#include "ImageView.h"

#include <QGraphicsPixmapItem>
#include <QGraphicsScene>
#include <QLabel>
#include <QMouseEvent>
#include <QResizeEvent>
#include <QtWidgets/QScrollBar>
#include <QStyle>
#include <QWheelEvent>
#include <QtMath>

namespace {
constexpr double kDefaultMinimumZoom = 0.02;
constexpr double kDefaultMaximumZoom = 20.0;
constexpr double kZoomStep = 1.25;
}

ImageView::ImageView(QWidget* parent)
    : QGraphicsView(parent),
      m_scene(new QGraphicsScene(this)),
      m_pixmapItem(nullptr),
      m_zoomLabel(new QLabel(this)),
      m_zoomRatio(1.0),
      m_minimumZoomRatio(kDefaultMinimumZoom),
      m_maximumZoomRatio(kDefaultMaximumZoom),
      m_imageAlignment(Qt::AlignCenter),
      m_panning(false),
      m_needsInitialFit(false)
{
    setScene(m_scene);
    setBackgroundBrush(QColor(35, 35, 35));
    setFrameShape(QFrame::NoFrame);
    setHorizontalScrollBarPolicy(Qt::ScrollBarAsNeeded);
    setVerticalScrollBarPolicy(Qt::ScrollBarAsNeeded);
    setTransformationAnchor(QGraphicsView::AnchorUnderMouse);
    setResizeAnchor(QGraphicsView::AnchorViewCenter);
    setAlignment(m_imageAlignment);
    setDragMode(QGraphicsView::NoDrag);
    setCursor(Qt::OpenHandCursor);

    m_zoomLabel->setObjectName(QStringLiteral("imageViewZoomLabel"));
    m_zoomLabel->setAlignment(Qt::AlignCenter);
    m_zoomLabel->setMinimumWidth(58);
    m_zoomLabel->setAttribute(Qt::WA_TransparentForMouseEvents);
    m_zoomLabel->setStyleSheet(QStringLiteral(
        "QLabel { color: white; background: transparent; border: none; }"));
    updateZoomLabel();
}

ImageView::~ImageView() = default;

void ImageView::setImage(const QImage& image)
{
    if (image.isNull()) {
        clearImage();
        return;
    }

    m_image = image;
    if (!m_pixmapItem) {
        m_pixmapItem = m_scene->addPixmap(QPixmap::fromImage(m_image));
    } else {
        m_pixmapItem->setPixmap(QPixmap::fromImage(m_image));
    }
    m_scene->setSceneRect(QRectF(QPointF(0.0, 0.0), QSizeF(m_image.size())));
    m_needsInitialFit = true;
    if (viewport()->width() > 0 && viewport()->height() > 0) {
        m_needsInitialFit = false;
        resetView();
    }
    emit imageChanged();
}

void ImageView::setImage(const QPixmap& pixmap)
{
    setImage(pixmap.toImage());
}

bool ImageView::loadImage(const QString& filePath)
{
    QImage loaded;
    if (!loaded.load(filePath)) {
        return false;
    }
    setImage(loaded);
    return true;
}

void ImageView::clearImage()
{
    m_image = QImage();
    m_scene->clear();
    m_pixmapItem = nullptr;
    m_scene->setSceneRect(QRectF());
    m_zoomRatio = 1.0;
    m_needsInitialFit = false;
    updateZoomLabel();
    viewport()->update();
    emit imageChanged();
}

bool ImageView::hasImage() const
{
    return !m_image.isNull();
}

QImage ImageView::image() const
{
    return m_image;
}

double ImageView::zoomRatio() const
{
    return m_zoomRatio;
}

void ImageView::setZoomRatio(double ratio)
{
    updateZoomRatio(ratio, true);
}

void ImageView::zoomIn(double factor)
{
    if (factor <= 1.0) {
        factor = kZoomStep;
    }
    updateZoomRatio(m_zoomRatio * factor, true);
}

void ImageView::zoomOut(double factor)
{
    if (factor <= 1.0) {
        factor = kZoomStep;
    }
    updateZoomRatio(m_zoomRatio / factor, true);
}

void ImageView::resetView()
{
    if (!hasImage() || !m_pixmapItem) {
        return;
    }

    const double previousRatio = m_zoomRatio;
    resetTransform();
    fitInView(m_pixmapItem, Qt::KeepAspectRatio);

    const double fittedRatio = qBound(m_minimumZoomRatio,
                                      transform().m11(),
                                      m_maximumZoomRatio);
    resetTransform();
    scale(fittedRatio, fittedRatio);
    m_zoomRatio = fittedRatio;
    centerOn(m_pixmapItem);
    updateZoomLabel();

