import Text.Pandoc.Writers.Math
import Text.Pandoc.Writers.Shared
import Text.Pandoc.XML (escapeStringForXML, fromEntities, toEntities)
#if MIN_VERSION_blaze_markup(0,6,3)
#else
import Text.Blaze.Internal (preEscapedString, preEscapedText)
#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 Control.Monad.Except (throwError)
import Data.Aeson (Value)
import System.FilePath (takeBaseName, takeExtension)
import Text.Blaze.Html.Renderer.Text (renderHtml)
import qualified Text.Blaze.XHtml1.Transitional as H
import qualified Text.Blaze.XHtml1.Transitional.Attributes as A
import Text.Pandoc.Class (PandocMonad, report, runPure)
import Text.Pandoc.Error
import Text.Pandoc.Logging
import Text.TeXMath
import Text.XML.Light (elChildren, unode, unqual)
import qualified Text.XML.Light as XML
import Text.XML.Light.Output

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
    , stHtml5        :: Bool    -- ^ Use HTML5
    , stEPUBVersion  :: Maybe EPUBVersion -- ^ EPUB version if for epub
    , stSlideVariant :: HTMLSlideVariant
    , stCodeBlockNum :: Int     -- ^ Number of code block
    }

defaultWriterState :: WriterState
defaultWriterState = WriterState {stNotes= [], stMath = False, stQuotes = False,
                                  stHighlighting = False, stSecNum = [],
                                  stElement = False, stHtml5 = False,
                                  stEPUBVersion = Nothing,
                                  stSlideVariant = NoSlides,
                                  stCodeBlockNum = 0}

-- 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 5 string.
writeHtml5String :: PandocMonad m => WriterOptions -> Pandoc -> m Text
writeHtml5String = writeHtmlString'
                      defaultWriterState{ stHtml5 = True }

-- | Convert Pandoc document to Html 5 structure.
writeHtml5 :: PandocMonad m => WriterOptions -> Pandoc -> m Html
writeHtml5 = writeHtml' defaultWriterState{ stHtml5 = True }

-- | Convert Pandoc document to Html 4 string.
writeHtml4String :: PandocMonad m => WriterOptions -> Pandoc -> m Text
writeHtml4String = writeHtmlString'
                      defaultWriterState{ stHtml5 = False }

-- | Convert Pandoc document to Html 4 structure.
writeHtml4 :: PandocMonad m => WriterOptions -> Pandoc -> m Html
writeHtml4 = writeHtml' defaultWriterState{ stHtml5 = False }

-- | Convert Pandoc document to Html appropriate for an epub version.
writeHtmlStringForEPUB :: PandocMonad m
                       => EPUBVersion -> WriterOptions -> Pandoc
                       -> m Text
writeHtmlStringForEPUB version o = writeHtmlString'
                      defaultWriterState{ stHtml5 = version == EPUB3,
                                          stEPUBVersion = Just version } o

-- | Convert Pandoc document to Reveal JS HTML slide show.
writeRevealJs :: PandocMonad m
              => WriterOptions -> Pandoc -> m Text
writeRevealJs = writeHtmlSlideShow' RevealJsSlides

-- | Convert Pandoc document to S5 HTML slide show.
writeS5 :: PandocMonad m
        => WriterOptions -> Pandoc -> m Text
writeS5 = writeHtmlSlideShow' S5Slides

-- | Convert Pandoc document to Slidy HTML slide show.
writeSlidy :: PandocMonad m
           => WriterOptions -> Pandoc -> m Text
writeSlidy = writeHtmlSlideShow' SlidySlides

-- | Convert Pandoc document to Slideous HTML slide show.
writeSlideous :: PandocMonad m
              => WriterOptions -> Pandoc -> m Text
writeSlideous = writeHtmlSlideShow' SlideousSlides

-- | Convert Pandoc document to DZSlides HTML slide show.
writeDZSlides :: PandocMonad m
              => WriterOptions -> Pandoc -> m Text
writeDZSlides = writeHtmlSlideShow' DZSlides

writeHtmlSlideShow' :: PandocMonad m
                    => HTMLSlideVariant -> WriterOptions -> Pandoc -> m Text
writeHtmlSlideShow' variant = writeHtmlString'
    defaultWriterState{ stSlideVariant = variant
                      , stHtml5 = case variant of
                                       RevealJsSlides -> True
                                       S5Slides       -> False
                                       SlidySlides    -> False
                                       DZSlides       -> True
                                       SlideousSlides -> False
                                       NoSlides       -> False
                      }

