CodeIgniter's index.php to handle multiple hosts

Environment_hooks.php

<?php

// put this on application/hooks/

defined('BASEPATH') or exit('No direct script access allowed');

class Environment_hooks
{
    /**
     * Handles app hosts.
     *
     * @return void
     */
    public function handleHosts()
    {
        // gets app instance
        $CI =& get_instance();

        // gets default app url
        $app_url = getenv('APP_URL');

        // checks ssl
        $connection_type = isset($_SERVER['HTTPS']) && $_SERVER['HTTPS'] == "on" ? 'https' : 'http';

        // checks to override app base url configuration
        if ($app_url && $CI->config->item('base_url') !== $app_url) {
            $CI->config->set_item('base_url', "$connection_type://$app_url");
        }
    }
}

hooks.php

<?php

// put this on application/config/

$hook['post_controller_constructor'][] = [
    'class' => 'Environment_hooks',
    'function' => 'handleHosts',
    'filename' => 'Environment_hooks.php',
    'filepath' => 'hooks',
    'params' => []
];

index.php

<?php

// modify this part on index.php file, in your codeigniter root folder

$domain = php_sapi_name() === 'cli' ? [0 => 'api'] : explode('.', $_SERVER['HTTP_HOST']);

switch ($domain[0]) {
    case 'api':
        $application_folder = 'api';
        break;

    case 'admin':
        $application_folder = 'admin';
        break;

    case 'bo':
        $application_folder = 'bo';
        break;

    default:
        $application_folder = 'application';
        break;
}