    if (!qFuzzyCompare(previousRatio, m_zoomRatio)) {
        emit zoomRatioChanged(m_zoomRatio);
    }
}

void ImageView::setZoomRange(double minimum, double maximum)
{
    if (minimum <= 0.0 || maximum < minimum) {
        return;
    }
    m_minimumZoomRatio = minimum;
    m_maximumZoomRatio = maximum;
    updateZoomRatio(m_zoomRatio, true);
}

double ImageView::minimumZoomRatio() const
{
    return m_minimumZoomRatio;
}

double ImageView::maximumZoomRatio() const
{
    return m_maximumZoomRatio;
}

void ImageView::setImageAlignment(Qt::Alignment alignment)
{
    if (!alignment) {
        alignment = Qt::AlignCenter;
    }
    m_imageAlignment = alignment;
    setAlignment(m_imageAlignment);
    if (hasImage()) {
        viewport()->update();
    }
}

Qt::Alignment ImageView::imageAlignment() const
{
    return m_imageAlignment;
}

void ImageView::resizeEvent(QResizeEvent* event)
{
    QGraphicsView::resizeEvent(event);
    if (m_needsInitialFit && hasImage() && viewport()->width() > 0 && viewport()->height() > 0) {
        m_needsInitialFit = false;
        resetView();
    }
    repositionZoomLabel();
}

void ImageView::wheelEvent(QWheelEvent* event)
{
    if (!hasImage() || event->angleDelta().y() == 0) {
        event->ignore();
        return;
    }

    const double factor = event->angleDelta().y() > 0 ? kZoomStep : 1.0 / kZoomStep;
    updateZoomRatio(m_zoomRatio * factor, true);
    event->accept();
}

void ImageView::mousePressEvent(QMouseEvent* event)
{
    if (event->button() == Qt::LeftButton && hasImage()) {
        m_panning = true;
        m_lastMousePosition = event->pos();
        setCursor(Qt::ClosedHandCursor);
        event->accept();
        return;
    }
    QGraphicsView::mousePressEvent(event);
}

void ImageView::mouseMoveEvent(QMouseEvent* event)
{
    if (m_panning) {
        const QPoint delta = event->pos() - m_lastMousePosition;
        m_lastMousePosition = event->pos();
        horizontalScrollBar()->setValue(horizontalScrollBar()->value() - delta.x());
        verticalScrollBar()->setValue(verticalScrollBar()->value() - delta.y());
        event->accept();
        return;
    }
    QGraphicsView::mouseMoveEvent(event);
}

void ImageView::mouseReleaseEvent(QMouseEvent* event)
{
    if (event->button() == Qt::LeftButton && m_panning) {
        m_panning = false;
        setCursor(Qt::OpenHandCursor);
        event->accept();
        return;
    }
    QGraphicsView::mouseReleaseEvent(event);
}

void ImageView::mouseDoubleClickEvent(QMouseEvent* event)
{
    if (event->button() == Qt::LeftButton && hasImage()) {
        resetView();
        event->accept();
        return;
    }
    QGraphicsView::mouseDoubleClickEvent(event);
}

void ImageView::updateZoomLabel()
{
    if (!hasImage()) {
        m_zoomLabel->setText(QStringLiteral("--"));
    } else {
        m_zoomLabel->setText(QStringLiteral("%1%")
                                 .arg(m_zoomRatio * 100.0, 0, 'f', 1));
    }
    m_zoomLabel->adjustSize();
    repositionZoomLabel();
}

void ImageView::updateZoomRatio(double ratio, bool keepCenter)
{
    if (!hasImage()) {
        return;
    }

    ratio = qBound(m_minimumZoomRatio, ratio, m_maximumZoomRatio);
    if (qFuzzyCompare(ratio, m_zoomRatio) && !transform().isIdentity()) {
        return;
    }

    const QPoint viewportCenter = viewport()->rect().center();
    const QPointF sceneCenter = mapToScene(viewportCenter);
    resetTransform();
    scale(ratio, ratio);
    m_zoomRatio = ratio;
    if (keepCenter) {
        centerOn(sceneCenter);
    }
    updateZoomLabel();
    emit zoomRatioChanged(m_zoomRatio);
}

void ImageView::repositionZoomLabel()
{
    if (!m_zoomLabel) {
        return;
    }
    const int margin = 8;
    const int scrollBarHeight = horizontalScrollBar()->isVisible()
        ? horizontalScrollBar()->height()
        : 0;
    m_zoomLabel->move(margin,
                      height() - m_zoomLabel->height() - margin - scrollBarHeight);
    m_zoomLabel->raise();
}