# Hooks & events

Hooks are how plugins intervene in the work of the core and of other plugins without changing their code. They're implemented WordPress-style by the `Celena\Core\Plugin\Hook` class. There are two kinds: **actions** (side effects) and **filters** (value transformation).

Name contract: `<area>.<event>` in lowercase, e.g. `news.published`.

## Actions

A side effect with no return value. There can be several subscribers; order doesn't matter.

```php
use Celena\Core\Plugin\Hook;

// Subscribe:
Hook::on('news.published', function (array $news): void {
    // e.g. send a notification
});

// Fire (the core/module does this):
Hook::action('news.published', $news);
```

## Filters

Transform a value, passing it down the chain of subscribers.

```php
// Subscribe (priority optional, lower = earlier):
Hook::addFilter('news.title', fn (string $t) => trim($t), 10);

// Apply:
$title = Hook::filter('news.title', $news['title'], $news);
```

## Built-in core hooks

| Hook | Type | Arguments |
|------|------|-----------|
| `kernel.boot` | action | `Container $c` |
| `request.before` | action | `Request $req` |
| `response.before_send` | filter | `Response $res, Request $req` |
| `user.registered` | action | `array $user` |
| `user.login.success` | action | `array $user` |
| `user.login.failed` | action | `string $email, string $ip` |
| `news.published` | action | `array $news` |
| `news.title` | filter | `string $title, array $news` |
| `template.render.before` | action | `string $template, array $vars` |
| `template.globals` | filter | `array $vars` |
| `admin.sidebar` | filter | `array $items` |
| `admin.notifications` | filter | `array $items` |
| `cache.cleared` | action | `string $type` |

The list grows as the core grows.

## Common scenarios

### Add an admin menu item

```php
Hook::addFilter('admin.sidebar', function (array $items): array {
    $icon = new \Celena\Core\Template\Tags\IconTag();
    $items[] = [
        'svg'          => $icon(['name' => 'mail', 'size' => 22, 'class' => 'sb-ico']),
        'label'        => 'Leads',
        'url'          => '/admin/forms',
        'slug'         => 'forms',
        'active_slugs' => ['forms', 'leads'],
        'children'     => [
            ['label' => 'Forms',    'url' => '/admin/forms', 'slug' => 'forms'],
            ['label' => 'All leads', 'url' => '/admin/leads', 'slug' => 'leads'],
        ],
    ];
    return $items;
});
```

### Pass a variable to all templates

```php
Hook::addFilter('template.globals', function (array $vars): array {
    $vars['my_flag'] = '1';   // available as {my_flag} in any template
    return $vars;
}, 0);
```

### Add a notification to the "bell"

```php
Hook::addFilter('admin.notifications', function (array $items): array {
    $items[] = ['title' => 'New leads', 'text' => '3 items', 'url' => '/admin/forms', 'time' => ''];
    return $items;
});
```

## Your own hooks in a plugin

A plugin can emit its own events so other extensions can subscribe:

```php
Hook::action('shop.order.created', $order);
$price = Hook::filter('shop.price', $price, $product);
```

Document such hooks in your plugin's `docs/hooks.md` — it's the contract for integrations.
