uc_free_order.module

<?php

/**
 * @file
 * Adds a payment method to handle free orders.
 */

/**
 * Implementation of hook_form_FORM_ID_alter().
 * for the uc_cart_checkout_form
 * In checkout determine whether the free order is available for use.
 */
function uc_free_order_form_uc_cart_checkout_form_alter(&$form, &$form_state, $form_id) {
  $order = $form['panes']['payment']['line_items']['#order'];
  $subtotal = $order->order_total;

  // remove the free order payment method when the total is higher than 0
  if ($subtotal >= 0.01) {
    unset($form['panes']['payment']['payment_method']['#options']['free_order']);
    return;
  }
  // copy the existing payment method for free order
  $free_order = $form['panes']['payment']['payment_method']['#options']['free_order'];

  // rewrite the list of options to only include the free order
  $form['panes']['payment']['payment_method']['#options'] = array('free_order' => $free_order);
  // make the form automatically select the free order without need for user input
  $form['panes']['payment']['payment_method']['#default_value'] = 'free_order';
  $form['panes']['payment']['payment_method']['#disabled'] = 'TRUE';
  // delete any details from old default payment like credit card options
  unset($form['panes']['payment']['details']);
}

/**
 * Implementation of hook_form_FORM_ID_alter().
 * for the uc_cart_checkout_review_form
 * In Check out at the review Step more validation for the free order payment method 
 */
function uc_free_order_form_uc_cart_checkout_review_form_alter(&$form, &$form_state, $form_id) {
  $order = uc_order_load($_SESSION['cart_order']);

  // only deal with cases where the payment method was set to free
  if ($order->payment_method != 'free_order') {
    return;
  }

  // validation for the amount
  if ($order->order_total >= 0.01) {
    drupal_set_message(t('We cannot process your order without payment.'), 'error');
    drupal_goto('cart/checkout');
  }
}

/**
 * Implementation of hook_uc_payment_method().
 */
function uc_free_order_uc_payment_method() {
  $zero = array('!zero' => uc_currency_format(0));
  $methods['free_order'] = array(
    'name' => t('Free order'),
    'title' => t('Free order - Payment not required.'),
    'desc' => t('Allow customers with !zero order totals to checkout without paying.', $zero),
    'callback' => 'uc_payment_method_free_order',
    'checkout' => TRUE,
    'no_gateway' => TRUE,
    'weight' => 0,
  );

  return $methods;
}

/**
 * Will show the user a message when the payment method is select.
 */
function uc_payment_method_free_order($op, &$order) {
  if ($op == 'cart-details') {
    $details = array(
      'uc_free_order_cart_details' => array(
        '#markup' => t('Continue with checkout to complete your free order.'),
      ),
    );
    return $details;
  }
}

/**
 * Implementation of hook_uc_order().
 * Will allow for a payment to be entered on this order that will allow
 * other modules to trigger events for conditional actions
 */
function uc_free_order_uc_order($op, &$order) {
  // During checkout, if the free order payment method is used, log a $0.00
  // payment for the order to trigger any necessary predicates.
  if ($op == 'submit' && $order->payment_method == 'free_order') {
    uc_payment_enter($order->order_id, 'free_order', 0, 0, NULL, t('Checkout completed for a free order.'));
  }
}