asciinema.org/app/decorators/asciicast_decorator.rb

class AsciicastDecorator < ApplicationDecorator

  THUMBNAIL_WIDTH = 20
  THUMBNAIL_HEIGHT = 10

  def user
    @user ||= UserDecorator.new(model.user || User.null)
  end

  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 || command || default_title
  end

  def default_title
    if private?
      "untitled"
    else
      "asciicast:#{to_param}"
    end
  end

  def command
    model.command != model.shell && model.command.presence
  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
    if user_agent =~ %r{^asciinema/\d(\.\d+)+ [^/\s]+/[^/\s]+ (.+)$}
      os = $2.sub('-', '/').split('/').first.sub(/[dD]arwin/, 'OS X')
      os[0].upcase + os[1..-1]
    else
      'unknown'
    end
  end

  def os_from_uname
    guess_os(uname)
  end

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

end