Port over the HTML conversion script to execute JS

Signed-off-by: Danila Fedorin <danila.fedorin@gmail.com>

Gemfile

@@ -5,3 +5,5 @@ source "https://rubygems.org"
 git_source(:github) {|repo_name| "https://github.com/#{repo_name}" }
 
 gem 'nokogiri'
+gem 'execjs'
+gem 'duktape'

Gemfile.lock

@@ -1,6 +1,8 @@
 GEM
   remote: https://rubygems.org/
   specs:
+    duktape (2.7.0.0)
+    execjs (2.9.1)
     mini_portile2 (2.8.6)
     nokogiri (1.15.6)
       mini_portile2 (~> 2.8.2)
@@ -11,6 +13,8 @@ PLATFORMS
   ruby
 
 DEPENDENCIES
+  duktape
+  execjs
   nokogiri
 
 BUNDLED WITH

convert.rb

@@ -0,0 +1,48 @@
+require "execjs"
+require "nokogiri"
+require "net/http"
+require "json"
+require "cgi"
+
+class KatexRenderer
+  def initialize(source)
+    @context = ExecJS.compile(source)
+    @inline_cache = {}
+    @display_cache = {}
+  end
+
+  def render(display, string)
+    cache = display ? @display_cache : @inline_cache
+    comment = display ? "display" : string
+    string = CGI.unescapeHTML string
+
+    cache.fetch(string) do
+      puts "  Rendering #{comment}"
+      options = { "throwOnError" => false, "displayMode" => display }
+      cache[string] = @context.call("katex.renderToString", string, options)
+    end
+  end
+
+  def substitute(content)
+    rendered = content.gsub /\\\(((?:[^\\]|\\[^\)])*)\\\)/ do |match|
+      render(false, $~[1])
+    end
+    rendered = rendered.gsub /\$\$((?:[^\$]|$[^\$])*)\$\$/ do |match|
+      render(true, $~[1])
+    end
+    return rendered
+  end
+end
+
+ExecJS.runtime = ExecJS::Runtimes::Duktape
+
+renderer = KatexRenderer.new(Net::HTTP.get(URI("https://static.danilafe.com/katex/katex.min.js")))
+files = ARGV[0..-1]
+files.each do |file|
+  puts "Rendering file: #{file}"
+  document = Nokogiri::HTML.parse(File.open(file))
+  document.search('//*[not(ancestor-or-self::code or ancestor-or-self::script)]/text()').each do |t|
+    t.replace(renderer.substitute(t.content))
+  end
+  File.write(file, document.to_html(encoding: 'UTF-8'))
+end