rename PlaylistTableModel::getDurationOfRows(), return mixxx::Duration, add comment

src/library/autodj/dlgautodj.cpp

@@ -363,18 +363,16 @@ void DlgAutoDJ::slotRepeatPlaylistChanged(int checkState) {
 }
 
 void DlgAutoDJ::updateSelectionInfo() {
-    double duration = 0.0;
-
     QModelIndexList indices = m_pTrackTableView->selectionModel()->selectedRows();
 
     // Derive total duration from the table model. This is much faster than
     // getting the duration from individual track objects.
-    duration = m_pAutoDJTableModel->getDurationOfRows(indices);
+    mixxx::Duration duration = m_pAutoDJTableModel->getTotalDuration(indices);
 
     QString label;
 
     if (!indices.isEmpty()) {
-        label.append(mixxx::DurationBase::formatTime(duration));
+        label.append(mixxx::DurationBase::formatTime(duration.toDoubleSeconds()));
         label.append(QString(" (%1)").arg(indices.size()));
         labelSelectionInfo->setToolTip(tr("Displays the duration and number of selected tracks."));
         labelSelectionInfo->setText(label);

src/library/playlisttablemodel.cpp

@@ -319,20 +319,20 @@ void PlaylistTableModel::shuffleTracks(const QModelIndexList& shuffle, const QMo
     m_pTrackCollectionManager->internalCollection()->getPlaylistDAO().shuffleTracks(m_iPlaylistId, positions, allIds);
 }
 
-double PlaylistTableModel::getDurationOfRows(const QModelIndexList& indices) {
-    double durationTotal = 0.0;
+mixxx::Duration PlaylistTableModel::getTotalDuration(const QModelIndexList& indices) {
     if (indices.isEmpty()) {
-        return durationTotal;
+        return mixxx::Duration::empty();
     }
 
+    double durationTotal = 0.0;
     const int durationColumnIndex = fieldIndex(ColumnCache::COLUMN_LIBRARYTABLE_DURATION);
     for (const auto& index : indices) {
         durationTotal += index.sibling(index.row(), durationColumnIndex)
                                  .data(Qt::EditRole)
                                  .toDouble();
     }
 
-    return durationTotal;
+    return mixxx::Duration::fromSeconds(durationTotal);
 }
 
 bool PlaylistTableModel::isColumnInternal(int column) {

src/library/playlisttablemodel.h

@@ -1,6 +1,7 @@
 #pragma once
 
 #include "library/trackset/tracksettablemodel.h"
+#include "util/duration.h"
 
 class PlaylistTableModel final : public TrackSetTableModel {
     Q_OBJECT
@@ -27,7 +28,8 @@ class PlaylistTableModel final : public TrackSetTableModel {
     int addTracks(const QModelIndex& index, const QList<QString>& locations) final;
     bool isLocked() final;
 
-    double getDurationOfRows(const QModelIndexList& indices);
+    /// Get the total duration of all tracks referenced by the given model indices
+    mixxx::Duration getTotalDuration(const QModelIndexList& indices);
 
     Capabilities getCapabilities() const final;