homescreens/folio: Prevent items from being added to favourites area if it's full

Fixes https://invent.kde.org/plasma/plasma-mobile/-/issues/323

containments/homescreens/folio/dragstate.cpp

@@ -328,6 +328,11 @@ void DragState::onDelegateDragPositionOverFavouritesChanged()
         m_favouritesInsertBetweenTimer->stop();
     }
 
+    // ignore this event if the favourites area is full already
+    if (FavouritesModel::self()->isFull()) {
+        return;
+    }
+
     // ignore widget drop delegates (since they can't be placed in the favourites)
     if (m_dropDelegate && m_dropDelegate->type() == FolioDelegate::Widget) {
         return;

containments/homescreens/folio/favouritesmodel.cpp

@@ -171,6 +171,17 @@ FolioDelegate *FavouritesModel::getEntryAt(int row)
     return m_delegates[row].delegate;
 }
 
+bool FavouritesModel::isFull() const
+{
+    bool isLocationBottom = HomeScreenState::self()->favouritesBarLocation() == HomeScreenState::Bottom;
+
+    if (isLocationBottom) {
+        return m_delegates.size() >= HomeScreenState::self()->pageColumns();
+    } else {
+        return m_delegates.size() >= HomeScreenState::self()->pageRows();
+    }
+}
+
 int FavouritesModel::getGhostEntryPosition()
 {
     for (int i = 0; i < m_delegates.size(); i++) {

containments/homescreens/folio/favouritesmodel.h

@@ -43,6 +43,9 @@ public:
     bool addEntry(int row, FolioDelegate *delegate);
     FolioDelegate *getEntryAt(int row);
 
+    // whether the dock is full, we can't add any more items
+    bool isFull() const;
+
     // for use with drag and drop, as the delegate is dragged around
     // ghost - fake delegate exists at an index, so a gap is created
     // invisible - existing delegate looks like it doesn't exist