README

A lightweight application kernel with service container bootstrapping, lifecycle callbacks, and PSR-14 event dispatching.

Installation

composer require georgeff/kernel

Usage

Basic Bootstrapping

use Georgeff\Kernel\Environment;
use Georgeff\Kernel\Kernel;

$kernel = new Kernel(Environment::Production);

$kernel
    ->addDefinition('logger', fn() => new FileLogger('/var/log/app.log'), shared: true)
    ->addDefinition('mailer', fn() => new SmtpMailer('localhost'), shared: true);

$kernel->boot();

$container = $kernel->getContainer();
$logger = $container->get('logger');

Environments

The Environment enum provides four application environments:

Environment::Production
Environment::Staging
Environment::Development
Environment::Testing

$kernel = new Kernel(Environment::Development, debug: true);

$kernel->getEnvironment(); // 'development'
$kernel->isDebug();        // true

Service Definitions

Register service definitions before booting. Each definition takes a factory callable, an optional shared flag, and optional aliases:

$kernel->addDefinition(
    'db.connection',
    fn() => new PdoConnection($dsn, $user, $pass),
    shared: true,
    aliases: [ConnectionInterface::class],
);

Definitions registered later with the same ID will overwrite earlier ones, allowing base definitions to be overridden.

Lifecycle Callbacks

Register onBooting callbacks to hook into the kernel boot lifecycle. Callbacks run before service definitions are registered with the container:

$kernel = new Kernel(Environment::Production);

$kernel->onBooting(function (KernelInterface $kernel) {
    // Called during boot, before services are registered
});

$kernel->boot();

onBooting callbacks must be registered before boot. They can also add definitions dynamically:

$kernel->onBooting(function (KernelInterface $kernel) {
    $kernel->addDefinition('dynamic', fn() => new SomeService(), shared: true);
});

onBooting returns the kernel for fluent chaining with addDefinition:

$kernel
    ->onBooting(function (KernelInterface $kernel) { /* ... */ })
    ->addDefinition('logger', fn() => new FileLogger(), shared: true);

Events

After boot completes, the kernel dispatches a KernelBooted event via PSR-14 if an EventDispatcherInterface is registered in the container:

use Georgeff\Kernel\Event\KernelBooted;
use Psr\EventDispatcher\EventDispatcherInterface;

$kernel->addDefinition(
    EventDispatcherInterface::class,
    fn() => new MyEventDispatcher(),
    shared: true,
);

$kernel->boot(); // dispatches KernelBooted

// In your listener:
function handleBooted(KernelBooted $event): void {
    $kernel = $event->kernel; // readonly public property
}

If no EventDispatcherInterface is registered, boot completes without dispatching.

Custom Service Registrar

The kernel uses a ServiceRegistrar interface to register definitions with the container. A DefaultServiceRegistrar backed by georgeff/container is used by default. Provide your own to use a different container implementation:

$registrar = new MyServiceRegistrar();
$kernel = new Kernel(Environment::Production, $registrar);

Debug Mode

When debug mode is enabled, the kernel profiles the boot process, wraps the container in a DebugContainer that tracks service resolutions, and collects debug info from any resolved service implementing DebuggableInterface:

$kernel = new Kernel(Environment::Development, debug: true);
$kernel->boot();

$kernel->getStartTime(); // float (microtime)
$kernel->getDebugInfo(); // boot profile + service resolution data

The getDebugInfo() array contains:

bootProfile — timing for each boot phase (preBoot, serviceRegistration, containerInit)
serviceResolutionProfile — which services were resolved and their resolution times
servicesDebugInfo — debug info collected from resolved services that implement DebuggableInterface

When debug is disabled, getStartTime() returns -INF and getDebugInfo() returns [].

DebuggableInterface

Services can implement DebuggableInterface to expose debug data. When resolved through the debug container, their getDebugInfo() output is collected automatically:

use Georgeff\Kernel\Debug\DebuggableInterface;

final class ConnectionPool implements DebuggableInterface
{
    public function getDebugInfo(): array
    {
        return ['active' => $this->activeCount, 'idle' => $this->idleCount];
    }
}

Reserved Services

The kernel registers the following services in the container during boot:

kernel (aliased to KernelInterface)
kernel.environment — the environment string value (e.g. 'production')
kernel.debug — the debug flag (bool)

These IDs cannot be overwritten via addDefinition.

Extending the Kernel

The Kernel class can be extended for specialized use cases such as HTTP or console kernels. A RunnableKernelInterface is provided for kernels that serve as an application entry point:

use Georgeff\Kernel\RunnableKernelInterface;

class ConsoleKernel extends Kernel implements RunnableKernelInterface
{
    public function run(): int
    {
        $this->boot();

        // dispatch console command...

        return 0;
    }
}

License

MIT

georgeff / kernel

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