require "open3"
require "nokogiri"

def render_cached(cache, command, string, render_comment = nil)
  cache.fetch(string) do |new|
    puts "  Rendering #{render_comment || new}"
    cache[string] = Open3.popen3(command) do |i, o, e, t|
      i.write new
      i.close
      o.read.force_encoding(Encoding::UTF_8).strip
    end
  end
end

def perform_katex_sub(inline_cache, display_cache, content)
  rendered = content.gsub /\\\(((?:[^\\]|\\[^\)])*)\\\)/ do |match|
    render_cached(inline_cache, "katex", $~[1])
  end
  rendered = rendered.gsub /\$\$((?:[^\$]|$[^\$])*)\$\$/ do |match|
    render_cached(display_cache, "katex -d", $~[1], "display")
  end
  return rendered
end

files = ARGV[0..-1]
inline_cache, display_cache = {}, {}

files.each do |file|
  puts "Rendering file: #{file}"
  document = Nokogiri::HTML.parse(File.open(file))
  document.search('//*[not(self::code)]/text()').each do |t|
    t.replace(perform_katex_sub(inline_cache, display_cache, t.content))
  end
  File.write(file, document.to_html)
end