#include <QtGui>
#include <QtGui/private/qhighdpiscaling_p.h>
#include <QtWidgets>

QScreen *screenForGeometry(const QRect &newGeometry, QScreen *currentScreen)
{
    QScreen *fallback = currentScreen;
    const auto screens = currentScreen->virtualSiblings();
    int largestIntersectionArea = 0;
    if (currentScreen) {
        for (QScreen *screen : screens) {
            QRect nativeScreenGeometry = QHighDpi::toNativePixels(screen->geometry(), screen);
            QRect nativeGeometry = QHighDpi::toNativePixels(newGeometry, screen);
            if (nativeScreenGeometry.contains(nativeGeometry.center())) {
                return screen;
            }
            QRect intersection = nativeScreenGeometry.intersected(nativeGeometry);
            int intesectionAria = intersection.width() * intersection.height() * screen->devicePixelRatio();
            if (!intersection.isEmpty() && intesectionAria > largestIntersectionArea)
            {
                largestIntersectionArea = intesectionAria;
                fallback = screen;
            }
        }
    }
    return fallback;
}

QScreen *screenForPos(const QPoint &pos, QScreen *currentScreen)
{
    return screenForGeometry(QRect(pos - QPoint(1, 1), QSize(3, 3)), currentScreen);
}

class Win : public QWidget
{
public:
    using QWidget::QWidget;

    void mousePressEvent(QMouseEvent *event) override
    {
        if (event->button() == Qt::RightButton) {
            QScreen *s = screen();
            if (s) {
                QPoint globalPos = mapToGlobal(event->pos());
                moveStartOffset = QHighDpi::toNativePixels(pos(), s)
                        - QHighDpi::toNativePixels(globalPos, screenForPos(globalPos, s));
                moveStartSize = size();
            }
        }
    }

    void mouseMoveEvent(QMouseEvent *event) override
    {
        if (event->buttons() & Qt::RightButton) {
            QScreen *s = screen();
            if (s && windowHandle()) {
                QPoint globalPos = mapToGlobal(event->pos());
                QScreen *cursorScreen = screenForPos(globalPos, s);
                QPoint newPos = QHighDpi::toNativePixels(globalPos, cursorScreen) + moveStartOffset;

                QSize size = QHighDpi::toNativePixels(moveStartSize, s);
                QRect nativeGeometry = QRect(newPos.x(), newPos.y(), size.width(), size.height());
                QRect newGeometry = QHighDpi::fromNativePixels(nativeGeometry, s);

                QScreen *newScreen = screenForGeometry(newGeometry, s);
                if (newScreen && newScreen != s) {
                    QSize newSize = QHighDpi::toNativePixels(moveStartSize, newScreen);
                    nativeGeometry =
                            QRect(newPos.x(), newPos.y(), newSize.width(), newSize.height());
                    s = newScreen;
                }

                newGeometry = QHighDpi::fromNativePixels(nativeGeometry, s);
                qDebug() << "Set" << newGeometry << "native:" << nativeGeometry;
                setGeometry(newGeometry);
            }
        }
    }

    QPoint moveStartOffset;
    QSize moveStartSize;
};

int main(int argc, char **argv)
{
    QApplication app(argc, argv);

    Win *window = new Win();
    Qt::WindowFlags flags = window->windowFlags() | Qt::FramelessWindowHint;
    window->setWindowFlags(flags);

    window->show();

    window->resize(874, 637);

    return app.exec();
}