Opencart + SweetAlert + Ajax. Why i can't catch POST request?

Question

I tried to create SweetAlert form with 3 inputs (name,email,text). This form, after submitting must to send Form Data to admin email. I have made it and everything work! But I am sure that my controller code is not valid.

CMS: OpenCart 2.3 + SweetAlert 2.

Here is SweetAlert form + Ajax request:

<script type="text/javascript">
  window.onload = function () {
    var a = document.getElementById('director');
    a.onclick = function() {
        Swal({
          type: 'warning',
          title: 'Your message',
          html:
            '<input name="name" id="swal-input1" class="swal2-input" placeholder="Your name">' +
            '<input name="email" id="swal-input2" class="swal2-input" placeholder="Email">' +
            '<textarea name="text" id="swal-textarea1" class="swal2-textarea" placeholder="Enter your text..." style="display: flex;"></textarea>',          
          showCancelButton: true,
          confirmButtonColor: '#ff5908',
          cancelButtonColor: '#666',
          confirmButtonText: 'Send',
          cancelButtonText: 'Cancel',
          preConfirm: function () {
            return new Promise(function (resolve) {
              resolve([
                $('#swal-input1').val(),
                $('#swal-input2').val(),
                $('#swal-textarea1').val()
              ])
            })
          },                    
        }).then(function (result) {
         if (result.value) { 
          var result = {};
          result.name = $('#swal-input1').val();
          result.email = $('#swal-input2').val(); 
          result.text = $('#swal-textarea1').val(); 
          var data = JSON.stringify(result);
            $.ajax({
               url:"index.php?route=common/message/index",
               type: "post",
                  data: data,                
                  dataType: "json",
               success: function() {Swal({type: 'success', text: 'Message sent'});},
               error: function(xhr,status,error){
               console.log(status);
               console.log(error);
               }
             })
         }
        })

        return false;
    }
}
</script>

After that, ajax request is sending to "Message" controller to "index" method.

<?php
class ControllerCommonMessage extends Controller {

  public function index() {

  $request_body = file_get_contents('php://input');
  $data = json_decode($request_body);

  $username = $data->name;
  $email = $data->email;
  $msg = $data->text;
       $subject = 'Test email from: '.$email;

  $mail = new Mail();

  $mail->protocol = $this->config->get('config_mail_protocol');
  $mail->parameter = $this->config->get('config_mail_parameter');
  $mail->smtp_hostname = $this->config->get('config_mail_smtp_hostname');
  $mail->smtp_username = $this->config->get('config_mail_smtp_username');
  $mail->smtp_password = html_entity_decode($this->config->get('config_mail_smtp_password'), ENT_QUOTES, 'UTF-8');
  $mail->smtp_port = $this->config->get('config_mail_smtp_port');
  $mail->smtp_timeout = $this->config->get('config_mail_smtp_timeout');

  $mail->setTo('mail@mail.com');
  $mail->setFrom($this->config->get('config_email'));
  $mail->setSender(html_entity_decode($this->config->get('config_name'), ENT_QUOTES, 'UTF-8'));
  $mail->setSubject(html_entity_decode($subject, ENT_QUOTES, 'UTF-8'));
  $mail->setHtml($msg);
  $mail->send();

    }   
}

So, the form is working, messages sending successfully. But, this section of code I don't like:

$request_body = file_get_contents('php://input');
$data = json_decode($request_body);

I also tried to write it like this:

if (isset($this->request->post['data'])) {
    $result = $this->request->post['data'];
    var_dump($result);
} else {
    echo 'empty';
}

But nothing works. "result" is empty. What I am doing wrong?