Trigger (some) of the events when the hook is triggered

[tristanlins]

Brainstorming result:

class SystemSubscriber
        implements EventSubscriberInterface
{
        /**
         * Handle a load language file event.
         *
         * @param LoadLanguageFileEvent $event The event.
         *
         * @return void
         */
        public function handleLoadLanguageFile(LoadLanguageFileEvent $event)
        {
            $hash = $event->getSemaphoreHash();

            if (LoadLanguageFileEvent::$cameFromHook[$hash] === false) {
                throw new \InvalidConditionException();
            }

            if (LoadLanguageFileEvent::$cameFromHook[$hash] === null) {
                LoadLanguageFileEvent::$cameFromHook[$hash] = false;

                \System::loadLanguageFile(
                    $event->getFileName(),
                    $event->getLanguage(),
                    $event->isCacheIgnored()
                );

                unset(LoadLanguageFileEvent::$cameFromHook[$hash]);
            }
        }
}

class TristanSubscriber
{
        public function handleLoadLanguageFile(LoadLanguageFileEvent $event)
        {
            // fire twice.
        }
}

$eventDispatcher->addSubscriber(new SystemSubscriber(), PHP_INT_MAX);

class SystemHookHandler
{
        public function loadLanguageFile($fileName, $language = null, $ignoreCache = false)
        {
            $hash = LoadLanguageFileEvent::generateSemaphoreHash($fileName, $language, $ignoreCache);

            if (LoadLanguageFileEvent::$cameFromHook[$hash] === true) {
                throw new \InvalidConditionException();
            }

            if (LoadLanguageFileEvent::$cameFromHook[$hash]=== null) {
                LoadLanguageFileEvent::$cameFromHook[$hash] = true;

                $event->setCameFromHook(true);            
                $eventDispatcher->dispatch($event);

                unset(LoadLanguageFileEvent::$cameFromHook[$hash]);
            }
        }
}

$GLOBALS['TL_HOOKS']['loadLanguageFile'][] = array('SystemHookHandler', 'loadLanguageFile');

class LoadLanguageFileEvent
{
        protected $fileName;

        protected $cameFromHook;

        public function getSemaphoreHash()
        {
            return self::generateSemaphoreHash($this->get....(), ...);
        }

        public static generateSemaphoreHash($filename, ...)
        {
            return md5($filename . ...);
        }
}

Via plain call:
1. $this->loadLanguageFile();
2. SystemHookHandler::loadLanguageFile(); => cameFromHook == true
3. dispatcher->dispatch()
4. SystemSubscriber::handleLoadLanguageFile(); == NO-OP
5. done

Via event:
1. dispatcher->dispatch() => cameFromHook == false
2. SystemSubscriber::LoadLanguageFileEvent(); ==> call \System::loadLanguageFile();
    2.1. SystemHookHandler::loadLanguageFile(); => cameFromHook == true
    2.2. dispatcher->dispatch()
    2.3. SystemSubscriber::handleLoadLanguageFile(); == NO-OP
3. SystemSubscriber::LoadLanguageFileEvent(); -> stop event