class LogMessageParser

class LogMessageParser implements LogMessageParserInterface {

  /**
   * {@inheritdoc}
   */
  public function parseMessagePlaceholders(&$message, array &$context) {
    $variables = [];
    $has_psr3 = FALSE;
    if (($start = strpos($message, '{')) !== FALSE && strpos($message, '}') > $start) {
      $has_psr3 = TRUE;

      // Transform PSR3 style messages containing placeholders to
      // \Drupal\Component\Render\FormattableMarkup style.
      $message = preg_replace('/\\{([^\\{}]*)\\}/U', '@$1', $message);
    }
    foreach ($context as $key => $variable) {

      // PSR3 style placeholders.
      if ($has_psr3) {

        // Keys are not prefixed with anything according to PSR3 specs.
        // If the message is "User {username} created" the variable key will be
        // just "username".
        if (str_contains($message, '@' . $key)) {
          $key = '@' . $key;
        }
      }

      // To be considered a valid placeholder, the key should be in
      // \Drupal\Component\Render\FormattableMarkup style and the variable
      // should be a string, number, or \Stringable object. For historical
      // reasons, Boolean and NULL placeholders are also allowed; NULL
      // placeholders are deprecated and may throw an error in the future.
      // @see https://www.drupal.org/node/3318826
      if (!empty($key) && ($key[0] === '@' || $key[0] === '%' || $key[0] === ':')) {
        if (is_scalar($variable) || is_null($variable) || $variable instanceof \Stringable) {
          $variables[$key] = $variable;
        }
      }
    }
    return $variables;
  }

}