Temp revert to previous FAQPages on Guides

This is a temporary reversion to the original implementation of FAQPage
schemas on Guides.  We're running user research next week, and want to
use this version's Google results.  If the research goes well, we'll make
a further decision then whether to roll this into the standard implementation.

It was [originally implemented in govuk_publishing_components](alphagov/govuk_publishing_components#1087)
but I don't want to revert it in publishing components yet because:

- Answers also use that implementation, and I don't want to mess with them right now
- This version is temporary until 31/10/2019 when we'll decide what to do

This version of the schema includes the entirety of a guide's content in the FAQPage
schema on the first chapter.  The subsequent chapters do not include an FAQPage
schema to avoid duplicating rich results (but do include the Article schema).

app/presenters/machine_readable/guide_faq_page_schema_presenter.rb

@@ -0,0 +1,74 @@
+module MachineReadable
+  class GuideFaqPageSchemaPresenter
+    attr_reader :guide
+
+    def initialize(guide)
+      @guide = guide
+    end
+
+    def structured_data
+      # http://schema.org/FAQPage
+      {
+        "@context" => "http://schema.org",
+        "@type" => "FAQPage",
+        "headline" => guide.title,
+        "description" => guide.description,
+        "publisher" => {
+          "@type" => "Organization",
+          "name" => "GOV.UK",
+          "url" => "https://www.gov.uk",
+          "logo" => {
+            "@type" => "ImageObject",
+            "url" => logo_url,
+          },
+        },
+      }
+      .merge(main_entity)
+    end
+
+  private
+
+    def main_entity
+      {
+        "mainEntity" => questions_and_answers,
+      }
+    end
+
+    def questions_and_answers
+      guide.parts.each_with_index.map do |part, index|
+        part_url = part_url(part, index)
+
+        {
+          "@type" => "Question",
+          "name" => part["title"],
+          "url" => part_url,
+          "acceptedAnswer" => {
+            "@type" => "Answer",
+            "url" => part_url,
+            "text" => part["body"],
+          },
+        }
+      end
+    end
+
+    def part_url(part, index)
+      if index.zero?
+        guide_url
+      else
+        guide_url + "/" + part["slug"]
+      end
+    end
+
+    def guide_url
+      Plek.new.website_root + guide.base_path
+    end
+
+    def logo_url
+      image_url("govuk_publishing_components/govuk-logo.png")
+    end
+
+    def image_url(image_file)
+      ActionController::Base.helpers.asset_url(image_file, type: :image)
+    end
+  end
+end

app/views/content_items/guide.html.erb

@@ -1,11 +1,17 @@
 <% content_for :extra_head_content do %>
   <%= machine_readable_metadata(
-    schema: :faq,
+    schema: :article,
     canonical_url: @content_item.canonical_url,
     body: @content_item.has_parts? ? @content_item.current_part_body : nil
   ) %>
 <% end %>
 
+<% unless @content_item.requesting_a_part? %>
+<script type="application/ld+json">
+  <%= raw MachineReadable::GuideFaqPageSchemaPresenter.new(@content_item).structured_data.to_json %>
+</script>
+<% end %>
+
 <% content_for :simple_header, true %>
 
 <div class="govuk-grid-row">

test/integration/guide_test.rb

@@ -81,16 +81,35 @@ class GuideTest < ActionDispatch::IntegrationTest
     setup_and_visit_content_item("guide")
     faq_schema = find_structured_data(page, "FAQPage")
 
-    assert_equal faq_schema["headline"], @content_item["title"]
-    assert_not_equal faq_schema["mainEntity"], []
+    assert_equal faq_schema["@type"], "FAQPage"
+    assert_equal faq_schema["headline"], "The national curriculum"
+
+    q_and_as = faq_schema["mainEntity"]
+    answers = q_and_as.map { |q_and_a| q_and_a["acceptedAnswer"] }
+
+    chapter_titles = [
+      "Overview",
+      "Key stage 1 and 2",
+      "Key stage 3 and 4",
+      "Other compulsory subjects",
+    ]
+    assert_equal chapter_titles, (q_and_as.map { |q_and_a| q_and_a["name"] })
+
+    guide_part_urls = [
+      "https://www.test.gov.uk/national-curriculum",
+      "https://www.test.gov.uk/national-curriculum/key-stage-1-and-2",
+      "https://www.test.gov.uk/national-curriculum/key-stage-3-and-4",
+      "https://www.test.gov.uk/national-curriculum/other-compulsory-subjects",
+    ]
+    assert_equal guide_part_urls, (q_and_as.map { |q_and_a| q_and_a["url"] })
+    assert_equal guide_part_urls, (answers.map { |answer| answer["url"] })
   end
 
-  test "guide chapters show the faq schema" do
+  test "guide chapters do not show the faq schema" do
     setup_and_visit_part_in_guide
     faq_schema = find_structured_data(page, "FAQPage")
 
-    assert_equal faq_schema["headline"], @content_item["title"]
-    assert_not_equal faq_schema["mainEntity"], []
+    assert_nil faq_schema
   end
 
   def setup_and_visit_part_in_guide