Add support for KaTeX HTML math

Closes #1626

3 files changed, 52 insertions, 3 deletions

diff --git a/pandoc.hs b/pandoc.hs
index a9bea12c6..71d0c4b98 100644
--- a/pandoc.hs
+++ b/pandoc.hs
@@ -58,7 +58,7 @@ import qualified Control.Exception as E
 import Control.Exception.Extensible ( throwIO )
 import qualified Text.Pandoc.UTF8 as UTF8
 import Control.Monad (when, unless, (>=>))
-import Data.Maybe (isJust)
+import Data.Maybe (isJust, fromMaybe)
 import Data.Foldable (foldrM)
 import Network.URI (parseURI, isURI, URI(..))
 import qualified Data.ByteString.Lazy as B
@@ -68,7 +68,7 @@ import qualified Data.Map as M
 import Data.Yaml (decode)
 import qualified Data.Yaml as Yaml
 import qualified Data.Text as T
-import Control.Applicative ((<$>))
+import Control.Applicative ((<$>), (<|>))
 import Text.Pandoc.Readers.Txt2Tags (getT2TMeta)
 import Data.Monoid
 
@@ -205,6 +205,8 @@ data Opt = Opt
     , optExtractMedia      :: Maybe FilePath -- ^ Path to extract embedded media
     , optTrace             :: Bool       -- ^ Print debug information
     , optTrackChanges      :: TrackChanges -- ^ Accept or reject MS Word track-changes.
+    , optKaTeXStylesheet   :: Maybe String     -- ^ Path to stylesheet for KaTeX
+    , optKaTeXJS           :: Maybe String     -- ^ Path to js file for KaTeX
     }
 
 -- | Defaults for command-line options.
@@ -263,6 +265,8 @@ defaultOpts = Opt
     , optExtractMedia          = Nothing
     , optTrace                 = False
     , optTrackChanges          = AcceptChanges
+    , optKaTeXStylesheet       = Nothing
+    , optKaTeXJS               = Nothing
     }
 
 -- | A list of functions, each transforming the options data structure
@@ -818,6 +822,21 @@ options =
                       return opt { optHTMLMathMethod = MathJax url'})
                   "URL")
                  "" -- "Use MathJax for HTML math"
+    , Option "" ["katex"]
+                 (OptArg
+                  (\arg opt ->
+                      return opt
+                        { optKaTeXJS =
+                           arg <|> Just "http://cdnjs.cloudflare.com/ajax/libs/KaTeX/0.1.0/katex.min.js"})
+                  "URL")
+                  "" -- Use KaTeX for HTML Math
+
+    , Option "" ["katex-stylesheet"]
+                 (ReqArg
+                  (\arg opt ->
+                      return opt { optKaTeXStylesheet = Just arg })
+                 "URL")
+                 "" -- Set the KaTeX Stylesheet location
 
     , Option "" ["gladtex"]
                  (NoArg
@@ -860,6 +879,7 @@ options =
 
     ]
 
+
 addMetadata :: String -> MetaValue -> M.Map String MetaValue
             -> M.Map String MetaValue
 addMetadata k v m = case M.lookup k m of
@@ -1027,7 +1047,7 @@ main = do
               , optHighlight             = highlight
               , optHighlightStyle        = highlightStyle
               , optChapters              = chapters
-              , optHTMLMathMethod        = mathMethod
+              , optHTMLMathMethod        = mathMethod'
               , optReferenceODT          = referenceODT
               , optReferenceDocx         = referenceDocx
               , optEpubStylesheet        = epubStylesheet
@@ -1056,6 +1076,8 @@ main = do
               , optExtractMedia          = mbExtractMedia
               , optTrace                 = trace
               , optTrackChanges          = trackChanges
+              , optKaTeXStylesheet       = katexStylesheet
+              , optKaTeXJS               = katexJS
              } = opts
 
   when dumpArgs $
@@ -1063,6 +1085,13 @@ main = do
        mapM_ (\arg -> UTF8.hPutStrLn stdout arg) args
        exitWith ExitSuccess
 
+  let csscdn = "http://cdnjs.cloudflare.com/ajax/libs/KaTeX/0.1.0/katex.min.css"
+  let mathMethod =
+        case (katexJS, katexStylesheet) of
+            (Nothing, _) -> mathMethod'
+            (Just js, ss) -> KaTeX js (fromMaybe csscdn ss)
+
+
   -- --bibliography implies -F pandoc-citeproc for backwards compatibility:
   let needsCiteproc = isJust (M.lookup "bibliography" metadata) &&
                       optCiteMethod opts `notElem` [Natbib, Biblatex] &&
diff --git a/src/Text/Pandoc/Options.hs b/src/Text/Pandoc/Options.hs
index 84ccbbdc9..ebfd8f8a9 100644
--- a/src/Text/Pandoc/Options.hs
+++ b/src/Text/Pandoc/Options.hs
@@ -251,6 +251,7 @@ data HTMLMathMethod = PlainMath
                     | WebTeX String               -- url of TeX->image script.
                     | MathML (Maybe String)       -- url of MathMLinHTML.js
                     | MathJax String              -- url of MathJax.js
+                    | KaTeX String String -- url of stylesheet and katex.js
                     deriving (Show, Read, Eq)
 
 data CiteMethod = Citeproc                        -- use citeproc to render them
diff --git a/src/Text/Pandoc/Writers/HTML.hs b/src/Text/Pandoc/Writers/HTML.hs
index 8106806cf..652fc979f 100644
--- a/src/Text/Pandoc/Writers/HTML.hs
+++ b/src/Text/Pandoc/Writers/HTML.hs
@@ -157,6 +157,10 @@ pandocToHtml opts (Pandoc meta blocks) = do
                               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"
@@ -728,6 +732,10 @@ inlineToHtml opts inline =
                                   case t of
                                     InlineMath  -> "\\(" ++ str ++ "\\)"
                                     DisplayMath -> "\\[" ++ str ++ "\\]"
+                               KaTeX _ _ -> return $ H.span ! A.class_ "math" $
+                                  toHtml (case t of
+                                            InlineMath -> str
+                                            DisplayMath -> "\\displaystyle " ++ str)
                                PlainMath -> do
                                   x <- inlineListToHtml opts (texMathToInlines t str)
                                   let m = H.span ! A.class_ "math" $ x
@@ -829,3 +837,14 @@ blockListToNote opts ref blocks =
                               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])"
+  , "}}"
+  ]