renderHtml' :: Html -> Text
renderHtml' = TL.toStrict . renderHtml

writeHtmlString' :: PandocMonad m
                 => WriterState -> WriterOptions -> Pandoc -> m Text
writeHtmlString' st opts d = do
  (body, context) <- evalStateT (pandocToHtml opts d) st
  (if writerPreferAscii opts then toEntities else id) <$>
    case writerTemplate opts of
       Nothing -> return $ renderHtml' body
       Just tpl -> do
         -- warn if empty lang
         when (isNothing (getField "lang" context :: Maybe String)) $
           report NoLangSpecified
         -- check for empty pagetitle
         context' <-
            case getField "pagetitle" context of
                 Just (s :: String) | not (null s) -> return context
                 _ -> do
                   let fallback = fromMaybe "Untitled" $ takeBaseName <$>
                           lookup "sourcefile" (writerVariables opts)
                   report $ NoTitleElement fallback
                   return $ resetField "pagetitle" fallback context
         renderTemplate' tpl
             (defField "body" (renderHtml' body) context')

writeHtml' :: PandocMonad m => WriterState -> WriterOptions -> Pandoc -> m Html
writeHtml' st opts d =
  case writerTemplate opts of
       Just _ -> preEscapedText <$> writeHtmlString' st opts d
       Nothing
         | writerPreferAscii opts
            -> preEscapedText <$> writeHtmlString' st opts d
         | otherwise -> do
            (body, _) <- evalStateT (pandocToHtml opts d) st
            return body

-- 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
  slideVariant <- gets stSlideVariant
  let sects = hierarchicalize $
              if slideVariant == NoSlides
                 then blocks
                 else prepSlides slideLevel blocks
  toc <- if writerTableOfContents opts && slideVariant /= S5Slides
            then fmap renderHtml' <$> tableOfContents opts sects
            else return Nothing
  blocks' <- liftM (mconcat . intersperse (nl opts)) $
                 mapM (elementToHtml slideLevel opts) sects
  st <- get
  notes <- footnoteSection opts (reverse (stNotes st))
  let thebody = blocks' >> notes
  let math = case writerHTMLMathMethod opts of
                      MathJax url
                        | slideVariant /= RevealJsSlides ->
                        -- mathjax is handled via a special plugin in revealjs
                         H.script ! A.src (toValue url)
                                  ! A.type_ "text/javascript"
                                  $ case slideVariant of
                                         SlideousSlides ->
                                            preEscapedString
                                            "MathJax.Hub.Queue([\"Typeset\",MathJax.Hub]);"
                                         _ -> mempty
                      KaTeX url -> do
                         H.script !
                           A.src (toValue $ url ++ "katex.min.js") $ mempty
                         H.script !
                           A.src (toValue $ url ++ "contrib/auto-render.min.js") $ mempty
                         H.script
                            "document.addEventListener(\"DOMContentLoaded\", function() {\n  renderMathInElement(document.body);\n});"
                         H.link ! A.rel "stylesheet" !
                           A.href (toValue $ url ++ "katex.min.css")

                      _ -> case lookup "mathml-script" (writerVariables opts) of
                                 Just s | not (stHtml5 st) ->
                                   H.script ! A.type_ "text/javascript"
                                      $ preEscapedString
                                       ("/*<![CDATA[*/\n" ++ s ++ "/*]]>*/\n")
                                        | otherwise -> mempty
                                 Nothing -> mempty
  let context =   (if stHighlighting st
                      then case writerHighlightStyle opts of
                                Just sty -> defField "highlighting-css"
                                              (styleToCss sty)
                                Nothing  -> id
                      else id) $
                  (if stMath st
                      then defField "math" (renderHtml' math)
                      else id) $
                  (case writerHTMLMathMethod opts of
                        MathJax u -> defField "mathjax" True .
                                     defField "mathjaxurl"
                                       (takeWhile (/='?') u)
                        _         -> defField "mathjax" False) $
                  defField "quotes" (stQuotes st) $
                  -- for backwards compatibility we populate toc
                  -- with the contents of the toc, rather than a
                  -- boolean:
                  maybe id (defField "toc") toc $
                  maybe id (defField "table-of-contents") 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"
                    ("https://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" (stHtml5 st)
                  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 :: PandocMonad m
       => (Html -> Html)
       -> WriterOptions
       -> [Html]
       -> StateT WriterState m Html
toList listop opts items = do
    slideVariant <- gets stSlideVariant
    return $
      if writerIncremental opts
         then if slideVariant /= RevealJsSlides
                 then  listop (mconcat items) ! A.class_ "incremental"
                 else listop $ mconcat $ map (! A.class_ "fragment") items
         else listop $ mconcat items

