Tree Model 2 Electric Boogaloo

This draws heavily on what @carlschwan did in network/neochat!1579 but I found it easier to start again and grab the bits as I needed them plus some other copying from what I did in the Space tree model.

From my current limited testing this seems to work nicely try and break it.

src/models/roomtreeitem.h

@@ -0,0 +1,78 @@
+// SPDX-FileCopyrightText: 2024 Carl Schwan <carl@carlschwan.eu>
+// SPDX-FileCopyrightText: 2024 James Graham <james.h.graham@protonmail.com>
+// SPDX-License-Identifier: GPL-2.0-only OR GPL-3.0-only OR LicenseRef-KDE-Accepted-GPL
+
+#include "enums/neochatroomtype.h"
+
+class NeoChatRoom;
+
+/**
+ * @class RoomTreeItem
+ *
+ * This class defines an item in the space tree hierarchy model.
+ *
+ * @note This is separate from Quotient::Room and NeoChatRoom because we don't have
+ *       full room information for any room/space the user hasn't joined and we
+ *       don't want to create one for ever possible child in a space as that would
+ *       be expensive.
+ *
+ * @sa Quotient::Room, NeoChatRoom
+ */
+class RoomTreeItem
+{
+public:
+    using TreeData = std::variant<NeoChatRoom *, NeoChatRoomType::Types>;
+
+    explicit RoomTreeItem(TreeData data, RoomTreeItem *parent = nullptr);
+
+    bool operator==(const RoomTreeItem &other) const;
+
+    /**
+     * @brief Return the child at the given row number.
+     *
+     * Nullptr is returned if there is no child at the given row number.
+     */
+    RoomTreeItem *child(int row);
+
+    /**
+     * @brief The number of children this item has.
+     */
+    int childCount() const;
+
+    /**
+     * @brief Insert the given child.
+     */
+    bool insertChild(std::unique_ptr<RoomTreeItem> newChild);
+
+    /**
+     * @brief Remove the child at the given row number.
+     *
+     * @return True if a child was removed, false if the given row isn't valid.
+     */
+    bool removeChild(int row);
+
+    /**
+     * @brief Return this item's parent.
+     */
+    RoomTreeItem *parentItem() const;
+
+    /**
+     * @brief Return the row number for this child relative to the parent.
+     *
+     * @return The row value if the child has a parent, 0 otherwise.
+     */
+    int row() const;
+
+    /**
+     * @brief Return this item's data.
+     */
+    TreeData data() const;
+
+    std::optional<int> rowForRoom(Quotient::Room *room) const;
+
+private:
+    std::vector<std::unique_ptr<RoomTreeItem>> m_children;
+    RoomTreeItem *m_parentItem;
+
+    TreeData m_data;
+};