gistfile1.rb

def create
  begin
    PublishBlogPost.new.call(post_id)
  rescue BlogPostNotFound
    redirect_to foo
  rescue AlreadyPublished
    flash[:error] = already_plublished_message
    render :foo
  end
end

class PublishBlogPost
  takes :db
  
  def call(post_id)
    post = db.find_post(post_id)  
    raise BlogPostNotFound if post.nil?
    raise AlreadyPublished if post.published?
    post.publish!
    db.save(post)
  end
end