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// This is a compact, minimal, single-file demo of deciding the backend at
// runtime while using the exact same shaders and rendering code without any
// branching whatsoever once the QWindow is up and the RHI is initialized.

#include <QGuiApplication>
#include <QCommandLineParser>
#include <QWindow>
#include <QPlatformSurfaceEvent>
#include <QElapsedTimer>

#include <QtGui/private/qshader_p.h>
#include <QFile>

#include <QtGui/private/qrhinull_p.h>

#ifndef QT_NO_OPENGL
#include <QtGui/private/qrhigles2_p.h>
#include <QOffscreenSurface>
#endif

#if QT_CONFIG(vulkan)
#include <QLoggingCategory>
#include <QtGui/private/qrhivulkan_p.h>
#endif

#ifdef Q_OS_WIN
#include <QtGui/private/qrhid3d11_p.h>
#endif

#if defined(Q_OS_MACOS) || defined(Q_OS_IOS)
#include <QtGui/private/qrhimetal_p.h>
#endif

static float vertexData[] = {
    // Y up (note clipSpaceCorrMatrix in m_proj), CCW
     0.0f,   0.5f,   1.0f, 0.0f, 0.0f,
    -0.5f,  -0.5f,   0.0f, 1.0f, 0.0f,
     0.5f,  -0.5f,   0.0f, 0.0f, 1.0f,
};

static QShader getShader(const QString &name)
{
    QFile f(name);
    if (f.open(QIODevice::ReadOnly))
        return QShader::fromSerialized(f.readAll());

    return QShader();
}

enum GraphicsApi
{
    OpenGL,
    Vulkan,
    D3D11,
    Metal,
    Null
};

static GraphicsApi graphicsApi;

static QString graphicsApiName()
{
    switch (graphicsApi) {
    case OpenGL:
        return QLatin1String("OpenGL 2.x");
    case Vulkan:
        return QLatin1String("Vulkan");
    case D3D11:
        return QLatin1String("Direct3D 11");
    case Metal:
        return QLatin1String("Metal");
    case Null:
        return QLatin1String("Null");
    default:
        break;
    }
    return QString();
}

class Window : public QWindow
{
public:
    Window();
    ~Window();

    void init();
    void releaseResources();
    void resizeSwapChain();
    void releaseSwapChain();
    void render();

    void exposeEvent(QExposeEvent *) override;
    bool event(QEvent *) override;

private:
    bool m_running = false;
    bool m_notExposed = false;
    bool m_newlyExposed = false;

    QRhi *m_r = nullptr;
    bool m_hasSwapChain = false;
    QRhiSwapChain *m_sc = nullptr;
    QRhiRenderBuffer *m_ds = nullptr;
    QRhiRenderPassDescriptor *m_rp = nullptr;
    QRhiBuffer *m_vbuf = nullptr;
    bool m_vbufReady = false;
    QRhiBuffer *m_ubuf = nullptr;
    QRhiShaderResourceBindings *m_srb = nullptr;
    QRhiGraphicsPipeline *m_ps = nullptr;
    QVector<QRhiResource *> releasePool;

    QMatrix4x4 m_proj;
    float m_rotation = 0;
    float m_opacity = 1;
    int m_opacityDir = -1;

    QElapsedTimer m_timer;
    qint64 m_elapsedMs;
    int m_elapsedCount;

#ifndef QT_NO_OPENGL
    QOffscreenSurface *m_fallbackSurface = nullptr;
#endif
};

Window::Window()
{
    // Tell the platform plugin what we want.
    switch (graphicsApi) {
    case OpenGL:
#if QT_CONFIG(opengl)
        setSurfaceType(OpenGLSurface);
        setFormat(QRhiGles2InitParams::adjustedFormat());
#endif
        break;
    case Vulkan:
        setSurfaceType(VulkanSurface);
        break;
    case D3D11:
        setSurfaceType(OpenGLSurface); // not a typo
        break;
    case Metal:
#if (QT_VERSION >= QT_VERSION_CHECK(5, 12, 0))
        setSurfaceType(MetalSurface);
#endif
        break;
    default:
        break;
    }
}

