```ruby
class PostIndexer
  include ApplicationHelper

  def initialize
    @sites = Groonga['Sites']
    @categories = Groonga['Categories']
    @participants = Groonga['Participants']
    @posts = Groonga['Posts']
  end

  def add(post)
    return if @posts.nil?
    site = @sites.add(post.site_id)
    if post.category
      category = @categories.add(post.category_id,
                                 name: post.category.name)
    else
      category = nil
    end
    participants = post.credits.map do |credit|
      @participants.add(credit.participant_id,
                        name: credit.participant.name,
                        description: credit.participant.description)
    end
    @posts.add(post.id,
               title: post.title,
               content: extract_content(post),
               published_at: post.published_at,
               site: site,
               category: category,
               participants: participants,
               public_id: post.public_id)
  end

  private

  def extract_content(post)
    Nokogiri::HTML(render_markdown(post.body)).inner_text
  end
end
```

Remove garbage from extracted content
user
```ruby
class PostIndexer
  include ApplicationHelper

  def initialize
    @sites = Groonga['Sites']
    @categories = Groonga['Categories']
    @participants = Groonga['Participants']
    @posts = Groonga['Posts']
  end

  def add(post)
    return if @posts.nil?
    site = @sites.add(post.site_id)
    if post.category
      category = @categories.add(post.category_id,
                                 name: post.category.name)
    else
      category = nil
    end
    participants = post.credits.map do |credit|
      @participants.add(credit.participant_id,
                        name: credit.participant.name,
                        description: credit.participant.description)
    end
    @posts.add(post.id,
               title: post.title,
               content: extract_content(post),
               published_at: post.published_at,
               site: site,
               category: category,
               participants: participants,
               public_id: post.public_id)
  end

  private

  def extract_content(post)
    html = render_markdown(post.body.gsub(/<!--nextpage-->/, ""))
    Nokogiri::HTML(html).inner_text.squeeze(" ")
  end
end
```
assistant