unordList :: PandocMonad m
          => WriterOptions -> [Html] -> StateT WriterState m Html
unordList opts = toList H.ul opts . toListItems opts

ordList :: PandocMonad m
        => WriterOptions -> [Html] -> StateT WriterState m Html
ordList opts = toList H.ol opts . toListItems opts

defList :: PandocMonad m
        => WriterOptions -> [Html] -> StateT WriterState m 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
  contents  <- mapM (elementToListItem opts) sects
  let tocList = catMaybes contents
  if null tocList
     then return Nothing
     else Just <$> unordList opts tocList

-- | Convert section number to string
showSecNum :: [Int] -> String
showSecNum = intercalate "." . 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 $ walk (deLink . deNote) headerText
  subHeads <- mapM (elementToListItem opts) subsecs >>= return . catMaybes
  subList <- if null subHeads
                then return mempty
                else unordList opts subHeads
  -- in reveal.js, we need #/apples, not #apples:
  slideVariant <- gets stSlideVariant
  let revealSlash = ['/' | slideVariant== 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

deLink :: Inline -> Inline
deLink (Link _ ils _) = Span nullAttr ils
deLink x              = x

-- | 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
  slideVariant <- gets stSlideVariant
  let slide = slideVariant /= NoSlides && level <= slideLevel
  let num' = zipWith (+) num (writerNumberOffset opts ++ repeat 0)
  modify $ \st -> st{stSecNum = num'}  -- update section number
  html5 <- gets stHtml5
  let titleSlide = slide && level < slideLevel
  header' <- if title' == [Str "\0"]  -- marker for hrule
                then return mempty
                else do
                  modify (\st -> st{ stElement = True})
                  let level' = if level <= slideLevel &&
                                  slideVariant == SlidySlides
                                  then 1 -- see #3566
                                  else level
                  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 slideVariant 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' = ["title-slide" | titleSlide] ++ ["slide" | slide] ++
                  ["section" | (slide || writerSectionDivs opts) &&
                               not html5 ] ++
                  ["level" ++ show level | slide || writerSectionDivs opts ]
                  ++ classes
  let secttag  = if html5
                    then H5.section
                    else H.div
  let attr = (id',classes',keyvals)
  if titleSlide
     then do
       t <- addAttrs opts attr $
                   secttag header'
       return $
         (if slideVariant == RevealJsSlides && not (null innerContents)
                then H5.section
                else id) $ mconcat $ t : innerContents
     else if writerSectionDivs opts || slide
          then addAttrs opts attr
               $ secttag $ inNl $ header' : innerContents
          else do
            t <- addAttrs opts attr header'
            return $ mconcat $ intersperse (nl opts) (t : innerContents)

-- | Convert list of Note blocks to a footnote <div>.
-- Assumes notes are sorted.
footnoteSection :: PandocMonad m
                => WriterOptions -> [Html] -> StateT WriterState m Html
footnoteSection opts notes = do
  html5 <- gets stHtml5
  slideVariant <- gets stSlideVariant
  let hrtag = if html5 then H5.hr else H.hr
  epubVersion <- gets stEPUBVersion
  let container x
        | html5
        , epubVersion == Just EPUB3
                = H5.section ! A.class_ "footnotes"
                             ! customAttribute "epub:type" "footnotes" $ x
        | html5 = H5.section ! A.class_ "footnotes" $ x
        | slideVariant /= NoSlides = H.div ! A.class_ "footnotes slide" $ x
        | otherwise = H.div ! A.class_ "footnotes" $ x
  return $
    if null notes
       then mempty
       else nl opts >> container (nl opts >> hrtag >> nl opts >>
              H.ol (mconcat notes >> nl opts) >> nl opts)

-- | Parse a mailto link; return Just (name, domain) or Nothing.
parseMailto :: String -> Maybe (String, String)
parseMailto s =
  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
              -> StateT WriterState m Html
obfuscateLink opts attr txt s | writerEmailObfuscation opts == NoObfuscation =
  addAttrs opts attr $ H.a ! A.href (toValue s) $ txt
obfuscateLink opts attr (TL.unpack . 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' ++ ")")
              (_, classNames, _) = attr
              classNamesStr = concatMap (' ':) classNames
          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" ++
                     classNamesStr ++ "\">'+" ++
                     linkText  ++ "+'<\\/'+'a'+'>');\n// -->\n")) >>
                     H.noscript (preEscapedString $ obfuscateString altText)
                _ -> throwError $ PandocSomeError $ "Unknown obfuscation method: " ++ show meth
        _ -> 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

