discourse/app/serializers/invited_user_serializer.rb

class InvitedUserSerializer < BasicUserSerializer

  attributes :topics_entered,
             :posts_read_count,
             :last_seen_at,
             :time_read,
             :days_visited,
             :days_since_created

  def time_read
    AgeWords.age_words(object.user_stat.time_read)
  end

  def days_visited
    object.user_stat.days_visited
  end

  def topics_entered
    object.user_stat.topics_entered
  end

  def posts_read_count
    object.user_stat.posts_read_count
  end

  def days_since_created
    ((Time.now - object.created_at) / 60 / 60 / 24).ceil
  end

end