Method createUrl

/**
 * Create a URL for a given help key reference
 *
 * @param   string   $ref           The name of the help screen (its key reference)
 * @param   boolean  $useComponent  Use the help file in the component directory
 * @param   string   $override      Use this URL instead of any other
 * @param   string   $component     Name of component (or null for current component)
 *
 * @return  string
 *
 * @since   1.5
 */
public static function createUrl($ref, $useComponent = false, $override = null, $component = null)
{
    $local = false;
    $app = Factory::getApplication();
    if ($component === null) {
        $component = ApplicationHelper::getComponentName();
    }
    //  Determine the location of the help file.  At this stage the URL
    //  can contain substitution codes that will be replaced later.
    if ($override) {
        $url = $override;
    } else {
        // Get the global help URL.
        $url = $app->get('helpurl');
        // Component help URL overrides user and global.
        if ($useComponent) {
            // Look for help URL in component parameters.
            $params = ComponentHelper::getParams($component);
            $url = $params->get('helpURL');
            if ($url == '') {
                $local = true;
                $url = 'components/{component}/help/{language}/{keyref}';
            }
        }
        // Set up a local help URL.
        if (!$url) {
            $local = true;
            $url = 'help/{language}/{keyref}';
        }
    }
    // If the URL is local then make sure we have a valid file extension on the URL.
    if ($local) {
        if (!preg_match('#\\.html$|\\.xml$#i', $ref)) {
            $url .= '.html';
        }
    }
    /*
     *  Replace substitution codes in the URL.
     */
    $lang = Factory::getLanguage();
    $version = new Version();
    $jver = explode('.', $version->getShortVersion());
    $jlang = explode('-', $lang->getTag());
    $debug = $lang->setDebug(false);
    $keyref = Text::_($ref);
    $lang->setDebug($debug);
    // Replace substitution codes in help URL.
    $search = array(
        // Application name (eg. 'Administrator')
        '{app}',
        // Component name (eg. 'com_content')
        '{component}',
        // Help screen key reference
        '{keyref}',
        // Full language code (eg. 'en-GB')
        '{language}',
        // Short language code (eg. 'en')
        '{langcode}',
        // Region code (eg. 'GB')
        '{langregion}',
        // Joomla major version number
        '{major}',
        // Joomla minor version number
        '{minor}',
        // Joomla maintenance version number
        '{maintenance}',
    );
    $replace = array(
        // {app}
        $app->getName(),
        // {component}
        $component,
        // {keyref}
        $keyref,
        // {language}
        $lang->getTag(),
        // {langcode}
        $jlang[0],
        // {langregion}
        $jlang[1],
        // {major}
        $jver[0],
        // {minor}
        $jver[1],
        // {maintenance}
        $jver[2],
    );
    // If the help file is local then check it exists.
    // If it doesn't then fallback to English.
    if ($local) {
        $try = str_replace($search, $replace, $url);
        if (!is_file(JPATH_BASE . '/' . $try)) {
            $replace[3] = 'en-GB';
            $replace[4] = 'en';
            $replace[5] = 'GB';
        }
    }
    $url = str_replace($search, $replace, $url);
    return $url;
}