Change quote_id(Cart) after logout in Magento CE 1.9

Question

Brief Introduction: I am trying to make custom rest api's for magento. To add a product in customer's cart, I followed following steps:

1) Log In customer(code):

public function loginUser( $email, $password){
         require_once ("app/Mage.php");
         umask(0);
         ob_start();
         session_start();
         Mage::app('default');
         Mage::getSingleton("core/session", array("name" => "frontend"));

      //   $websiteId = Mage::app()->getWebsite()->getId();
         $store = Mage::app()->getStore();
         $customer = Mage::getModel("customer/customer");
         $customer = Mage::getModel('customer/customer')->setWebsiteId(1);
         $customer->setStore($store);
         try {
             $customer->loadByEmail($email);
             $session = Mage::getSingleton('customer/session')->setCustomerAsLoggedIn($customer);
             $session->login($email, $password);
          }catch(Exception $e){

          }
    } 

2) To add product to customer's cart(code):

Mage::init('default');
$id = '1'; 
$qty = '1';
$_product = Mage::getModel('catalog/product')->load($id);
$cart = Mage::getModel('checkout/cart');
$cart->init();
$cart->addProduct($_product, array('qty' => $qty));
$cart->save();
Mage::getSingleton('checkout/session')->setCartWasUpdated(true);

3) Logout Customer:

Mage::getSingleton("customer/session")->logout();

Problem: After Login I added a product into cart, it successfully added in corresponding customer's cart after that I logged out and then added a product to cart as a guest but the product was added in same(previous) QUOTE_ID and then again logged in from different account(not previous customer) and again I added a product and it again added in same QUOTE_ID. The Resultant carts of both user's are like this:

customer1: 3 products
customer2: 3 products

But they should be like this:

customer1: 1 product
customer2: 2 product

To Remove quote id, in logout I add reserveOrderId to null(generally it is used after checkout) but no solution:

Mage::getSingleton('checkout/session')->getQuote()->setReservedOrderId(null);

For more Information:

• customer_id = 1 and quote_id = 5 returns after 1st add(Got customer ID from session)

• customer_id = null and quote_id = 5 returns after 2nd add(after logout)

• customer_id = 2 and quote_id = 5 returs after 3rd add(logged in from different account)

Answer 1

To reset the quote either of the following should work.

Mage::getSingleton('checkout/session')->clear();

Mage::getSingleton('checkout/session')->setQuoteId(null);

QuoteId is checked if not empty when called on. If empty (null) a new one is generated which would return a new quote.