Knockout-Lite/app/BbCode/Tag/Link.php

<?php

namespace App\BbCode\Tag;

use Knockout\BbCode\Tag\TagInterface;
use Knockout\BbCode\Tokenizer\Tag as TokenTag;

class Link implements TagInterface
{

    const REG_EXP_VALID_URL = '~https?://[a-zA-Z0-9_\-.:/#?]+~';

    public function format(TokenTag $tokenTag): string
    {
        $args = $tokenTag->parseArgument();
        $url = $args['href'] ?? null;

        if (!preg_match(self::REG_EXP_VALID_URL, $url)) {
            $simpleTag = new Unknown();
            return $simpleTag->format($tokenTag);
        }

        return "<a href=\"{$url}\" target=\"_blank\">{$tokenTag->getText()}</a>";
    }

    public function getName(): string
    {
        return 'url';
    }

    public function getOriginalText(TokenTag $tokenTag) : string
    {
        return "[url={$tokenTag->getArgument()}]{$tokenTag->getText()}[/url]";
    }
}