commerce_coupon_custom_form.php

/**
 * Coupon Form
 *
 * Generate a simple coupon form that accepts a coupon code or allows the user
 * to remove that coupon code.
 */
function MYMODULE_discounts_coupon_form($form, &$form_state) {
  global $user;

  $order = commerce_cart_order_load($user->uid);
  $order_wrapper = entity_metadata_wrapper('commerce_order', $order);
  $max_coupons_reached = _MYMODULE_discounts_max_coupons_reached($order);

  $form_state['order'] = $order;

  if (!$max_coupons_reached) {
    // Coupon Code Field
    $form['coupon_code'] = array(
      '#type' => 'textfield',
      '#title' => t('Coupon code'),
      '#title_display' => 'invisible',
      '#attributes' => array(
        'placeholder' => t('Have a discount code?'),
      ),
    );
    // Apply Coupon Code Button
    $form['coupon_add'] = array(
      '#type' => 'submit',
      '#value' => t('Apply Code'),
      '#name' => 'coupon_add',
    );
  }

  // List of applies coupons along with option to remove.
  if (isset($order_wrapper->commerce_coupons)) {
    $form['applied_coupons'] = array(
      '#prefix' => '<div class="applied-coupons">',
      '#suffix' => '</div>',
    );

    foreach ($order_wrapper->commerce_coupons as $coupon_wrapper) {
      $coupon_id = $coupon_wrapper->coupon_id->value();
      $coupon_code = $coupon_wrapper->code->value();

      $options = array(
        'query' => drupal_get_destination() + array('token' => drupal_get_token('commerce_coupon_remove_checkout:' . $coupon_id . ':' . $order->order_id)),
        'attributes' => array(
          'class' => array('btn', 'secondary'),
        ),
      );

      $form['applied_coupons'][$coupon_id] = array(
        '#prefix' => '<div class="applied-coupon">',
        'message' => array(
          '#markup' => t('Coupon @coupon_code has been applied!', array('@coupon_code' => $coupon_code)),
        ),
        'coupon_remove' => array(
          '#markup' => l(t('Remove'), 'commerce/coupons/order/remove/' . $coupon_id . '/' . $order->order_id, $options),
        ),
        '#suffix' => '</div>',
      );

    }
  }

  return $form;
}

/**
 * Validate handler for MYMODULE_discounts_coupon_form().
 *
 * @see commerce_coupon_handler_area_cart_form_validate()
 */
function MYMODULE_discounts_coupon_form_validate($form, &$form_state) {
  $coupon_code  = $form_state['values']['coupon_code'];
  $order = $form_state['order'];

  $error = '';

  // No code provided
  if (empty($coupon_code)) {
    $error = t('Please enter a coupon code.');
  }
  else {
    // Check if the coupon code has already been applied.
    $coupon = commerce_coupon_load_by_code($coupon_code);

    if (empty($coupon)) {
      $error = t('Please enter a valid coupon code.');
    }
    else {
      // The same coupon cannot be added twice.
      $order_wrapper = entity_metadata_wrapper('commerce_order', $order);
      foreach ($order_wrapper->commerce_coupons as $order_coupon_wrapper) {
        if ($order_coupon_wrapper->coupon_id->value() == $coupon->coupon_id) {
          $error = t('The coupon you have entered has already been applied to your order');
        }
      }
    }
  }

  // If a coupon was invalidated during the cart refresh (e.g. if its
  // discounts failed their conditions), an error message will have been
  // set.
  if (empty($error)) {
    $error = &drupal_static('commerce_coupon_error_' . strtolower($coupon_code));
  }
  // If we have errors set the form error.
  if (!empty($error)) {
    form_set_error('coupon_code', $error);
  }
}

/**
 * Submit handler for MYMODULE_discounts_coupon_form().
 *
 * @see commerce_coupon_handler_area_cart_form_submit()
 */
function MYMODULE_discounts_coupon_form_submit($form, &$form_state) {
  $coupon_code  = $form_state['values']['coupon_code'];
  $order = $form_state['order'];

  $error = '';

  // Redeem the coupon.
  $coupon = commerce_coupon_redeem_coupon_code($coupon_code, $order, $error);
  $order = commerce_order_load($order->order_id);

  // Error found during redeem.
  if (!empty($error)) {
    watchdog('MYMODULE_discounts', 'An error occurred redeeming a coupon: @error', array('@error' => $error), WATCHDOG_ERROR);
    drupal_set_message('Unable to redeem coupon.');
    commerce_coupon_remove_coupon_from_order($order, $coupon);
  }

  if ($coupon) {
    // Allow modules/rules to act when a coupon has been successfully added
    // to the cart.
    rules_invoke_all('commerce_coupon_applied_to_cart', $coupon, $order);
  }
}