feat: use the Rails asset host to generate the URL of the static section screenshots

app/services/maglev/fetch_section_screenshot_url.rb

@@ -8,7 +8,18 @@ class FetchSectionScreenshotUrl
     argument :section
 
     def call
-      fetch_section_screenshot_path.call(section: section) + "?#{section.screenshot_timestamp}"
+      screenshot_path = fetch_section_screenshot_path.call(section: section) + query_string
+      asset_host ? URI.join(asset_host, screenshot_path).to_s : screenshot_path
+    end
+
+    private
+
+    def asset_host
+      Rails.application.config.asset_host
+    end
+
+    def query_string
+      "?#{section.screenshot_timestamp}"
     end
   end
 end

lib/maglev.rb

@@ -29,7 +29,7 @@ def config
         c.uploader = :active_storage
         c.site_publishable = false
         c.preview_host = nil
-        c.asset_host = Rails.application.config.action_controller.asset_host
+        c.asset_host = Rails.application.config.asset_host
         c.ui_locale = nil
         c.back_action = nil
         c.services = {}

spec/services/maglev/fetch_section_screenshot_url_spec.rb

@@ -13,4 +13,14 @@
   it 'returns the url to the screenshot of the section' do
     expect(subject).to eq '/theme/jumbotron.png?42'
   end
+
+  context 'when there is a Rails asset host set' do
+    before do
+      allow(Rails.application.config).to receive(:asset_host).and_return('https://assets.maglev.local')
+    end
+
+    it 'uses the Rails asset host to build the url' do
+      expect(subject).to eq 'https://assets.maglev.local/theme/jumbotron.png?42'
+    end
+  end
 end