create country drop down on cart page with same functionality as on onestepcheckout page magento 1.9

Question

On onestepcheckout page, in billing section we have a country field select box, on selecting country from drop-down, ajax request is send and the selected country is set as billing address's country. I want to create a country drop down with same functionality on cart page. I have created the country select box using the following code

  <?php $_countries = Mage::getModel('directory/country')
                                              ->getResourceCollection()
                                              ->loadByStore()
                                              ->toOptionArray(true);?>

and using foreach loop to show the options in a select box. Now I have problem with the functionality. On onestepcheckout page when the country is selected, an ajax request is send and the following country gets selected. I am trying to copy this process but could not succeed.Here is my ajax code in cart.phtml file

jQuery('#country').change(function(){
var countryName = (jQuery(this).val());
jQuery.ajax({
    type: 'POST',
    url: "<?php echo $this->getUrl('checkout/cart/estimatePost')?>",
    data: {'country_id' : countryName},
    success: function(data){
        alert(data);
    }

}); });

On onestepcheckout page ajax request hits the following url

  url: "<?php echo $this->getUrl('onestepcheckout/ajax/save_billing')?>"

I am trying to copy this function on cart page but could not understand how to proceed. Please any one have any idea on how to proceed.

save_billingAction() in Ajaxcontroller.php has lot of functionalities which I could not understand. I just want to save the country so that when the page is reloaded that country is set as billing address's country. Any one could help me how to proceed

Answer 1

For showing select box the below code is used

<?php echo Mage::getBlockSingleton('directory/data')->getCountryHtmlSelect() ?>

It shows country dropdown. Then on selecting the country the ajax request is

jQuery('#country').change(function(){
var countryId = (jQuery(this).val());
jQuery.ajax({
    type: 'POST',
    url: "<?php echo $this->getUrl('checkout/cart/custom_update_billing')?>",
    data: {'country_id': countryId},
    success: function(data){
    }
});

});

Now the function custom_update_billing that set country as billing address's default country

public function custom_update_billingAction()
{
    $country_id = $this->getRequest()->getParam('country_id');
    $address = $this->_getQuote()->getBillingAddress()->setCountryId($country_id);
    $this->_getQuote()->save();
}