class PixivUgoiraConverter
  def convert(source_path, output_path, preview_path, frame_data)
    folder = Zip::File.new(source_path)
    write_webm(folder, output_path, frame_data)
    write_preview(folder, preview_path)
  end

  def write_webm(folder, write_path, frame_data)
    Dir.mktmpdir do |tmpdir|
      FileUtils.mkdir_p("#{tmpdir}/images")
      folder.each_with_index do |file, i|
        path = File.join(tmpdir, "images", file.name)
        image_blob = file.get_input_stream {|is| is.read}
        File.open(path, "wb") do |f|
          f.write(image_blob)
        end
      end
      
      # Duplicate last frame to avoid it being displayed only for a very short amount of time.
      last_file_name = folder.to_a.last.name
      last_file_name =~ /\A(\d{6})(\.\w{,4})\Z/
      new_last_index = $1.to_i + 1
      file_ext = $2
      new_last_filename = ("%06d" % new_last_index) + file_ext
      path_from = File.join(tmpdir, "images", last_file_name)
      path_to = File.join(tmpdir, "images", new_last_filename)
      FileUtils.cp(path_from, path_to)
      
      delay_sum = 0
      timecodes_path = File.join(tmpdir, "timecodes.tc")
      File.open(timecodes_path, "w+") do |f|
        f.write("# timecode format v2\n")
        frame_data.each do |img|
          f.write("#{delay_sum}\n")
          delay_sum += img["delay"]
        end
        f.write("#{delay_sum}\n")
        f.write("#{delay_sum}\n")
      end

      ext = folder.first.name.match(/\.(\w{,4})$/)[1]
      system("ffmpeg -loglevel quiet -i #{tmpdir}/images/%06d.#{ext} -codec:v libvpx -crf 4 -b:v 5000k -an #{tmpdir}/tmp.webm")
      system("mkvmerge -q -o #{write_path} --webm --timecodes 0:#{tmpdir}/timecodes.tc #{tmpdir}/tmp.webm")
    end      
  end

  def write_preview(folder, path)
    file = folder.first
    image_blob = file.get_input_stream {|is| is.read}
    image = Magick::Image.from_blob(image_blob).first
    image.write(path)
  end
end