[Plugin: Woocommerce] charge x amount shipping on orders over y amount

I think I’ve done this now in code. By making a woocommerce shipping method plugin (using the shipping api).

It would be great to get some feedback from anyone who understands this kind of thing.

public function calculate_shipping($package = array()) {

                    global $woocommerce;
                    $cartTotal = $woocommerce->cart->get_cart_total();

                    $cartTotalNumber = preg_replace("/([^0-9\\.])/i", "", $cartTotal); // remove all chars except numbers and dot 

                    $minimumOrderTotalToQualifyForThisShippingRate = 100;

                    if ($cartTotalNumber <= $minimumOrderTotalToQualifyForThisShippingRate) // cart not qualify for this shipping rate if less than 100 total
                        return;

                    //echo "qualifys for this rate";
                    $rate = array(
                        'id' => $this->id,
                        'label' => $this->title,
                        'cost' => 5, /* shipping rate for the order */
                    );

                    // Register the rate
                    $this->add_rate($rate);
                }