#include <QtCore>
#include <QtGui>
#include <QtWidgets>

class ContentWidget : public QWidget
{
public:
	ContentWidget(QWidget* parent = 0) : QWidget(parent) {}

protected:
	void paintEvent(QPaintEvent *event) override
	{
		QPainter painter(this);
		painter.save();

		QRect rect = geometry();
		QRect local = QRect(mapFromParent(rect.topLeft()), mapFromParent(rect.bottomRight()));
		painter.setPen(QPen(QColor(255, 0, 0, 255), 1.0f, Qt::SolidLine));
		painter.drawRect(local.left(), local.top(), local.width() - 1, local.height() - 1);
		painter.fillRect(local, QColor(255, 0, 0, 10));
		if (testAttribute(Qt::WA_NativeWindow))
		{
			const HWND hwnd = (HWND)winId();
			if (IsWindow(hwnd))
			{
				RECT wndRect;
				GetWindowRect(hwnd, &wndRect);
				QRect wndLocal = QRect(mapFromGlobal({ wndRect.left, wndRect.top }), mapFromGlobal({ wndRect.right, wndRect.bottom }));
				painter.setPen(QPen(QColor(0, 255, 0, 255), 1.0f, Qt::DotLine));
				painter.drawRect(local.left(), local.top(), local.width() - 1, local.height() - 1);
				painter.fillRect(local, QColor(0, 255, 0, 10));
			}
		}
		painter.restore();
	}
	void resizeEvent(QResizeEvent *event) override
	{
		QWidget::resizeEvent(event);
	}
};


int main(int argc, char *argv[])
{
	QApplication a(argc, argv);

	QMainWindow mainWindow;
	mainWindow.resize(300, 300);
	mainWindow.setMenuBar(new QMenuBar);

	auto contatinerWidget = new QWidget;
	{
		auto layout = new QBoxLayout(QBoxLayout::TopToBottom);
		contatinerWidget->setLayout(layout);
	}
	auto rootSplitter = new QSplitter(Qt::Horizontal, contatinerWidget);
	rootSplitter->setChildrenCollapsible(false);
	contatinerWidget->layout()->addWidget(rootSplitter);
	mainWindow.setCentralWidget(contatinerWidget);

	auto areaWidget = new QWidget(contatinerWidget);
	{
		auto layout = new QBoxLayout(QBoxLayout::TopToBottom);
		areaWidget->setLayout(layout);
	}

	auto contentWidget = new ContentWidget;
	contentWidget->setAttribute(Qt::WA_NativeWindow, true);
	contentWidget->setParent(nullptr);
	areaWidget->layout()->addWidget(contentWidget);

	rootSplitter->addWidget(areaWidget);

	if (QAction* resetLayout = mainWindow.menuBar()->addAction("Reset"))
	{
		mainWindow.addAction(resetLayout);

		QObject::connect(resetLayout, &QAction::triggered, [&]()
		{
			if (areaWidget)
			{
				auto item = areaWidget->layout()->takeAt(0);
				assert(item);
				contentWidget->setParent(nullptr);
				areaWidget->setParent(nullptr);
				areaWidget->deleteLater();
				areaWidget = nullptr;
			}

			if (!areaWidget)
			{
				areaWidget = new QWidget(contatinerWidget);
				auto layout = new QBoxLayout(QBoxLayout::TopToBottom);
				areaWidget->setLayout(layout);
#define LAYOUT_BUG
#ifdef LAYOUT_BUG
				areaWidget->layout()->addWidget(contentWidget);
				rootSplitter->addWidget(areaWidget);
#else
				rootSplitter->addWidget(areaWidget);
				areaWidget->layout()->addWidget(contentWidget);
#endif
			}
		});
	}

	mainWindow.show();
	return a.exec();
}