re-cover copy-settings through single-building blueprints

src/lib/sim/PlacementRules.h

@@ -30,9 +30,27 @@ bool bodyCellsWithinWorldBounds(const FactoryState& state, const GameConfig& con
 bool isPlacementValid(const FactoryState& state, const GameConfig& config,
                       BuildingType type, QPoint anchor, Rotation rotation);
 
+// An existing building or site whose footprint a ghost exactly covers.
+struct CoincidingBuilding
+{
+    BuildingId id;
+    Rotation   rotation;
+};
+
+// The building or site whose footprint a ghost of the given type/anchor/rotation
+// exactly covers: same type, same body cells, a single owner. Operational buildings
+// and construction sites alike. Rotation is not part of the test -- the target's own
+// facing is reported so each caller can apply its own rule to it.
+std::optional<CoincidingBuilding> findCoincidingSameTypeBuilding(const FactoryState& state,
+                                                                 const GameConfig& config,
+                                                                 BuildingType type,
+                                                                 QPoint anchor,
+                                                                 Rotation rot);
+
 // The building or site that a ghost of the given type/anchor/rotation would
 // rotate in place rather than replace: same type, same body cells, one owner
-// (REQ-BLD-ROTATE-IN-PLACE). Tunnels never qualify.
+// (REQ-BLD-ROTATE-IN-PLACE). Tunnels never qualify. Builder mode only; blueprint
+// placement mode never rotates anything -- see resolveBlueprintGhost.
 std::optional<BuildingId> findRotateInPlaceTarget(const FactoryState& state,
                                                   const GameConfig& config,
                                                   BuildingType type, QPoint anchor,
@@ -46,6 +64,36 @@ std::optional<BuildingId> findRotateInPlaceTarget(const FactoryState& state,
 bool canPlaceBuilding(const FactoryState& state, const GameConfig& config,
                       BuildingType type, QPoint anchor, Rotation rotation);
 
+// What one ghost of a blueprint would do at its resolved tile.
+enum class BlueprintGhostAction
+{
+    PlaceNew,           // free, valid cells: a new construction site, charged for
+    CompatibleOverlap,  // the same building is already there: left untouched, free
+                        // (REQ-UI-BLUEPRINT-OVERLAP)
+    Transfer,           // hand this blueprint's settings to the building already there,
+                        // free (REQ-UI-BLUEPRINT-TRANSFER)
+    Invalid             // terrain, bounds, or an overlap that is neither of the above
+};
+
+struct BlueprintGhostResolved
+{
+    BlueprintGhostAction      action;
+    std::optional<BuildingId> targetId;  // set for CompatibleOverlap and Transfer
+};
+
+// Classifies one ghost of a blueprint against the current factory state
+// (REQ-UI-BLUEPRINT-OVERLAP, REQ-UI-BLUEPRINT-TRANSFER). `blueprintHoldsOneBuilding` is
+// the blueprint's stored size, counted before locked types are dropped, so the gesture
+// does not change behavior as the player unlocks things.
+//
+// Shared by the ghost coloring and the click path so a preview cannot disagree with what
+// the click then does -- the same reason resolveBeltDragPath is shared.
+BlueprintGhostResolved resolveBlueprintGhost(const FactoryState& state,
+                                             const GameConfig& config,
+                                             BuildingType type, QPoint anchor,
+                                             Rotation rotation,
+                                             bool blueprintHoldsOneBuilding);
+
 // What a belt drag would do to one tile of its path (REQ-BLD-BELT-DRAG).
 enum class BeltTileAction
 {