PaymentExtension.php

<?php

namespace MyCompany\Bundle\PaymentBundle\DependencyInjection;

use Symfony\Component\DependencyInjection\Extension\Extension;
use Symfony\Component\DependencyInjection\ContainerBuilder;

class PaymentExtension extends Extension
{
    /**
     * Loads the services based on your application configuration.
     * The full configuration is as follows:
     *
     * payment.config:
     *   paypal:
     *     username: [email protected]
     *     token:    XXXXX-XXXXX-XXX-X
     *   authorize_net:
     *     config:
     *       username: [email protected]
     *       token:    XXXXXX-XXXXX-XXX-X
     *       version:  V2
     *
     * @param mixed $config
     */
    public function configLoad($config, ContainerBuilder $container)
    {
        if (!$container->hasDefinition('payment_gateway')) {
            $loader = new XmlFileLoader($container, __DIR__.'/../Resources/config');
            $loader->load('services.xml');
        }
        if (isset($config['paypal'])) {
            foreach (array('username', 'token') as $key) {
                if (isset($config['paypal'][$key]) {
                    $container->setParameter('payment_gateway.adapter.paypal.'.$key, $config['paypal'][$key]);
                }
            }
        }
        if (isset($config['authorize_net']['config'])) {
            $parameters = $container->getParameter('payment_gateway.adapter.authorize_net.config');
            foreach (array('username', 'token', 'version') as $key) {
                if (isset($config['authorize_net']['config'][$key])) {
                    $parameters[$key] = $config['authorize_net']['config'][$key];
                }
            }
            $container->setParameter('payment_gateway.adapter.authorize_net.config', $parameters);
        }
    }

    /**
     * @inheritDoc
     */
    public function getXsdValidationBasePath()
    {
        return __DIR__.'/../Resources/config/schema';
    }

    /**
     * @inheritDoc
     */
    public function getNamespace()
    {
        return 'http://avalanche123.com/schema/dic/payment';
    }

    /**
     * @inheritDoc
     */
    public function getAlias()
    {
        return 'payment';
    }
}

services.php

<?php

use Symfony\Component\DependencyInjection\Container;

$container = new Container();

$container->setParameter('payment_gateway.adapter.paypal.username', 'API_USERNAME');
$container->setParameter('payment_gateway.adapter.paypal.token', 'API_TOKEN');
$container->setParameter('payment_gateway.adapter.authorize_net.config', array(
    'username' => 'API_USERNAME',
    'token'    => 'API_TOKEN',
    'version'  => 'V2',
));

$paypal = new \MyCompany\Component\Payment\Gateway\Adapter\Paypal(
    $container->getParameter('payment_gateway.adapter.paypal.username'),
    $container->getParameter('payment_gateway.adapter.paypal.token')
);
$container->setService('payment_gateway.adapter.paypal', $paypal);

$authorizeNet = new \MyCompany\Component\Payment\Gateway\Adapter\AuthorizeNet(
    $container->getParameter('payment_gateway.adapter.authorize_net.config')
);
$container->setService('payment_gateway.adapter.authorize_net', $authorizeNet);

$gateway = new \MyCompany\Component\Payment\Gateway();
$gateway->setAdapter('paypal', $container->getService('payment_gateway.adapter.paypal'));
$gateway->setAdapter('authorize_net', $container->getService('payment_gateway.adapter.authorize_net'));
$container->setService('payment_gateway', $gateway);

services.xml

<?xml version="1.0" ?>

<container xmlns="http://www.symfony-project.org/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.symfony-project.org/schema/dic/services http://www.symfony-project.org/schema/dic/services/services-1.0.xsd">
    <parameters>
        <parameter key="payment_gateway.adapter.paypal.username">API_USERNAME</parameter>
        <parameter key="payment_gateway.adapter.paypal.token">API_TOKEN</parameter>
        <parameter key="payment_gateway.adapter.authorize_net.config" type="collection">
            <parameter key="username">API_USERNAME</parameter>
            <parameter key="token">API_TOKEN</parameter>
            <parameter key="version">V2</parameter>
        </parameter>
    </parameters>
    <services>
        <service id="payment_gateway.adapter.paypal" class="MyCompany\Component\Payment\Gateway\Adapter\Paypal">
            <argument>%payment_gateway.adapter.paypal.username%</argument>
            <argument>%payment_gateway.adapter.paypal.token%</argument>
        </service>
        <service id="payment_gateway.adapter.authorize_net" class="MyCompany\Component\Payment\Gateway\Adapter\AuthorizeNet">
            <argument>%payment_gateway.adapter.authorize_net.config%</argument>
        </service>
        <service id="payment_gateway" class="MyCompany\Component\Payment\Gateway">
            <call method="setAdapter">
                <argument>paypal</argument>
                <argument type="service" id="payment_gateway.adapter.paypal" />
            </call>
            <call method="setAdapter">
                <argument>authorize_net</argument>
                <argument type="service" id="payment_gateway.adapter.authorize_net" />
            </call>
        </service>
    </services>
</container>