inject.php

// strip table tag
        $doc = new \DOMDocument();
        $doc->loadHTML($text);
        $xpath = new \DOMXPath($doc);
        foreach ($xpath->query('//table') as $node) {
            $node->parentNode->removeChild($node);
        }
        $textWithoutTable = $doc->saveHTML();

        // controlla che ci siano almeno X paragrafi
        $count = count(explode("</p>", $textWithoutTable));
        if ($count > $insertAfter) {

            $regex = <<<'regex'
                ~
                # let's define something
                (?(DEFINE)
                   (?P<table>                     # To match nested table tags
                      <table\b[^>]*>
                         (?:
                            (?!</?table\b[^>]*>).
                         |
                            (?&table)
                         )*
                      </table\s*>
                   )
                   (?P<paragraph>                 # To match nested p tags
                      <p\b[^>]*>
                         (?:
                            (?!</?p\b[^>]*>).
                         |
                            (?&paragraph)
                         )*
                      </p\s*>
                   )
                )
                (?&table)(*SKIP)(*FAIL)           # Let's skip table tags
                |
                (?&paragraph)                     # And match p tags
                ~xsi
regex;

            $output = preg_replace_callback($regex, function($m)use($insertAfter, $code){
                static $counter = 0; # A counter
                $counter++;
                if ($counter === $insertAfter) { # Should I explain?
                    return $m[0] . $code;
                } else {
                    return $m[0];
                }
            }, $text);

            if (empty($output)) {
                return $text . $code;
            }

            return $output;

        }
        else {
            // se non ci sono abbastanza paragrafi inserisce il codice alla fine del testo
            return $text . $code;
        }