Speedup startup by caching last message timestamp

The cache is only approximate, i.e. it doesn't skip edits and similar,
but this might be good enough? Also no migration right now.

Speeds up startup by about 5x on my system.

Half the startup time is now loading the powerlevels for each room. We
can probably lazily load those too in the future.

src/Cache.cpp

@@ -1570,6 +1570,47 @@ Cache::updateState(const std::string &room, const mtx::responses::StateEvents &s
     txn.commit();
 }
 
+namespace {
+template<typename T>
+auto
+isMessage(const mtx::events::RoomEvent<T> &e)
+  -> std::enable_if_t<std::is_same<decltype(e.content.msgtype), std::string>::value, bool>
+{
+    return true;
+}
+
+template<typename T>
+auto
+isMessage(const mtx::events::Event<T> &)
+{
+    return false;
+}
+
+template<typename T>
+auto
+isMessage(const mtx::events::EncryptedEvent<T> &)
+{
+    return true;
+}
+
+auto
+isMessage(const mtx::events::RoomEvent<mtx::events::msg::CallInvite> &)
+{
+    return true;
+}
+
+auto
+isMessage(const mtx::events::RoomEvent<mtx::events::msg::CallAnswer> &)
+{
+    return true;
+}
+auto
+isMessage(const mtx::events::RoomEvent<mtx::events::msg::CallHangUp> &)
+{
+    return true;
+}
+}
+
 void
 Cache::saveState(const mtx::responses::Sync &res)
 {
@@ -1623,6 +1664,25 @@ Cache::saveState(const mtx::responses::Sync &res)
         saveTimelineMessages(txn, eventsDb, room.first, room.second.timeline);
 
         RoomInfo updatedInfo;
+        {
+            // retrieve the old tags and modification ts
+            std::string_view data;
+            if (roomsDb_.get(txn, room.first, data)) {
+                try {
+                    RoomInfo tmp     = json::parse(std::string_view(data.data(), data.size()));
+                    updatedInfo.tags = std::move(tmp.tags);
+
+                    updatedInfo.approximate_last_modification_ts =
+                      tmp.approximate_last_modification_ts;
+                } catch (const json::exception &e) {
+                    nhlog::db()->warn("failed to parse room info: room_id ({}), {}: {}",
+                                      room.first,
+                                      std::string(data.data(), data.size()),
+                                      e.what());
+                }
+            }
+        }
+
         updatedInfo.name       = getRoomName(txn, statesdb, membersdb).toStdString();
         updatedInfo.topic      = getRoomTopic(txn, statesdb).toStdString();
         updatedInfo.avatar_url = getRoomAvatarUrl(txn, statesdb, membersdb).toStdString();
@@ -1666,7 +1726,6 @@ Cache::saveState(const mtx::responses::Sync &res)
                 rooms_with_space_updates.insert(room.first);
         }
 
-        bool has_new_tags = false;
         // Process the account_data associated with this room
         if (!room.second.account_data.events.empty()) {
             auto accountDataDb = getAccountDataDb(txn, room.first);
@@ -1691,7 +1750,8 @@ Cache::saveState(const mtx::responses::Sync &res)
                 // for tag events
                 if (std::holds_alternative<AccountDataEvent<account_data::Tags>>(evt)) {
                     auto tags_evt = std::get<AccountDataEvent<account_data::Tags>>(evt);
-                    has_new_tags  = true;
+
+                    updatedInfo.tags.clear();
                     for (const auto &tag : tags_evt.content.tags) {
                         updatedInfo.tags.push_back(tag.first);
                     }
@@ -1704,20 +1764,12 @@ Cache::saveState(const mtx::responses::Sync &res)
                 }
             }
         }
-        if (!has_new_tags) {
-            // retrieve the old tags, they haven't changed
-            std::string_view data;
-            if (roomsDb_.get(txn, room.first, data)) {
-                try {
-                    RoomInfo tmp     = json::parse(std::string_view(data.data(), data.size()));
-                    updatedInfo.tags = tmp.tags;
-                } catch (const json::exception &e) {
-                    nhlog::db()->warn("failed to parse room info: room_id ({}), {}: {}",
-                                      room.first,
-                                      std::string(data.data(), data.size()),
-                                      e.what());
-                }
-            }
+
+        for (const auto &e : room.second.timeline.events) {
+            if (!std::visit([](const auto &e) -> bool { return isMessage(e); }, e))
+                continue;
+            updatedInfo.approximate_last_modification_ts =
+              mtx::accessors::origin_server_ts(e).toMSecsSinceEpoch();
         }
 
         roomsDb_.put(txn, room.first, json(updatedInfo).dump());
@@ -4709,6 +4761,8 @@ to_json(json &j, const RoomInfo &info)
     j["join_rule"]    = info.join_rule;
     j["guest_access"] = info.guest_access;
 
