Use GraphQL for rendering news articles

This retrieves the content from Publishing API, instead of Content
Store, using a GraphQL query.

Note this has been done in the way that reduces the number of changes
needed in this application. As a result, we have introduced a small
"hack" to return the data in `GdsApi::Response` format but with this app
rewriting the hash keys to make them all underscore based.

app/controllers/content_items_controller.rb

@@ -136,16 +136,43 @@ def set_guide_draft_access_token
     @content_item.draft_access_token = params[:token]
   end
 
-  def load_content_item
-    content_item = Services.content_store.content_item(content_item_path)
-
-    content_item["links"]["ordered_related_items"] = ordered_related_items(content_item["links"]) if content_item["links"]
+  class GdsApi::Response
+    def update_response_body
+      updated_response = JSON.parse(@http_response.body).dig("data", "edition").deep_transform_keys(&:underscore)
+      @http_response = RestClient::Response.create(
+        updated_response.to_json,
+        @http_response.net_http_res,
+        @http_response.request,
+      )
+    end
+  end
 
-    @content_item = PresenterBuilder.new(
-      content_item,
-      content_item_path,
-      view_context,
-    ).presenter
+  def load_content_item
+    ## TODO: how do we know this is a news article before we request the item from content store?
+    ## i.e., how do we know which GraphQL query to use?
+    @content_item = if Features.graphql_feature_enabled? || params.include?(:graphql)
+                      graphql_response = Services
+                        .publishing_api
+                        .graphql_query(Graphql::NewsArticleQuery.new(content_item_path).query)
+
+                      graphql_response.update_response_body
+
+                      PresenterBuilder.new(
+                        graphql_response,
+                        content_item_path,
+                        view_context,
+                      ).presenter
+                    else
+                      content_item = Services.content_store.content_item(content_item_path)
+
+                      content_item["links"]["ordered_related_items"] = ordered_related_items(content_item["links"]) if content_item["links"]
+
+                      PresenterBuilder.new(
+                        content_item,
+                        content_item_path,
+                        view_context,
+                      ).presenter
+                    end
   end
 
   def ordered_related_items(links)

app/queries/graphql/news_article_query.rb

@@ -0,0 +1,75 @@
+class Graphql::NewsArticleQuery
+  def initialize(base_path)
+    @base_path = base_path
+  end
+
+  def query
+    <<-QUERY
+        {
+          edition(
+            basePath: "#{@base_path}",
+            contentStore: "live",
+          ) {
+            ... on NewsArticle {
+              basePath
+              description
+              details
+              documentType
+              firstPublishedAt
+              links {
+                availableTranslations {
+                  basePath
+                  locale
+                }
+                government {
+                  details {
+                    current
+                  }
+                  title
+                }
+                organisations {
+                  basePath
+                  contentId
+                  title
+                }
+                people {
+                  basePath
+                  contentId
+                  title
+                }
+                taxons {
+                  basePath
+                  contentId
+                  documentType
+                  phase
+                  title
+                  links {
+                    parentTaxons {
+                      basePath
+                      contentId
+                      documentType
+                      phase
+                      title
+                    }
+                  }
+                }
+                topicalEvents {
+                  basePath
+                  contentId
+                  title
+                }
+                worldLocations {
+                  basePath
+                  contentId
+                  title
+                }
+              }
+              locale
+              schemaName
+              title
+            }
+          }
+        }
+    QUERY
+  end
+end