-- | Create HTML tag with attributes.
tagWithAttributes :: WriterOptions
                  -> Bool -- ^ True for HTML5
                  -> Bool -- ^ True if self-closing tag
                  -> Text -- ^ Tag text
                  -> Attr -- ^ Pandoc style tag attributes
                  -> Text
tagWithAttributes opts html5 selfClosing tagname attr =
  let mktag = (TL.toStrict . renderHtml <$> evalStateT
               (addAttrs opts attr (customLeaf (textTag tagname) selfClosing))
               defaultWriterState{ stHtml5 = html5 })
  in  case runPure mktag of
           Left _  -> mempty
           Right t -> t

addAttrs :: PandocMonad m
         => WriterOptions -> Attr -> Html -> StateT WriterState m Html
addAttrs opts attr h = foldl (!) h <$> attrsToHtml opts attr

toAttrs :: PandocMonad m
        => [(String, String)] -> StateT WriterState m [Attribute]
toAttrs kvs = do
  html5 <- gets stHtml5
  mbEpubVersion <- gets stEPUBVersion
  return $ mapMaybe (\(x,y) ->
            if html5
               then
                  if x `Set.member` html5Attributes
                     || ':' `elem` x -- e.g. epub: namespace
                     || "data-" `isPrefixOf` x
                     then Just $ customAttribute (fromString x) (toValue y)
                     else Just $ customAttribute (fromString ("data-" ++ x))
                                  (toValue y)
               else
                 if mbEpubVersion == Just EPUB2 &&
                    not (x `Set.member` html4Attributes ||
                         "xml:" `isPrefixOf` x)
                    then Nothing
                    else Just $ customAttribute (fromString x) (toValue y))
            kvs

attrsToHtml :: PandocMonad m
            => WriterOptions -> Attr -> StateT WriterState m [Attribute]
attrsToHtml opts (id',classes',keyvals) = do
  attrs <- toAttrs keyvals
  return $
    [prefixedId opts id' | not (null id')] ++
    [A.class_ (toValue $ unwords classes') | not (null classes')] ++ attrs

imgAttrsToHtml :: PandocMonad m
               => WriterOptions -> Attr -> StateT WriterState m [Attribute]
imgAttrsToHtml opts attr = do
  attrs <- attrsToHtml opts (ident,cls,kvs')
  dimattrs <- toAttrs (dimensionsToAttrList attr)
  return $ attrs ++ dimattrs
  where
    (ident,cls,kvs) = attr
    kvs' = filter isNotDim kvs
    isNotDim ("width", _)  = False
    isNotDim ("height", _) = False
    isNotDim _             = True

dimensionsToAttrList :: Attr -> [(String, String)]
dimensionsToAttrList attr = consolidateStyles $ go Width ++ go Height
  where
    consolidateStyles :: [(String, String)] -> [(String, String)]
    consolidateStyles xs =
      case partition isStyle xs of
           ([], _)    -> xs
           (ss, rest) -> ("style", intercalate ";" $ map snd ss) : rest
    isStyle ("style", _) = True
    isStyle _            = False
    go dir = case dimension dir attr of
               (Just (Pixel a)) -> [(show dir, show a)]
               (Just x)         -> [("style", show dir ++ ":" ++ show x)]
               Nothing          -> []

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 = maybe fp uriPath (parseURIReference fp)
      ext  = map toLower $ drop 1 $ takeExtension path
  in  null ext || ext `elem` imageExts

figure :: PandocMonad m
       => WriterOptions -> Attr -> [Inline] -> (String, String)
       -> StateT WriterState m Html
figure opts attr txt (s,tit) = do
  img <- inlineToHtml opts (Image attr txt (s,tit))
  html5 <- gets stHtml5
  let tocapt = if html5
                  then H5.figcaption
                  else H.p ! A.class_ "caption"
  capt <- if null txt
             then return mempty
             else tocapt `fmap` inlineListToHtml opts txt
  return $ if html5
              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]