Window::~Window()
{
    releaseResources();
}

void Window::exposeEvent(QExposeEvent *)
{
    // initialize and start rendering when the window becomes usable for graphics purposes
    if (isExposed() && !m_running) {
        m_running = true;
        init();
        resizeSwapChain();
    }

    // stop pushing frames when not exposed (or size is 0)
    if ((!isExposed() || (m_hasSwapChain && m_sc->surfacePixelSize().isEmpty())) && m_running)
        m_notExposed = true;

    // continue when exposed again and the surface has a valid size.
    // note that the surface size can be (0, 0) even though size() reports a valid one...
    if (isExposed() && m_running && m_notExposed && !m_sc->surfacePixelSize().isEmpty()) {
        m_notExposed = false;
        m_newlyExposed = true;
    }

    // always render a frame on exposeEvent() (when exposed) in order to update
    // immediately on window resize.
    if (isExposed() && !m_sc->surfacePixelSize().isEmpty())
        render();
}

bool Window::event(QEvent *e)
{
    switch (e->type()) {
    case QEvent::UpdateRequest:
        render();
        break;

    case QEvent::PlatformSurface:
        // this is the proper time to tear down the swapchain (while the native window and surface are still around)
        if (static_cast<QPlatformSurfaceEvent *>(e)->surfaceEventType() == QPlatformSurfaceEvent::SurfaceAboutToBeDestroyed)
            releaseSwapChain();
        break;

    default:
        break;
    }

    return QWindow::event(e);
}

void Window::init()
{
    if (graphicsApi == Null) {
        QRhiNullInitParams params;
        m_r = QRhi::create(QRhi::Null, &params);
    }

#ifndef QT_NO_OPENGL
    if (graphicsApi == OpenGL) {
        m_fallbackSurface = QRhiGles2InitParams::newFallbackSurface();
        QRhiGles2InitParams params;
        params.fallbackSurface = m_fallbackSurface;
        params.window = this;
        m_r = QRhi::create(QRhi::OpenGLES2, &params);
    }
#endif

#if QT_CONFIG(vulkan)
    if (graphicsApi == Vulkan) {
        QRhiVulkanInitParams params;
        params.inst = vulkanInstance();
        params.window = this;
        m_r = QRhi::create(QRhi::Vulkan, &params);
    }
#endif

#ifdef Q_OS_WIN
    if (graphicsApi == D3D11) {
        QRhiD3D11InitParams params;
        m_r = QRhi::create(QRhi::D3D11, &params);
    }
#endif

#if defined(Q_OS_MACOS) || defined(Q_OS_IOS)
    if (graphicsApi == Metal) {
        QRhiMetalInitParams params;
        m_r = QRhi::create(QRhi::Metal, &params);
    }
#endif

    if (!m_r)
        qFatal("Failed to create RHI backend");

    // now onto the backend-independent init

    m_sc = m_r->newSwapChain();
    // allow depth-stencil, although we do not actually enable depth test/write for the triangle
    m_ds = m_r->newRenderBuffer(QRhiRenderBuffer::DepthStencil,
                                QSize(), // no need to set the size here, due to UsedWithSwapChainOnly
                                1,
                                QRhiRenderBuffer::UsedWithSwapChainOnly);
    releasePool << m_ds;
    m_sc->setWindow(this);
    m_sc->setDepthStencil(m_ds);
    m_rp = m_sc->newCompatibleRenderPassDescriptor();
    releasePool << m_rp;
    m_sc->setRenderPassDescriptor(m_rp);

    m_vbuf = m_r->newBuffer(QRhiBuffer::Immutable, QRhiBuffer::VertexBuffer, sizeof(vertexData));
    releasePool << m_vbuf;
    m_vbuf->build();
    m_vbufReady = false;

    m_ubuf = m_r->newBuffer(QRhiBuffer::Dynamic, QRhiBuffer::UniformBuffer, 68);
    releasePool << m_ubuf;
    m_ubuf->build();

    m_srb = m_r->newShaderResourceBindings();
    releasePool << m_srb;
    m_srb->setBindings({
        QRhiShaderResourceBinding::uniformBuffer(0, QRhiShaderResourceBinding::VertexStage | QRhiShaderResourceBinding::FragmentStage, m_ubuf)
    });
    m_srb->build();

    m_ps = m_r->newGraphicsPipeline();
    releasePool << m_ps;

