fix AI if no paths or full action targets are available

2 files changed, 61 insertions, 2 deletions

diff --git a/go/game/ai.go b/go/game/ai.go
index faf8f11b..f630b41b 100644
--- a/go/game/ai.go
+++ b/go/game/ai.go
@@ -399,6 +399,9 @@ func moveTowardsNearestEnemyUnit(ai *UnitAI) Action {
 	}
 
 	paths := findPathsToUnits(graph, ai.s.Map(), ai.u, enemyUnits)
+	if len(paths) == 0 {
+		return nil
+	}
 	return actionFromPaths(ai, graph, paths)
 }
 
@@ -410,6 +413,9 @@ func moveTowardsNearestTargetOption(ai *UnitAI, options []any) Action {
 	graph := ai.s.Map().generateMapGraphFor(ai.u)
 
 	paths := findPathsToInterface(graph, ai.s.Map(), ai.u, options)
+	if len(paths) == 0 {
+		return nil
+	}
 	return actionFromPaths(ai, graph, paths)
 }
 
@@ -433,6 +439,7 @@ func fullAction(ai *UnitAI) Action {
 	if a.Targets() != nil && a.Targets().RequireSelection() {
 		err := selectRandomTargets(ai.s.Rand, a.Targets())
 		if err != nil {
+			log.Println("ai full action error:", err)
 			return nil
 		}
 	}
@@ -493,8 +500,10 @@ out:
 		}
 	}
 	if !inEnemyAttackRange && ai.u.HasFullAction() {
-		ai.actions <- fullAction(ai)
-		return
+		if a := fullAction(ai); a != nil {
+			ai.actions <- a
+			return
+		}
 	}
 
 	// 2.
diff --git a/go/game/ai_test.go b/go/game/ai_test.go
index 9c90c729..8c3ba0f9 100644
--- a/go/game/ai_test.go
+++ b/go/game/ai_test.go
@@ -315,3 +315,53 @@ symbols:
 		t.Fatal("AI did not finish after issuing a FullAction")
 	}
 }
+
+func TestBlockedPathUnitAI(t *testing.T) {
+	mapDef := `map: |1-
+ WSW
+ WSW
+ WSW
+ SSS
+symbols:
+  T: tower
+  H: house
+  F: farm
+  S: street
+  W: deep water
+`
+	s := NewLocalState()
+
+	m, _ := readMap(strings.NewReader(mapDef))
+	s.SetMap(m)
+
+	p := s.AddNewPlayer("p", NewDeck())
+	o := s.AddNewPlayer("o", NewDeck())
+
+	s.addNewUnit(NewCard("base/archer"), Position{1, 3}, p)
+	f1 := s.addNewUnit(NewCard("base/fighter"), Position{1, 1}, o)
+	f2 := s.addNewUnit(NewCard("base/fighter"), Position{1, 0}, o)
+
+	// Move f1
+	ai := NewUnitAI(s, f1)
+	if ai == nil {
+		t.Fatal("ai is nil")
+	}
+	ai.promptAction()
+	a, _ := ai.NextAction()
+	if a == nil {
+		t.Fatal("Nil action received from aggressive AI")
+	}
+	s.ResolveAction(a)
+
+	// Move f2
+	ai = NewUnitAI(s, f2)
+	if ai == nil {
+		t.Fatal("ai is nil")
+	}
+	ai.promptAction()
+	a, _ = ai.NextAction()
+	if a == nil {
+		t.Fatal("Nil action received from aggressive AI")
+	}
+	s.ResolveAction(a)
+}