-- | 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
blockToHtml opts (Para [Image attr@(_,classes,_) txt (src,tit)])
  | "stretch" `elem` classes = do
  slideVariant <- gets stSlideVariant
  case slideVariant of
       RevealJsSlides ->
         -- a "stretched" image in reveal.js must be a direct child
         -- of the slide container
         inlineToHtml opts (Image attr txt (src, tit))
       _ -> figure opts attr txt (src, tit)
-- title beginning with fig: indicates that the image is a figure
blockToHtml opts (Para [Image attr txt (s,'f':'i':'g':':':tit)]) =
  figure opts attr txt (s,tit)
blockToHtml opts (Para lst) = do
  contents <- inlineListToHtml opts lst
  case contents of
       Empty _ | not (isEnabled Ext_empty_paragraphs opts) -> return mempty
       _ -> return $ H.p contents
blockToHtml opts (LineBlock lns) =
  if writerWrapText opts == WrapNone
  then blockToHtml opts $ linesToPara lns
  else do
    htmlLines <- inlineListToHtml opts $ intercalate [LineBreak] lns
    return $ H.div ! A.class_ "line-block" $ htmlLines
blockToHtml opts (Div attr@(ident, classes, kvs') bs) = do
  html5 <- gets stHtml5
  slideVariant <- gets stSlideVariant
  let kvs = [(k,v) | (k,v) <- kvs', k /= "width"] ++
            [("style", "width:" ++ w ++ ";")
             | ("width",w) <- kvs', "column" `elem` classes]
  let speakerNotes = "notes" `elem` classes
  -- we don't want incremental output inside speaker notes, see #1394
  let opts' = if | speakerNotes -> opts{ writerIncremental = False }
                 | "incremental" `elem` classes -> opts{ writerIncremental = True }
                 | "nonincremental" `elem` classes -> opts{ writerIncremental = False }
                 | otherwise -> opts
      -- we remove "incremental" and "nonincremental" if we're in a
      -- slide presentaiton format.
      classes' = case slideVariant of
        NoSlides -> classes
        _ -> filter (\k -> k /= "incremental" && k /= "nonincremental") classes
  contents <- if "columns" `elem` classes'
                 then -- we don't use blockListToHtml because it inserts
                      -- a newline between the column divs, which throws
                      -- off widths! see #4028
                      mconcat <$> mapM (blockToHtml opts) bs
                 else blockListToHtml opts' bs
  let contents' = nl opts >> contents >> nl opts
  let (divtag, classes'') = if html5 && "section" `elem` classes'
                            then (H5.section, filter (/= "section") classes')
                            else (H.div, classes')
  if speakerNotes
     then case slideVariant of
               RevealJsSlides -> addAttrs opts' attr $
                           H5.aside contents'
               DZSlides       -> do
                 t <- addAttrs opts' attr $
                             H5.div contents'
                 return $ t ! H5.customAttribute "role" "note"
               NoSlides       -> addAttrs opts' attr $
                           H.div contents'
               _              -> return mempty
     else addAttrs opts (ident, classes'', kvs) $
              divtag contents'
blockToHtml opts (RawBlock f str) = do
  ishtml <- isRawHtml f
  if ishtml
     then return $ preEscapedString str
     else if (f == Format "latex" || f == Format "tex") &&
             allowsMathEnvironments (writerHTMLMathMethod opts) &&
             isMathEnvironment str
             then blockToHtml opts $ Plain [Math DisplayMath str]
             else do
               report $ BlockNotRendered (RawBlock f str)
               return mempty
blockToHtml _ HorizontalRule = do
  html5 <- gets stHtml5
  return $ if html5 then H5.hr else H.hr
blockToHtml opts (CodeBlock (id',classes,keyvals) rawCode) = do
  id'' <- if null id'
             then do
               modify $ \st -> st{ stCodeBlockNum = stCodeBlockNum st + 1 }
               codeblocknum <- gets stCodeBlockNum
               return ("cb" ++ show codeblocknum)
             else return id'
  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 isJust (writerHighlightStyle opts)
                    then highlight (writerSyntaxMap opts) formatHtmlBlock
                            (id'',classes',keyvals) adjCode
                    else Left ""
  case hlCode of
         Left msg -> do
           unless (null msg) $
             report $ CouldNotHighlight msg
           addAttrs opts (id',classes,keyvals)
             $ H.pre $ H.code $ toHtml adjCode
         Right h -> modify (\st -> st{ stHighlighting = True }) >>
                    addAttrs opts (id'',[],keyvals) h
blockToHtml opts (BlockQuote blocks) = do
  -- in S5, treat list in blockquote specially
  -- if default is incremental, make it nonincremental;
  -- otherwise incremental
  slideVariant <- gets stSlideVariant
  if slideVariant /= 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
  (if inElement then return 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
  unordList opts contents
blockToHtml opts (OrderedList (startnum, numstyle, _) lst) = do
  contents <- mapM (blockListToHtml opts) lst
  html5 <- gets stHtml5
  let numstyle' = case numstyle of
                       Example -> "decimal"
                       _       -> camelCaseToHyphenated $ show numstyle
  let attribs = [A.start $ toValue startnum | startnum /= 1] ++
                [A.class_ "example" | numstyle == Example] ++
                (if numstyle /= DefaultStyle
                   then if html5
                           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 [])
  l <- ordList opts contents
  return $ foldl (!) l attribs
blockToHtml opts (DefinitionList lst) = do
  contents <- mapM (\(term, defs) ->
                  do term' <- 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
  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
  html5 <- gets stHtml5
  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 html5
                               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'' <- zipWithM
            (\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
  html5 <- gets stHtml5
  let alignStr = alignmentToString align'
  let attribs = if html5
                   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 =
  (mconcat . intersperse (nl opts) . filter nonempty)
    <$> mapM (blockToHtml opts) lst
  where nonempty (Empty _) = False
        nonempty _         = True

