bool TransferListSortModel::lessThan(const QModelIndex &left, const QModelIndex &right) const
{
    const int column  = sortColumn();

    if (column == TorrentModel::TR_NAME) {
        QVariant vL = left.data();
        QVariant vR = right.data();
        if (!vL.isValid() || !vR.isValid() || (vL == vR))
            return lowerPositionThan(left, right);

        bool res = false;
        if (Utils::String::naturalSort(vL.toString(), vR.toString(), res))
            return res;

        return QSortFilterProxyModel::lessThan(left, right);
    }
    else if (column == TorrentModel::TR_ADD_DATE || column == TorrentModel::TR_SEED_DATE || column == TorrentModel::TR_SEEN_COMPLETE_DATE) {
        QDateTime vL = left.data().toDateTime();
        QDateTime vR = right.data().toDateTime();

        //not valid dates should be sorted at the bottom.
        if (!vL.isValid()) return false;
        if (!vR.isValid()) return true;

        return vL < vR;
    }
    else if (column == TorrentModel::TR_PRIORITY) {
        return lowerPositionThan(left, right);
    }
    else if (column == TorrentModel::TR_PEERS || column == TorrentModel::TR_SEEDS) {
        int left_active = left.data().toInt();
        int left_total = left.data(Qt::UserRole).toInt();
        int right_active = right.data().toInt();
        int right_total = right.data(Qt::UserRole).toInt();

        // Active peers/seeds take precedence over total peers/seeds.
        if (left_active == right_active) {
            if (left_total == right_total)
                return lowerPositionThan(left, right);
            return (left_total < right_total);
        }
        else {
            return (left_active < right_active);
        }
    }
    else if (column == TorrentModel::TR_ETA) {
        TorrentModel *model = qobject_cast<TorrentModel *>(sourceModel());
        const int prioL = model->data(model->index(left.row(), TorrentModel::TR_PRIORITY)).toInt();
        const int prioR = model->data(model->index(right.row(), TorrentModel::TR_PRIORITY)).toInt();
        const qlonglong etaL = left.data().toLongLong();
        const qlonglong etaR = right.data().toLongLong();
        const bool ascend = (sortOrder() == Qt::AscendingOrder);
        const bool invalidL = (etaL < 0 || etaL >= MAX_ETA);
        const bool invalidR = (etaR < 0 || etaR >= MAX_ETA);
        const bool seedingL = (prioL < 0);
        const bool seedingR = (prioR < 0);

        bool activeR = TorrentFilter::ActiveTorrent.match(model->torrentHandle(model->index(right.row())));
        bool activeL = TorrentFilter::ActiveTorrent.match(model->torrentHandle(model->index(right.row())));

        // Sorting rules prioritized.
        // 1. Active torrents at the top
        // 2. Seeding torrents at the bottom
        // 3. Torrents with invalid ETAs at the bottom

        if (activeL != activeR) return activeL;
        if (seedingL != seedingR) {
            if (seedingL) return !ascend;
            else return ascend;
        }

        if (invalidL && invalidR) {
            if (seedingL) { //Both seeding
                QDateTime dateL = model->data(model->index(left.row(), TorrentModel::TR_SEED_DATE)).toDateTime();
                QDateTime dateR = model->data(model->index(right.row(), TorrentModel::TR_SEED_DATE)).toDateTime();

                //not valid dates should be sorted at the bottom.
                if (!dateL.isValid()) return false;
                if (!dateR.isValid()) return true;

                return dateL < dateR;
            }
            else {
                return prioL < prioR;
            }
        }
        else if (!invalidL && !invalidR) {
            return etaL < etaR;
        }
        else {
            return !invalidL;
        }
    }
    else if (column == TorrentModel::TR_LAST_ACTIVITY) {
        const qlonglong vL = left.data().toLongLong();
        const qlonglong vR = right.data().toLongLong();

        if (vL == -1) return false;
        if (vR == -1) return true;

        return vL < vR;
    }
    else if (column == TorrentModel::TR_RATIO_LIMIT) {
        const qreal vL = left.data().toDouble();
        const qreal vR = right.data().toDouble();

        if (vL == -1) return false;
        if (vR == -1) return true;

        return vL < vR;
    }

    if (left.data() == right.data())
        return lowerPositionThan(left, right);

