Magento2 – How to Add Radio Option in Magento 2

I was not able to get the selected custom option on event checkout_cart_product_add_after

however, i was successful in getting the values using checkout_cart_save_before event.

For those who might need it in future. The code for retrieving the custom options is as below:

public function execute(\Magento\Framework\Event\Observer $observer) {  
    /* Fetches data of items available in cart. */
    $cart = $observer->getEvent()->getData('cart');
    $cartItems = $cart->getItems();

    foreach($cartItems as $item){
        //here you do what you want with the product.
        $_customOptions = $item->getProduct()->getTypeInstance(true)->getOrderOptions($item->getProduct()); 
        if(array_key_exists('options', $_customOptions)){
            //print_r($_customOptions);
            foreach($_customOptions['options'] as $option){
                print_r($option);
            }
        }
    }
}

Hope it helps. I am accepting this answer as this is the closest I could get to. I will be happy to accept the solution if someone posts it.

Here is an easy clean way to achieve this without overriding Magento core. Create NameSpace\ModuleName\etc\frontend\di.xml file with current configuration:

<!-- Adding Sort by Bestsellers functionality -->
<type name="Magento\Catalog\Block\Product\ProductList\Toolbar">
    <plugin name="before_set_collection" type="NameSpace\ModuleName\Plugin\Catalog\Product\Sorting\Bestsellers" />
</type>
<type name="Magento\Catalog\Model\Config">
    <plugin name="after_get_available_orders" type="NameSpace\ModuleName\Plugin\Catalog\Product\Sorting\Bestsellers" />
</type>

Then create plugin class NameSpace\ModuleName\Plugin\Catalog\Product\Sorting\Bestsellers.php:

namespace NameSpace\ModuleName\Plugin\Catalog\Product\Sorting;

use Magento\Catalog\Block\Product\ProductList\Toolbar;
use Magento\Catalog\Model\Config;
use Magento\Framework\Data\Collection;

class Bestsellers 
{
/**
* Bestsellers sorting attribute
*/
const BESTSELLERS_SORT_BY = 'bestsellers';

/**
 * @param Config $subject
 * @param $result
 * @return array
 */
public function afterGetAttributeUsedForSortByArray(Config $subject, $result)
{
    return array_merge($result, [self::BESTSELLERS_SORT_BY => __('Bestsellers')]);
}

/**
 * @param Toolbar $subject
 * @param Collection $collection
 */
public function beforeSetCollection(Toolbar $subject, Collection $collection)
{
    if ($subject->getCurrentOrder() == self::BESTSELLERS_SORT_BY) {
        $collection->getSelect()->joinLeft(
            'sales_order_item',
            'e.entity_id = sales_order_item.product_id',
            array('qty_ordered'=>'SUM(sales_order_item.qty_ordered)'))
            ->group('e.entity_id')
            ->order('qty_ordered '.$subject->getCurrentDirection());
    }
}
}

And enjoy =)