Callback example

1-without_callbacks.rb

# uses exception-throwing !-methods in lower level code to communicate errors

class ApiController < ApplicationController
  def update
    publisher = PublishingService.new
    publisher.update(params[:article], params[:author])
    render_success
  rescue => e
    render_failure("Failed to publish article: #{e.message}")
  end
...
end

class PublishingService
  def initialize
    @purger = CachePurger.new
  end

  def update(article, author)
    @article = article
    @author = author

    update_author
    update_article
  end

  private
  def update_author
    UpdatesAuthor.call(@author)
    @purger.purge(author_path)
  end

  def update_article
    UpdatesArticle.call(@article)
    @purger.purge(article_path)
  end
...
end

class UpdatesAuthor
  def self.call(params)
    Author.update_attributes!(params)
  end
end

class UpdatesArticle
  def self.call(params)
    Article.update_attributes!(params)
  end
end

class CachePurger
...
  def purge(path)
    @cache.purge!(path)
  end
end

2-with_callbacks.rb

class ApiController < ApplicationController
  def update
    publisher = PublishingService.new(self)
    publisher.update(params[:article], params[:author])
  end

  def update_success
    render_success
  end

  def update_failure(message)
    render_failure("Failed to publish article: #{message}")
  end
...
end

class PublishingService
  def initialize(listener)
    @listener = listener
    @purger = CachePurger.new
  end

  def update(article, author)
    @article = article
    @author = author

    update_author
    update_article

    @listener.update_success
  end
  
  def update_author_failure(message)
    @listener.update_failure(message)
  end

  def update_author_success
    @purger.purge(author_path, self)
  end

  def purge_cache_failure(message)
    @listener.update_failure(message)
  end

  def update_article_failure(message)
    @listener.update_failure(message)
  end

  def update_article_success
    @purger.purge(article_path, self)
  end

  private
  def update_author
    UpdatesAuthor.call(@author, self)
  end

  def update_article
    UpdatesArticle.call(@article, self)
  end
...
end

...