TextHelper.php

<?php

declare(strict_types=1);

namespace App\Helpers;

use JetBrains\PhpStorm\Pure;

class TextHelper
{
    #[Pure]
    public static function maskEmailAddress(string $email): ?string
    {
        $mail_parts = explode('@', $email);
        $domain_parts = explode('.', $mail_parts[1]);

        $mail_parts[0] = self::mask($mail_parts[0], 2, 1); // show first 2 letters and last 1 letter
        $domain_parts[0] = self::mask($domain_parts[0], 2, 1); // same here
        $mail_parts[1] = implode('.', $domain_parts);

        return implode('@', $mail_parts);

        return null;
    }

    public static function mask($str, $first, $last): string
    {
        $len = strlen($str);
        $toShow = $first + $last;

        return substr($str, 0, $len <= $toShow ? 0 : $first).str_repeat('*', $len - ($len <= $toShow ? 0 : $toShow)).substr($str, $len - $last, $len <= $toShow ? 0 : $last);
    }
}