pixelfed/app/Util/Lexer/Nickname.php

<?php

namespace App\Util\Lexer;

class Nickname {

    public static function normalizeProfileUrl($url)
    {
      if(starts_with($url, 'acct:')) {
        $url = str_replace('acct:', '', $url);
      }

      if(!str_contains($url, '@') && filter_var($url, FILTER_VALIDATE_URL)) {
        $parsed = parse_url($url);
        $username = str_replace(['/','\\','@'], '', $parsed['path']);
        return ['domain' => $parsed['host'], 'username' => $username];
      }
      $parts = explode('@', $url);
      $username = null;
      $domain = null;

      foreach ($parts as $part) {

        // skip empty array slices
        if(empty($part)) { 
          continue; 
        }

        // if slice contains . assume its a domain
        if(str_contains($part, '.')) {
          $domain = filter_var($part, FILTER_VALIDATE_URL) ?  
                    parse_url($part, PHP_URL_HOST) : 
                    $part;
        } else {
          $username = $part;
        }

      }
      return ['domain' => $domain, 'username' => $username];
    }

}