Document creating backend pages

docs/extensions/pages.md

@@ -1,4 +1,140 @@
 Adding Pages in the backend
 ===========================
 
-[todo] Write some stuff here adding pages in the backend, that kinda look like they fit in with the overall backend.
+## Create a page in the Bolt's backend
+
+You can add pages to Bolt's backend by creating a custom
+Controller in the `src` folder of your project.
+
+To configure it as a backend Controller, two steps are necessary:
+* The Controller class needs to implement the `BackendZoneInterface`
+ that Bolt provides
+* The `routes.yaml` file needs to add Bolt backend prefix for
+the controller's routes.
+
+### Creating a backend page Controller
+
+```php
+<?php
+
+namespace App;
+
+use Symfony\Component\Routing\Annotation\Route;
+use Bolt\Controller\Backend\BackendZoneInterface;
+use Symfony\Component\HttpFoundation\Response;
+
+class UserContentController extends TwigAwareController implements BackendZoneInterface
+{
+    /**
+     * @Route("/content-user/", name="app_content_user")
+     */
+    public function viewEdits(): Response
+    {
+        // content_user.html.twig is a custom file 
+        // that needs to be located in the `templates`
+        // folder in the root of your project.
+        return $this->render('content_user.html.twig', [
+            'title' => 'User content'
+        ]);
+    }
+}
+```
+
+
+### Defining the controller route with the backend url prefix
+
+Locale the `config/routes.yaml` file and add the following **after** 
+`project`:
+
+```yaml
+app_panel:
+    resource: '../src/UserContentController.php'
+    prefix: '%bolt.backend_url%'
+    type: annotation
+```
+
+<p class="note">Make sure to replace <code>UserContentController.php</code>
+with the name of your Controller class.</p>
+
+### Using a Twig template to render the page
+
+You can use any Twig template of your choosing to render the page.
+In this example, the Controller defined `content_user.html.twig` as
+the template that will be used to generate the response. Make sure
+to create a file with that name in the `templates` folder in the root of
+your project.
+
+For example, the `content_user.html.twig` file may contain the following:
+
+```twig
+{% extends '@bolt/_base/layout.html.twig' %}
+
+{% block main %}
+    <p>This is the content for a user. It is currently empty.</p>
+{% endblock %}
+```
+
+#### Provided templates
+
+Bolt provides two templates that you can extend when creating
+custom backend pages:
+
+| Template | Function | Link |
+| --- | --- | --- |
+| `@bolt/_base/layout.html.twig` | This is the standard template that any Bolt page uses. It contains the top bar, the sidebar and aside components. | [Layout link][layout-link]
+| `@bolt/_base/layout_blank.html.twig` | This is the barebones version of the layout. Use it only if you do not want to show the default Bolt backend look and feel. | [Blank layout link][blank-layout-link]
+
+All available templates that Bolt uses under the hood are available in Bolt's [repository][https://github.com/bolt/core/tree/master/templates].
+
+## Add a page to Bolt's sidebar menu
+
+Bolt allows the sidebar menu to be extended to add extra items and links.
+To do so, create a class inside the `src` folder of your project that 
+implements the `ExtensionBackendMenuInterface`.
+
+The example below defines a new menu section for the User Content page shown above.
+
+```php
+<?php
+
+
+namespace App;
+
+use Bolt\Menu\ExtensionBackendMenuInterface;
+use Knp\Menu\MenuItem;
+use Symfony\Component\Routing\Generator\UrlGeneratorInterface;
+
+class UserContentMenu implements ExtensionBackendMenuInterface
+{
+    /** @var UrlGeneratorInterface */
+    private $urlGenerator;
+
+    public function __construct(UrlGeneratorInterface $urlGenerator)
+    {
+        $this->urlGenerator = $urlGenerator;
+    }
+
+    public function addItems(MenuItem $menu): void
+    {
+        // This adds a new heading
+        $menu->addChild('User Content Extension', [
+            'extras' => [
+                'name' => 'User Content Extension',
+                'type' => 'separator',
+            ]
+        ]);
+
+        // This adds the link
+        $menu->addChild('Content list', [
+           'uri' => $this->urlGenerator->generate('app_content_user'),
+            'extras' => [
+                'icon' => 'fa-user-circle'
+            ]
+        ]);
+    }
+}
+```
+
+[layout-link]: https://github.com/bolt/core/blob/master/templates/_base/layout.html.twig
+[blank-layout-link]: https://github.com/bolt/core/blob/master/templates/_base/layout_blank.html.twig
+[all-templates]: https://github.com/bolt/core/tree/master/templates