add local anchors to headers

Utils.hs

@@ -1,3 +1,5 @@
+{-# LANGUAGE OverloadedStrings #-}
+
 module Utils where
 
 import Control.Monad.IO.Class
@@ -41,6 +43,20 @@ walkURLs f = Text.Pandoc.Walk.walkM go
       pure $ Image a i (u', t)
     go x = pure x
 
+-- | A pandoc walker for adding the local links to the headings (links are
+-- appended and get a given class)
+addHeadingLinks ::
+     T.Text -> Text.Pandoc.Definition.Pandoc -> Text.Pandoc.Definition.Pandoc
+addHeadingLinks cls = Text.Pandoc.Walk.walk go
+  where
+    go h@(Header lvl attr@(id, _, _) inlines) =
+      Header
+        lvl
+        attr
+        (inlines ++
+         [Link ("", [cls], []) [Str "#"] ("#" <> id, "Link to this section")])
+    go x = x
+
 hasUriScheme :: String -> String -> Bool
 hasUriScheme x = all id . zipWith (==) x . (++ ":")
 

assets/style.css

@@ -43,6 +43,17 @@ a:hover {
 	text-decoration: underline;
 }
 
+a.header-local-anchor {
+	color: #eee;
+	font-weight: 300;
+	padding-left: 0.5em;
+}
+
+a.header-local-anchor:hover {
+	text-decoration: none;
+	color: #0ad;
+}
+
 body {
 	margin: 0;
 	background: white;

site.hs

@@ -178,7 +178,9 @@ installPage mount pi = do
   fixedUrlDoc <-
     walkURLs (processLink $ pi ^. pagePath . to takeDirectory) $ pi ^. pageDoc
   checkTarget file
-  body <- io . runIOorExplode $ writeHtml5String htmlWriteOpts fixedUrlDoc
+  body <-
+    io . runIOorExplode $ writeHtml5String htmlWriteOpts $
+    addHeadingLinks "header-local-anchor" fixedUrlDoc
   let Y.Object meta' = pi ^. pageMeta
       meta = Y.Object $ KM.insert "body" (Y.String body) meta'
   meta <- addGlobalMeta meta >>= addPageMeta pi