class TemplateManager {

protected $basePath;
protected $currentTemplate;
protected $currentTPLFile;


public function __construct(string $basepath, $currentTemplate = "admin/home.tpl"){
    $this->setBasePath($basepath . '/Templates/');
    $this->setCurrentTemplate($this->getBasePath() . $currentTemplate);
    $this->setCurrentTPLFile($currentTemplate);

}


public function getTemplate($page, $isAdmin = false){
    return ($isAdmin ? $this->getBasePath() ."admin/" . $page .".tpl"  : "Templates/client/" . $page . ".tpl");
}



/**
 * Get the value of currentTemplate
 */ 
public function getCurrentTemplate()
{
    return $this->currentTemplate;
}

/**
 * Set the value of currentTemplate
 *
 * @return  self
 */ 
public function setCurrentTemplate($currentTemplate)
{
    $this->currentTemplate = $currentTemplate;

    return $this;
}

/**
 * Get the value of basePath
 */ 
public function getBasePath()
{
    return $this->basePath;
}

/**
 * Set the value of basePath
 *
 * @return  self
 */ 
public function setBasePath($basePath)
{
    $this->basePath = $basePath;

    return $this;
}

/**
 * Get the value of currentTPLFile
 */ 
public function getCurrentTPLFile()
{
return $this->currentTPLFile;
}

/**
 * Set the value of currentTPLFile
 *
 * @return  self
 */ 
public function setCurrentTPLFile($currentTPLFile)
{
$this->currentTPLFile = $currentTPLFile;

return $this;
}
}

function module_output($vars) {
$smarty = new Smarty();
    $_lang = $vars['_lang'];
    $TPLManager = new TemplateManager(dirname(__FILE__), "admin/home.tpl");
    $page = isset($_GET['page']) ? $_GET['page'] : 'home';
    
    $smarty->assign('modulelink', $vars['modulelink'] );
    $smarty->caching = false; // Debugging
    $smarty->compile_dir = $GLOBALS['templates_compiledir'];

    $CustomFunction = "template_" . $page;

    $smarty->assign('tplVars', (new TemplateService)->$CustomFunction($vars));


    //Load Template
	$smarty->display($TPLManager->getTemplate($page, true));
	
}

function module_clientarea($vars){
(...)
 $TPLManager = new TemplateManager(dirname(__FILE__), "admin/home.tpl");
 return array(
        'pagetitle'     => 'Page Title',
        'templatefile'  => $TPLManager->getTemplate($page),
        'requirelogin'  => true, # accepts true/false
        'forcessl'      => true, # accepts true/false
        'vars'          => array(
            'modulelink'    => $modulelink,
            'moduleversion' => $version,
            'currentPage'   => $page,
            'tplVars'       => (new TemplateService)->$CustomFunction($vars),
            'addonlang'     => $_lang,
        ),
    );

}

class TemplateService {

      public function template_home($vars) { // home is the name of the template file that will be displayed
        return []; // Return a Value or a Array with additional variables that need to be available inside the template.
       }
}