PHPで文字列を最初の20単語まで切り詰める方法は?

function limit_text($text, $limit) {
    if (str_word_count($text, 0) > $limit) {
        $words = str_word_count($text, 2);
        $pos   = array_keys($words);
        $text  = substr($text, 0, $pos[$limit]) . '...';
    }
    return $text;
}

function limit_text_regex($text, $limit) {
    return preg_replace('/\s+.*?(?:\s+|$)/s', '...', $text, $limit);
}

$input = 'Hello here is a long sentence that will be truncated by the';
$truncated = limit_text($input, 5);
echo $truncated; // Output: Hello here is a long ...