Drupal Commerce instant buy link

instant_buy.module

<?php

/**
 * @file
 *
 * This super small module adds a page that creates an order with a product
 * and redirects to the payment platform.
 *
 * It can be used as sample or base for simple commerce workflows. It
 * doesn't need to be a menu item, can be done in a form submit callback.
 *
 * If you have different payment methods, you can change the checkout_payment
 * status to checkout_review so the user can select the payment method or add
 * some logic to select each payment method.
 *
 * We use it to have buttons with each payment method that we can put in a
 * block in different pages.
 */

/**
 * Implements hook_menu().
 */
function instant_buy_menu() {
  $menu['product/%'] = array(
    'title' => 'Instant buy',
    'page callback' => 'instant_buy_create_order',
    'page arguments' => array(1),
    'access arguments' => array('access checkout'),
    'type' => MENU_CALLBACK,
  );
  return $menu;
}

/**
 * Page callback that creates an order and redirects to the payment redirect page.
 */
function instant_buy_create_order($sku) {
  global $user;
  $product = commerce_product_load_by_sku($sku);
  $order = ($user->uid) ? commerce_order_new($user->uid, 'checkout_checkout') : commerce_cart_order_new();
  // Save to get the Order ID.
  commerce_order_save($order);

  $line_item = commerce_product_line_item_new($product, 1, $order->order_id);
  commerce_line_item_save($line_item);
  $order_wrapper = entity_metadata_wrapper('commerce_order', $order);
  $order_wrapper->commerce_line_items[] = $line_item;

  // Select here the payment method. Usually something like:
  // [module_name]|commerce_payment_[module_name]
  $order->data['payment_method'] = 'commerce_sermepa|commerce_payment_commerce_sermepa';
  commerce_order_save($order);

  // Set status to order checkout to go to the payment platform redirect.
  commerce_order_status_update($order, 'checkout_payment');

  drupal_goto('checkout/' . $order->order_id);
}