Determine url base reliably

url_base.php

<?php

class Controller {

    private $_base_url;

    // ...

    public function base_url()
    {
        if (empty($this->_base_url))
        {
            $https = (isset($_SERVER['HTTPS']) && strtolower($_SERVER['HTTPS']) !== 'off');
            $protocol = ($https) ? 'https' : 'http';
            $host = $_SERVER['HTTP_HOST'];
            $path = str_replace(basename($_SERVER['SCRIPT_NAME']), '', $_SERVER['SCRIPT_NAME']);
            $this->_base_url = $protocol . '://' . $host . $path;
        }
        
        return $this->_base_url;
    }
}