Don't keep fetching history on non-visible timelines

If the user switched to another timeline before the current timeline
filled up with messages, nheko would keep fetching history.

Now it will check periodically if the timeline became visible so
it can decide whether or not to stop fetching history.

include/timeline/TimelineView.h

@@ -27,13 +27,14 @@
 #include <QStyle>
 #include <QStyleOption>
 
-#include <mtx.hpp>
+#include <mtx/events.hpp>
+#include <mtx/responses/messages.hpp>
 
 #include "MatrixClient.h"
+#include "ScrollBar.h"
 #include "TimelineItem.h"
 
 class FloatingButton;
-class ScrollBar;
 struct DescInfo;
 
 // Contains info about a message shown in the history view
@@ -122,6 +123,7 @@ private:
         void updateLastSender(const QString &user_id, TimelineDirection direction);
         void notifyForLastEvent();
         void readLastEvent() const;
+        bool isScrollbarActivated() { return scroll_area_->verticalScrollBar()->value() != 0; }
         QString getLastEventId() const;
         QString getEventSender(const mtx::events::collections::TimelineEvents &event) const;
 

src/timeline/TimelineView.cc

@@ -21,7 +21,6 @@
 
 #include "FloatingButton.h"
 #include "RoomMessages.h"
-#include "ScrollBar.h"
 
 #include "timeline/TimelineView.h"
 #include "timeline/widgets/AudioItem.h"
@@ -83,12 +82,18 @@ TimelineView::sliderRangeChanged(int min, int max)
 void
 TimelineView::fetchHistory()
 {
-        bool hasEnoughMessages = scroll_area_->verticalScrollBar()->isVisible();
+        if (!isScrollbarActivated() && !isTimelineFinished) {
+                if (!isVisible()) {
+                        // Check again later if the timeline became visible.
+                        // TODO: Use a backoff strategy.
+                        paginationTimer_->start(3000);
+                        return;
+                }
 
-        if (!hasEnoughMessages && !isTimelineFinished) {
                 isPaginationInProgress_ = true;
                 client_->messages(room_id_, prev_batch_token_);
-                paginationTimer_->start(500);
+                paginationTimer_->start(1500);
+
                 return;
         }