class RequestStack

class RequestStack {
    
    /**
     * @var Request[]
     */
    private array $requests = [];
    
    /**
     * @param Request[] $requests
     */
    public function __construct(array $requests = []) {
        foreach ($requests as $request) {
            $this->push($request);
        }
    }
    
    /**
     * Pushes a Request on the stack.
     *
     * This method should generally not be called directly as the stack
     * management should be taken care of by the application itself.
     */
    public function push(Request $request) : void {
        $this->requests[] = $request;
    }
    
    /**
     * Pops the current request from the stack.
     *
     * This operation lets the current request go out of scope.
     *
     * This method should generally not be called directly as the stack
     * management should be taken care of by the application itself.
     */
    public function pop() : ?Request {
        if (!$this->requests) {
            return null;
        }
        return array_pop($this->requests);
    }
    public function getCurrentRequest() : ?Request {
        return end($this->requests) ?: null;
    }
    
    /**
     * Gets the main request.
     *
     * Be warned that making your code aware of the main request
     * might make it un-compatible with other features of your framework
     * like ESI support.
     */
    public function getMainRequest() : ?Request {
        if (!$this->requests) {
            return null;
        }
        return $this->requests[0];
    }
    
    /**
     * Returns the parent request of the current.
     *
     * Be warned that making your code aware of the parent request
     * might make it un-compatible with other features of your framework
     * like ESI support.
     *
     * If current Request is the main request, it returns null.
     */
    public function getParentRequest() : ?Request {
        $pos = \count($this->requests) - 2;
        return $this->requests[$pos] ?? null;
    }
    
    /**
     * Gets the current session.
     *
     * @throws SessionNotFoundException
     */
    public function getSession() : SessionInterface {
        if (null !== ($request = end($this->requests) ?: null) && $request->hasSession()) {
            return $request->getSession();
        }
        throw new SessionNotFoundException();
    }

}