Speed up lookup operation in TransferListModel

Previously lookup is O(n), add operation is O(n), remove operation is
O(n).
Now lookup is O(1), add operation is O(1), remove operation is O(n).
n is the number of torrents already recorded.

src/gui/transferlistmodel.cpp

@@ -77,15 +77,13 @@ TransferListModel::TransferListModel(QObject *parent)
     connect(Session::instance(), &Session::torrentFinishedChecking, this, &TransferListModel::handleTorrentStatusUpdated);
 }
 
-int TransferListModel::rowCount(const QModelIndex &index) const
+int TransferListModel::rowCount(const QModelIndex &) const
 {
-    Q_UNUSED(index);
-    return m_torrents.size();
+    return m_torrentList.size();
 }
 
-int TransferListModel::columnCount(const QModelIndex &parent) const
+int TransferListModel::columnCount(const QModelIndex &) const
 {
-    Q_UNUSED(parent);
     return NB_COLUMNS;
 }
 
@@ -164,7 +162,7 @@ QVariant TransferListModel::data(const QModelIndex &index, const int role) const
 {
     if (!index.isValid()) return {};
 
-    const BitTorrent::TorrentHandle *torrent = m_torrents.value(index.row());
+    const BitTorrent::TorrentHandle *torrent = m_torrentList.value(index.row());
     if (!torrent) return {};
 
     if ((role == Qt::DecorationRole) && (index.column() == TR_NAME))
@@ -251,11 +249,9 @@ QVariant TransferListModel::data(const QModelIndex &index, const int role) const
 
 bool TransferListModel::setData(const QModelIndex &index, const QVariant &value, int role)
 {
-    qDebug() << Q_FUNC_INFO << value;
     if (!index.isValid() || (role != Qt::DisplayRole)) return false;
 
-    qDebug("Index is valid and role is DisplayRole");
-    BitTorrent::TorrentHandle *const torrent = m_torrents.value(index.row());
+    BitTorrent::TorrentHandle *const torrent = m_torrentList.value(index.row());
     if (!torrent) return false;
 
     // Category and Name columns can be edited
@@ -275,12 +271,15 @@ bool TransferListModel::setData(const QModelIndex &index, const QVariant &value,
 
 void TransferListModel::addTorrent(BitTorrent::TorrentHandle *const torrent)
 {
-    if (!m_torrents.contains(torrent)) {
-        const int row = m_torrents.size();
-        beginInsertRows(QModelIndex(), row, row);
-        m_torrents << torrent;
-        endInsertRows();
-    }
+    if (m_torrentMap.contains(torrent))
+        return;
+
+    const int row = m_torrentList.size();
+
+    beginInsertRows({}, row, row);
+    m_torrentList << torrent;
+    m_torrentMap[torrent] = row;
+    endInsertRows();
 }
 
 Qt::ItemFlags TransferListModel::flags(const QModelIndex &index) const
@@ -295,32 +294,39 @@ BitTorrent::TorrentHandle *TransferListModel::torrentHandle(const QModelIndex &i
 {
     if (!index.isValid()) return nullptr;
 
-    return m_torrents.value(index.row());
+    return m_torrentList.value(index.row());
 }
 
 void TransferListModel::handleTorrentAboutToBeRemoved(BitTorrent::TorrentHandle *const torrent)
 {
-    const int row = m_torrents.indexOf(torrent);
-    if (row >= 0) {
-        beginRemoveRows(QModelIndex(), row, row);
-        m_torrents.removeAt(row);
-        endRemoveRows();
+    const int row = m_torrentMap.value(torrent, -1);
+    if (row < 0)
+        return;
+
+    beginRemoveRows({}, row, row);
+    m_torrentList.removeAt(row);
+    m_torrentMap.remove(torrent);
+    for (int &value : m_torrentMap) {
+        if (value > row)
+            --value;
     }
+    endRemoveRows();
 }
 
 void TransferListModel::handleTorrentStatusUpdated(BitTorrent::TorrentHandle *const torrent)
 {
-    const int row = m_torrents.indexOf(torrent);
-    if (row >= 0)
-        emit dataChanged(index(row, 0), index(row, columnCount() - 1));
+    const int row = m_torrentMap.value(torrent, -1);
+    if (row < 0)
+        return;
+
+    emit dataChanged(index(row, 0), index(row, columnCount() - 1));
 }
 
 void TransferListModel::handleTorrentsUpdated(const QVector<BitTorrent::TorrentHandle *> &torrents)
 {
     const int columns = (columnCount() - 1);
-
     for (BitTorrent::TorrentHandle *const torrent : torrents) {
-        const int row = m_torrents.indexOf(torrent);
+        const int row = m_torrentMap.value(torrent, -1);
 
         if (row < 0)
             continue;

src/gui/transferlistmodel.h

@@ -84,8 +84,8 @@ public:
 
     explicit TransferListModel(QObject *parent = nullptr);
 
-    int rowCount(const QModelIndex &index = {}) const override;
-    int columnCount(const QModelIndex &parent=QModelIndex()) const override;
+    int rowCount(const QModelIndex &parent = {}) const override;
+    int columnCount(const QModelIndex &parent = {}) const override;
     QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const override;
     bool setData(const QModelIndex &index, const QVariant &value, int role) override;
     QVariant headerData(int section, Qt::Orientation orientation, int role) const override;
@@ -100,7 +100,8 @@ private slots:
     void handleTorrentsUpdated(const QVector<BitTorrent::TorrentHandle *> &torrents);
 
 private:
-    QList<BitTorrent::TorrentHandle *> m_torrents;
+    QList<BitTorrent::TorrentHandle *> m_torrentList;  // maps row number to torrent handle
+    QHash<BitTorrent::TorrentHandle *, int> m_torrentMap;  // maps torrent handle to row number
 };
 
 #endif // TRANSFERLISTMODEL_H