wireguard: add 'Start Server' button with confirmation page

Adds explicit UI flow to generate server keypair and interface.

- New EnableServerView
- Conditional 'Start Server' button on main page when no wg0
- Button switches to 'Add Client' after server setup

Solves circular dependency UX issue when connecting two FBs

EDIT: Following review feedback, I removed the intermediate
confirmation page.
The “Start WireGuard Server” button now sends a POST
directly from the main page.

Signed-off-by: Frederico Gomes <fredericojfgomes@gmail.com>
Reviewed-by: James Valleroy <jvalleroy@mailbox.org>
[jvalleroy: Change from TemplateView to View]
[jvalleroy: Remove redundant import]
Signed-off-by: James Valleroy <jvalleroy@mailbox.org>

plinth/modules/wireguard/templates/wireguard.html

@@ -56,14 +56,26 @@
   </p>
 
   <div class="btn-toolbar">
-    <a title="{% trans 'Add a new peer' %}"
-       role="button" class="btn btn-default btn-add-client"
-       href="{% url 'wireguard:add-client' %}">
-      <span class="fa fa-plus" aria-hidden="true"></span>
-      {% trans "Add Allowed Client" %}
-    </a>
+    {% if not server.public_key %}
+      <form method="post" action="{% url 'wireguard:enable-server' %}">
+        {% csrf_token %}
+        <button type="submit" class="btn btn-primary"
+                title="{% trans 'Start WireGuard Server' %}">
+          <span class="fa fa-rocket" aria-hidden="true"></span>
+          {% trans "Start WireGuard Server" %}
+        </button>
+      </form>
+    {% else %}
+      <a title="{% trans 'Add a new peer' %}"
+         role="button" class="btn btn-default btn-add-client"
+         href="{% url 'wireguard:add-client' %}">
+        <span class="fa fa-plus" aria-hidden="true"></span>
+        {% trans "Add Allowed Client" %}
+      </a>
+    {% endif %}
   </div>
 
+
   <h3>{% trans "As a Client" %}</h3>
   <p>
     {% blocktrans trimmed %}

plinth/modules/wireguard/urls.py

@@ -9,6 +9,8 @@ from plinth.modules.wireguard import views
 
 urlpatterns = [
     re_path(r'^apps/wireguard/$', views.WireguardView.as_view(), name='index'),
+    re_path(r'^apps/wireguard/enable-server/$',
+            views.EnableServerView.as_view(), name='enable-server'),
     re_path(r'^apps/wireguard/client/add/$', views.AddClientView.as_view(),
             name='add-client'),
     re_path(r'^apps/wireguard/client/(?P<public_key>[^/]+)/show/$',

plinth/modules/wireguard/views.py

@@ -11,7 +11,7 @@ from django.http import Http404
 from django.shortcuts import redirect
 from django.urls import reverse_lazy
 from django.utils.translation import gettext as _
-from django.views.generic import FormView, TemplateView
+from django.views.generic import FormView, TemplateView, View
 
 from plinth import network
 from plinth.modules.names.components import DomainName
@@ -252,3 +252,19 @@ class DeleteServerView(SuccessMessageMixin, TemplateView):
         network.delete_connection(connection.get_uuid())
         messages.success(request, _('Server deleted.'))
         return redirect('wireguard:index')
+
+
+class EnableServerView(SuccessMessageMixin, View):
+    """View to enable the WireGuard server."""
+
+    def post(self, request):
+        """Create server interface."""
+        try:
+            utils.setup_server()
+            messages.success(request,
+                             _('WireGuard server started successfully.'))
+        except Exception as error:
+            messages.error(
+                request,
+                _('Failed to start WireGuard server: {}').format(error))
+        return redirect('wireguard:index')