deselect build tool when it becomes unaffordable and fix stale enabled button

src/ui/BuildButtonGrid.h

@@ -1,46 +1,56 @@
 #pragma once
 
 #include <map>
+#include <optional>
 #include <vector>
 
 #include <QWidget>
 
 #include "BuilderModeExitedEvent.h"
 #include "BuildHotkeyPressedEvent.h"
+#include "BuildingBlocksChangedEvent.h"
 #include "BuildingType.h"
 #include "DemolishModeChangedEvent.h"
 #include "EventHandler.h"
 #include "GameConfig.h"
 
 class QPushButton;
+class Simulation;
 
 class BuildButtonGrid : public QWidget,
                         public CombinedEventHandler<BuilderModeExitedEvent,
                                                     DemolishModeChangedEvent,
-                                                    BuildHotkeyPressedEvent>
+                                                    BuildHotkeyPressedEvent,
+                                                    BuildingBlocksChangedEvent>
 {
     Q_OBJECT
 
 public:
-    BuildButtonGrid(const GameConfig* config, QWidget* parent = nullptr);
+    BuildButtonGrid(Simulation* sim, const GameConfig* config, QWidget* parent = nullptr);
     ~BuildButtonGrid() override;
 
-    void updateAffordability(int buildingBlocks);
     void clearActiveButton();
 
 private:
+    // Re-evaluates which build buttons are enabled from the current building block
+    // stock (read from the simulation). If the currently selected tool can no longer
+    // be afforded, it exits builder mode so the button does not stay selected.
+    void updateAffordability();
+
     void handleEvent(std::shared_ptr<const BuilderModeExitedEvent> event) override;
     void handleEvent(std::shared_ptr<const DemolishModeChangedEvent> event) override;
     void handleEvent(std::shared_ptr<const BuildHotkeyPressedEvent> event) override;
+    void handleEvent(std::shared_ptr<const BuildingBlocksChangedEvent> event) override;
 
 private slots:
     void onBuildButton(int index);
 
 private:
+    Simulation*                      m_sim;
     const GameConfig*                m_config;
     std::vector<BuildingType>        m_types;
     std::vector<QPushButton*>        m_buttons;
     std::map<BuildingType, int>      m_costs;
-    int                              m_activeIndex;
+    std::optional<std::size_t>       m_activeIndex;
     QPushButton*                     m_demolishButton;
 };