    return QSortFilterProxyModel::lessThan(left, right);
}
bool TransferListSortModel::lessThan(const QModelIndex &left, const QModelIndex &right) const
{
    switch (sortColumn()) {
    case TransferListModel::TR_CATEGORY:
    case TransferListModel::TR_TAGS:
    case TransferListModel::TR_NAME: {
            const QVariant vL = left.data();
            const QVariant vR = right.data();
            if (!vL.isValid() || !vR.isValid() || (vL == vR))
                return lowerPositionThan(left, right);

            const int result = Utils::String::naturalCompare(vL.toString(), vR.toString(), Qt::CaseInsensitive);
            return (result < 0);
        }

    case TransferListModel::TR_STATUS: {
            // QSortFilterProxyModel::lessThan() uses the < operator only for specific QVariant types
            // so our custom type is outside that list.
            // In this case QSortFilterProxyModel::lessThan() converts other types to QString and
            // sorts them.
            // Thus we can't use the code in the default label.
            const auto leftValue = left.data().value<BitTorrent::TorrentState>();
            const auto rightValue = right.data().value<BitTorrent::TorrentState>();
            if (leftValue != rightValue)
                return leftValue < rightValue;

            return lowerPositionThan(left, right);
        }

    case TransferListModel::TR_ADD_DATE:
    case TransferListModel::TR_SEED_DATE:
    case TransferListModel::TR_SEEN_COMPLETE_DATE: {
        return dateLessThan(sortColumn(), left, right, true);
        }

    case TransferListModel::TR_PRIORITY: {
        return lowerPositionThan(left, right);
        }

    case TransferListModel::TR_SEEDS:
    case TransferListModel::TR_PEERS: {
            const int leftActive = left.data().toInt();
            const int leftTotal = left.data(Qt::UserRole).toInt();
            const int rightActive = right.data().toInt();
            const int rightTotal = right.data(Qt::UserRole).toInt();

            // Active peers/seeds take precedence over total peers/seeds.
            if (leftActive != rightActive)
                return (leftActive < rightActive);

            if (leftTotal != rightTotal)
                return (leftTotal < rightTotal);

            return lowerPositionThan(left, right);
        }

    case TransferListModel::TR_ETA: {
            const TransferListModel *model = qobject_cast<TransferListModel *>(sourceModel());

            // Sorting rules prioritized.
            // 1. Active torrents at the top
            // 2. Seeding torrents at the bottom
            // 3. Torrents with invalid ETAs at the bottom

            const bool isActiveL = TorrentFilter::ActiveTorrent.match(model->torrentHandle(model->index(left.row())));
            const bool isActiveR = TorrentFilter::ActiveTorrent.match(model->torrentHandle(model->index(right.row())));
            if (isActiveL != isActiveR)
                return isActiveL;

            const int prioL = model->data(model->index(left.row(), TransferListModel::TR_PRIORITY)).toInt();
            const int prioR = model->data(model->index(right.row(), TransferListModel::TR_PRIORITY)).toInt();
            const bool isSeedingL = (prioL < 0);
            const bool isSeedingR = (prioR < 0);
            if (isSeedingL != isSeedingR) {
                const bool isAscendingOrder = (sortOrder() == Qt::AscendingOrder);
                if (isSeedingL)
                    return !isAscendingOrder;

                return isAscendingOrder;
            }

            const qlonglong etaL = left.data().toLongLong();
            const qlonglong etaR = right.data().toLongLong();
            const bool isInvalidL = ((etaL < 0) || (etaL >= MAX_ETA));
            const bool isInvalidR = ((etaR < 0) || (etaR >= MAX_ETA));
            if (isInvalidL && isInvalidR) {
                if (isSeedingL)  // Both seeding
                    return dateLessThan(TransferListModel::TR_SEED_DATE, left, right, true);

                return (prioL < prioR);
            }
            if (!isInvalidL && !isInvalidR) {
                return (etaL < etaR);
            }

            return !isInvalidL;
        }

    case TransferListModel::TR_LAST_ACTIVITY: {
            const int vL = left.data().toInt();
            const int vR = right.data().toInt();

            if (vL < 0) return false;
            if (vR < 0) return true;

            return (vL < vR);
        }

    case TransferListModel::TR_RATIO_LIMIT: {
            const qreal vL = left.data().toReal();
            const qreal vR = right.data().toReal();

            if (vL < 0) return false;
            if (vR < 0) return true;

            return (vL < vR);
        }

    default: {
        if (left.data() != right.data())
            return QSortFilterProxyModel::lessThan(left, right);

        return lowerPositionThan(left, right);
        }
    }
}