Magento custom sessions JSONP API.

custom-sessions-api.php

<?php

/**
 * Magento custom sessions API
 * 
 * @see http://fishpig.co.uk/magento/tutorials/run-magento-code-externally/
 */
require_once 'app/Mage.php';

umask( 0 );

Mage::app();

// @see http://magento.stackexchange.com/questions/8814/how-to-get-all-items-in-cart-currently
$cart_items = Mage::getSingleton( 'checkout/cart' )->getItems();

// @see http://stackoverflow.com/questions/416553/current-user-in-magento
$customer = Mage::getSingleton( 'customer/session' );

// JSON
$data = new stdClass();
$data->cart_count = count( $cart_items );
$data->email      = $customer->getEmail();

// Response
// @see http://stackoverflow.com/questions/6809053/simple-jquery-php-and-jsonp-example
// @see http://stackoverflow.com/questions/1678214/javascript-how-do-i-create-jsonp
if ( filter_has_var( INPUT_GET, 'callback' ) ) {
	header( 'Content-Type: application/json' );

	$callback = filter_input( INPUT_GET, 'callback', FILTER_SANITIZE_STRING );
	
	echo $callback, '(', json_encode( $data ), ');';
} else {
	echo json_encode( $data );
}

IndexController.php

<?php

class Mct_Wordpress_IndexController extends Mage_Core_Controller_Front_Action {

    public function indexAction(){
        // JSON
        $data = new stdClass();

        // CART
        /** @var Mage_Checkout_Model_Cart $cart */
        $cart = Mage::getSingleton('checkout/cart');
        $data->cart         = new stdClass();
        $data->cart->qty    = $cart->getSummaryQty();
        $data->cart->url    = Mage::helper('checkout/cart')->getCartUrl();
        $data->cart->price  = Mage::helper('checkout')->formatPrice($this->_getCartSubtotal($cart));

        // CUSTOMER
        /** @var Mage_Customer_Model_Session $session */
        $session = Mage::getSingleton('customer/session');
        $customer = $session->getCustomer();
        $data->customer     = new stdClass();
        if($session->isLoggedIn()) {
            $data->customer->loggedin   = $session->isLoggedIn();
            $data->customer->id         = $customer->getId();
            $data->customer->email      = $customer->getEmail();
            $data->customer->name       = $customer->getName();
        } else {
            $data->customer->loggedin   = $session->isLoggedIn();
        }

        // Response
        $this->getResponse()->setHeader('Content-type', 'application/json');
        if (filter_has_var(INPUT_GET, 'callback')) {
            $callback = filter_input(INPUT_GET, 'callback', FILTER_SANITIZE_STRING);
            echo $callback, '(', json_encode($data), ');';
        } else {
            echo json_encode($data);
        }
    }

    protected function _getCartSubtotal($cart) {
        $skipTax = true;
        $subtotal = 0;
        $totals = $cart->getQuote()->getTotals();
        /** @var Mage_Tax_Model_Config $config */
        $config = Mage::getSingleton('tax/config');
        if (isset($totals['subtotal'])) {
            if ($config->displayCartSubtotalBoth()) {
                if ($skipTax) {
                    $subtotal = $totals['subtotal']->getValueExclTax();
                } else {
                    $subtotal = $totals['subtotal']->getValueInclTax();
                }
            } elseif($config->displayCartSubtotalInclTax()) {
                $subtotal = $totals['subtotal']->getValueInclTax();
            } else {
                $subtotal = $totals['subtotal']->getValue();
                if (!$skipTax && isset($totals['tax'])) {
                    $subtotal+= $totals['tax']->getValue();
                }
            }
        }

        return $subtotal;
    }

}