How to call Laravel helper method in Config/Constants.php

Question

I am giving this error Call to undefined function getDefaultConfigByHost() In constants.php line 5:

In helper.php

function getDefaultConfigByHost($developmentValue = null, $testValue = null, 

    $productionValue = null)
    {
        try {
            if (! isset($_SERVER['HTTP_HOST'])) {
                return null;
            }
            $domain = $_SERVER['HTTP_HOST'];
            switch ($domain) {
                case 'xxx.gglemd.com':
                    return $developmentValue;
                case '192.168.1.18:8001':
                    return $testValue;
                case 'yyy.service.com':
                    return $productionValue;
                default:
                    return '';
            }
        } catch (Exception  $exception) {
            return '';
        }
    }

In constants.php

<?php
 return [
    'api' => [
        'base'        => env('API_BASE', getDefaultConfigByHost(),
        'sfile_base'  => env('SXFILE_API_BASE', getDefaultConfigByHost('')),
        'private_key' => env('API_REQUEST_PRIVATE_KEY', 'bn-sjaddasdsadsadasdas'),
    ],
];