Create an commerce order programmatically

The following steps to describe about to create an commerce order programmatically in Drupal

global $user;
$product_id = 100;
$quantity = 1;

$order = commerce_order_new($user->uid, 'cart');
commerce_order_save($order);
$line_item = commerce_product_line_item_new($product, $quantity, $order->order_id);
commerce_line_item_save($line_item);
$order_wrapper = entity_metadata_wrapper('commerce_order', $order);
$order_wrapper->commerce_line_items[] = $line_item;
commerce_order_save($order);