gistfile1.php

<?php
/**
 * Render promo
 */
function promo_preprocess_node(&$vars, $hook) {
  $vars['custom_share_title'] = '';
  $vars['custom_promo'] ='';
  $class = '';
  $style = '';
  $node = $vars['node'];

  $wrapper = entity_metadata_wrapper('node', $vars['node']);
  if ($node->type == 'promo') {
    if(!empty($node->field_link)) {
      $vars['classes_array'][] = 'has-link';
    }
    $vars['classes_array'][] = 'node-' . $node->nid;
    $style = $wrapper->field_promo_style->value()->name;
    $class = strtolower(str_replace(' ', '-', $style));
    $vars['classes_array'][] = $class;
  }
}
?>