-- | 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 = do
  html5 <- gets stHtml5
  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 $ do
                        if html5 then H5.br else H.br
                        strToHtml "\n"
    (Span (id',classes,kvs) ils)
                     -> inlineListToHtml opts ils >>=
                           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
                             Left msg -> do
                               unless (null msg) $
                                 report $ CouldNotHighlight msg
                               addAttrs opts attr $ H.code $ strToHtml str
                             Right h -> do
                               modify $ \st -> st{ stHighlighting = True }
                               addAttrs opts (id',[],keyvals) h
                        where (id',_,keyvals) = attr
                              hlCode = if isJust (writerHighlightStyle opts)
                                          then highlight
                                                 (writerSyntaxMap opts)
                                                 formatHtmlInline attr str
                                          else Left ""
    (Strikeout lst)  -> inlineListToHtml opts lst >>=
                        return . H.del
    (SmallCaps lst)   -> inlineListToHtml opts lst >>=
                         return . (H.span ! A.class_ "smallcaps")
    (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
           WebTeX url -> do
              let imtag = if html5 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 html5 then H5.br else H.br
              return $ case t of
                        InlineMath  -> m
                        DisplayMath -> brtag >> m >> brtag
           GladTeX ->
              return $
                customParent (textTag "eq") !
                  customAttribute "env"
                    (toValue $ if t == InlineMath
                                  then ("math" :: Text)
                                  else "displaymath") $ strToHtml str
           MathML -> do
              let conf = useShortEmptyTags (const False)
                           defaultConfigPP
              res <- lift $ convertMath writeMathML t str
              case res of
                    Right r  -> return $ preEscapedString $
                        ppcElement conf (annotateMML r str)
                    Left il  -> (H.span ! A.class_ mathClass) <$>
                                   inlineToHtml opts il
           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 -> "\\[" ++ str ++ "\\]"
           PlainMath -> do
              x <- lift (texMathToInlines t str) >>= inlineListToHtml opts
              let m = H.span ! A.class_ mathClass $ x
              let brtag = if html5 then H5.br else H.br
              return  $ case t of
                         InlineMath  -> m
                         DisplayMath -> brtag >> m >> brtag
    (RawInline f str) -> do
      ishtml <- isRawHtml f
      if ishtml
         then return $ preEscapedString str
         else if (f == Format "latex" || f == Format "tex") &&
                allowsMathEnvironments (writerHTMLMathMethod opts) &&
                isMathEnvironment str
                then inlineToHtml opts $ Math DisplayMath str
                else do
                  report $ InlineNotRendered inline
                  return mempty
    (Link attr txt (s,_)) | "mailto:" `isPrefixOf` s -> do
                        linkText <- inlineListToHtml opts txt
                        obfuscateLink opts attr linkText s
    (Link (ident,classes,kvs) txt (s,tit)) -> do
                        linkText <- inlineListToHtml opts txt
                        slideVariant <- gets stSlideVariant
                        let s' = case s of
                                   '#':xs -> let prefix = if slideVariant == RevealJsSlides
                                                             then "/"
                                                             else writerIdentifierPrefix opts
                                             in  '#' : prefix ++ xs
                                   _ -> s
                        let link = H.a ! A.href (toValue s') $ linkText
                        link' <- addAttrs opts (ident, classes, kvs) 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
                        slideVariant <- gets stSlideVariant
                        let isReveal = slideVariant == RevealJsSlides
                        attrs <- imgAttrsToHtml opts attr
                        let attributes =
                              -- reveal.js uses data-src for lazy loading
                              (if isReveal
                                  then customAttribute "data-src" $ toValue s
                                  else A.src $ toValue s) :
                              [A.title $ toValue tit | not (null tit)] ++
                              [A.alt $ toValue alternate' | not (null txt)] ++
                              attrs
                        let tag = if html5 then H5.img else H.img
                        return $ foldl (!) tag attributes
                        -- note:  null title included, as in Markdown.pl
    (Image attr _ (s,tit)) -> do
                        slideVariant <- gets stSlideVariant
                        let isReveal = slideVariant == RevealJsSlides
                        attrs <- imgAttrsToHtml opts attr
                        let attributes =
                              (if isReveal
                                  then customAttribute "data-src" $ toValue s
                                  else A.src $ toValue s) :
                              [A.title $ toValue tit | not (null tit)] ++
                              attrs
                        return $ foldl (!) H5.embed attributes
                        -- note:  null title included, as in Markdown.pl
    (Note contents) -> do
                        notes <- gets stNotes
                        let number = length notes + 1
                        let ref = show number
                        htmlContents <- blockListToNote opts ref contents
                        epubVersion <- gets stEPUBVersion
                        -- push contents onto front of notes
                        modify $ \st -> st {stNotes = htmlContents:notes}
                        slideVariant <- gets stSlideVariant
                        let revealSlash = ['/' | slideVariant == RevealJsSlides]
                        let link = H.a ! A.href (toValue $ "#" ++
                                         revealSlash ++
                                         writerIdentifierPrefix opts ++ "fn" ++ ref)
                                       ! A.class_ "footnote-ref"
                                       ! prefixedId opts ("fnref" ++ ref)
                                       $ (if isJust epubVersion
                                             then id
                                             else H.sup)
                                       $ toHtml ref
                        return $ case epubVersion 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 html5
                                    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 ("",["footnote-back"],[]) [Str "↩"] ("#" ++ "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
         epubVersion <- gets stEPUBVersion
         let noteItem' = case epubVersion of
                              Just EPUB3 -> noteItem ! customAttribute "epub:type" "footnote"
                              _          -> noteItem
         return $ nl opts >> noteItem'

