engine/app/models/layout.rb

class Layout < LiquidTemplate

  ## associations ##
  has_many_related :pages
  embeds_many :parts, :class_name => 'PagePart'

  ## callbacks ##
  before_save :build_parts_from_value
  after_save :update_parts_in_pages

  ## validations ##
  validates_format_of :value, :with => Locomotive::Regexps::CONTENT_FOR_LAYOUT, :message => :missing_content_for_layout

  ## methods ##

  protected

  def build_parts_from_value
    if self.value_changed? || self.new_record?
      self.parts.each { |p| p.disabled = true }

      self.value.scan(Locomotive::Regexps::CONTENT_FOR).each do |attributes|
        slug = attributes[0].strip.downcase
        name = slug.humanize
        name = I18n.t('attributes.defaults.page_parts.name') if slug == 'layout'

        if part = self.parts.detect { |p| p.slug == slug }
          part.name = name if name.present?
          part.disabled = false
        else
          self.parts.build :slug => slug, :name => name || slug
        end
      end

      # body always first
      body = self.parts.detect { |p| p.slug == 'layout' }
      self.parts.delete(body)
      self.parts.insert(0, body)

      @_update_pages = true if self.value_changed?
    end
  end

  def update_parts_in_pages
    self.pages.each { |p| p.send(:update_parts!, self.parts) } if @_update_pages
  end

end