Drupal Commerce: учим rules работать с полем Price у заказа

function ИМЯМОДУЛЯ_rules_action_info() {
  $actions = array();

  // Prepare an array of arithmetical actions for altering prices.
  $action_types = array(
    'frz_tweaks_commerce_order_price_multiply' => array(
      'label' => t('Multiply the order price by some amount'),
      'amount description' => t('Specify the numeric amount by which to multiply the price.'),
    ),
    'frz_tweaks_commerce_order_price_amount' => array(
      'label' => t('Set the order price to a specific amount'),
      'amount description' => t('Specify the numeric amount to set the price to.'),
    ),
  );

  // Define the action using a common set of parameters.
  foreach ($action_types as $key => $value) {
    $actions[$key] = array(
      'label' => $value['label'],
      'parameter' => array(
        'commerce_order' => array(
          'type' => 'commerce_order',
          'label' => t('Order'),
        ),
        'amount' => array(
          'type' => 'decimal',
          'label' => t('Amount'),
          'description' => $value['amount description'],
        ),
        'component_name' => array(
          'type' => 'text',
          'label' => t('Price component type'),
          'description' => t('Price components track changes to prices made during the price calculation process, and they are carried over from the unit price to the total price of a line item. When an order total is calculated, it combines all the components of every line item on the order. When the unit price is altered by this action, the selected type of price component will be added to its data array and reflected in the order total display when it is formatted with components showing. Defaults to base price, which displays as the order Subtotal.'),
          'options list' => 'commerce_price_component_titles',
          'default value' => 'base_price',
        ),
        'round_mode' => array(
          'type' => 'integer',
          'label' => t('Price rounding mode'),
          'description' => t('Round the resulting price amount after performing this operation.'),
          'options list' => 'commerce_round_mode_options_list',
          'default value' => COMMERCE_ROUND_HALF_UP,
        ),
      ),
      'group' => t('Commerce Order'),
    );
  }
  return $actions;
}

/*
 * Это действие умножает цену на какое-то ваше значение
 *
 */
function frz_tweaks_commerce_order_price_multiply($commerce_order, $amount, $component_name, $round_mode) {
  if (is_numeric($amount)) {
    $wrapper = entity_metadata_wrapper('commerce_order', $commerce_order);
    $unit_price = $wrapper->commerce_order_total->value();

    // Calculate the updated amount and create a price array representing the
    // difference between it and the current amount.

    $current_amount = $unit_price['amount'];
    $updated_amount = commerce_round($round_mode, $current_amount * $amount);

    $difference = array(
      'amount' => $updated_amount - $current_amount,
      'currency_code' => $unit_price['currency_code'],
      'data' => array(),
    );

    // Set the amount of the unit price and add the difference as a component.
    $wrapper->commerce_order_total->amount = $updated_amount;

    $wrapper->commerce_order_total->data = commerce_price_component_add(
      $wrapper->commerce_order_total->value(),
      $component_name,
      $difference,
      TRUE
    );
  }
}

/*
 * А это действие устанавливает цену в какое-то ваше значение.
 * Т.е. в правилах вы сможете сначала вычислить новое значение для своей цены по Вашим формулам,
 * а затем записать его в поле
 */
function frz_tweaks_commerce_order_price_amount($commerce_order, $amount, $component_name, $round_mode) {
  if (is_numeric($amount)) {
    $wrapper = entity_metadata_wrapper('commerce_order', $commerce_order);
    $unit_price = $wrapper->commerce_order_total->value();

    // Calculate the updated amount and create a price array representing the
    // difference between it and the current amount.
    $current_amount = $unit_price['amount'];
    $updated_amount = commerce_round($round_mode, $amount);

    $difference = array(
      'amount' => $updated_amount - $current_amount,
      'currency_code' => $unit_price['currency_code'],
      'data' => array(),
    );

    // Set the amount of the unit price and add the difference as a component.
    $wrapper->commerce_order_total->amount = $updated_amount;

    $wrapper->commerce_order_total->data = commerce_price_component_add(
      $wrapper->commerce_order_total->value(),
      $component_name,
      $difference,
      TRUE
    );
  }
}