How to load order data and set order as paid in PHP script that is loaded by AJAX?

[Kamil Szmit]

I am creating payment module for PrestaShop. I have a class in "controllers/front/payment.php":

class paymentModuleFrontController extends ModuleFrontController
{
    public function initContent()
    {
        $this->display_column_left = false;
        parent::initContent();
        $control=(int)Tools::getValue('control');
        $cart = $this->context->cart;
        if (!empty($control))
            $cart = new Cart($control);
        if ($cart->id_customer == 0 || $cart->id_address_delivery == 0 || $cart->id_address_invoice == 0 || !$this->module->active)
                Tools::redirect('index.php?controller=order&step=1');
        $customer = new Customer($cart->id_customer);
        if (!Validate::isLoadedObject($customer))
                Tools::redirect('index.php?controller=order&step=1');
        $address = new Address($cart->id_address_invoice);
        $params = null;
        $template = "payment_return";
        if ($cart->OrderExists() == true)
            Tools::redirect('index.php?controller=order-confirmation&id_cart='.$cart->id.'&id_module='.$this->module->id.'&id_order='.Order::getOrderByCartId($cart->id).'&key='.$customer->secure_key);
        elseif (Tools::getValue("status") == "OK")
            // (...)
        {
            // (...)
            $template = "payment";
            $form_url = "";
            $currency = Currency::getCurrency($cart->id_currency);
            if (Configuration::get('DP_TEST')==1) $form_url.="test_payment/";
            $params = array(
                    'id' => Configuration::get('DP_ID'),
                    'amount' => (float)$cart->getOrderTotal(true, Cart::BOTH),
                    'currency' => $currency["iso_code"],
                    'description' => Configuration::get('PS_SHOP_NAME'),
                    //(...)
                    'type' => 0,
                    // (...)
                    'control' => $cart->id,
                    'firstname' => $customer->firstname,
                    'lastname' => $customer->lastname,
                    'email' => $customer->email,
                    'street' => $address->address1,
                    'city' => $address->city,
                    'postcode'=> $address->postcode,
                    'api_version' => 'legacy'
            );
            $chk = $params['id'].$params['amount'].$params['currency'].$params['description'].$params['control'].Configuration::get('DP_PIN');
            $chk = rawurlencode($chk);
            if(Configuration::get('DP_CHK'))
                $params['chk']=hash('md5', $chk);
        }
        $this->context->smarty->assign(array(
            'params' => $params,
            'module_dir' => $this->module->getPathUri(),
            'form_url' => $form_url,
            ));
        $this->setTemplate($template.".tpl");
    }
}

I have created JavaScript script, which send AJAX request with "{$cart_id}", in template 'views/templates/front/payment.tpl''. The module creates a type of payment and runs JavaScript script after choosing this type of payment during making an order.

I would like to create PHP script that process AJAX request, loads information about the order and executes it. I created script "payment.php":

require_once(dirname(__FILE__).'../../../config/config.inc.php');
//require_once(dirname(__FILE__).'../../../init.php'); // I have problem with flushing output when I am including this script
require "processing.inc.php";
$myShop->paymentInitiation();

and "processing.inc.php":

//require ...
//$myShop = new ...
$myShop->user(function ($requestData, $cb)
{
	$cb($requestData->user);
}
)->products(function ($requestData, $cb)
{
	$cb(array(18, 30));
}
)->product(function ($requestData, $itemId, $cb)
{
	if ($itemId == 18) 
		   {
		$cb(array(
				          "item_id"=> "18",
// (...)
		));
	}
	else if ($itemId == 30)
		   {
		$cb(array(
				             "item_id"=>  "30",
// (...)
		));
	}
}
// (...)
)->productDelivery(function ($requestData, $items, $cb) 
{
	$cb(array(
		        "delivery_id"=> "",
// (...)
	));
})->currency(function ($requestData, $cb)
{
	$cb('PLN');
}
)->paymentTitle(function ($requestData, $items, $delivery, $cb) {
	$cb('Tytuł płatności');
}
// (...)
)->merchant(function ($requestData, $items, $delivery, $cb) {
	$cb(array("company" => array("name" => "Default", "NIP" => "", "REGON" => "", "KRS" => ""), "person" => array("first_name" => "Default", "last_name" => "", "PESEL" => ""), "address" => array("street" => "Default", "city" => "Default", "zip" => "00-000", "country" => ""), "fax" => "", "www" => "", "email" => ""));
}
)->documentParse(function ($requestData, $document, $cb) {
$cb(false);
}
)->onFinishedPayment(function ($items, $delivery_option, $document, $requestData) {

}
);

How to load order data in PHP script "processing.inc.php", which is run by AJAX, having "cart_id"? How to set order as paid in functions that is argument of my method "onFinishedPayment"? Could you help me?