    QRhiGraphicsPipeline::TargetBlend premulAlphaBlend;
    premulAlphaBlend.enable = true;
    m_ps->setTargetBlends({ premulAlphaBlend });

    const QShader vs = getShader(QLatin1String(":/color.vert.qsb"));
    if (!vs.isValid())
        qFatal("Failed to load shader pack (vertex)");
    const QShader fs = getShader(QLatin1String(":/color.frag.qsb"));
    if (!fs.isValid())
        qFatal("Failed to load shader pack (fragment)");

    m_ps->setShaderStages({
        { QRhiShaderStage::Vertex, vs },
        { QRhiShaderStage::Fragment, fs }
    });

    QRhiVertexInputLayout inputLayout;
    inputLayout.setBindings({
        { 5 * sizeof(float) }
    });
    inputLayout.setAttributes({
        { 0, 0, QRhiVertexInputAttribute::Float2, 0 },
        { 0, 1, QRhiVertexInputAttribute::Float3, 2 * sizeof(float) }
    });

    m_ps->setVertexInputLayout(inputLayout);
    m_ps->setShaderResourceBindings(m_srb);
    m_ps->setRenderPassDescriptor(m_rp);

    m_ps->build();
}

void Window::releaseResources()
{
    qDeleteAll(releasePool);
    releasePool.clear();

    delete m_sc; // native swapchain is likely released already
    m_sc = nullptr;

    delete m_r;

#ifndef QT_NO_OPENGL
    delete m_fallbackSurface;
#endif
}

void Window::resizeSwapChain()
{
    m_hasSwapChain = m_sc->buildOrResize(); // also handles m_ds

    m_elapsedMs = 0;
    m_elapsedCount = 0;

    const QSize outputSize = m_sc->currentPixelSize();
    m_proj = m_r->clipSpaceCorrMatrix();
    m_proj.perspective(45.0f, outputSize.width() / (float) outputSize.height(), 0.01f, 100.0f);
    m_proj.translate(0, 0, -4);
}

void Window::releaseSwapChain()
{
    if (m_hasSwapChain) {
        m_hasSwapChain = false;
        m_sc->release();
    }
}

void Window::render()
{
    if (!m_hasSwapChain || m_notExposed)
        return;

    // If the window got resized or got newly exposed, resize the swapchain.
    // (the newly-exposed case is not actually required by some
    // platforms/backends, but f.ex. Vulkan on Windows seems to need it)
    if (m_sc->currentPixelSize() != m_sc->surfacePixelSize() || m_newlyExposed) {
        resizeSwapChain();
        if (!m_hasSwapChain)
            return;
        m_newlyExposed = false;
    }

    // Start a new frame. This is where we block when too far ahead of
    // GPU/present, and that's what throttles the thread to the refresh rate.
    // (except for OpenGL where it happens either in endFrame or somewhere else
    // depending on the GL implementation)
    QRhi::FrameOpResult r = m_r->beginFrame(m_sc);
    if (r == QRhi::FrameOpSwapChainOutOfDate) {
        resizeSwapChain();
        if (!m_hasSwapChain)
            return;
        r = m_r->beginFrame(m_sc);
    }
    if (r != QRhi::FrameOpSuccess) {
        requestUpdate();
        return;
    }

    if (m_elapsedCount)
        m_elapsedMs += m_timer.elapsed();
    m_timer.restart();
    m_elapsedCount += 1;
    if (m_elapsedMs >= 4000) {
        qDebug("%f", m_elapsedCount / 4.0f);
        m_elapsedMs = 0;
        m_elapsedCount = 0;
    }

    // Set up buffer updates.
    QRhiResourceUpdateBatch *u = m_r->nextResourceUpdateBatch();
    if (!m_vbufReady) {
        m_vbufReady = true;
        u->uploadStaticBuffer(m_vbuf, vertexData);
    }
    m_rotation += 1.0f;
    QMatrix4x4 mvp = m_proj;
    mvp.rotate(m_rotation, 0, 1, 0);
    u->updateDynamicBuffer(m_ubuf, 0, 64, mvp.constData());
    m_opacity += m_opacityDir * 0.005f;
    if (m_opacity < 0.0f || m_opacity > 1.0f) {
        m_opacityDir *= -1;
        m_opacity = qBound(0.0f, m_opacity, 1.0f);
    }
    u->updateDynamicBuffer(m_ubuf, 64, 4, &m_opacity);

