class MemoryBackend

class MemoryBackend implements FloodInterface, PrefixFloodInterface {
    
    /**
     * The request stack.
     *
     * @var \Symfony\Component\HttpFoundation\RequestStack
     */
    protected $requestStack;
    
    /**
     * An array holding flood events, keyed by event name and identifier.
     *
     * @var array
     */
    protected $events = [];
    
    /**
     * Construct the MemoryBackend.
     *
     * @param \Symfony\Component\HttpFoundation\RequestStack $request_stack
     *   The request stack used to retrieve the current request.
     */
    public function __construct(RequestStack $request_stack) {
        $this->requestStack = $request_stack;
    }
    
    /**
     * {@inheritdoc}
     */
    public function register($name, $window = 3600, $identifier = NULL) {
        if (!isset($identifier)) {
            $identifier = $this->requestStack
                ->getCurrentRequest()
                ->getClientIp();
        }
        // We can't use REQUEST_TIME here, because that would not guarantee
        // uniqueness.
        $time = microtime(TRUE);
        $this->events[$name][$identifier][] = [
            'expire' => $time + $window,
            'time' => $time,
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public function clear($name, $identifier = NULL) {
        if (!isset($identifier)) {
            $identifier = $this->requestStack
                ->getCurrentRequest()
                ->getClientIp();
        }
        unset($this->events[$name][$identifier]);
    }
    
    /**
     * {@inheritdoc}
     */
    public function clearByPrefix(string $name, string $prefix) : void {
        foreach ($this->events as $event_name => $identifier) {
            $identifier_key = key($identifier);
            $identifier_parts = explode("-", $identifier_key);
            $identifier_prefix = reset($identifier_parts);
            if ($prefix == $identifier_prefix && $name == $event_name) {
                unset($this->events[$event_name][$identifier_key]);
            }
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function isAllowed($name, $threshold, $window = 3600, $identifier = NULL) {
        if (!isset($identifier)) {
            $identifier = $this->requestStack
                ->getCurrentRequest()
                ->getClientIp();
        }
        if (!isset($this->events[$name][$identifier])) {
            return $threshold > 0;
        }
        $limit = microtime(TRUE) - $window;
        $number = count(array_filter($this->events[$name][$identifier], function ($entry) use ($limit) {
            return $entry['time'] > $limit;
        }));
        return $number < $threshold;
    }
    
    /**
     * {@inheritdoc}
     */
    public function garbageCollection() {
        foreach ($this->events as $name => $identifiers) {
            foreach ($this->events[$name] as $identifier => $entries) {
                // Remove expired entries.
                $this->events[$name][$identifier] = array_filter($entries, function ($entry) {
                    return $entry['expire'] > microtime(TRUE);
                });
            }
        }
    }

}