Use fetchMore for native lazy loading of item model data

resources/qml/TimelineView.qml

@@ -93,13 +93,9 @@ Item {
 					currentIndex = newIndex
 					model.currentIndex = newIndex
 				}
-
-				if (contentHeight < height && model) {
-					model.fetchHistory();
-				}
 			}
 
-			onAtYBeginningChanged: if (atYBeginning) { chat.model.currentIndex = 0; chat.currentIndex = 0; model.fetchHistory(); }
+			onAtYBeginningChanged: if (atYBeginning) { chat.model.currentIndex = 0; chat.currentIndex = 0; }
 
 			function updatePosition() {
 				for (var y = chat.contentY + chat.height; y > chat.height; y -= 9) {

src/timeline/TimelineModel.cpp

@@ -349,6 +349,50 @@ TimelineModel::data(const QModelIndex &index, int role) const
         }
 }
 
+bool
+TimelineModel::canFetchMore(const QModelIndex &) const
+{
+        if (eventOrder.empty())
+                return true;
+        if (!std::holds_alternative<mtx::events::StateEvent<mtx::events::state::Create>>(
+              events[eventOrder.back()]))
+                return true;
+        else
+
+                return false;
+}
+
+void
+TimelineModel::fetchMore(const QModelIndex &)
+{
+        if (paginationInProgress) {
+                nhlog::ui()->warn("Already loading older messages");
+                return;
+        }
+
+        paginationInProgress = true;
+        mtx::http::MessagesOpts opts;
+        opts.room_id = room_id_.toStdString();
+        opts.from    = prev_batch_token_.toStdString();
+
+        nhlog::ui()->debug("Paginationg room {}", opts.room_id);
+
+        http::client()->messages(
+          opts, [this, opts](const mtx::responses::Messages &res, mtx::http::RequestErr err) {
+                  if (err) {
+                          nhlog::net()->error("failed to call /messages ({}): {} - {}",
+                                              opts.room_id,
+                                              mtx::errors::to_string(err->matrix_error.errcode),
+                                              err->matrix_error.error);
+                          paginationInProgress = false;
+                          return;
+                  }
+
+                  emit oldMessagesRetrieved(std::move(res));
+                  paginationInProgress = false;
+          });
+}
+
 void
 TimelineModel::addEvents(const mtx::responses::Timeline &timeline)
 {
@@ -465,37 +509,6 @@ TimelineModel::internalAddEvents(
         return ids;
 }
 
-void
-TimelineModel::fetchHistory()
-{
-        if (paginationInProgress) {
-                nhlog::ui()->warn("Already loading older messages");
-                return;
-        }
-
-        paginationInProgress = true;
-        mtx::http::MessagesOpts opts;
-        opts.room_id = room_id_.toStdString();
-        opts.from    = prev_batch_token_.toStdString();
-
-        nhlog::ui()->info("Paginationg room {}", opts.room_id);
-
-        http::client()->messages(
-          opts, [this, opts](const mtx::responses::Messages &res, mtx::http::RequestErr err) {
-                  if (err) {
-                          nhlog::net()->error("failed to call /messages ({}): {} - {}",
-                                              opts.room_id,
-                                              mtx::errors::to_string(err->matrix_error.errcode),
-                                              err->matrix_error.error);
-                          paginationInProgress = false;
-                          return;
-                  }
-
-                  emit oldMessagesRetrieved(std::move(res));
-                  paginationInProgress = false;
-          });
-}
-
 void
 TimelineModel::setCurrentIndex(int index)
 {

src/timeline/TimelineModel.h

@@ -154,6 +154,9 @@ public:
         int rowCount(const QModelIndex &parent = QModelIndex()) const override;
         QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const override;
 
+        bool canFetchMore(const QModelIndex &) const override;
+        void fetchMore(const QModelIndex &) override;
+
         Q_INVOKABLE QColor userColor(QString id, QColor background);
         Q_INVOKABLE QString displayName(QString id) const;
         Q_INVOKABLE QString avatarUrl(QString id) const;
@@ -175,7 +178,6 @@ public:
         void sendMessage(const T &msg);
 
 public slots:
-        void fetchHistory();
         void setCurrentIndex(int index);
         int currentIndex() const { return idToIndex(currentId); }
         void markEventsAsRead(const std::vector<QString> &event_ids);