Method snapshot

app/src/Misc/BackupManager.cpp:115–169

* @brief Write a snapshot of the current ProjectModel state; returns the absolute path (or the * existing path if content is byte-identical to the previous snapshot). */

 * existing path if content is byte-identical to the previous snapshot).
 */
QString Misc::BackupManager::snapshot(const QString& label)
{
  if (!m_enabled)
    return {};

  auto& pm        = DataModel::ProjectModel::instance();
  const auto stem = currentProjectStem();
  const auto dir  = resolveBackupDir(stem);
  if (dir.isEmpty())
    return {};

  auto serialised = pm.serializeToJson();
  if (serialised.isEmpty())
    return {};

  const auto payloadBytes = QJsonDocument(serialised).toJson(QJsonDocument::Compact);
  const auto newHash      = QCryptographicHash::hash(payloadBytes, QCryptographicHash::Sha1);

  QJsonObject meta;
  meta.insert(QStringLiteral("format"), kSnapshotFormat);
  meta.insert(QStringLiteral("takenAt"), QDateTime::currentDateTimeUtc().toString(Qt::ISODate));
  meta.insert(QStringLiteral("label"), label);
  meta.insert(QStringLiteral("sha1"), QString::fromLatin1(newHash.toHex()));
  serialised.insert(kBackupMetaKey, meta);

  const auto bytes = QJsonDocument(serialised).toJson(QJsonDocument::Compact);

  if (m_lastContentHash.isEmpty())
    seedDedupFromNewest(dir);

  if (!m_lastContentHash.isEmpty() && newHash == m_lastContentHash)
    return m_lastSnapshotPath;

  QString fileName = fsSafeIsoTimestamp();
  if (!label.isEmpty()) {
    const auto cleanLabel = sanitiseLabel(label);
    if (!cleanLabel.isEmpty())
      fileName += QStringLiteral("__") + cleanLabel;
  }
  fileName += QStringLiteral(".ssproj");

  const auto fullPath = QDir(dir).filePath(fileName);
  QSaveFile out(fullPath);
  if (!out.open(QIODevice::WriteOnly | QIODevice::Truncate))
    return {};

  if (out.write(bytes) != bytes.size() || !out.commit())
    return {};

  m_lastSnapshotPath = fullPath;
  m_lastContentHash  = newHash;
  enforceRetention(dir);
  Q_EMIT snapshotTaken(fullPath);
  return fullPath;
}

/**
 * @brief Load a snapshot file back into ProjectModel; returns true on success.