article_channel.rb

class ArticleChannel < ApplicationCable::Channel

  def subscribed
    @article = Article.find(params[:article_id])
    @editor_id = params[:editor_id]

    # Write it only if the editor is truly nil in a single query to avoid race conditions
    Article.where(id: @article.id, editor: nil).update(editor: @editor_id)

    stream_for @article

    # Send this even if we're not the editor. If we are the editor, it'll confirm it
    # If we're not the editor, it'll let us know that too
    NotifyArticleUpdateJob.perform_later(@article)
  end

  def unsubscribed
    Rails.logger.debug "ActionCable unsubscribe"
    user_has_left
  end

  def unsubscribe_from_channel
    Rails.logger.debug "ActionCable unsubscribe_from_channel"
    user_has_left
  end

  private

    def user_has_left
      stop_all_streams

      if @editor_id && @article
        reloaded = Article.find_by(id: @article.id)

        # Dumping the DB at the end of a spec can blow up here
        return if reloaded.nil? && Rails.env.test?

        if reloaded.editor == @editor_id
          @article.update(editor: nil)
          NotifyArticleUpdateJob.perform_later(@article)
        end
      end

      @article = nil
    end

end