chatgui: remember last read message, restore scroll position, show unread count badge

Store read/scroll positions per channel via ui_state table (key-value).
Draw red +N badge on channel list items for unread messages.
Fix getMessages() to fetch last N messages (was fetching first N).

tools/chatgui/src/messagelist.cpp

@@ -167,6 +167,11 @@ MessageList::MessageList(DbManager* db, QWidget *parent)
 
 void MessageList::loadChannel(const QString& channelId) {
     QWidget* prevFocus = QApplication::focusWidget();
+
+    /* Save state of current channel before switching */
+    if (!m_currentChannelId.isEmpty() && m_currentChannelId != channelId)
+        saveChannelState();
+
     m_model->clear();
     m_avatarCache.clear();
     m_currentChannelId = channelId;
@@ -174,9 +179,6 @@ void MessageList::loadChannel(const QString& channelId) {
 
     auto msgs = m_db->getMessages(channelId, 100);
 
-    struct ReactionKey { qint64 msgId; quint64 node; QString emoji; };
-    QHash<qint64, QHash<QString, QList<QColor>>> reactMap;
-
     for (const auto& m : msgs) {
         AccountRow acc = m_db->getAccount(m.authorNodeId);
         QString author  = m_db->getDisplayName(m.authorNodeId);
@@ -194,11 +196,12 @@ void MessageList::loadChannel(const QString& channelId) {
         auto *item = new QStandardItem();
         setMsg(item, author, QString::fromUtf8(m.data), time, avatar, false,
                false, QString(), QString(), reacts);
+        item->setData(m.id, MsgIdRole);
         m_model->appendRow(item);
     }
 
-    if (m_model->rowCount() > 0)
-        m_view->scrollToBottom();
+    restoreScrollPosition(channelId);
+
     if (prevFocus)
         prevFocus->setFocus();
     else
@@ -238,3 +241,60 @@ void MessageList::addMessage(const QString& channelId, quint64 authorNodeId,
 
     m_view->scrollToBottom();
 }
+
+void MessageList::saveChannelState() {
+    if (m_currentChannelId.isEmpty() || m_model->rowCount() == 0) return;
+
+    int vpHeight = m_view->viewport()->height();
+    QModelIndex topIdx = m_view->indexAt(QPoint(0, 0));
+    QModelIndex bottomIdx = m_view->indexAt(QPoint(0, vpHeight - 1));
+
+    qint64 lastReadMsgId = 0;
+    qint64 lastPosMsgId  = 0;
+
+    if (topIdx.isValid())
+        lastPosMsgId = topIdx.data(MsgIdRole).toLongLong();
+    if (bottomIdx.isValid())
+        lastReadMsgId = bottomIdx.data(MsgIdRole).toLongLong();
+    else if (m_model->rowCount() > 0)
+        lastReadMsgId = m_model->item(m_model->rowCount() - 1)->data(MsgIdRole).toLongLong();
+
+    if (lastReadMsgId == 0 && lastPosMsgId == 0) return;
+
+    QByteArray cid = m_currentChannelId.toUtf8();
+    auto saveKey = [&cid](const char* suffix, qint64 val) {
+        QByteArray key = "ch_" + cid + suffix;
+        QByteArray valStr = QByteArray::number(val);
+        size_t klen = key.size(), vlen = valStr.size();
+        size_t total = klen + 1 + vlen + 1;
+        if (total > 256) return;
+        void* arg = u_malloc(total);
+        memcpy(arg, key.constData(), klen + 1);
+        memcpy((char*)arg + klen + 1, valStr.constData(), vlen + 1);
+        gui_bridge_post_uasync_fn(chat_core_save_ui_state_trampoline, arg);
+    };
+
+    if (lastReadMsgId > 0) saveKey("_last_read", lastReadMsgId);
+    if (lastPosMsgId > 0)  saveKey("_last_pos", lastPosMsgId);
+}
+
+void MessageList::restoreScrollPosition(const QString& channelId) {
+    if (!m_db || m_model->rowCount() == 0) {
+        return;
+    }
+
+    qint64 lastPosMsgId = m_db->getUiStateInt64(
+        QStringLiteral("ch_%1_last_pos").arg(channelId), 0);
+
+    if (lastPosMsgId > 0) {
+        for (int row = 0; row < m_model->rowCount(); row++) {
+            QStandardItem* item = m_model->item(row);
+            if (item && item->data(MsgIdRole).toLongLong() == lastPosMsgId) {
+                m_view->scrollTo(m_model->index(row, 0), QAbstractItemView::PositionAtTop);
+                return;
+            }
+        }
+    }
+
+    m_view->scrollToBottom();
+}