Brought the UIStack over from the previous game to use here.

include/guecs/uistack.hpp

@@ -0,0 +1,97 @@
+#include <guecs/ui.hpp>
+#include <flat_map>
+#include <cassert>
+
+namespace gui {
+  template<typename SCREEN_TYPE>
+    struct UIStack {
+      using UIStackMap = std::flat_map<std::string, std::shared_ptr<SCREEN_TYPE>>;
+
+      UIStackMap screens{};
+      bool visible = false;
+
+      UIStackMap::iterator $current{screens.begin()};
+      SCREEN_TYPE* $active = nullptr;
+
+      void add(const std::string& name, std::shared_ptr<SCREEN_TYPE> screen) {
+        screens.insert_or_assign(name, screen);
+        update_active(screens.begin());
+      }
+
+      void update_active(const UIStackMap::iterator& itr) {
+        $current = itr;
+        $active = (*$current).second.get();
+      }
+
+      void set_active(const std::string& name) {
+        assert(screens.contains(name) && "no screen with that name");
+        update_active(screens.find(name));
+      }
+
+      void set_visible(bool new_value) {
+        visible = new_value;
+      }
+
+      bool is_visible() {
+        return visible;
+      }
+
+      void render(sf::RenderTarget& target) {
+        assert($active != nullptr && "you didn't set active");
+        $active->render(target);
+      }
+
+      void update() {
+        assert($active != nullptr && "you didn't set active");
+        $active->update();
+      }
+
+      bool mouse(float x, float y, guecs::Modifiers mods = guecs::NO_MODS) {
+        assert($active != nullptr && "you didn't set active");
+        return $active->mouse(x, y, mods);
+      }
+
+      bool move(const UIStackMap::iterator& itr, const UIStackMap::iterator& avoid, const UIStackMap::iterator& result) {
+        if(itr != avoid) {
+          update_active(result);
+          return true;
+        } else {
+          return false;
+        }
+      }
+
+      bool next() {
+        return move($current + 1, screens.end(), $current + 1);
+      }
+
+      bool prev() {
+        return move($current, screens.begin(), $current - 1);
+      }
+
+      void first() {
+        update_active(screens.begin());
+      }
+
+      void last() {
+        update_active(screens.end() - 1);
+      }
+
+      const std::string& active_name() {
+        assert($active != nullptr && "you didn't set active");
+        return (*$current).first;
+      }
+
+      std::shared_ptr<SCREEN_TYPE> active_ui() {
+        assert($active != nullptr && "you didn't set active");
+        return (*$current).second;
+      }
+
+      std::shared_ptr<SCREEN_TYPE> at(const std::string& name) {
+        return screens.at(name);
+      }
+
+      const UIStackMap::key_container_type& names() {
+        return screens.keys();
+      }
+    };
+}