implement bfs multi-target distance calculation to nearest winning state

include/state.hpp

@@ -2,6 +2,7 @@
 #define __STATE_HPP_
 
 #include "config.hpp"
+#include "distance.hpp"
 #include "physics.hpp"
 #include "puzzle.hpp"
 
@@ -15,10 +16,23 @@ public:
 
   std::vector<State> presets;
 
+  // Some stuff is faster to map from state to mass (e.g. in the renderer)
   std::unordered_map<State, std::size_t> states;
   std::unordered_set<State> winning_states;
   std::unordered_set<State> visited_states;
 
+  // Other stuff maps from mass to state :/
+  std::unordered_map<std::size_t, State> masses;
+  std::vector<std::size_t> winning_path;
+
+  // Fuck it, duplicate the springs too, we don't even need to copy them from
+  // the physics thread then...
+  std::vector<std::pair<std::size_t, std::size_t>> springs;
+
+  // Distance calculation result can be buffered and reused to calculate a new
+  // path on the same graph
+  DistanceResult target_distances;
+
   int current_preset;
   State starting_state;
   State current_state;
@@ -62,6 +76,10 @@ public:
 
   auto FindWinningStates() -> void;
 
+  auto FindTargetDistances() -> void;
+
+  auto FindTargetPath() -> void;
+
   auto CurrentMassIndex() const -> std::size_t;
 };