Drupal 8 & 9: Creating modal windows (pop-ups) with a form and to send a mail programmatically

contact teachers:
  title: 'Contact teachers'

tl_session.open_teacher_form:
  path: '/contact-teacher/{teacher}'
  defaults:
    _title: 'Contact form'
    _controller: '\Drupal\tl_session\Controller\TeacherContactController::openModalForm'
  requirements:
    _permission: 'contact teachers'

<?php
 
namespace Drupal\tl_session\Controller;
 
use Symfony\Component\DependencyInjection\ContainerInterface;
use Drupal\Core\Ajax\AjaxResponse;
use Drupal\Core\Ajax\OpenModalDialogCommand;
use Drupal\Core\Controller\ControllerBase;
use Drupal\Core\Form\FormBuilder;
 
/**
 * Class TeacherContactController
 *
 * @package Drupal\tl_session\Controller
 */
class TeacherContactController extends ControllerBase {
 
  /**
   * The form builder.
   *
   * @var \Drupal\Core\Form\FormBuilder
   */
  protected $formBuilder;
 
  /**
   * The TeacherContactController constructor.
   *
   * @param \Drupal\Core\Form\FormBuilder $formBuilder
   *   The form builder.
   */
  public function __construct(FormBuilder $formBuilder) {
    $this->formBuilder = $formBuilder;
  }
 
  /**
   * {@inheritdoc}
   *
   * @param \Symfony\Component\DependencyInjection\ContainerInterface $container
   * The Drupal service container.
   *
   * @return static
   */
  public static function create(ContainerInterface $container) {
    return new static($container->get('form_builder'));
  }
 
  /**
   * Callback for opening the modal form.
   */
  public function openModalForm() {
    $response = new AjaxResponse();
    // Get the modal form using the form builder.
    $modal_form = $this->formBuilder->getForm('Drupal\tl_session\Form\TeacherForm');
    // Add an AJAX command to open a modal dialog with the form as the content.
    $response->addCommand(new OpenModalDialogCommand('Contact form', $modal_form, ['width' => '555']));
 
    return $response;
  }
}

<?php
 
namespace Drupal\tl_session\Form;
 
use Drupal\Core\Form\FormBase;
use Drupal\Core\Form\FormStateInterface;
use Drupal\Core\Ajax\AjaxResponse;
use Drupal\Core\Ajax\OpenModalDialogCommand;
use Drupal\Core\Ajax\ReplaceCommand;
 
/**
 * TeacherForm class.
 */
class TeacherForm extends FormBase {
 
  /**
   * {@inheritdoc}
   */
  public function getFormId() {
    return 'tl_teacher_modal_form';
  }
 
  /**
   * {@inheritdoc}
   */
  public function buildForm(array $form, FormStateInterface $form_state, $options = NULL) {
    $teacher_id = \Drupal::request()->get('teacher');
    $teacher_details = \Drupal\user\Entity\User::load($teacher_id);
    $teacher_name = alex_tweaks_get_real_name($teacher_details);
    $teacher_details = alex_tweaks_get_extra_info($teacher_details);
    $teacher_mail = $teacher_details['mail'];
 
    $account_details = tl_session_get_user_details();
 
    $form['#prefix'] = '<div id="tl_teacher_form">';
    $form['#suffix'] = '</div>';
 
    // The status messages that will contain any form errors.
    $form['status_messages'] = [
      '#type' => 'status_messages',
      '#weight' => -10,
    ];
 
    $form['contact_name'] = [
      '#type' => 'hidden',
      '#value' => $teacher_name,
    ];
    $form['contact_mail'] = [
      '#type' => 'hidden',
      '#value' => $teacher_mail,
    ];
    $form['email_type'] = [
      '#type' => 'hidden',
      '#value' => 'send_message',
    ];
    $form['name'] = [
      '#type' => 'textfield',
      '#title' => t('Your name'),
      '#default_value' => $account_details['name'],
      '#required' => TRUE,
    ];
    $form['email'] = [
      '#type' => 'email',
      '#title' => t('Your email'),
      '#default_value' => $account_details['mail'],
      '#required' => TRUE,
    ];
    $form['phone'] = [
      '#type' => 'tel',
      '#title' => t('Your telephone'),
      '#default_value' => $account_details['phone'],
      '#required' => FALSE,
    ];
    $form['message'] = [
      '#type' => 'textarea',
      '#default_value' => 'Dear ' . $teacher_name . ',',
      '#rows' => 8,
      '#resizable' => FALSE,
      '#title' => t('Message'),
      '#required' => TRUE,
    ];
 
