---
url: /foehn-framework/api/kernel.md
---
# Kernel

The main bootstrap class for Føhn.

## Signature

```php
<?php

namespace Studiometa\Foehn;

use Tempest\Container\Container;

final class Kernel
{
    /**
     * Boot the kernel.
     *
     * @param string $appPath Path to the app directory to scan
     * @param array<string, mixed> $config Configuration options
     */
    public static function boot(string $appPath, array $config = []): self;

    /**
     * Get the kernel instance.
     *
     * @throws RuntimeException If kernel not booted
     */
    public static function getInstance(): self;

    /**
     * Get the container instance.
     */
    public static function container(): Container;

    /**
     * Get a service from the container.
     *
     * @template T of object
     * @param class-string<T> $class
     * @return T
     */
    public static function get(string $class): object;

    /**
     * Get the app path.
     */
    public function getAppPath(): string;

    /**
     * Get a configuration value.
     */
    public function getConfig(string $key, mixed $default = null): mixed;

    /**
     * Get the Foehn configuration.
     */
    public function getFoehnConfig(): FoehnConfig;

    /**
     * Check if the kernel has been booted.
     */
    public function isBooted(): bool;
}
```

## Methods

### boot()

Initialize and boot the kernel. Call this once in `functions.php`.

```php
use Studiometa\Foehn\Kernel;

Kernel::boot(__DIR__ . '/app');
```

Configuration is handled via config files in your app directory (recommended):

```php
<?php
// app/foehn.config.php
use Studiometa\Foehn\Config\FoehnConfig;
use Tempest\Discovery\DiscoveryCacheStrategy;

return new FoehnConfig(
    discoveryCacheStrategy: DiscoveryCacheStrategy::FULL,
    hooks: [
        \Studiometa\Foehn\Hooks\Cleanup\DisableEmoji::class,
        \Studiometa\Foehn\Hooks\Security\SecurityHeaders::class,
    ],
);
```

A legacy array-based approach is also supported:

```php
Kernel::boot(__DIR__ . '/app', [
    'discovery_cache' => 'full',
    'hooks' => [DisableEmoji::class],
]);
```

See [FoehnConfig](./foehn-config), [Discovery Cache](/guide/discovery-cache), and [Built-in Hooks](/guide/hooks#built-in-hooks) for details.

### Registered Services

The kernel automatically registers these services as singletons:

| Service                   | Implementation     | Description                     |
| ------------------------- | ------------------ | ------------------------------- |
| `CacheInterface`          | `TransientCache`   | WordPress transient-based cache |
| `ViewEngineInterface`     | `TimberViewEngine` | Twig template rendering         |
| `ContextProviderRegistry` | —                  | Context provider management     |
| `DiscoveryRunner`         | —                  | Discovery orchestration         |
| `AcfBlockRenderer`        | —                  | ACF block rendering             |
| `SectionRequest`          | —                  | Current section selection       |
| `SectionCollector`        | —                  | Page-local section declarations |
| `SectionRenderer`         | —                  | Atomic section HTML rendering   |

### getInstance()

Get the singleton kernel instance.

```php
$kernel = Kernel::getInstance();
$appPath = $kernel->getAppPath();
```

### container()

Access the Tempest DI container.

```php
$container = Kernel::container();
$container->singleton(MyService::class, fn() => new MyService());
```

### get()

Retrieve a service from the container.

```php
$viewEngine = Kernel::get(ViewEngineInterface::class);
$myService = Kernel::get(MyService::class);
```

### getConfig()

Get configuration values.

```php
$viewsPath = Kernel::getInstance()->getConfig('timber.views');
$default = Kernel::getInstance()->getConfig('missing.key', 'default');
```

## Lifecycle Hooks

The kernel hooks into WordPress lifecycle:

1. **`after_setup_theme`** — Early discoveries (theme setup)
2. **`init`** — Main discoveries (post types, taxonomies, blocks)
3. **`wp_loaded`** — Late discoveries (REST routes, templates)

## Usage

### Basic Setup

```php
<?php
// functions.php

require_once __DIR__ . '/vendor/autoload.php';

use Studiometa\Foehn\Kernel;

Kernel::boot(__DIR__ . '/app');
```

### Accessing Services

```php
// In any class with DI
public function __construct(
    private readonly ViewEngineInterface $view,
) {}

// Or manually
$view = Kernel::get(ViewEngineInterface::class);
```

### Registering Custom Services

```php
// In a hook or early in bootstrap
use Studiometa\Foehn\Kernel;

add_action('after_setup_theme', function () {
    $container = Kernel::container();

    $container->singleton(MyService::class, function () {
        return new MyService(
            apiKey: defined('MY_API_KEY') ? MY_API_KEY : '',
        );
    });
}, 0);
```

## Related

* [Guide: Getting Started](/guide/getting-started)
* [Guide: Installation](/guide/installation)
* [Guide: Discovery Cache](/guide/discovery-cache)
* [Helpers](./helpers)