function add_product_to_cart() {
    if (!is_admin()) {
        global $woocommerce;
        $items = $woocommerce->cart->get_cart();
        $live_product_ids = array(10305, 10302, 10300, 10303, 10301);
        $live_upsell_id = 10311;
        $suff_found = false;
        $upsell_found = false;
        $coupon_code = 'nutreincesufficiencyquiznakedcalories';
        //check if nut suff is already in cart
        if (sizeof($items) > 0) {
            foreach ($items as $cart_item_key => $values) {
                $_product = $values['data'];
                if (in_array($_product->id, $live_product_ids))
                    $suff_found = true;
                if ($_product->id == $live_upsell_id)
                    $upsell_found = true;
            }
            // if upsell product not found, add it
            if ($suff_found) {
                if (!$upsell_found)
                    $woocommerce->cart->add_to_cart($live_upsell_id);
                if (!$woocommerce->cart->has_discount($coupon_code))
                    $woocommerce->cart->add_discount($coupon_code);
            }
        }
    }
}
add_action('wp_loaded', 'add_product_to_cart');