class ActiveStorage::Previewer::VideoPreviewer

def accept?(blob)
  blob.video? && ffmpeg_exists?
end

def draw_relevant_frame_from(file, &block)
  draw self.class.ffmpeg_path, "-i", file.path, *Shellwords.split(ActiveStorage.video_preview_arguments), "-", &block
end

def ffmpeg_exists?
  return @ffmpeg_exists if defined?(@ffmpeg_exists)
  @ffmpeg_exists = system(ffmpeg_path, "-version", out: File::NULL, err: File::NULL)
end

def ffmpeg_path
  ActiveStorage.paths[:ffmpeg] || "ffmpeg"
end

def preview(**options)
  download_blob_to_tempfile do |input|
    draw_relevant_frame_from input do |output|
      yield io: output, filename: "#{blob.filename.base}.jpg", content_type: "image/jpeg", **options
    end
  end
end