Fix back links when viewing a broadcast

Where you go back to from a broadcast can now depend on whether it’s
a current or previous broadcast.

app/main/views/broadcast.py

@@ -295,6 +295,14 @@ def view_broadcast(service_id, broadcast_message_id):
     return render_template(
         'views/broadcast/view-message.html',
         broadcast_message=broadcast_message,
+        back_link={
+            'main.view_current_broadcast': url_for(
+                '.broadcast_dashboard', service_id=current_service.id
+            ),
+            'main.view_previous_broadcast': url_for(
+                '.broadcast_dashboard_previous', service_id=current_service.id
+            ),
+        }[request.endpoint],
     )
 
 

app/templates/views/broadcast/view-message.html

@@ -34,7 +34,7 @@
 
 {% block maincolumn_content %}
 
-  {{ govukBackLink({ "href": url_for('.broadcast_dashboard', service_id=current_service.id) }) }}
+  {{ govukBackLink({ "href": back_link }) }}
 
   {% if broadcast_message.status == 'pending-approval' %}
     {% if broadcast_message.created_by == current_user and current_user.has_permissions('send_messages') %}