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The Separation of Concerns

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The Separation of Concerns¶

One down-side of our framework right now is that we need to copy and paste the code in front.php each time we create a new website. 60 lines of code is not that much, but it would be nice if we could wrap this code into a proper class. It would bring us better reusability and easier testing to name just a few benefits.

If you have a closer look at the code, front.php has one input, the Request and one output, the Response. Our framework class will follow this simple principle: the logic is about creating the Response associated with a Request.

Let's create our very own namespace for our framework: Simplex. Move the request handling logic into its own Simplex\\Framework class:

// example.com/src/Simplex/Framework.php
namespace Simplex;

use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpFoundation\Response;
use Symfony\Component\HttpKernel\Controller\ArgumentResolver;
use Symfony\Component\HttpKernel\Controller\ControllerResolver;
use Symfony\Component\Routing\Exception\ResourceNotFoundException;
use Symfony\Component\Routing\Matcher\UrlMatcher;

class Framework
{
    protected $matcher;
    protected $controllerResolver;
    protected $argumentResolver;

    public function __construct(UrlMatcher $matcher, ControllerResolver $controllerResolver, ArgumentResolver $argumentResolver)
    {
        $this->matcher = $matcher;
        $this->controllerResolver = $controllerResolver;
        $this->argumentResolver = $argumentResolver;
    }

    public function handle(Request $request)
    {
        $this->matcher->getContext()->fromRequest($request);

        try {
            $request->attributes->add($this->matcher->match($request->getPathInfo()));

            $controller = $this->controllerResolver->getController($request);
            $arguments = $this->argumentResolver->getArguments($request, $controller);

            return call_user_func_array($controller, $arguments);
        } catch (ResourceNotFoundException $e) {
            return new Response('Not Found', 404);
        } catch (\Exception $e) {
            return new Response('An error occurred', 500);
        }
    }
}

And update example.com/web/front.php accordingly:

// example.com/web/front.php

// ...
$request = Request::createFromGlobals();
$routes = include __DIR__.'/../src/app.php';

$context = new Routing\RequestContext();
$matcher = new Routing\Matcher\UrlMatcher($routes, $context);

$controllerResolver = new ControllerResolver();
$argumentResolver = new ArgumentResolver();

$framework = new Simplex\Framework($matcher, $controllerResolver, $argumentResolver);
$response = $framework->handle($request);

$response->send();

To wrap up the refactoring, let's move everything but routes definition from example.com/src/app.php into yet another namespace: Calendar.

For the classes defined under the Simplex and Calendar namespaces to be autoloaded, update the composer.json file:

{
    "...": "...",
    "autoload": {
        "psr-4": { "": "src/" }
    }
}

Note

For the Composer autoloader to be updated, run composer dump-autoload.

Move the controller to Calendar\Controller\LeapYearController:

// example.com/src/Calendar/Controller/LeapYearController.php
namespace Calendar\Controller;

use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpFoundation\Response;
use Calendar\Model\LeapYear;

class LeapYearController
{
    public function indexAction(Request $request, $year)
    {
        $leapyear = new LeapYear();
        if ($leapyear->isLeapYear($year)) {
            return new Response('Yep, this is a leap year!');
        }

        return new Response('Nope, this is not a leap year.');
    }
}

And move the is_leap_year() function to its own class too:

// example.com/src/Calendar/Model/LeapYear.php
namespace Calendar\Model;

class LeapYear
{
    public function isLeapYear($year = null)
    {
        if (null === $year) {
            $year = date('Y');
        }

        return 0 == $year % 400 || (0 == $year % 4 && 0 != $year % 100);
    }
}

Don't forget to update the example.com/src/app.php file accordingly:

$routes->add('leap_year', new Routing\Route('/is_leap_year/{year}', array(
    'year' => null,
    '_controller' => 'Calendar\Controller\LeapYearController::indexAction',
)));

To sum up, here is the new file layout:

example.com
├── composer.json
├── composer.lock
├── src
│   ├── app.php
│   └── Simplex
│       └── Framework.php
│   └── Calendar
│       └── Controller
│       │   └── LeapYearController.php
│       └── Model
│           └── LeapYear.php
├── vendor
│   └── autoload.php
└── web
    └── front.php

That's it! Our application has now four different layers and each of them has a well defined goal:

web/front.php: The front controller; the only exposed PHP code that makes the interface with the client (it gets the Request and sends the Response) and provides the boiler-plate code to initialize the framework and our application;
src/Simplex: The reusable framework code that abstracts the handling of incoming Requests (by the way, it makes your controllers/templates easily testable -- more about that later on);
src/Calendar: Our application specific code (the controllers and the model);
src/app.php: The application configuration/framework customization.

This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.