gistfile1.txt

function scolaris_mhe_search_form_views_exposed_form_alter(&$form, FormStateInterface $form_state, $form_id) {
  if ($form['#id'] == 'views-exposed-form-search-page-1') {
    $current_route = \Drupal::routeMatch()->getRouteName();
    $options = FALSE;
    // Check if we're on a node page.
    if ($current_route == 'entity.node.canonical') {
      $node = \Drupal::routeMatch()->getParameter('node');
      // We only want additional options for the book, chapter
      // and section node types.
      $allowed_types = ['item_book', 'item_chapter', 'item_section'];
      // Setup our options for allowed types.
      if (in_array($node->getType(), $allowed_types)) {
        dsm('node');
        ksm($node->getTitle(), 'node');
        $facet_query = ['content_source:' . $node->getTitle()];

        $options = [
          'within' => t('Within this book'),
          'all' => t('All of AccessEngineering'),
        ];
      }
    }
    // Check if we're on the search page.
    elseif ($current_route == 'view.search.page_1') {

      // Retain any facet query parameters are provided.
      $facet_query = \Drupal::request()->query->filter('f');

      // Setup our options for the search page.
      $options = [
        'within' => t('Within your selection'),
        'all' => t('All of AccessEngineering'),
      ];
    }

    
    // If we have options, add the select list with
    // said options.
    if ($options) {
      $form['search_context'] = [
        '#type' => 'select',
        '#title' => t('Search Context'),
        '#options' => $options,
        '#weight' => -10,
      ];

      if (!empty($facet_query)) {
        #dsm('facet query found');
        foreach ($facet_query as $i => $facet_query_param) {
          #ksm($facet_query_param, 'facet_query_param');
          $form['f[' . $i . ']'] = [
            '#type' => 'hidden',
            '#value' => $facet_query_param,
            '#weight' => 0,
          ];
        }

      }

    }
    $form['#validate'][] = 'scolaris_mhe_search_form_validate';
    $form['#submit'][] = 'scolaris_mhe_search_form_submit';
    #ksm($form, 'form from my custom code');
  }
}

function scolaris_mhe_search_form_validate($form, FormStateInterface &$form_state) {
  $search_context = $form_state->getValue('search_context');
  #dsm('validate! form and formstate');
  #ksm($form, $form_state);

  if ($search_context == 'all') {
    #dsm('search context == all, dont set any query facet params!');

  }

}

function scolaris_mhe_search_form_submit($form, FormStateInterface &$form_state) {
  $search_context = $form_state->getValue('search_context');
  dsm('submit! form and formstate');
  ksm($form, $form_state);

  if ($search_context == 'all') {
    dsm('sssssearch context == all, dont set any query facet params!');
    ksm($form_state->getValues());
    ksm($form_state->getUserInput());
    $user_input = $form_state->getUserInput();
    $value = ['search_context'];
    $form_state->setValue(['search_context'], 'content_source:Foobar');
    $form_state->setRebuild();
    ksm($form_state->getValues());
    $form['f[0]'] = [
      '#type' => 'hidden',
      '#value' => '',
      '#weight' => 0,
    ];
  }

}