Dependency Injection with PHP

factory.php

<?php

class Configuration
{
    private $settings = [];

    public function __construct(array $settings)
    {
        $this->settings = $settings;
    }

    public function getDatabaseConnection()
    {
        return new DatabaseConnection($this->settings['host'], $this->settings['username'], $this->settings['password']);
    }
}

class DatabaseConnection
{
    private $host;
    private $username;
    private $password;

    public function __construct($host, $username, $password)
    {
        $this->host = $host;
        $this->username = $username;
        $this->password = $password;
    }

    public function host()
    {
        return $this->host;
    }

    public function username()
    {
        return $this->username;
    }

    public function password()
    {
        return $this->password;
    }
}

class Factory
{
    private $configuration;
    private $mysqli;

    public function __construct(Configuration $configuration)
    {
        $this->configuration = $configuration;
    }

    public function createCustomerRepository() :CustomerRepository
    {
        return new MysqlCustomerRepository($this->getMysqli());
    }

    public function createControllerLocator() :ControllerLocator
    {
        return new ControllerLocator($this);
    }

    public function createController() :Controller
    {
        return new Controller($this->createCustomerRepository());
    }

    private function getMysqli() :MysqliWrapper
    {
        if ($this->mysqli === null) {
            $this->mysqli = $this->createMysqli();
        }

        return $this->mysqli;
    }

    private function createMysqli()
    {
        $databaseConnection = $this->configuration->getDatabaseConnection();
        return new MysqliWrapper($databaseConnection->host(), $databaseConnection->username(), $databaseConnection->password());
    }
}

class MysqliWrapper
{
}

interface CustomerRepository
{
    public function add(Customer $customer);
    public function findById(CustomerId $id);
    public function commit();
}

class Customer
{
    public function promoteToVip()
    {
        var_dump('vip');
    }
}

class CustomerId
{
    private $id;

    public function __construct($id)
    {
        $this->id = $id;
    }

    public function equals(CustomerId $customerId)
    {
        return $this->id == $customerId->id;
    }

    public function __toString()
    {
        return (string)$this->id;
    }
}

class MySqlCustomerRepository implements CustomerRepository
{
    /**
     * @var MysqliWrapper
     */
    private $mysqli;

    public function __construct(MysqliWrapper $mysqli)
    {
        $this->mysqli = $mysqli;
    }

    public function add(Customer $customer)
    {
    }

    public function findById(CustomerId $id)
    {
        return new Customer;
    }

    public function commit()
    {
    }
}

class Controller
{
    /**
     * @var CustomerRepository
     */
    private $customerRepository;

    public function __construct(CustomerRepository $customerRepository)
    {
        $this->customerRepository = $customerRepository;
    }

    public function execute(HttpRequest $request)
    {
        $id = $request->get('customer_id');

        $customer = $this->customerRepository->findById(new CustomerId($id));
        $customer->promoteToVip();
        $this->customerRepository->commit();
    }
}

class HttpRequest
{
    public function get($parameter)
    {
        return 'the-parameter';
    }
}

class ControllerLocator
{
    private $factory;

    public function __construct(Factory $factory)
    {
        $this->factory = $factory;
    }

    public function locateControllerFor($url) :Controller
    {
        return $this->factory->createController();
    }
}

$configuration = new Configuration(parse_ini_file('configuration.ini'));
$factory = new Factory($configuration);

$locator = $factory->createControllerLocator();

$controller = $locator->locateControllerFor('the-url');
$controller->execute(new HttpRequest);