Don't reorder the torrents in the transfer list if not necessary

The current sorting algorithm is not stable and causes undesidered
rearrangements of the transfer list when different torrents have same
values in respect to the current sorting criterion. Fix this by using
the priority, the seed date and the hash of the torrents as fallback
values to determine the order.

Closes #2158.
Closes #2526.

src/gui/transferlistsortmodel.cpp

@@ -93,10 +93,13 @@ bool TransferListSortModel::lessThan(const QModelIndex &left, const QModelIndex
         QVariant vL = left.data();
         QVariant vR = right.data();
         if (!(vL.isValid() && vR.isValid()))
-            return QSortFilterProxyModel::lessThan(left, right);
+            return lowerPositionThan(left, right);
         Q_ASSERT(vL.isValid());
         Q_ASSERT(vR.isValid());
 
+        if (vL == vR)
+            return lowerPositionThan(left, right);
+
         bool res = false;
         if (misc::naturalSort(vL.toString(), vR.toString(), res))
             return res;
@@ -114,26 +117,7 @@ bool TransferListSortModel::lessThan(const QModelIndex &left, const QModelIndex
         return vL < vR;
     }
     else if (column == TorrentModelItem::TR_PRIORITY) {
-        const int vL = left.data().toInt();
-        const int vR = right.data().toInt();
-
-        // Seeding torrents should be sorted by their completed date instead.
-        if (vL == -1 && vR == -1) {
-            QAbstractItemModel *model = sourceModel();
-            const QDateTime dateL = model->data(model->index(left.row(), TorrentModelItem::TR_SEED_DATE)).toDateTime();
-            const QDateTime dateR = model->data(model->index(right.row(), TorrentModelItem::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;
-        }
-
-        // Seeding torrents should be at the bottom
-        if (vL == -1) return false;
-        if (vR == -1) return true;
-        return vL < vR;
+        return lowerPositionThan(left, right);
     }
     else if (column == TorrentModelItem::TR_PEERS || column == TorrentModelItem::TR_SEEDS) {
         int left_active = left.data().toInt();
@@ -142,9 +126,14 @@ bool TransferListSortModel::lessThan(const QModelIndex &left, const QModelIndex
         int right_total = right.data(Qt::UserRole).toInt();
 
         // Active peers/seeds take precedence over total peers/seeds.
-        if (left_active == right_active)
+        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 {
+            return (left_active < right_active);
+        }
     }
     else if (column == TorrentModelItem::TR_ETA) {
         const QAbstractItemModel *model = sourceModel();
@@ -212,7 +201,7 @@ bool TransferListSortModel::lessThan(const QModelIndex &left, const QModelIndex
             }
         }
         else if ((invalidL == false) && (invalidR == false)) {
-            return QSortFilterProxyModel::lessThan(left, right);
+            return lowerPositionThan(left, right);
         }
         else {
             return !invalidL;
@@ -237,9 +226,46 @@ bool TransferListSortModel::lessThan(const QModelIndex &left, const QModelIndex
         return vL < vR;
     }
 
+    if (left.data() == right.data())
+        return lowerPositionThan(left, right);
+
     return QSortFilterProxyModel::lessThan(left, right);
 }
 
+bool TransferListSortModel::lowerPositionThan(const QModelIndex &left, const QModelIndex &right) const
+{
+    const TorrentModel *model = dynamic_cast<TorrentModel*>(sourceModel());
+
+    // Sort according to TR_PRIORITY
+    const int queueL = model->data(model->index(left.row(), TorrentModelItem::TR_PRIORITY)).toInt();
+    const int queueR = model->data(model->index(right.row(), TorrentModelItem::TR_PRIORITY)).toInt();
+    if (!(queueL < 0 && queueR < 0)) {
+        if (queueL > 0 && queueR > 0)
+            return queueL < queueR;
+        else if (queueL < 0)
+            return false;
+        else
+            return true;
+    }
+
+    // Sort according to TR_SEED_DATE
+    const QDateTime dateL = model->data(model->index(left.row(), TorrentModelItem::TR_SEED_DATE)).toDateTime();
+    const QDateTime dateR = model->data(model->index(right.row(), TorrentModelItem::TR_SEED_DATE)).toDateTime();
+    if (dateL.isValid() && dateR.isValid()) {
+        if (dateL != dateR)
+            return dateL < dateR;
+    }
+    else if (dateL.isValid())
+        return false;
+    else if (dateR.isValid())
+        return true;
+
+    // Finally, sort by hash
+    const QString hashL(model->torrentHash(left.row()));
+    const QString hashR(model->torrentHash(right.row()));
+    return hashL < hashR;
+}
+
 bool TransferListSortModel::filterAcceptsRow(int sourceRow, const QModelIndex &sourceParent) const
 {
     return matchStatusFilter(sourceRow, sourceParent)

src/gui/transferlistsortmodel.h

@@ -50,6 +50,7 @@ public:
 
 private:
     bool lessThan(const QModelIndex &left, const QModelIndex &right) const;
+    bool lowerPositionThan(const QModelIndex &left, const QModelIndex &right) const;
     bool filterAcceptsRow(int sourceRow, const QModelIndex &sourceParent) const;
 
     bool matchStatusFilter(int sourceRow, const QModelIndex &sourceParent) const;