Add FAQPage schema

What
----
This will be used on Guides to present the chapters in an improved way in
featured snippets.

Implemented as per: https://developers.google.com/search/docs/data-types/faqpage

Why
---
SEO improvement. It allows users to read more of the content in Google,
hopefully allowing them to make better decisions about whether to read more of
the content and thus shortening their journeys.

We will measure the effects of this change.

CHANGELOG.md

@@ -10,6 +10,7 @@
 ## Unreleased
 
 * Fix components focus state spacing (PR #1054)
+* Add FAQPage schema (PR #1087)
 
 ## 19.0.0
 

lib/govuk_publishing_components/presenters/machine_readable/faq_page_schema.rb

@@ -0,0 +1,52 @@
+module GovukPublishingComponents
+  module Presenters
+    class FaqPageSchema
+      attr_reader :page
+
+      def initialize(page)
+        @page = page
+      end
+
+      def structured_data
+        # http://schema.org/FAQPage
+        data = CreativeWorkSchema.new(@page).structured_data
+          .merge(main_entity)
+        data["@type"] = "FAQPage"
+        data
+      end
+
+    private
+
+      def main_entity
+        {
+          "mainEntity" => questions_and_answers
+        }
+      end
+
+      def questions_and_answers
+        page.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?
+          page.canonical_url
+        else
+          page.canonical_url + "/" + part["slug"]
+        end
+      end
+    end
+  end
+end

lib/govuk_publishing_components/presenters/machine_readable/page.rb

@@ -58,6 +58,10 @@ def content_item
       def logo_url
         local_assigns[:logo_url]
       end
+
+      def parts
+        content_item.dig("details", "parts") || []
+      end
     end
   end
 end

lib/govuk_publishing_components/presenters/schema_org.rb

@@ -1,6 +1,7 @@
 require 'govuk_publishing_components/presenters/machine_readable/page'
 require 'govuk_publishing_components/presenters/machine_readable/article_schema'
 require 'govuk_publishing_components/presenters/machine_readable/creative_work_schema'
+require 'govuk_publishing_components/presenters/machine_readable/faq_page_schema'
 require 'govuk_publishing_components/presenters/machine_readable/has_part_schema'
 require 'govuk_publishing_components/presenters/machine_readable/is_part_of_schema'
 require 'govuk_publishing_components/presenters/machine_readable/news_article_schema'
@@ -19,7 +20,9 @@ def initialize(page)
       end
 
       def structured_data
-        if page.schema == :article
+        if page.schema == :faq
+          FaqPageSchema.new(page).structured_data
+        elsif page.schema == :article
           ArticleSchema.new(page).structured_data
         elsif page.schema == :news_article
           NewsArticleSchema.new(page).structured_data

spec/lib/govuk_publishing_components/presenters/schema_org_spec.rb

@@ -62,6 +62,43 @@
       expect(structured_data['@type']).to eql("NewsArticle")
     end
 
+    it "generates schema.org FAQPages" do
+      content_item = GovukSchemas::RandomExample.for_schema(frontend_schema: "guide") do |random_item|
+        random_item.merge(
+          "base_path" => "/how-to-train-your-dragon",
+          "details" => {
+            "parts" => [
+              {
+                "title" => "Overview",
+                "slug" => "overview",
+                "body" => "<p>First catch your dragon</p>"
+              },
+              {
+                "title" => "Insurance",
+                "slug" => "insurance",
+                "body" => "<p>Contact the Berk insurance bureau for more details.</p>"
+              }
+            ]
+          }
+        )
+      end
+
+      structured_data = generate_structured_data(
+        content_item: content_item,
+        schema: :faq,
+      ).structured_data
+
+      expect(structured_data['@type']).to eql("FAQPage")
+
+      q_and_a_pairs = structured_data['mainEntity']
+      expect(q_and_a_pairs.count).to eq(2)
+      expect(q_and_a_pairs.first["url"]).to eq("http://www.dev.gov.uk/how-to-train-your-dragon")
+      expect(q_and_a_pairs.second["url"]).to eq("http://www.dev.gov.uk/how-to-train-your-dragon/insurance")
+
+      expect(q_and_a_pairs.first["name"]).to eq("Overview")
+      expect(q_and_a_pairs.first["acceptedAnswer"]["text"]).to eq("<p>First catch your dragon</p>")
+    end
+
     it "generates schema.org Person" do
       content_item = GovukSchemas::RandomExample.for_schema(frontend_schema: "person")