This does a 'fit_sort' whenever the state is changed. fit_sort effectively sorts the actions by distance+cost so that the cost is actually present unlike the original algorithm.

ai.cpp

@@ -155,6 +155,7 @@ namespace ai {
   }
 
   void set(State& state, std::string name, bool value) {
+    // resort by best fit
     state.set(state_id(name), value);
   }
 
@@ -162,39 +163,32 @@ namespace ai {
     return state.test(state_id(name));
   }
 
-  ai::Action& EntityAI::best_fit() {
-    dbc::check(plan.script.size() > 0, "empty action plan script");
-    int lowest_cost = plan.script[0].cost;
-    size_t best_action = 0;
-
-    for(size_t i = 0; i < plan.script.size(); i++) {
-      auto& action = plan.script[i];
-      if(!action.can_effect(start)) continue;
-
-      if(action.cost < lowest_cost) {
-        lowest_cost = action.cost;
-        best_action = i;
-      }
+  void EntityAI::fit_sort() {
+    if(active()) {
+      std::sort(plan.script.begin(), plan.script.end(),
+          [&](auto& l, auto& r) {
+            int l_cost = l.cost + (!l.can_effect(start) * ai::SCORE_MAX);
+            int r_cost = r.cost + (!r.can_effect(start) * ai::SCORE_MAX);
+            return l_cost < r_cost;
+          });
     }
-
-    return plan.script[best_action];
   }
 
   bool EntityAI::wants_to(std::string name) {
     ai::check_valid_action(name, "EntityAI::wants_to");
-    dbc::check(plan.script.size() > 0, "empty action plan script");
-    return best_fit().name == name;
+    return plan.script.size() > 0 && plan.script[0].name == name;
   }
 
   bool EntityAI::active() {
     if(plan.script.size() == 1) {
       return plan.script[0] != FINAL_ACTION;
     } else {
-      return plan.script.size() == 0;
+      return plan.script.size() != 0;
     }
   }
 
   void EntityAI::set_state(std::string name, bool setting) {
+    fit_sort();
     ai::set(start, name, setting);
   }
 
@@ -204,6 +198,7 @@ namespace ai {
 
   void EntityAI::update() {
     plan = ai::plan(script, start, goal);
+    fit_sort();
   }
 
   AIProfile* profile() {

ai.hpp

@@ -23,7 +23,7 @@ namespace ai {
     EntityAI() {};
 
     bool wants_to(std::string name);
-    ai::Action& best_fit();
+    void fit_sort();
 
     bool active();
 

goap.cpp

@@ -4,6 +4,8 @@
 #include "stats.hpp"
 #include <queue>
 
+// #define DEBUG_CYCLES 1
+
 namespace ai {
 
   using namespace nlohmann;
@@ -63,11 +65,8 @@ namespace ai {
     }
   }
 
-  inline void path_invariant(std::unordered_map<Action, Action>& came_from, Action& current) {
-#if defined(NDEBUG)
-    (void)came_from; // disable errors about unused
-    (void)current;
-#else
+  inline void path_invariant(std::unordered_map<Action, Action>& came_from, Action current) {
+#if defined(DEBUG_CYCLES)
     bool final_found = current == FINAL_ACTION;
 
     for(size_t i = 0; i <= came_from.size() && came_from.contains(current); i++) {
@@ -79,6 +78,9 @@ namespace ai {
       dump_came_from("CYCLE DETECTED!", came_from, current);
       dbc::sentinel("AI CYCLE FOUND!");
     }
+#else
+    (void)came_from; // disable errors about unused
+    (void)current;
 #endif
   }
 
@@ -156,15 +158,21 @@ namespace ai {
         auto neighbor = neighbor_action.apply_effect(current.state);
         if(closed_set.contains(neighbor)) continue;
 
+        // BUG: no matter what I do cost really doesn't impact the graph
+        // Additionally, every other GOAP implementation has the same problem, and
+        // it's probably because the selection of actions is based more on sets matching
+        // than actual weights of paths.  This reduces the probability that an action will
+        // be chosen over another due to only cost.
         int d_score = d(current.state, neighbor) + neighbor_action.cost;
 
         int tentative_g_score = g_score[current.state] + d_score;
         int neighbor_g_score = g_score.contains(neighbor) ? g_score[neighbor] : SCORE_MAX;
 
-        if(tentative_g_score < neighbor_g_score) {
+        if(tentative_g_score + neighbor_action.cost < neighbor_g_score) {
           came_from.insert_or_assign(neighbor_action, current.action);
 
           g_score.insert_or_assign(neighbor, tentative_g_score);
+
           ActionState neighbor_as{neighbor_action, neighbor};
 
           int score = tentative_g_score + h(neighbor, goal);

tests/ai.cpp

@@ -205,7 +205,5 @@ TEST_CASE("Confirm EntityAI behaves as expected", "[ai]") {
   enemy.set_state("in_combat", true);
   enemy.set_state("health_good", false);
   enemy.update();
-  auto& best = enemy.best_fit();
-  REQUIRE(best.name == "run_away");
   REQUIRE(enemy.wants_to("run_away"));
 }

tests/combat.cpp

@@ -19,8 +19,10 @@ TEST_CASE("cause scared rat won't run away bug", "[combat-fail]") {
   ai::EntityAI rat("Enemy::actions", ai_start, ai_goal);
   rat.set_state("tough_personality", false);
   rat.set_state("health_good", false);
+  REQUIRE(!rat.active());
   battle.add_enemy(rat_id, rat);
   battle.plan();
+  REQUIRE(rat.active());
   rat.dump();
   REQUIRE(rat.wants_to("run_away"));
 }