class RssFields

class RssFields extends RowPluginBase {

  /**
   * Does the row plugin support to add fields to it's output.
   *
   * @var bool
   */
  protected $usesFields = TRUE;
  protected function defineOptions() {
    $options = parent::defineOptions();
    $options['title_field'] = array(
      'default' => '',
    );
    $options['link_field'] = array(
      'default' => '',
    );
    $options['description_field'] = array(
      'default' => '',
    );
    $options['creator_field'] = array(
      'default' => '',
    );
    $options['date_field'] = array(
      'default' => '',
    );
    $options['guid_field_options']['guid_field'] = array(
      'default' => '',
    );
    $options['guid_field_options']['guid_field_is_permalink'] = array(
      'default' => TRUE,
      'bool' => TRUE,
    );
    return $options;
  }
  public function buildOptionsForm(&$form, &$form_state) {
    parent::buildOptionsForm($form, $form_state);
    $initial_labels = array(
      '' => t('- None -'),
    );
    $view_fields_labels = $this->displayHandler
      ->getFieldLabels();
    $view_fields_labels = array_merge($initial_labels, $view_fields_labels);
    $form['title_field'] = array(
      '#type' => 'select',
      '#title' => t('Title field'),
      '#description' => t('The field that is going to be used as the RSS item title for each row.'),
      '#options' => $view_fields_labels,
      '#default_value' => $this->options['title_field'],
      '#required' => TRUE,
    );
    $form['link_field'] = array(
      '#type' => 'select',
      '#title' => t('Link field'),
      '#description' => t('The field that is going to be used as the RSS item link for each row. This must be a drupal relative path.'),
      '#options' => $view_fields_labels,
      '#default_value' => $this->options['link_field'],
      '#required' => TRUE,
    );
    $form['description_field'] = array(
      '#type' => 'select',
      '#title' => t('Description field'),
      '#description' => t('The field that is going to be used as the RSS item description for each row.'),
      '#options' => $view_fields_labels,
      '#default_value' => $this->options['description_field'],
      '#required' => TRUE,
    );
    $form['creator_field'] = array(
      '#type' => 'select',
      '#title' => t('Creator field'),
      '#description' => t('The field that is going to be used as the RSS item creator for each row.'),
      '#options' => $view_fields_labels,
      '#default_value' => $this->options['creator_field'],
      '#required' => TRUE,
    );
    $form['date_field'] = array(
      '#type' => 'select',
      '#title' => t('Publication date field'),
      '#description' => t('The field that is going to be used as the RSS item pubDate for each row. It needs to be in RFC 2822 format.'),
      '#options' => $view_fields_labels,
      '#default_value' => $this->options['date_field'],
      '#required' => TRUE,
    );
    $form['guid_field_options'] = array(
      '#type' => 'details',
      '#title' => t('GUID settings'),
      '#collapsible' => FALSE,
      '#collapsed' => FALSE,
    );
    $form['guid_field_options']['guid_field'] = array(
      '#type' => 'select',
      '#title' => t('GUID field'),
      '#description' => t('The globally unique identifier of the RSS item.'),
      '#options' => $view_fields_labels,
      '#default_value' => $this->options['guid_field_options']['guid_field'],
      '#required' => TRUE,
    );
    $form['guid_field_options']['guid_field_is_permalink'] = array(
      '#type' => 'checkbox',
      '#title' => t('GUID is permalink'),
      '#description' => t('The RSS item GUID is a permalink.'),
      '#default_value' => $this->options['guid_field_options']['guid_field_is_permalink'],
    );
  }
  public function validate() {
    $errors = parent::validate();
    $required_options = array(
      'title_field',
      'link_field',
      'description_field',
      'creator_field',
      'date_field',
    );
    foreach ($required_options as $required_option) {
      if (empty($this->options[$required_option])) {
        $errors[] = t('Row style plugin requires specifying which views fields to use for RSS item.');
        break;
      }
    }

    // Once more for guid.
    if (empty($this->options['guid_field_options']['guid_field'])) {
      $errors[] = t('Row style plugin requires specifying which views fields to use for RSS item.');
    }
    return $errors;
  }
  function render($row) {
    static $row_index;
    if (!isset($row_index)) {
      $row_index = 0;
    }
    if (function_exists('rdf_get_namespaces')) {

      // Merge RDF namespaces in the XML namespaces in case they are used
      // further in the RSS content.
      $xml_rdf_namespaces = array();
      foreach (rdf_get_namespaces() as $prefix => $uri) {
        $xml_rdf_namespaces['xmlns:' . $prefix] = $uri;
      }
      $this->view->style_plugin->namespaces += $xml_rdf_namespaces;
    }

    // Create the RSS item object.
    $item = new \stdClass();
    $item->title = $this
      ->get_field($row_index, $this->options['title_field']);
    $item->link = url($this
      ->get_field($row_index, $this->options['link_field']), array(
      'absolute' => TRUE,
    ));
    $item->description = $this
      ->get_field($row_index, $this->options['description_field']);
    $item->elements = array(
      array(
        'key' => 'pubDate',
        'value' => $this
          ->get_field($row_index, $this->options['date_field']),
      ),
      array(
        'key' => 'dc:creator',
        'value' => $this
          ->get_field($row_index, $this->options['creator_field']),
        'namespace' => array(
          'xmlns:dc' => 'http://purl.org/dc/elements/1.1/',
        ),
      ),
    );
    $guid_is_permalink_string = 'false';
    $item_guid = $this
      ->get_field($row_index, $this->options['guid_field_options']['guid_field']);
    if ($this->options['guid_field_options']['guid_field_is_permalink']) {
      $guid_is_permalink_string = 'true';
      $item_guid = url($item_guid, array(
        'absolute' => TRUE,
      ));
    }
    $item->elements[] = array(
      'key' => 'guid',
      'value' => $item_guid,
      'attributes' => array(
        'isPermaLink' => $guid_is_permalink_string,
      ),
    );
    $row_index++;
    foreach ($item->elements as $element) {
      if (isset($element['namespace'])) {
        $this->view->style_plugin->namespaces = array_merge($this->view->style_plugin->namespaces, $element['namespace']);
      }
    }
    return theme($this
      ->themeFunctions(), array(
      'view' => $this->view,
      'options' => $this->options,
      'row' => $item,
      'field_alias' => isset($this->field_alias) ? $this->field_alias : '',
    ));
  }

  /**
   * Retrieves a views field value from the style plugin.
   *
   * @param $index
   *   The index count of the row as expected by views_plugin_style::get_field().
   * @param $field_id
   *   The ID assigned to the required field in the display.
   */
  function get_field($index, $field_id) {
    if (empty($this->view->style_plugin) || !is_object($this->view->style_plugin) || empty($field_id)) {
      return '';
    }
    return $this->view->style_plugin
      ->get_field($index, $field_id);
  }

}