docbrown/app/controllers/display_ads_controller.rb

class DisplayAdsController < ApplicationController
  before_action :set_cache_control_headers, only: %i[show], unless: -> { current_user }
  include DisplayAdHelper
  CACHE_EXPIRY_FOR_DISPLAY_ADS = 15.minutes.to_i.freeze

  def show
    skip_authorization
    set_cache_control_headers(CACHE_EXPIRY_FOR_DISPLAY_ADS) unless session_current_user_id

    if placement_area
      if params[:username].present? && params[:slug].present?
        @article = Article.find_by(slug: params[:slug])
      end

      @display_ad = DisplayAd.for_display(
        area: placement_area,
        user_signed_in: user_signed_in?,
        user_id: current_user&.id,
        article: @article ? ArticleDecorator.new(@article) : nil,
        user_tags: user_tags,
      )

      if @display_ad && !session_current_user_id
        set_surrogate_key_header @display_ad.record_key
      end
    end

    render layout: false
  end

  private

  def placement_area
    params[:placement_area]
  end

  def user_tags
    return unless feed_targeted_tag_placement?(placement_area)

    current_user.cached_followed_tag_names
  end
end