implement copy building settings with shift + click gesture

src/lib/sim/BuildingConfig.cpp

@@ -0,0 +1,51 @@
+#include "BuildingConfig.h"
+
+#include "BeltSystem.h"
+#include "Building.h"
+#include "BuildingSystem.h"
+#include "Simulation.h"
+
+std::optional<BuildingConfig> readBuildingConfig(const Simulation& sim, BuildingId id)
+{
+    const Building*         building = sim.buildings().findBuilding(id);
+    const ConstructionSite* site     = building ? nullptr : sim.buildings().findSite(id);
+    if (!building && !site)
+    {
+        return std::nullopt;
+    }
+
+    BuildingConfig config;
+    config.type = building ? building->type : site->type;
+
+    const std::string& recipeId = building ? building->recipeId : site->recipeId;
+    if (!recipeId.empty())
+    {
+        config.recipeId = recipeId;
+    }
+
+    config.shipLayout = building ? building->shipLayout : site->shipLayout;
+
+    if (config.type == BuildingType::Splitter)
+    {
+        config.isSplitter = true;
+        if (building)
+        {
+            // Operational splitter filters live in the BeltSystem, keyed by tile.
+            const std::optional<BeltSystem::SplitterInfo> info =
+                sim.belts().getSplitterInfo(building->anchor);
+            if (info.has_value())
+            {
+                config.splitterFilterA = info->filterA;
+                config.splitterFilterB = info->filterB;
+            }
+        }
+        else
+        {
+            // A site keeps its pre-completion filters on the ConstructionSite.
+            config.splitterFilterA = site->splitterFilterA;
+            config.splitterFilterB = site->splitterFilterB;
+        }
+    }
+
+    return config;
+}