Field Formatter to add an Read More Link in text body

gistfile1.aw

/**
 * Implements hook_field_formatter_info().
 */
function hook_field_formatter_info() {
  return array(
    // The 'summary or trimmed' field formatter for text_with_summary
    // fields displays returns the summary element of the field or, if
    // the summary is empty, the trimmed version of the full element
    // of the field.
    // If the Read More link option is used, a link will be placed after
    // the text.
    'text_summary_or_trimmed_link' => array(
      'label' => t('Summary or trimmed with link'),
      'field types' => array('text_with_summary'),
      'settings' => array(
        'trim_length' => 600,
        'link' => 'content',
      ),
    ),
  );
}

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

  $element = array();

  if (strpos($display['type'], '_trimmed_link') !== FALSE) {
    $element['trim_length'] = array(
      '#title' => t('Trim length'),
      '#type' => 'textfield',
      '#size' => 10,
      '#default_value' => $settings['trim_length'],
      '#element_validate' => array('element_validate_integer_positive'),
      '#required' => TRUE,
    );
    $element['read_more'] = array(
      '#title' => t('Read more link'),
      '#type' => 'textfield',
      '#size' => 50,
      '#default_value' => $settings['read_more'],
    );
  }

  return $element;
}

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

  $summary = '';

  if (strpos($display['type'], '_trimmed_link') !== FALSE) {
    $summary = t('Trim length') . ': ' . $settings['trim_length'];
  }

  if (!empty($settings['read_more'])) {
    $summary .= '<br />' . t('Link') . ': ' . $settings['read_more'];
  }

  return $summary;
}

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

  if ($display['type'] == 'text_summary_or_trimmed_link') {
    foreach ($items as $delta => $item) {
      if (!empty($item['summary'])) {
        $output = _text_sanitize($instance, $langcode, $item, 'summary');
      }
      else {
        $output = _text_sanitize($instance, $langcode, $item, 'value');
        $output = text_summary($output, $instance['settings']['text_processing'] ? $item['format'] : NULL, $display['settings']['trim_length']);
      }

      // Add the read more link.
      if (!empty($display['settings']['read_more'])) {
        $read_more_link = l(t($display['settings']['read_more']), 'node/' . $entity->nid);

        $output = preg_replace('/<\/p>$/m', ' ' . $read_more_link . '</p>', $output, 1);
      }

      $element[$delta] = array('#markup' => $output);
    }
  }

  return $element;
}