invoiceninja/app/Http/ValidationRules/NewUniqueUserRule.php

<?php
/**
 * Invoice Ninja (https://invoiceninja.com).
 *
 * @link https://github.com/invoiceninja/invoiceninja source repository
 *
 * @copyright Copyright (c) 2020. Invoice Ninja LLC (https://invoiceninja.com)
 *
 * @license https://opensource.org/licenses/AAL
 */

namespace App\Http\ValidationRules;

use App\Libraries\MultiDB;
use Illuminate\Contracts\Validation\Rule;

/**
 * Class NewUniqueUserRule.
 */
class NewUniqueUserRule implements Rule
{
    /**
     * @param string $attribute
     * @param mixed $value
     * @return bool
     */
    public function passes($attribute, $value)
    {
        return ! $this->checkIfEmailExists($value); //if it exists, return false!
    }

    /**
     * @return string
     */
    public function message()
    {
        return ctrans('texts.email_already_register');
    }

    /**
     * @param $email
     * @return bool
     */
    private function checkIfEmailExists($email) : bool
    {
        return MultiDB::checkUserEmailExists($email);
    }
}