asciinema.org/app/decorators/asciicast_decorator.rb

class AsciicastDecorator < ApplicationDecorator

  THUMBNAIL_WIDTH = 20
  THUMBNAIL_HEIGHT = 10

  decorates_association :user

  def os
    if user_agent.present?
      os_from_user_agent
    elsif uname.present?
      os_from_uname
    else
      'unknown'
    end
  end

  def terminal_type
    model.terminal_type.presence || '?'
  end

  def shell
    File.basename(model.shell.to_s)
  end

  def title
    model.title.presence || model.command.presence || "asciicast:#{id}"
  end

  def thumbnail(width = THUMBNAIL_WIDTH, height = THUMBNAIL_HEIGHT)
    snapshot = Snapshot.build(model.snapshot || [[]] * height)
    thumbnail = SnapshotDecorator.new(snapshot.thumbnail(width, height))
    h.render 'asciicasts/thumbnail', :thumbnail => thumbnail
  end

  def description
    if model.description.present?
      text = model.description.to_s
      markdown(text)
    end
  end

  def author_link
    user.link
  end

  def author_img_link
    user.img_link
  end

  def formatted_duration
    duration = model.duration.to_i
    minutes = duration / 60
    seconds = duration % 60

    "%02d:%02d" % [minutes, seconds]
  end

  def theme_name
    (model.theme || user.theme || Theme.default).name
  end

  private

  def os_from_user_agent
    os_part = user_agent.split(' ')[2]
    os = os_part.split('/').first

    guess_os(os)
  end

  def os_from_uname
    guess_os(uname)
  end

  def guess_os(text)
    if text =~ /Linux/
      'Linux'
    elsif text =~ /Darwin/
      'OS X'
    else
      text.split(' ', 2)[0]
    end
  end

end