    $form['actions'] = ['#type' => 'actions'];
    $form['actions']['send'] = [
      '#type' => 'submit',
      '#value' => $this->t('Send message'),
      '#attributes' => [
        'class' => [
          'use-ajax',
        ],
      ],
      '#ajax' => [
        'callback' => [
          $this,
          'submitModalFormAjax'
        ],
        'event' => 'click',
      ],
    ];
    $form['#attached']['library'][] = 'core/drupal.dialog.ajax';
 
    return $form;
  }
 
  /**
   * AJAX callback handler that displays any errors or a success message.
   */
  public function submitModalFormAjax(array $form, FormStateInterface $form_state) {
    $response = new AjaxResponse();
 
    // If there are any form errors, re-display the form.
    if ($form_state->hasAnyErrors()) {
      $response->addCommand(new ReplaceCommand('#tl_teacher_form', $form));
    }
    else {
      $message = $this->t('The email has been sent.');
      drupal_set_message($message);
      \Drupal::logger('tl_session')->notice($message);
      $response->addCommand(new OpenModalDialogCommand("Success!", $message, ['width' => 555]));
    }
    return $response;
  }
 
  /**
   * {@inheritdoc}
   */
  public function validateForm(array &$form, FormStateInterface $form_state) {
    // TODO: Check if it looks like we are going to exceed the flood limit.
    // Not ported to Drupal 8.0.3 yet.
  }
 
  /**
   * {@inheritdoc}
   */
  public function submitForm(array &$form, FormStateInterface $form_state) {
    $data['contact_name'] = trim($form_state->getValue('contact_name'));
    $data['mail_to'] = trim($form_state->getValue('contact_mail'));
    $data['mail_type'] = trim($form_state->getValue('email_type'));
    $data['sender_name'] = trim($form_state->getValue('name'));
    $data['sender_email'] = trim($form_state->getValue('email'));
    $data['sender_phone'] = trim($form_state->getValue('phone'));
    $data['sender_message'] = trim($form_state->getValue('message'));
    tl_session_send_mail($data);
  }
 
  /**
   * Gets the configuration names that will be editable.
   *
   * @return array
   * An array of configuration object names that are editable if called in
   * conjunction with the trait's config() method.
   */
  protected function getEditableConfigNames() {
    //return ['config.tl_session_modal_form'];
  }
}

<?php
 
use Drupal\Component\Utility\Html;
 
/**
 * Helper function to get basic user details.
 *
 * @return array
 */
function tl_session_get_user_details() {
  $details = [
    'name' => '',
    'mail' => '',
    'phone' => '',
  ];
 
  $account = \Drupal::currentUser();
  if ($account->id() > 0) {
    $details['name'] = alex_tweaks_get_real_name($account);
    $extra_info = alex_tweaks_get_extra_info($account);
    $details['mail'] = $extra_info['mail'];
    $details['phone'] = $extra_info['phone'];
  }
 
 
  return $details;
}
 
/**
 * Implements hook_mail().
 */
function tl_session_mail($key, &$message, $params) {
  switch ($key) {
    case 'send_enquiry':
    case 'send_message':
      $message['from'] = 'no-reply@stat.org.uk';
      $message['subject'] = Html::escape($params['subject']);
      $message['body'][] = Html::escape($params['message']);
      break;
  }
}
 
/**
 * Custom function for mail.
 *
 * @param $data
 */
function tl_session_send_mail($data) {
  // Load the site name out of configuration.
  $config = \Drupal::config('system.site');
  $site_name = $config->get('name');
 
  $mailManager = \Drupal::service('plugin.manager.mail');
  $module = 'tl_session';
  $key = $data['mail_type'];
  $to = $data['mail_to'];
  // Uncomment for testing.
  // $to = \Drupal::currentUser()->getEmail();
  $params['reply-to'] = $data['sender_email'];
 
  $params['subject'] = $site_name . ' ' . $data['sender_name'] . ' sent you a message';
  $params['message'] = 'Dear ' . $data['contact_name'] . ',
' . $data['sender_name'] . ' has sent you a message via your contact form at ' . $site_name . '.
 
Message:
' . $data['sender_message'] . '
 
---
 
Contact
Name: ' . $data['sender_name'] . '
Email: ' . $data['sender_email'] . '
Phone: ' . $data['sender_phone'];
 
  $langcode = \Drupal::currentUser()->getPreferredLangcode();
  $send = TRUE;
 
  $result = $mailManager->mail($module, $key, $to, $langcode, $params, NULL, $send);
  if ($result['result'] != TRUE) {
    $message = t('There was a problem sending your email notification to @email.', ['@email' => $to]);
    drupal_set_message($message, 'error');
    \Drupal::logger('tl_session')->error($message);
    return;
  }
}