Implement simple scroll state handling

resources/qml/TimelineView.qml

@@ -2,6 +2,7 @@ import QtQuick 2.6
 import QtQuick.Controls 2.5
 import QtQuick.Layouts 1.5
 import QtGraphicalEffects 1.0
+import QtQuick.Window 2.2
 
 import com.github.nheko 1.0
 
@@ -28,14 +29,51 @@ Rectangle {
 		visible: timelineManager.timeline != null
 		anchors.fill: parent
 
+		model: timelineManager.timeline
+
+		onModelChanged: {
+			if (model) {
+				currentIndex = model.currentIndex
+				if (model.currentIndex == count - 1) {
+					positionViewAtEnd()
+				} else {
+					positionViewAtIndex(model.currentIndex, ListView.End)
+				}
+			}
+		}
+
 		ScrollBar.vertical: ScrollBar {
 			id: scrollbar
 			anchors.top: parent.top
 			anchors.right: parent.right
 			anchors.bottom: parent.bottom
+			onPressedChanged: if (!pressed) chat.updatePosition()
 		}
 
-		model: timelineManager.timeline
+		property bool atBottom: false
+		onCountChanged: {
+			if (atBottom && Window.active) {
+				var newIndex = count - 1 // last index
+				positionViewAtEnd()
+				currentIndex = newIndex
+				model.currentIndex = newIndex
+			}
+		}
+
+		function updatePosition() {
+			for (var y = chat.contentY + chat.height; y > chat.height; y -= 5) {
+				var i = chat.itemAt(100, y);
+				if (!i) continue;
+				if (!i.isFullyVisible()) continue;
+				chat.model.currentIndex = i.getIndex();
+				chat.currentIndex = i.getIndex()
+				atBottom = i.getIndex() == count - 1;
+				console.log("bottom:" + atBottom)
+				break;
+			}
+		}
+		onMovementEnded: updatePosition()
+
 		spacing: 4
 		delegate: RowLayout {
 			anchors.leftMargin: 52
@@ -43,6 +81,13 @@ Rectangle {
 			anchors.right: parent.right
 			anchors.rightMargin: scrollbar.width
 
+			function isFullyVisible() {
+				return (y - chat.contentY - 1) + height < chat.height
+			}
+			function getIndex() {
+				return index;
+			}
+
 			Loader {
 				id: loader
 				Layout.fillWidth: true

src/timeline2/TimelineModel.cpp

@@ -625,3 +625,22 @@ TimelineModel::replyAction(QString id)
 
         emit ChatPage::instance()->messageReply(related);
 }
+
+int
+TimelineModel::idToIndex(QString id) const
+{
+        if (id.isEmpty())
+                return -1;
+        for (int i = 0; i < (int)eventOrder.size(); i++)
+                if (id == eventOrder[i])
+                        return i;
+        return -1;
+}
+
+QString
+TimelineModel::indexToId(int index) const
+{
+        if (index < 0 || index >= (int)eventOrder.size())
+                return "";
+        return eventOrder[index];
+}

src/timeline2/TimelineModel.h

@@ -81,6 +81,8 @@ struct DecryptionResult
 class TimelineModel : public QAbstractListModel
 {
         Q_OBJECT
+        Q_PROPERTY(
+          int currentIndex READ currentIndex WRITE setCurrentIndex NOTIFY currentIndexChanged)
 
 public:
         explicit TimelineModel(QString room_id, QObject *parent = 0);
@@ -112,6 +114,8 @@ public:
         Q_INVOKABLE QString escapeEmoji(QString str) const;
         Q_INVOKABLE void viewRawMessage(QString id) const;
         Q_INVOKABLE void replyAction(QString id);
+        Q_INVOKABLE int idToIndex(QString id) const;
+        Q_INVOKABLE QString indexToId(int index) const;
 
         void addEvents(const mtx::responses::Timeline &events);
         template<class T>
@@ -119,6 +123,12 @@ public:
 
 public slots:
         void fetchHistory();
+        void setCurrentIndex(int index)
+        {
+                currentId = indexToId(index);
+                emit currentIndexChanged(index);
+        }
+        int currentIndex() const { return idToIndex(currentId); }
 
 private slots:
         // Add old events at the top of the timeline.
@@ -129,6 +139,7 @@ signals:
         void oldMessagesRetrieved(const mtx::responses::Messages &res);
         void messageFailed(const std::string txn_id);
         void messageSent(const std::string txn_id, std::string event_id);
+        void currentIndexChanged(int index);
 
 private:
         DecryptionResult decryptEvent(
@@ -146,6 +157,7 @@ private:
         bool paginationInProgress = false;
 
         QHash<QString, QColor> userColors;
+        QString currentId;
 };
 
 template<class T>

src/timeline2/TimelineViewManager.cpp

@@ -14,7 +14,6 @@ TimelineViewManager::TimelineViewManager(QWidget *parent)
                                          0,
                                          "MtxEvent",
                                          "Can't instantiate enum!");
-
         view      = new QQuickView();
         container = QWidget::createWindowContainer(view, parent);
         container->setMinimumSize(200, 200);