Rework roommanager for improved stability

Fixes #645

- Active space handling is moved from QML to RoomManager
- Active tab in SpaceDrawer (space / no space / DM) is unified in a single variable
- RoomList & RoomPage loading is simplified: We're always pushing a RoomPage now; if there is no room, a placeholder is shown
- SpaceHomePage is moved into RoomPage; This replaces the entire push/replace room/spacehome logic
- If the current room is a space, the space home is shown, otherwise the timeline
- The concept of "previous room" is removed entirely. If we're leaving the active room, the placeholder room page is shown
- When clicking on a space in the list, the space room list is switched and the space home page is shown

In short, these changes should (after some initial regressions) lead to a less crashy NeoChat :)

src/roommanager.h

@@ -9,7 +9,6 @@
 #include <QQmlEngine>
 #include <Quotient/room.h>
 #include <Quotient/uriresolver.h>
-#include <KConfigGroup>
 
 #include "chatdocumenthandler.h"
 #include "enums/messagecomponenttype.h"
@@ -21,12 +20,6 @@
 class NeoChatRoom;
 class NeoChatConnection;
 
-namespace Quotient
-{
-class Room;
-class User;
-}
-
 using namespace Quotient;
 
 /**
@@ -52,6 +45,14 @@ class RoomManager : public QObject, public UriResolverBase
      */
     Q_PROPERTY(NeoChatRoom *currentRoom READ currentRoom NOTIFY currentRoomChanged)
 
+    /**
+     * @brief The id of the space currently opened in the space drawer.
+     *
+     * If this is an empty string, the uncategorized rooms are shown.
+     * If it is the string "DM", the DMs are shown.
+     */
+    Q_PROPERTY(QString currentSpace READ currentSpace WRITE setCurrentSpace NOTIFY currentSpaceChanged)
+
     /**
      * @brief The TimelineModel that should be used for room message visualisation.
      *
@@ -87,16 +88,6 @@ class RoomManager : public QObject, public UriResolverBase
      */
     Q_PROPERTY(bool hasOpenRoom READ hasOpenRoom NOTIFY currentRoomChanged)
 
-    /**
-     * @brief The room ID of the last space entered.
-     */
-    Q_PROPERTY(QString lastSpaceId READ lastSpaceId WRITE setLastSpaceId NOTIFY directChatsActiveChanged)
-
-    /**
-     * @brief Whether the last SpaceDrawer category selected was direct chats.
-     */
-    Q_PROPERTY(bool directChatsActive READ directChatsActive WRITE setDirectChatsActive NOTIFY directChatsActiveChanged)
-
     /**
      * @brief The ChatDocumentHandler for the open room.
      *
@@ -183,11 +174,6 @@ public:
      */
     Q_INVOKABLE void viewEventMenu(const QString &eventId, NeoChatRoom *room, const QString &selectedText = {});
 
-    /**
-     * @brief Call this when the current used connection is dropped.
-     */
-    Q_INVOKABLE void reset();
-
     ChatDocumentHandler *chatDocumentHandler() const;
     void setChatDocumentHandler(ChatDocumentHandler *handler);
 
@@ -196,8 +182,7 @@ public:
      */
     void setUrlArgument(const QString &arg);
 
-    QString lastSpaceId() const;
-    void setLastSpaceId(const QString &lastSpaceId);
+    QString currentSpace() const;
 
     bool directChatsActive() const;
     void setDirectChatsActive(bool directChatsActive);
@@ -213,47 +198,6 @@ Q_SIGNALS:
 
     void currentRoomChanged();
 
-    /**
-     * @brief Push a new room page.
-     *
-     * Signal triggered when the main window pageStack should push a new page with
-     * the message list for the given room.
-     *
-     * @param room the room to be shown on the new page.
-     * @param event the event to got to if available.
-     */
-    void pushRoom(NeoChatRoom *room, const QString &event);
-
-    /**
-     * @brief Replace the existing room.
-     *
-     * Signal triggered when the room displayed by the message list should be changed.
-     *
-     * @param room the room to be shown on the new page.
-     * @param event the event to got to if available.
-     */
-    void replaceRoom(NeoChatRoom *room, const QString &event);
-
-    /**
-     * @brief Push a new space home page.
-     *
-     * Signal triggered when the main window pageStack should push a new page with
-     * the space home for the given space room.
-     *
-     * @param spaceRoom the space room to be shown on the new page.
-     */
-    void pushSpaceHome(NeoChatRoom *spaceRoom);
-
-    /**
-     * @brief Replace the existing space home.
-     *
-     * Signal triggered when the currently displayed room page should be changed
-     * to the space home for the given space room.
-     *
-     * @param spaceRoom the space room to be shown on the new page.
-     */
-    void replaceSpaceHome(NeoChatRoom *spaceRoom);
-
     /**
      * @brief Go to the specified event in the current room.
      */
@@ -324,15 +268,24 @@ Q_SIGNALS:
     void connectionChanged();
 
     void directChatsActiveChanged();
-    void lastSpaceIdChanged();
 
     void externalUrl(const QUrl &url);
 
+    void currentSpaceChanged();
+
 private:
     void openRoomForActiveConnection();
 
+    /** The room currently being shown in the main view (RoomPage.qml). This can be null, if there is no room.
+     * If this is a space, the space home page is shown.
+     */
     QPointer<NeoChatRoom> m_currentRoom;
-    NeoChatRoom *m_lastCurrentRoom;
+
+    /** The id of the space currently opened in the space drawer. If this is empty, the uncategorized rooms are shown.
+     * If it is "DM", the direct messages are shown. Otherwise it's the id of a toplevel space.
+     */
+    QString m_currentSpaceId;
+
     QString m_arg;
     KSharedConfig::Ptr m_config;
     KConfigGroup m_lastRoomConfig;
@@ -345,6 +298,11 @@ private:
     MediaMessageFilterModel *m_mediaMessageFilterModel;
     NeoChatConnection *m_connection;
 
+    void setCurrentRoom(const QString &roomId);
+
+    // Space ID, "DM", or empty string
+    void setCurrentSpace(const QString &spaceId, bool setRoom = true);
+
     /**
      * @brief Resolve a user URI.
      *