support magicbook (external/internal) links generation

magicbook.json

@@ -2,7 +2,8 @@
   "title": "Nature of Code",
   "addPlugins": [
     "magicbook-codesplit",
-    "magicbook-katex"
+    "magicbook-katex",
+    "magicbook/plugins/relative-links.js"
   ],
   "destination": "build",
   "files": [

magicbook/plugins/relative-links.js

@@ -0,0 +1,43 @@
+const through = require('through2');
+const cheerio = require('cheerio');
+
+const Plugin = function (registry) {
+  registry.after(
+    'markdown:convert',
+    'relativelinks:updatehref',
+    this.removeRelativeLinksPath,
+  );
+};
+
+Plugin.prototype = {
+  removeRelativeLinksPath: function (config, stream, extras, callback) {
+    stream = stream.pipe(
+      through.obj(function (file, _, cb) {
+        file.$el = file.$el || cheerio.load(file.contents.toString());
+        let found = false;
+
+        file.$el('a').each(function () {
+          const jel = file.$el(this);
+          const prefHref = jel.attr('href');
+
+          // test if is a valid relative link
+          if (prefHref && prefHref.indexOf('://') < 0) {
+            // remove the relative path
+            jel.attr('href', `#${prefHref.split('#')[1]}`);
+            found = true;
+          }
+        });
+
+        if (found) {
+          file.contents = Buffer.from(file.$el.html());
+        }
+
+        cb(null, file);
+      }),
+    );
+
+    callback(null, config, stream, extras);
+  },
+};
+
+module.exports = Plugin;

magicbook/stylesheets/pdf/_page.scss

@@ -162,7 +162,7 @@ section[data-type="toc"] {
 a[href]::after {
     content: " (see page " target-counter(attr(href), page) ")";
 }
-a[href^="http:"]::after {
+a[href^="http"]::after {
     content: " ("attr(href)")";
 }
 a[href].index-term-link::after {