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

isRawHtml :: PandocMonad m => Format -> StateT WriterState m Bool
isRawHtml f = do
  html5 <- gets stHtml5
  return $ f == Format "html" ||
           ((html5 && f == Format "html5") || f == Format "html4")

html5Attributes :: Set.Set String
html5Attributes = Set.fromList
  [ "abbr"
  , "accept"
  , "accept-charset"
  , "accesskey"
  , "action"
  , "allowfullscreen"
  , "allowpaymentrequest"
  , "allowusermedia"
  , "alt"
  , "as"
  , "async"
  , "autocomplete"
  , "autofocus"
  , "autoplay"
  , "charset"
  , "checked"
  , "cite"
  , "class"
  , "color"
  , "cols"
  , "colspan"
  , "content"
  , "contenteditable"
  , "controls"
  , "coords"
  , "crossorigin"
  , "data"
  , "datetime"
  , "default"
  , "defer"
  , "dir"
  , "dirname"
  , "disabled"
  , "download"
  , "draggable"
  , "enctype"
  , "for"
  , "form"
  , "formaction"
  , "formenctype"
  , "formmethod"
  , "formnovalidate"
  , "formtarget"
  , "headers"
  , "height"
  , "hidden"
  , "high"
  , "href"
  , "hreflang"
  , "http-equiv"
  , "id"
  , "inputmode"
  , "integrity"
  , "is"
  , "ismap"
  , "itemid"
  , "itemprop"
  , "itemref"
  , "itemscope"
  , "itemtype"
  , "kind"
  , "label"
  , "lang"
  , "list"
  , "loop"
  , "low"
  , "manifest"
  , "max"
  , "maxlength"
  , "media"
  , "method"
  , "min"
  , "minlength"
  , "multiple"
  , "muted"
  , "name"
  , "nomodule"
  , "nonce"
  , "novalidate"
  , "onabort"
  , "onafterprint"
  , "onauxclick"
  , "onbeforeprint"
  , "onbeforeunload"
  , "onblur"
  , "oncancel"
  , "oncanplay"
  , "oncanplaythrough"
  , "onchange"
  , "onclick"
  , "onclose"
  , "oncontextmenu"
  , "oncopy"
  , "oncuechange"
  , "oncut"
  , "ondblclick"
  , "ondrag"
  , "ondragend"
  , "ondragenter"
  , "ondragexit"
  , "ondragleave"
  , "ondragover"
  , "ondragstart"
  , "ondrop"
  , "ondurationchange"
  , "onemptied"
  , "onended"
  , "onerror"
  , "onfocus"
  , "onhashchange"
  , "oninput"
  , "oninvalid"
  , "onkeydown"
  , "onkeypress"
  , "onkeyup"
  , "onlanguagechange"
  , "onload"
  , "onloadeddata"
  , "onloadedmetadata"
  , "onloadend"
  , "onloadstart"
  , "onmessage"
  , "onmessageerror"
  , "onmousedown"
  , "onmouseenter"
  , "onmouseleave"
  , "onmousemove"
  , "onmouseout"
  , "onmouseover"
  , "onmouseup"
  , "onoffline"
  , "ononline"
  , "onpagehide"
  , "onpageshow"
  , "onpaste"
  , "onpause"
  , "onplay"
  , "onplaying"
  , "onpopstate"
  , "onprogress"
  , "onratechange"
  , "onrejectionhandled"
  , "onreset"
  , "onresize"
  , "onscroll"
