#include <QApplication>
#include <QGraphicsView>
#include <QGraphicsScene>
#include <QGestureEvent>
#include <QMainWindow>
#include <QGraphicsRectItem>
#include <QRandomGenerator>
#include <QGesture>

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();
};

class GraphicsView : public QGraphicsView
{
public:
    GraphicsView(QWidget * parent);

    void initialiseScene();
    bool event(QEvent * event) override;
    bool gestureEvent(QGestureEvent * event);
    void setScale(double scale);

    QGraphicsScene mScene;
    Qt::GestureState mLastState{ Qt::GestureState::NoGesture };
};


MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent) {
    setCentralWidget(new GraphicsView{ this });
}

MainWindow::~MainWindow(){
}


namespace {
    QRandomGenerator& rng() { static QRandomGenerator sRng; return sRng; }
    QColor randomColour() {
        return QColor{ rng().bounded(64, 255), rng().bounded(64, 255), rng().bounded(64, 255) };
    }
}

GraphicsView::GraphicsView(QWidget * parent) : QGraphicsView{ parent } {
    setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
    setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
    setScene(&mScene);
    initialiseScene();
    grabGesture(Qt::PinchGesture);
}

void GraphicsView::initialiseScene() {
    for (int i = 0; i < 10; i++) {
        for (int j = 0; j < 10; j++) {
            mScene.addRect({ i * 100.0, j * 100.0, 100, 100 }, Qt::NoPen, QBrush{ ::randomColour() });
        }
    }
}

bool GraphicsView::event(QEvent * event) {
    if (event->type() == QEvent::Gesture) {
        return gestureEvent(static_cast<QGestureEvent*>(event));
    }
    else if (event->type() == QEvent::TouchBegin ||
               event->type() == QEvent::TouchUpdate ||
               event->type() == QEvent::TouchEnd) {
        qDebug() << "touch event" << static_cast<QTouchEvent *>(event)->points().size() << "points";
    }
    return QGraphicsView::event(event);
}

bool GraphicsView::gestureEvent(QGestureEvent * event) {
    bool result{ false };

    if (QGesture * gesture = event->gesture(Qt::PinchGesture)) {
        QPinchGesture * pinch{ static_cast<QPinchGesture *>(gesture) };
        QPinchGesture::ChangeFlags changeFlags = pinch->changeFlags();
        Qt::GestureState state = pinch->state();
        if (state == Qt::GestureState::GestureFinished) {
            if (mLastState == Qt::GestureState::GestureStarted) {
                qDebug() << "gesture finished without updates";
            }
        }
        mLastState = state;
        if (changeFlags & QPinchGesture::ScaleFactorChanged){
            double scaleFactor = pinch->totalScaleFactor();
            setScale(scaleFactor);
        }
        if (changeFlags & QPinchGesture::CenterPointChanged) {
        }
        if (gesture->state() == Qt::GestureFinished) {
        }
        result = true;
    }
    if (QGesture * gesture = event->gesture(Qt::TapGesture)) {
    }
    if (QGesture * gesture = event->gesture(Qt::TapAndHoldGesture)) {
    }
    return result;
}

void GraphicsView::setScale(double scale) {
    QTransform transform;
    transform.scale(scale, scale);
    setTransform(transform);
}


int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
    return a.exec();
}
#include "main.moc"