Limit number of products used with a coupon (code included)

I had a requirement recently to limit the number of total products, and/or the qty of each product, that can be used with a particular coupon. They wanted to be able to set the limit in the coupon edit form.

Not sure how common the requirement would be but I thought I'd post the code back to the project in case someone else could use it.

/**
 * Adds option to uc_coupon edit form
 */
function storemod_form_uc_coupon_add_form_alter(&$form, &$form_state, $coupon) {
  $value = $form['#uc_coupon'];
  $form['order_max'] = array(
    '#type' => 'fieldset',
    '#title' => t('Maximum order limits'),
    '#collapsible' => TRUE,
    '#collapsed' => TRUE,
  );
  $form['order_max']['maximum_qty'] = array(
    '#type' => 'textfield',
    '#title' => t('Maximum order quantity'),
    '#default_value' => isset($value->data['maximum_qty']) ? $value->data['maximum_qty'] : '',
    '#size' => 5,
    '#description' => t('If set, this is the maximum number of products in the cart for the coupon to be accepted.'),
  );
  $form['order_max']['maximum_qty_error'] = array(
    '#type' => 'textarea',
    '#title' => t('Max order quantity error message'),
    '#default_value' => isset($value->data['maximum_qty_error']) ? $value->data['maximum_qty_error'] : '',
    '#size' => 5,
    '#description' => t('Enter the message you would like to display when the coupon fails this validation.'),
  );
  $form['order_max']['maximum_qty_per_product'] = array(
    '#type' => 'textfield',
    '#title' => t('Maximum quantity per product'),
    '#default_value' => isset($value->data['maximum_qty_per_product']) ? $value->data['maximum_qty_per_product'] : '',
    '#size' => 5,
    '#description' => t('If set, this is the maximum number of each product in the cart for the coupon to be accepted.'),
  );
  $form['order_max']['maximum_qty_per_product_error'] = array(
    '#type' => 'textarea',
    '#title' => t('Max per product error message'),
    '#default_value' => isset($value->data['maximum_qty_per_product_error']) ? $value->data['maximum_qty_per_product_error'] : '',
    '#size' => 5,
    '#description' => t('Enter the message you would like to display when the coupon fails this validation.'),
  );
}

/**
 * hook_uc_coupon_presave().
 */
function storemod_uc_coupon_presave(&$coupon, $edit) {
  // Set max qty
  if (isset($edit['maximum_qty'])) {
    $coupon->data['maximum_qty'] = $edit['maximum_qty'];
    $coupon->data['maximum_qty_error'] = $edit['maximum_qty_error'];
  }
  // Set max qty per product
  if (isset($edit['maximum_qty_per_product'])) {
    $coupon->data['maximum_qty_per_product'] = $edit['maximum_qty_per_product'];
    $coupon->data['maximum_qty_per_product_error'] = $edit['maximum_qty_per_product_error'];
  }
}

/**
 * Add extra validation to a coupon.
 */
function storemod_uc_coupon_validate(&$coupon, $order, $account) {
  $qty = 0;
  $max_per_product = isset($coupon->data['maximum_qty_per_product']) && $coupon->data['maximum_qty_per_product'] > 0 ? $coupon->data['maximum_qty_per_product'] : NULL;
  
  // Run through products, building qty and checking for max per product
  $product_count = count($order->products);
  if ($product_count > 0) {
    foreach ($order->products as $product) {
      $qty += $product->qty;
      if (isset($max_per_product) && $product->qty > $max_per_product) {
        return !empty($coupon->data['maximum_qty_per_product_error']) ? $coupon->data['maximum_qty_per_product_error'] : t('This coupon is not valid for more than :product_count products.', array(':product_count' => $coupon->data['maximum_qty_per_product']));
      }
    }
  }
  // Max qty check
  if (isset($coupon->data['maximum_qty']) && $coupon->data['maximum_qty'] > 0) {
    if ($qty > $coupon->data['maximum_qty']) {
      return !empty($coupon->data['maximum_qty_error']) ? $coupon->data['maximum_qty_error'] : t('This coupon is not valid for more than :product_count products.', array(':product_count' => $coupon->data['maximum_qty']));
    }
  }
}