Add building status light

src/lib/sim/BuildingSystem.h

@@ -26,6 +26,18 @@
 
 class Hasher;
 
+// Production state of a building for the UI status light (REQ-UI-STATUS-LIGHT).
+// The simulation owns the classification so it stays in sync with the
+// production-cycle predicates (REQ-MAT-CYCLE); the UI maps each value to a fill
+// color.
+enum class ProductionStatus
+{
+    Unconfigured,  // no recipe/schematic selected (grey)
+    Producing,     // a production cycle is active (green)
+    Starved,       // idle: a required input is missing / Salvage Bay empty (red)
+    Blocked,       // idle: output buffer full, inputs otherwise present (yellow)
+};
+
 // Manages building placement, construction queuing, and the per-tick
 // production loop (belt→building pull, production, building→belt push).
 // All types including Belt and Splitter are stored as Building instances;
@@ -122,6 +134,12 @@ public:
     // REQ-UI-DEBUG-OVERLAY "Current Factory Production": subset of the above
     // that currently has an active production cycle.
     int getActiveProductionBuildingCount() const;
+
+    // Production state for the UI status light (REQ-UI-STATUS-LIGHT). Returns
+    // nullopt for building types that show no light (belts, splitters, tunnels,
+    // HQ, defence stations). The Salvage Bay is a two-state special case:
+    // Producing while its output buffer holds scrap, Starved when empty.
+    std::optional<ProductionStatus> getProductionStatus(const Building& building) const;
     std::vector<BeltTileInfo> getAllBeltTiles()             const;
     bool                      isTileOccupied(QPoint tile) const;
 
@@ -200,6 +218,22 @@ private:
                                                 const Port& outputPort,
                                                 const Item& item);
 
+    // Candidate recipes an idle building would try this tick: an auto-recipe
+    // building (Smelter, Reprocessing Plant) offers every recipe of its type with
+    // inputs; other buildings offer only their selected recipe. Shared by
+    // tickProduction and the status classifier (REQ-MAT-CYCLE, REQ-UI-STATUS-LIGHT).
+    std::vector<const RecipeDef*> gatherCandidateRecipes(const Building& b) const;
+    // True if every input of `recipe` is present in `b`'s input buffers in the
+    // required per-cycle amount (REQ-MAT-CYCLE input check).
+    bool                recipeInputsAvailable(const Building& b,
+                                              const RecipeDef& recipe) const;
+    // Combined base + module materials a shipyard needs per ship (REQ-BLD-SHIPYARD).
+    std::map<std::string, int> computeShipyardRequiredMaterials(const Building& b) const;
+    // True if the building currently has all inputs/materials to start a cycle
+    // (ignoring output-buffer space); drives the Starved/Blocked distinction of
+    // the status light (REQ-UI-STATUS-LIGHT).
+    bool                hasInputsToStart(const Building& b) const;
+
     const BuildingDef*  findBuildingDef(BuildingType type) const;
     const RecipeDef*    findRecipe(const std::string& id, BuildingType type) const;
     const ShipDef*      findShipDef(const std::string& id) const;