Fix select_top_level_html_files ignoring custom http_prefix

  The parent URL check was hardcoded to "/" so top-level pages were filtered out when http_prefix was set to a custom path.

Author: nulty

lib/govuk_tech_docs/table_of_contents/helpers.rb

@@ -30,14 +30,16 @@ def sort_resources_stably(resources)
           .to_a
       end
 
-      def select_top_level_html_files(resources)
+      def select_top_level_html_files(resources, config)
+        home_url = config[:http_prefix].end_with?("/") ? config[:http_prefix] : "#{config[:http_prefix]}/"
+
         resources
-          .select { |r| r.path.end_with?(".html") && (r.parent.nil? || r.parent.url == "/") }
+          .select { |r| r.path.end_with?(".html") && (r.parent.nil? || r.parent.url == home_url) }
       end
 
       def multi_page_table_of_contents(resources, current_page, config, current_page_html = nil)
         resources = sort_resources_stably(
-          select_top_level_html_files(resources),
+          select_top_level_html_files(resources, config),
         )
 
         render_page_tree(resources, current_page, config, current_page_html)

spec/table_of_contents/helpers_spec.rb

@@ -342,6 +342,24 @@ def is_a?(klass)
       expect(subject.multi_page_table_of_contents(resources, current_page, config, current_page_html).strip).to eq(expected_multi_page_table_of_contents.strip)
     end
 
+    it "selects top-level pages whose parent URL matches the http prefix" do
+      prefix_root = FakeResource.new("/prefix/", "")
+      resources = []
+      resources[0] = FakeResource.new("/prefix/index.html", '<h1 id="heading-one">Heading one</h1>', 10, "Index", prefix_root)
+      resources[1] = FakeResource.new("/prefix/a.html", '<h1 id="heading-one">Heading one</h1>', 20, "Page A", prefix_root)
+
+      config = {
+        http_prefix: "/prefix",
+        tech_docs: {
+          max_toc_heading_level: 3,
+        },
+      }
+
+      result = subject.select_top_level_html_files(resources, config)
+
+      expect(result).to eq(resources)
+    end
+
     it "builds a table of contents from a single page resources" do
       resources = []
       resources.push FakeResource.new("/index.html", '<h1 id="heading-one">Heading one</h1><h2 id="heading-two">Heading two</h2><h1 id="heading-one">Heading one</h1><h2 id="heading-two">Heading two</h2><h1 id="heading-one">Heading one</h1><h2 id="heading-two">Heading two</h2>')