  , "onsecuritypolicyviolation"
  , "onseeked"
  , "onseeking"
  , "onselect"
  , "onstalled"
  , "onstorage"
  , "onsubmit"
  , "onsuspend"
  , "ontimeupdate"
  , "ontoggle"
  , "onunhandledrejection"
  , "onunload"
  , "onvolumechange"
  , "onwaiting"
  , "onwheel"
  , "open"
  , "optimum"
  , "pattern"
  , "ping"
  , "placeholder"
  , "playsinline"
  , "poster"
  , "preload"
  , "readonly"
  , "referrerpolicy"
  , "rel"
  , "required"
  , "reversed"
  , "rows"
  , "rowspan"
  , "sandbox"
  , "scope"
  , "selected"
  , "shape"
  , "size"
  , "sizes"
  , "slot"
  , "span"
  , "spellcheck"
  , "src"
  , "srcdoc"
  , "srclang"
  , "srcset"
  , "start"
  , "step"
  , "style"
  , "tabindex"
  , "target"
  , "title"
  , "translate"
  , "type"
  , "typemustmatch"
  , "updateviacache"
  , "usemap"
  , "value"
  , "width"
  , "workertype"
  , "wrap"
  ]

html4Attributes :: Set.Set String
html4Attributes = Set.fromList
  [ "abbr"
  , "accept"
  , "accept-charset"
  , "accesskey"
  , "action"
  , "align"
  , "alink"
  , "alt"
  , "archive"
  , "axis"
  , "background"
  , "bgcolor"
  , "border"
  , "cellpadding"
  , "cellspacing"
  , "char"
  , "charoff"
  , "charset"
  , "checked"
  , "cite"
  , "class"
  , "classid"
  , "clear"
  , "code"
  , "codebase"
  , "codetype"
  , "color"
  , "cols"
  , "colspan"
  , "compact"
  , "content"
  , "coords"
  , "data"
  , "datetime"
  , "declare"
  , "defer"
  , "dir"
  , "disabled"
  , "enctype"
  , "face"
  , "for"
  , "frame"
  , "frameborder"
  , "headers"
  , "height"
  , "href"
  , "hreflang"
  , "hspace"
  , "http-equiv"
  , "id"
  , "ismap"
  , "label"
  , "lang"
  , "language"
  , "link"
  , "longdesc"
  , "marginheight"
  , "marginwidth"
  , "maxlength"
  , "media"
  , "method"
  , "multiple"
  , "name"
  , "nohref"
  , "noresize"
  , "noshade"
  , "nowrap"
  , "object"
  , "onblur"
  , "onchange"
  , "onclick"
  , "ondblclick"
  , "onfocus"
  , "onkeydown"
  , "onkeypress"
  , "onkeyup"
  , "onload"
  , "onmousedown"
  , "onmousemove"
  , "onmouseout"
  , "onmouseover"
  , "onmouseup"
  , "onreset"
  , "onselect"
  , "onsubmit"
  , "onunload"
  , "profile"
  , "prompt"
  , "readonly"
  , "rel"
  , "rev"
  , "rows"
  , "rowspan"
  , "rules"
  , "scheme"
  , "scope"
  , "scrolling"
  , "selected"
  , "shape"
  , "size"
  , "span"
  , "src"
  , "standby"
  , "start"
  , "style"
  , "summary"
  , "tabindex"
  , "target"
  , "text"
  , "title"
  , "usemap"
  , "valign"
  , "value"
  , "valuetype"
  , "version"
  , "vlink"
  , "vspace"
  , "width"
  ]