private function executeTableShowHeader(array $columns): void
  {
    $separator = '+';
    $header    = '|';

    foreach ($columns as $column)
    {
      $separator .= str_repeat('-', $column['length'] + 2).'+';
      $spaces    = ($column['length'] + 2) - mb_strlen((string)$column['header']);

      $spacesLeft  = (int)floor($spaces / 2);
      $spacesRight = (int)ceil($spaces / 2);

      $fillerLeft  = ($spacesLeft>0) ? str_repeat(' ', $spacesLeft) : '';
      $fillerRight = ($spacesRight>0) ? str_repeat(' ', $spacesRight) : '';

      $header .= $fillerLeft.$column['header'].$fillerRight.'|';
    }

    echo "\n", $separator, "\n";
    echo $header, "\n";
    echo $separator, "\n";
  }