require "open3"
require "nokogiri"

def perform_katex_sub(content)
  rendered = content.gsub /\\\(((?:[^\\]|\\[^\)])*)\\\)/ do |match|
    puts "  Rendering #{$~[1]}"
    Open3.popen3("katex") do |i, o, e, t|
      i.write $~[1]
      i.close
      o.read.force_encoding(Encoding::UTF_8).strip
    end
  end
  rendered = rendered.gsub /\$\$((?:[^\$]|$[^\$])*)\$\$/ do |match|
    puts "  Rendering display."
    Open3.popen3("katex -d") do |i, o, e, t|
      i.write $~[1]
      i.close
      o.read.force_encoding(Encoding::UTF_8).strip
    end
  end
  return rendered
end

files = ARGV[0..-1]

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