Drupal : text => link formatter

gistfile1.php

<?php

/**
 * Implements hook_field_formatter_info().
 */
function mymodule_field_formatter_info() {
  return array(
    'mymodule_link' => array(
      'label' => 'Link for ingenie site/email',
      'field types' => array('text'),
      'settings' => array(
        'link_type' => 'http'
      ),
    ),  
  );
}

/**
 * Implements hook_field_formatter_settings_form().
 * @return array
 */
function mymodule_field_formatter_settings_form($field, $instance, $view_mode, $form, &$form_state) {
  $display = $instance['display'][$view_mode];
  $settings = $display['settings'];

  $element = array();
  if ($display['type'] == 'mymodule_link') {
    $element['link_type'] = array(
      '#title' => t("Type of link"),
      '#type' => 'radios',
      '#options' => array(
        'http' => "http://",
        'mailto' => "mailto:",
      ),
      '#default_value' => ($settings['link_type']) ? $settings['link_type'] : 'http',
    );
  }

  return $element;
}


/**
 * Implements hook_field_formatter_settings_summary().
 */
function mymodule_field_formatter_settings_summary($field, $instance, $view_mode) {
  $display = $instance['display'][$view_mode];
  $settings = $display['settings'];

  $summary = array();
  if ($display['type'] == 'mymodule_link') {
    $summary[] = ($settings['link_type'] == 'http') ? "http://" : "mailto:";
  }

  return implode('<br />', $summary);
}



/**
 * Implements hook_field_formatter_view().
 */
function mymodule_field_formatter_view($entity_type, $entity, $field, $instance, $langcode, $items, $display) {
  $element = array();
  $settings = $display['settings'];

  switch ($display['type']) {
    case 'mymodule_link':
      foreach ($items as $delta => $item) {
        $url = $item['value'];

        if(!empty($url)) {

          switch($settings['link_type']) {
            case 'http':
              // Force url to begin with http
              if (strpos($url, 'http://') !== 0 && strpos($url, 'https://') !== 0) {
                $url = 'http://' . $url;
              }
              break;
            case 'mailto':
              $url = 'mailto:'.$url;
              break;
          }

          // Return link
          $element[$delta] = array(
            '#theme' => 'link',
            '#text' => check_plain($item['value']),
            '#path' => $url,
            '#options' => array(
              'html' => FALSE,
              'absolute' => TRUE,
              'external' => TRUE,
              'attributes' => array(
                'target' => '_blank',
                'title' => entity_label($entity_type, $entity)
              )
            )
          );

        } // if(!empty($url)) {
      }
      break;
  }

  return $element;
}