```ruby
class InternalPost < Post
  belongs_to :user
  validates :user, presence: true
  has_many :comments, as: :parent

  before_save do
    parser = Redcarpet::Markdown.new(Redcarpet::Render::HTML, autolink: true)
    self.body_html = parser.render(body_markdown)
  end

  after_create :notify_twitter
  # TODO: move this to background job

  def notify_twitter
    $twitter_client.update(tweet_content)
  end

  def tweet_content
    url = Rails.application.routes.url_helpers.
      post_short_link_url(self, host: "rbga.me")
    url = " #{url}"
    max_title_length = 140 - url.length
    title[0...max_title_length] + url
  end

  def username
    self.user.username
  end

  def number_of_comments
    comments.count 
  end

end
```

Improve code according houndci comments
user
```ruby
class InternalPost < Post
  belongs_to :user
  validates :user, presence: true
  has_many :comments, as: :parent

  before_save do
    parser = Redcarpet::Markdown.new(Redcarpet::Render::HTML, autolink: true)
    self.body_html = parser.render(body_markdown)
  end

  after_create :notify_twitter
  # TODO: move this to background job

  def notify_twitter
    $twitter_client.update(tweet_content)
  end

  def tweet_content
    url = Rails.application.routes.url_helpers.
      post_short_link_url(self, host: "rbga.me")
    url = " #{url}"
    max_title_length = 140 - url.length
    title[0...max_title_length] + url
  end

  def username
    self.user.username
  end

  def number_of_comments
    comments.count
  end
end
```
assistant