ServiceSearchForm.php

<?php

namespace Drupal\uw_ct_service\Form;

use Drupal\Core\Form\FormBase;
use Drupal\Core\Form\FormStateInterface;
use Drupal\Core\Url;

/**
 * Class ServiceSearchForm.
 *
 * Form for searching services.
 */
class ServiceSearchForm extends FormBase {

  /**
   * Returns a unique string identifying the form.
   *
   * The returned ID should be a unique string that can be a valid PHP function
   * name, since it's used in hook implementation names such as
   * hook_form_FORM_ID_alter().
   *
   * @return string
   *   The unique string identifying the form.
   */
  public function getFormId(): string {
    return 'service_search_form';
  }

  /**
   * Form constructor.
   *
   * @param array $form
   *   An associative array containing the structure of the form.
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   The current state of the form.
   * @param string|null $description
   *   The description for the input element.
   * @param string|null $placeholder
   *   The placeholder string.
   *
   * @return array
   *   The form structure.
   */
  public function buildForm(array $form, FormStateInterface $form_state, string $description = NULL, string $placeholder = NULL): array {

    // If there is no placeholder sent, then set it to
    // search all services.
    if (!$placeholder) {
      $placeholder = 'Search within all services';
    }

    // The search input.
    $form['search_input'] = [
      '#type' => 'textfield',
      '#placeholder' => $placeholder,
      '#description' => $description ?? NULL,
      '#required' => TRUE,
    ];

    // Add a submit button that handles the submission of the form.
    $form['submit'] = [
      '#type' => 'submit',
      '#value' => '',
      '#attributes' => ['aria-label' => 'search'],
    ];

    return $form;
  }

  /**
   * Form submission handler.
   *
   * @param array $form
   *   An associative array containing the structure of the form.
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   The current state of the form.
   */
  public function submitForm(array &$form, FormStateInterface $form_state) {

    // Get the values of the form state.
    $values = $form_state->getValues();

    // This is an internal URL.
    $url = 'internal:/services';

    // Add the search string.
    $url .= '/search?search-input=' . $values['search_input'];

    // Get a URL object.
    $url = Url::fromUri($url);

    // Set the form redirection URL.
    $form_state->setRedirectUrl($url);
  }

}