Add service navigation to the header

Enable navigation between the visualisation graph and tabular view pages.

Doesn't include the visualisation list page for now, since that's not a
 main page.

Author: mtaylorgds

app.py

@@ -61,7 +61,7 @@ def graph_page():
                 case _:
                     error = f"Graph for '{run_path_param}' failed to generate."
 
-        return render_template("graph-unavailable.html", message=error)
+        return render_template("graph-unavailable.html", message=error, run_path=run_path_param)
 
     @app.route("/visualisations", methods=["GET"])
     def visualisations_page():

templates/base.html

@@ -39,6 +39,43 @@
           </div>
         </div>
       </div>
+      <section aria-label="Service information" class="govuk-service-navigation"
+        data-module="govuk-service-navigation">
+        <div class="govuk-width-container">
+          <div class="govuk-service-navigation__container">
+            <nav aria-label="Menu" class="govuk-service-navigation__wrapper">
+              <ul class="govuk-service-navigation__list" id="navigation">
+                {% if request.path == url_for('graph_page') %}
+                <li class="govuk-service-navigation__item govuk-service-navigation__item--active">
+                  <a class="govuk-service-navigation__link" href="{{ url_for('graph_page', run_path=run_path) }}" aria-current="true">
+                    <strong class="govuk-service-navigation__active-fallback">Graph</strong>
+                  </a>
+                </li>
+                {% else %}
+                <li class="govuk-service-navigation__item">
+                  <a class="govuk-service-navigation__link" href="{{ url_for('graph_page', run_path=run_path) }}">
+                    Graph
+                  </a>
+                </li>
+                {% endif %}
+                {% if request.path == url_for('metrics_page') %}
+                <li class="govuk-service-navigation__item govuk-service-navigation__item--active">
+                  <a class="govuk-service-navigation__link" href="{{ url_for('metrics_page', run_path=run_path) }}" aria-current="true">
+                    <strong class="govuk-service-navigation__active-fallback">Metrics</strong>
+                  </a>
+                </li>
+                {% else %}
+                <li class="govuk-service-navigation__item">
+                  <a class="govuk-service-navigation__link" href="{{ url_for('metrics_page', run_path=run_path) }}">
+                    Metrics
+                  </a>
+                </li>
+                {% endif %}
+              </ul>
+            </nav>
+          </div>
+        </div>
+      </section>
     </header>
 
     <main>