Make member list sorted a bit more efficient

I don't have any hard numbers on what difference this makes, but it's
definitely a positive improvement. I noticed and fixed a few issues that
were made more glaring by recent changes in libQuotient:

1. Room::memberJoined is called during the historical loading or
whatever, when we only need that *after* stuff is settled.
2. We really don't need to sort the room's members immediately - it's
only relevant when UserListModel is used (and I think this was previous
behavior?) So now its done lazily.
3. We do not want to call Room::effectivePowerLevel willy-nilly. It may
become a more expensive lookup, and it's also varying levels of wasteful
depending on which sorting algorithm the STL uses. It doesn't cost much
for us to keep a temporary cache for the lambda function to use.

src/libneochat/models/userlistmodel.cpp

@@ -172,6 +172,10 @@ void UserListModel::refreshAllMembers()
 {
     beginResetModel();
     if (m_currentRoom != nullptr) {
+        // Only sort members when this model needs to be refreshed.
+        if (m_currentRoom->sortedMemberIds().isEmpty()) {
+            m_currentRoom->sortAllMembers();
+        }
         m_members = m_currentRoom->sortedMemberIds();
     } else {
         m_members.clear();

src/libneochat/neochatroom.cpp

@@ -175,9 +175,16 @@ NeoChatRoom::NeoChatRoom(Connection *connection, QString roomId, JoinState joinS
     connect(neochatconnection, &NeoChatConnection::globalUrlPreviewEnabledChanged, this, &NeoChatRoom::urlPreviewEnabledChanged);
     connect(this, &Room::fullyReadMarkerMoved, this, &NeoChatRoom::invalidateLastUnreadHighlightId);
 
-    // Wait until the initial member list is available before sorting
+    // This may look weird, but this is actually for performance.
-    connect(this, &Room::memberListChanged, this, &NeoChatRoom::refreshAllMembers, Qt::SingleShotConnection);
+    // We only want to listen to new member joining *when* the initial member list was loaded.
-    connect(this, &Room::memberJoined, this, &NeoChatRoom::insertMemberSorted);
+    connect(
+        this,
+        &Room::memberListChanged,
+        this,
+        [this] {
+            connect(this, &Room::memberJoined, this, &NeoChatRoom::insertMemberSorted);
+        },
+        Qt::SingleShotConnection);
 }
 
 bool NeoChatRoom::visible() const
@@ -1917,14 +1924,21 @@ void NeoChatRoom::invalidateLastUnreadHighlightId(const QString &fromEventId, co
     }
 }
 
-void NeoChatRoom::refreshAllMembers()
+void NeoChatRoom::sortAllMembers()
 {
     m_sortedMemberIds = memberIds();
 
+    // Build up a temporary cache, because we may be checking the same member over and over while sorting.
+    QHash<QString, int> effectivePowerLevels;
+    effectivePowerLevels.reserve(m_sortedMemberIds.size());
+    for (const auto &member : m_sortedMemberIds) {
+        effectivePowerLevels[member] = memberEffectivePowerLevel(member);
+    }
+
     MemberSorter sorter;
-    std::ranges::sort(m_sortedMemberIds, [this, &sorter](const auto &left, const auto &right) {
+    std::ranges::sort(m_sortedMemberIds, [&sorter, &effectivePowerLevels](const auto &left, const auto &right) {
-        const auto leftPl = memberEffectivePowerLevel(left);
+        const auto leftPl = effectivePowerLevels[left];
-        const auto rightPl = memberEffectivePowerLevel(right);
+        const auto rightPl = effectivePowerLevels[right];
         if (leftPl > rightPl) {
             return true;
         }

src/libneochat/neochatroom.h

@@ -683,6 +683,8 @@ public:
 
     /**
      * @return List of members in this room, sorted by power level and then by name.
+     *
+     * This list is only populated after sortAllMembers() is called.
      */
     QList<QString> sortedMemberIds() const;
 
@@ -721,6 +723,13 @@ public:
      */
     Q_INVOKABLE void clearSelectedMessages();
 
+    /**
+     * @brief Sort all members based on their display name, and power level.
+     *
+     * @note This is a very expensive operation, and should only be done when truly needed.
+     */
+    void sortAllMembers();
+
 private:
     bool m_visible = false;
 
@@ -767,8 +776,6 @@ private Q_SLOTS:
 
     void invalidateLastUnreadHighlightId(const QString &fromEventId, const QString &toEventId);
 
-    void refreshAllMembers();
-
     void insertMemberSorted(Quotient::RoomMember member);
 
 Q_SIGNALS: