src/thumbnailcache.cpp

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/*
MIT License

Copyright (c) 2026 Poul Sander

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.

*/

#include "thumbnailcache.h"

#include <QCryptographicHash>
#include <QDir>
#include <QFile>
#include <QStandardPaths>
#include <QTemporaryFile>
#include <QUrl>

#include <sys/stat.h>

namespace
{
constexpr const char *kSoftware = "SagoImageBrowser";

QFile::Permissions filePerms()
{
    return QFile::ReadOwner | QFile::WriteOwner;
}

QFile::Permissions dirPerms()
{
    return QFile::ReadOwner | QFile::WriteOwner | QFile::ExeOwner;
}
} // namespace

QString ThumbnailCache::cacheRoot()
{
    QString base = QStandardPaths::writableLocation(QStandardPaths::GenericCacheLocation);
    if (base.isEmpty())
        base = QDir::homePath() + "/.cache";
    return base + "/thumbnails";
}

QString ThumbnailCache::subdirFor(Size size)
{
    const char *name = (size == Size::Large) ? "large" : "normal";
    return cacheRoot() + "/" + name;
}

QByteArray ThumbnailCache::canonicalUri(const QByteArray &absPath)
{
    // Build a correct file:// URI by percent-encoding the raw byte path.
    // Forward slashes are kept unencoded; all other bytes (including non-UTF-8
    // ones such as Latin-1 \xF8) are percent-encoded.
    return "file://" + QUrl::toPercentEncoding(absPath, "/");
}

QString ThumbnailCache::hashedName(const QByteArray &canonicalUri)
{
    QByteArray hash =
        QCryptographicHash::hash(canonicalUri, QCryptographicHash::Md5).toHex();
    return QString::fromLatin1(hash) + ".png";
}

bool ThumbnailCache::isInsideCache(const QByteArray &absPath)
{
    QByteArray root = cacheRoot().toUtf8(); // cache root is always valid UTF-8
    return absPath.startsWith(root + '/') || absPath == root;
}

// THREADING: Called from worker threads (ThumbnailWorker::run()).  This
// function is free of shared mutable state — it only performs filesystem I/O
// using its arguments.  Safe to call concurrently from multiple threads.
QImage ThumbnailCache::load(const QByteArray &sourcePath, Size size)
{
    struct ::stat st{};
    if (::stat(sourcePath.constData(), &st) != 0 || !S_ISREG(st.st_mode))
        return {};

    const QByteArray uri = canonicalUri(sourcePath);
    const QString cachePath = subdirFor(size) + "/" + hashedName(uri);

    QImage img;
    if (!img.load(cachePath, "PNG"))
        return {};

    const qint64 mtime = static_cast<qint64>(st.st_mtime);
    bool ok = false;
    const qint64 cachedMTime = img.text("Thumb::MTime").toLongLong(&ok);
    if (!ok || cachedMTime != mtime)
        return {};

    return img;
}

// THREADING: Called from worker threads (ThumbnailWorker::run()).  This
// function is free of shared mutable state — it only performs filesystem I/O
// using its arguments.  Writes are atomic (temp file + rename) so concurrent
// calls for different source files are safe.
void ThumbnailCache::save(const QByteArray &sourcePath, Size size, const QImage &thumbImage)
{
    if (thumbImage.isNull())
        return;

    struct ::stat st{};
    if (::stat(sourcePath.constData(), &st) != 0 || !S_ISREG(st.st_mode))
        return;

    const QByteArray uri = canonicalUri(sourcePath);
    const QString subdir = subdirFor(size);
    const QString finalPath = subdir + "/" + hashedName(uri);

    QDir dir;
    if (!dir.mkpath(subdir))
        return;
    QFile::setPermissions(subdir, dirPerms());
    QFile::setPermissions(cacheRoot(), dirPerms());

    QImage tagged = thumbImage;
    tagged.setText("Thumb::URI", QString::fromLatin1(uri));
    tagged.setText("Thumb::MTime",
                   QString::number(static_cast<qint64>(st.st_mtime)));
    tagged.setText("Thumb::Size", QString::number(static_cast<qint64>(st.st_size)));
    tagged.setText("Software", QString::fromLatin1(kSoftware));

    QTemporaryFile tmp(subdir + "/tmp_XXXXXX.png");
    tmp.setAutoRemove(false);
    if (!tmp.open())
        return;
    const QString tmpPath = tmp.fileName();
    tmp.close();

    if (!tagged.save(tmpPath, "PNG"))
    {
        QFile::remove(tmpPath);
        return;
    }

    QFile::setPermissions(tmpPath, filePerms());

    // Atomic replace: remove existing target then rename.
    QFile::remove(finalPath);
    if (!QFile::rename(tmpPath, finalPath))
        QFile::remove(tmpPath);
}