goatoh_training_server/modules/chat.mod.php

<?php

class
Chat
{
  private $db;

  function
  __construct ()
  {
    $config = include (__DIR__ . '/config.php');

    $db_host = $config['host'];
    $db_port = $config['port'];
    $db_user = $config['user'];
    $db_pass = $config['pass'];

    $this -> db = new mysqli ($db_host, $db_user, $db_pass, 'goatoh_training',
                              $db_port);
  }

  function
  send (
      int     $user_id,
      string  $text):
  void
  {
    $sql = "
        INSERT INTO
          chats (
            user_id,
            text)
          VALUES
            (
              $user_id,
              '$text')";
    $this -> db -> query ($sql) or die ("db_insert error $sql");
  }
}