refactor of https://github.com/alphagov/specialist-publisher/blob/hide-publish-button-if-document-cant-be-published/app/helpers/application_helper.rb

application_helper.rb

  def publish_form(slug_unique, publishable, document)
    PublishFormRenderer.render(slug_unique: slug_unique, publishable: publishable, document: document, context: self)
  end

publish_form_renderer.rb

PublishFormLocals = Struct.new(:warning, :notification, :disabled, :document)

class PublishFormRenderer
  class << self
    def render(*args)
      new(*args).render
    end
  end


  attr_accessor :slug_unique,
                :slug_not_unique,
                :publishable,
                :not_publishable,
                :document,
                :context,
                :form_locals


  def initialize(slug_unique:, publishable:, document:, context:)
    self.slug_unique = slug_unique
    self.slug_not_unique = !slug_unique
    self.publishable = publishable
    self.not_publishable = !publishable
    self.document = document
    self.context = context
    self.form_locals = PublishFormLocals.new(disabled: false)
  end


  def render
    set_errors if current_user_cant_publish(document.document_type) || slug_not_unique || not_publishable
    set_warnings if publishable
    
    context.render(partial: "specialist_documents/publish_form", locals: form_locals.to_h)
  end


  def set_errors
    form_locals.disabled = true
    form_locals.warning = "You can't publish this document"

    form_locals.notification = if current_user_cant_publish(document.document_type)
      "You don't have permission to publish."
    elsif not_publishable
      "There's no changes to publish."
    elsif slug_not_unique
      "This document as a duplicate slug.<br />\nYou need to #{context.link_to "edit the document", [:edit, document]} and change the title to be able to be published".html_safe
    end
  end


  def set_warnings
    form_locals.notification = "This will email subscribers to #{context.current_finder[:title]}."
    
    if document_change_note_given?
      warn_major_change
    elsif minor_update?
      notify_minor_change
    end
  end


  def warn_major_change
    form_locals.warning = "You are about to publish a <strong>major edit</strong> with a public change note.".html_safe
  end


  def notify_minor_change
    form_locals.notification = "You are about to publish a <strong>minor edit</strong>.".html_safe
  end


  def document_change_note_given?
    document.change_note.present?
  end


  def minor_update?
    document.minor_update
  end
end