refactor PreviewContent to be a class

lib/engines/content_block_manager/app/controllers/content_block_manager/content_block/editions/host_content_controller.rb

@@ -2,6 +2,6 @@ class ContentBlockManager::ContentBlock::Editions::HostContentController < Conte
   def preview
     host_content_id = params[:host_content_id]
     content_block_edition = ContentBlockManager::ContentBlock::Edition.find(params[:id])
-    @preview_content = ContentBlockManager::GetPreviewContent.new(content_id: host_content_id, content_block_edition:).preview_content
+    @preview_content = ContentBlockManager::PreviewContent.for_content_id(content_id: host_content_id, content_block_edition:)
   end
 end

lib/engines/content_block_manager/app/services/content_block_manager/preview_content.rb

@@ -0,0 +1,67 @@
+require "net/http"
+require "json"
+require "uri"
+
+module ContentBlockManager
+  class PreviewContent < Data.define(:title, :html)
+    class << self
+      def for_content_id(content_id:, content_block_edition:)
+        @content_id = content_id
+        @content_block_edition = content_block_edition
+        PreviewContent.new(title: content_item["title"], html:)
+      end
+
+    private
+
+      def html
+        @html ||= preview_html
+      end
+
+      def content_item
+        @content_item ||= begin
+          response = Services.publishing_api.get_content(@content_id)
+          response.parsed_content
+        end
+      end
+
+      def frontend_base_path
+        Rails.env.development? ? Plek.external_url_for("government-frontend") : Plek.website_root
+      end
+
+      def frontend_path
+        frontend_base_path + content_item["base_path"]
+      end
+
+      def preview_html
+        uri = URI(frontend_path)
+        nokogiri_html = Nokogiri::HTML.parse(Net::HTTP.get(uri))
+        replace_existing_content_blocks(nokogiri_html)
+      end
+
+      def replace_existing_content_blocks(nokogiri_html)
+        replace_blocks(nokogiri_html)
+        style_blocks(nokogiri_html)
+        nokogiri_html
+      end
+
+      def replace_blocks(nokogiri_html)
+        @preview_content_block_render ||= @content_block_edition.render
+        content_block_spans(nokogiri_html).each do |span|
+          span.replace @preview_content_block_render
+        end
+      end
+
+      BLOCK_STYLE = "background-color: yellow;".freeze
+
+      def style_blocks(nokogiri_html)
+        content_block_spans(nokogiri_html).each do |span|
+          span["style"] = BLOCK_STYLE
+        end
+      end
+
+      def content_block_spans(nokogiri_html)
+        nokogiri_html.css("span[data-content-id=\"#{@content_block_edition.document.content_id}\"]")
+      end
+    end
+  end
+end

lib/engines/content_block_manager/app/views/content_block_manager/content_block/editions/host_content/preview.html.erb

@@ -1,16 +1,16 @@
 <% content_for :page_title, "Preview content block in host document" %>
 <% content_for :context, "Preview content block" %>
-<% content_for :title, @preview_content[:title] %>
+<% content_for :title, @preview_content.title %>
 <% content_for :title_margin_bottom, 0 %>
 
 <div class="govuk-grid-row">
   <div class="govuk-grid-column-two-thirds govuk-body govuk-!-margin-bottom-0">
-    <p><strong>Document title: </strong><%= @preview_content[:title] %></p>
+    <p><strong>Document title: </strong><%= @preview_content.title %></p>
   </div>
 </div>
 <hr class="govuk-section-break govuk-!-margin-bottom-8 govuk-section-break--visible">
 <div class="govuk-grid-row">
   <div class="govuk-grid-column-full">
-    <iframe id="preview" style="width:100%;height:80vh;" srcdoc="<%= @preview_content[:html] %>"></iframe>
+    <iframe id="preview" style="width:100%;height:80vh;" srcdoc="<%= @preview_content.html %>"></iframe>
   </div>
 </div>

lib/engines/content_block_manager/test/unit/app/services/get_preview_content_test.rb → lib/engines/content_block_manager/test/unit/app/services/preview_content_test.rb

@@ -1,9 +1,9 @@
 require "test_helper"
 
-class ContentBlockManager::GetPreviewContentTest < ActiveSupport::TestCase
+class ContentBlockManager::PreviewContentTest < ActiveSupport::TestCase
   extend Minitest::Spec::DSL
 
-  let(:described_class) { ContentBlockManager::GetPreviewContent }
+  let(:described_class) { ContentBlockManager::PreviewContent }
   let(:host_content_id) { SecureRandom.uuid }
   let(:preview_content_id) { SecureRandom.uuid }
   let(:host_title) { "Test" }
@@ -42,13 +42,13 @@ class ContentBlockManager::GetPreviewContentTest < ActiveSupport::TestCase
         html: Nokogiri::HTML.parse(expected_html),
       }
 
-      actual_content = ContentBlockManager::GetPreviewContent.new(
+      actual_content = ContentBlockManager::PreviewContent.for_content_id(
         content_id: host_content_id,
         content_block_edition: block_to_preview,
-      ).preview_content
+      )
 
-      assert_equal expected_content[:title], actual_content[:title]
-      assert_equal expected_content[:html].to_s, actual_content[:html].to_s
+      assert_equal expected_content[:title], actual_content.title
+      assert_equal expected_content[:html].to_s, actual_content.html.to_s
     end
   end
 end