Routing to specific controller in case controller/method is not found.

Hello again;

Thanks for everyone who tried to help me in this thread.  I appreciate your interest.

I've solved my issue with following approach. (I know it's a little bit dirty but i couldn't find an elegant solution to this.)

PHP Code:

$route['(:any)'] = function($slug)
{
    // find out which class(controller)/method to execute.
    $validated = $this->_validate_request( array_values($this->uri->segments) );
    
    // cleanup. (which set by _validate_request())
    $directory = $this->directory;
    $this->directory = NULL;

    // extract class(controller) & method name.
    if(array_key_exists(0,$validated))
    {
        // class(controller) name found.
        $class_name = ucfirst($validated[0]);
    }
    else
    {
        // class(controller) name not found. route to desired controller.
        return 'page/view/'.$slug;
    }
    $method_name = array_key_exists(1,$validated) ? $validated[1] : 'index';
    
    // class(controller) file to load.
    $class_path = APPPATH.'controllers/'. $directory . $class_name . '.php';
    
    // cleanup. (which set by _validate_request())
    $this->directory = NULL;
    
    // class(controller) exists?
    if(file_exists($class_path))
    {
        // load CI_Controller core class and our class(controller).
        include_once(FCPATH.'system/core/Controller.php');
        include_once($class_path);
        
        // does method exists?
        if(method_exists($class_name,$method_name))
        {
            // if class(controller) and method exists, we should execute it.
            return implode('/',$this->uri->segments);
        }
        else
        {
            // well, if not, it's time to route to desired controller.
            return 'page/view/'.$slug;
        }
    }
    else
    {
        // if class(controller) doesnt exists, route to desired controller.
        return 'page/view/'.$slug;
    }
}; 


This code works as follows:

Scenario: Physically Exists
example.com/controller/method => controllers/Controller.php->method();
example.com/controller => controllers/Controller.php->index();

Scenario: Not Exists
example.com/non-controller => controllers/page.php->view($slug);


Sub-Site Example

PHP Code:

$route['subsite/(:any)'] = /* same code as above */ 


Scenario: Physically Exists
example.com/subsite/controller/method => controllers/subsite/Controller.php->method();
example.com/subsite/controller => controllers/subsite/Controller.php->index();

Scenario: Not Exists
example.com/subsite/non-controller => controllers/page.php->view($slug);