#pragma once

#include <QtGlobal>
#include <QImageReader>
#include <QRect>
#include <QSize>

#include <algorithm>
#include <cmath>

namespace core {
namespace image_decode {

/// 提高 Qt6 解码像素上限，避免大图被 reader 直接拒绝（单位 MB）
inline void prepareLargeImageReader() {
#if QT_VERSION >= QT_VERSION_CHECK(6, 0, 0)
    QImageReader::setAllocationLimit(4096);
#endif
}

/// 裁剪对话框等「仅预览」场景：像素上限（libvips 缩略与 Qt 回退共用）
[[maybe_unused]] constexpr qint64 kPreviewMaxPixels = 16LL * 1000 * 1000;

/// 编辑器 / 帧图替换：缩略像素上限（libvips 与 Qt 回退共用）
[[maybe_unused]] constexpr qint64 kWorkspaceMaxPixels = 48LL * 1000 * 1000;

/// 在 read() 前调用：若像素数超过 maxPixels，则 setScaledSize 按比例缩小（不解码全图）
inline void downscaleReaderIfExceeds(QImageReader& reader, qint64 maxPixels) {
    const QSize sz = reader.size();
    if (!sz.isValid() || sz.width() <= 0 || sz.height() <= 0) {
        return;
    }
    const qint64 pixels = qint64(sz.width()) * qint64(sz.height());
    if (pixels <= maxPixels) {
        return;
    }
    const double s = std::sqrt(double(maxPixels) / double(pixels));
    const int nw = std::max(1, int(std::lround(sz.width() * s)));
    const int nh = std::max(1, int(std::lround(sz.height() * s)));
    reader.setScaledSize(QSize(nw, nh));
}

/// 将 rect 从 fromSize 坐标系线性映射到 toSize（例如预览图上的选区 → 原图逻辑像素）
inline QRect mapRectBetweenSizes(const QRect& rect, const QSize& fromSize, const QSize& toSize) {
    if (!rect.isValid() || fromSize.width() <= 0 || fromSize.height() <= 0 || toSize.width() <= 0 ||
        toSize.height() <= 0) {
        return {};
    }
    const qreal sx = qreal(toSize.width()) / qreal(fromSize.width());
    const qreal sy = qreal(toSize.height()) / qreal(fromSize.height());
    const int x0 = int(std::floor(qreal(rect.left()) * sx));
    const int y0 = int(std::floor(qreal(rect.top()) * sy));
    const int x1 = int(std::ceil(qreal(rect.right() + 1) * sx));
    const int y1 = int(std::ceil(qreal(rect.bottom() + 1) * sy));
    QRect out(x0, y0, x1 - x0, y1 - y0);
    return out.normalized().intersected(QRect(0, 0, toSize.width(), toSize.height()));
}

}  // namespace image_decode
}  // namespace core