    QRhiCommandBuffer *cb = m_sc->currentFrameCommandBuffer();
    const QSize outputSizeInPixels = m_sc->currentPixelSize();

    // Apply buffer updates, clear, start the renderpass (where applicable).
    cb->beginPass(m_sc->currentFrameRenderTarget(), QColor::fromRgbF(0.4f, 0.7f, 0.0f, 1.0f), { 1.0f, 0 }, u);

    cb->setGraphicsPipeline(m_ps);
    cb->setViewport({ 0, 0, float(outputSizeInPixels.width()), float(outputSizeInPixels.height()) });
    cb->setShaderResources();

    const QRhiCommandBuffer::VertexInput vbufBinding(m_vbuf, 0);
    cb->setVertexInput(0, 1, &vbufBinding);
    cb->draw(3);

    cb->endPass();

    // Submit.
    m_r->endFrame(m_sc);

    requestUpdate(); // render continuously, throttled by the presentation rate (due to beginFrame above)
}

int main(int argc, char **argv)
{
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
    QGuiApplication app(argc, argv);

    // Defaults.
#if defined(Q_OS_WIN)
    graphicsApi = D3D11;
#elif defined(Q_OS_MACOS) || defined(Q_OS_IOS)
    graphicsApi = Metal;
#elif QT_CONFIG(vulkan)
    graphicsApi = Vulkan;
#else
    graphicsApi = OpenGL;
#endif

    // Allow overriding via the command line.
    QCommandLineParser cmdLineParser;
    cmdLineParser.addHelpOption();
    QCommandLineOption glOption({ "g", "opengl" }, QLatin1String("OpenGL (2.x)"));
    cmdLineParser.addOption(glOption);
    QCommandLineOption vkOption({ "v", "vulkan" }, QLatin1String("Vulkan"));
    cmdLineParser.addOption(vkOption);
    QCommandLineOption d3dOption({ "d", "d3d11" }, QLatin1String("Direct3D 11"));
    cmdLineParser.addOption(d3dOption);
    QCommandLineOption mtlOption({ "m", "metal" }, QLatin1String("Metal"));
    cmdLineParser.addOption(mtlOption);
    QCommandLineOption nullOption({ "n", "null" }, QLatin1String("Null"));
    cmdLineParser.addOption(nullOption);
    cmdLineParser.process(app);
    if (cmdLineParser.isSet(glOption))
        graphicsApi = OpenGL;
    if (cmdLineParser.isSet(vkOption))
        graphicsApi = Vulkan;
    if (cmdLineParser.isSet(d3dOption))
        graphicsApi = D3D11;
    if (cmdLineParser.isSet(mtlOption))
        graphicsApi = Metal;
    if (cmdLineParser.isSet(nullOption))
        graphicsApi = Null;

    // Vulkan setup.
#if QT_CONFIG(vulkan)
    QVulkanInstance inst;
    if (graphicsApi == Vulkan) {
        if (!inst.create()) {
            qWarning("Failed to create Vulkan instance, switching to OpenGL");
            graphicsApi = OpenGL;
        }
    }
#endif

    // Create and show the window.
    Window w;
#if QT_CONFIG(vulkan)
    if (graphicsApi == Vulkan)
        w.setVulkanInstance(&inst);
#endif
    w.resize(1280, 720);
    w.setTitle(graphicsApiName());
    w.show();

    // Window::event() will not get invoked when the
    // PlatformSurfaceAboutToBeDestroyed event is sent during the QWindow
    // destruction. That happens only when exiting via app::quit() instead of
    // the more common QWindow::close(). Take care of it: if the
    // QPlatformWindow is still around (there was no close() yet), get rid of
    // the swapchain while it's not too late.
    if (w.handle())
        w.releaseSwapChain();

    return app.exec();
}