//prevent the logged-in user to purchase twice the same product
    add_filter ( 'woocommerce_add_to_cart_validation', '__woocommerce_add_to_cart_validation', 99, 3 );
    function __woocommerce_add_to_cart_validation( $status, $product_id, $quantity )
        {
            if ( is_user_logged_in() ===    FALSE )
                return FALSE;

            //rtrieve all previous orders for the current user
            $args = array(
                            'customer_id'   => get_current_user_id(),
                            'limit'         => -1, // to retrieve _all_ orders by this user
                        );
            $orders = wc_get_orders($args);

            $found_product  =   FALSE;
            $check_for_product_ids  =   array( 1, 10, 194 );

            foreach ( $orders   as $order )
                {
                    foreach ( $order->get_items() as $item_id => $item )
                        {
                            if ( in_array ( $item->get_product_id(), $check_for_product_ids )   &&  $product_id ==  $item->get_product_id() )
                                {
                                    $found_product  =   TRUE;
                                    break 2;
                                }
                        }
                }

            if ( ! $found_product )
                return $status;

            //wc_add_to_cart_message( array( $product_id => $quantity ), true );
            wc_add_notice ('Product already purchased', 'error');

            return FALSE;
        }