contact-groups: Prevent new groups without a channel

Without channels, most of the configuration is not possible.
Technically, channels are not required for groups, but we
want to guide new users to the channel configuration because
of its importance. Once there is a channel, groups can be
created but we still hint that there are no contacts yet.

Author: nilmerg

application/controllers/ContactGroupsController.php

@@ -7,6 +7,7 @@
 use Icinga\Module\Notifications\Common\Database;
 use Icinga\Module\Notifications\Common\Links;
 use Icinga\Module\Notifications\Forms\ContactGroupForm;
+use Icinga\Module\Notifications\Model\Channel;
 use Icinga\Module\Notifications\Model\Contact;
 use Icinga\Module\Notifications\Model\Contactgroup;
 use Icinga\Module\Notifications\View\ContactgroupRenderer;
@@ -15,6 +16,7 @@
 use Icinga\Module\Notifications\Widget\MemberSuggestions;
 use Icinga\Web\Notification;
 use ipl\Html\Form;
+use ipl\Html\HtmlString;
 use ipl\Html\TemplateString;
 use ipl\Stdlib\Filter;
 use ipl\Web\Compat\CompatController;
@@ -90,15 +92,27 @@ public function indexAction(): void
 
         $emptyStateMessage = null;
         if (Contact::on(Database::get())->columns('1')->limit(1)->first() === null) {
-            $addButton->disable($this->translate('A contact is required to add a contact group'));
-
-            $emptyStateMessage = TemplateString::create(
-                $this->translate(
-                    'No contact groups found. To add a new contact group,'
-                    . ' please {{#link}}add a contact{{/link}} first.'
-                ),
-                ['link' => (new ActionLink(null, Links::contactAdd()))->setBaseTarget('_next')]
-            );
+            if (Channel::on(Database::get())->columns('1')->limit(1)->first() === null) {
+                $addButton->disable($this->translate('A channel is required to add a contact group'));
+
+                $emptyStateMessage = TemplateString::create(
+                    // translators: %1$s will be replaced by a line break
+                    'No contact groups found.%1$sTo add new contact group, please {{#link}}configure a Channel{{/link}}'
+                    . ' first.%1$sOnce done, you should proceed by creating your first contact.',
+                    ['link' => (new ActionLink(null, Links::channelAdd()))->setBaseTarget('_next')],
+                    [HtmlString::create('<br>')]
+                );
+            } else {
+                $emptyStateMessage = TemplateString::create(
+                    $this->translate(
+                        'No contact groups found. Do not forget to also'
+                        . ' {{#link}}create your first contact!{{/link}}'
+                    ),
+                    ['link' => (new ActionLink(null, Links::contactAdd()))->setBaseTarget('_next')]
+                );
+
+                $addButton->openInModal();
+            }
         } else {
             $addButton->openInModal();
         }