warnings.rb

class Post < ApplicaationRecord
  attribute :warnings, array: true, default: Set.new

  def has_warnings?
    publishing_checklist.any?
  end
  
  private
  
  def publishing_checklist
    # return a list of warnings or an empty set
    warnings.clear
    warnings.add 'Slug should begin with the publish date as YYYY-MM-DD' unless dated_slug?)
    warnings.add 'Slug should be formatted in kebab-case' unless kebab_slug?
    warnings.add 'Comments are disabled' unless commentable?
    warnings.add 'Missing an image' if default_picture?
    warnings.add 'Body is missing' unless body?
    warnings.add 'Keywords are missing' unless keywords?
    warnings.add 'Publish date is not set' unless publish_on?

    warnings
  end

  def dated_slug?
    slug.to_s&.match?(%r[\A#{(publish_on || Date.today).to_date}-])
  end

  def kebab_slug?
    slug.to_s == slug.to_s.titleize.parameterize
  end

  def default_picture?
    first_picture == Image::FALLBACK_IMAGE
  end
end


class PostsController < ApplicationController
  before_action :set_post, only: [:show, :edit, :update, :destroy]
  before_action :show_warnings, only: %i[show edit]

  ...
  
  private

  def show_warnings
    flash.now[:warning] = helpers.publish_warnings(@post) if @post.has_warnings?
  end
end


module PublishHelper
  def publish_warnings(record)
    tag.div do
      concat tag.h5 'Publish warnings:'
      concat publish_warnings_summary(record)
    end
  end

  def publish_warnings_summary(record)
    tag.ul class: "rails-bootstrap-forms-error-summary" do
      record.warnings.each do |error|
        concat tag.li(error)
      end
    end
  end
  
  def publish_warnings_icon(record)
    tag.i '', title: "#{record.warnings.join("\n")}",
          class: 'fa fa-warning text-warning get-info' if record.has_warnings?
  end
end