+    j["app_l_ts"] = info.approximate_last_modification_ts;
+
     j["notification_count"] = info.notification_count;
     j["highlight_count"]    = info.highlight_count;
 
@@ -4732,6 +4786,8 @@ from_json(const json &j, RoomInfo &info)
     info.join_rule    = j.at("join_rule");
     info.guest_access = j.at("guest_access");
 
+    info.approximate_last_modification_ts = j.value("app_l_ts", 0);
+
     info.notification_count = j.value("notification_count", 0);
     info.highlight_count    = j.value("highlight_count", 0);
 

src/CacheStructs.h

@@ -49,7 +49,7 @@ struct DescInfo
     QString userid;
     QString body;
     QString descriptiveTime;
-    uint64_t timestamp;
+    uint64_t timestamp = 0;
     QDateTime datetime;
 };
 
@@ -89,6 +89,10 @@ struct RoomInfo
     //! The list of tags associated with this room
     std::vector<std::string> tags;
 
+    //! An approximate timestamp of when the last message was sent in the room.
+    //! Use the TimelineModel::lastMessage for an accurate timestamp.
+    uint64_t approximate_last_modification_ts = 0;
+
     uint16_t highlight_count    = 0;
     uint16_t notification_count = 0;
 };

src/timeline/RoomlistModel.cpp

@@ -121,7 +121,7 @@ RoomlistModel::data(const QModelIndex &index, int role) const
             case Roles::Time:
                 return room->lastMessage().descriptiveTime;
             case Roles::Timestamp:
-                return QVariant{static_cast<quint64>(room->lastMessage().timestamp)};
+                return QVariant{static_cast<quint64>(room->lastMessageTimestamp())};
             case Roles::HasUnreadMessages:
                 return this->roomReadStatus.count(roomid) && this->roomReadStatus.at(roomid);
             case Roles::HasLoudNotification:
@@ -333,7 +333,7 @@ RoomlistModel::addRoom(const QString &room_id, bool suppressInsertNotification)
             emit totalUnreadMessageCountUpdated(total_unread_msgs);
         });
 
-        newRoom->updateLastMessage();
+        // newRoom->updateLastMessage();
 
         std::vector<QString> previewsToAdd;
         if (newRoom->isSpace()) {

src/timeline/TimelineModel.cpp

@@ -353,14 +353,13 @@ TimelineModel::TimelineModel(TimelineViewManager *manager, QString room_id, QObj
   , manager_(manager)
   , permissions_{room_id_}
 {
-    lastMessage_.timestamp = 0;
-
     this->isEncrypted_ = cache::isRoomEncrypted(room_id_.toStdString());
 
     auto roomInfo            = cache::singleRoomInfo(room_id_.toStdString());
     this->isSpace_           = roomInfo.is_space;
     this->notification_count = roomInfo.notification_count;
     this->highlight_count    = roomInfo.highlight_count;
+    lastMessage_.timestamp   = roomInfo.approximate_last_modification_ts;
 
     // this connection will simplify adding the plainRoomNameChanged() signal everywhere that it
     // needs to be
@@ -1025,10 +1024,21 @@ isYourJoin(const mtx::events::Event<T> &)
     return false;
 }
 
+DescInfo
+TimelineModel::lastMessage() const
+{
+    if (lastMessage_.event_id.isEmpty())
+        QTimer::singleShot(0, this, &TimelineModel::updateLastMessage);
+
+    return lastMessage_;
+}
+
 void
 TimelineModel::updateLastMessage()
 {
-    for (auto it = events.size() - 1; it >= 0; --it) {
+    // only try to generate a preview for the last 1000 messages
+    auto end = std::max(events.size() - 1001, 0);
+    for (auto it = events.size() - 1; it >= end; --it) {
         auto event = events.get(it, decryptDescription);
         if (!event)
             continue;

src/timeline/TimelineModel.h

@@ -311,7 +311,9 @@ public:
     void sendMessageEvent(const T &content, mtx::events::EventType eventType);
     RelatedInfo relatedInfo(const QString &id);
 
-    DescInfo lastMessage() const { return lastMessage_; }
+    DescInfo lastMessage() const;
+    uint64_t lastMessageTimestamp() const { return lastMessage_.timestamp; }
+
     bool isSpace() const { return isSpace_; }
     bool isEncrypted() const { return isEncrypted_; }
     crypto::Trust trustlevel() const;