feat: startup validation of opposite-direction exits between rooms

3 files changed, 94 insertions, 0 deletions

diff --git a/internal/validate/checks.go b/internal/validate/checks.go
index 7da2e4a..87c078e 100644
--- a/internal/validate/checks.go
+++ b/internal/validate/checks.go
@@ -1087,9 +1087,56 @@ func validateTalkConfig(prefix string, cfg *behavior.TalkConfig, itemIDs map[str
 			}
 		}
 	}
+
 	return issues
 }
 
+func validateExitReciprocity(s Source) []Issue {
+	var issues []Issue
+	roomIndex := s.World.RoomIndex()
+
+	for srcID := range roomIndex {
+		src, err := s.World.LoadRoom(srcID)
+		if err != nil {
+			continue
+		}
+		for dir, exit := range src.Exits {
+			if exit.Room <= 0 || !roomIndex[exit.Room] {
+				continue
+			}
+			if srcID >= exit.Room {
+				continue
+			}
+			dst, err := s.World.LoadRoom(exit.Room)
+			if err != nil {
+				continue
+			}
+			expected := world.OppositeExit[dir]
+			hasCorrect := false
+			var returnDirs []string
+			for retDir, retExit := range dst.Exits {
+				if retExit.Room == srcID {
+					if retDir == expected {
+						hasCorrect = true
+						break
+					}
+					returnDirs = append(returnDirs, string(retDir))
+				}
+			}
+			if !hasCorrect && len(returnDirs) > 0 {
+				issues = append(issues, Issue{
+					Level: "WARN",
+					Type:  "integrity",
+					Message: fmt.Sprintf(
+						"Room %d: exit %q to room %d, but return exit(s) %s are not the expected opposite direction %q",
+						srcID, dir, exit.Room, returnDirs, expected),
+				})
+			}
+		}
+	}
+
+	return issues
+}
 func validateUseConfig(prefix string, cfg *behavior.UseConfig, itemIDs map[string]bool) []Issue {
 	var issues []Issue
 	if cfg == nil {
diff --git a/internal/validate/local_test.go b/internal/validate/local_test.go
index 23bf8ca..d37838e 100644
--- a/internal/validate/local_test.go
+++ b/internal/validate/local_test.go
@@ -116,6 +116,52 @@ objects:
 	}
 }
 
+func TestValidateExitReciprocityOK(t *testing.T) {
+	dir := t.TempDir()
+	writeFile(t, filepath.Join(dir, "rooms", "1.yaml"), `name: Room One
+exits:
+  north: 2
+`)
+	writeFile(t, filepath.Join(dir, "rooms", "2.yaml"), `name: Room Two
+exits:
+  south: 1
+`)
+	issues := validateExitReciprocity(newSource(dir))
+	if len(issues) != 0 {
+		t.Errorf("expected no issues for correct reciprocal exits, got: %+v", issues)
+	}
+}
+
+func TestValidateExitReciprocityMismatch(t *testing.T) {
+	dir := t.TempDir()
+	writeFile(t, filepath.Join(dir, "rooms", "1.yaml"), `name: Room One
+exits:
+  down: 2
+`)
+	writeFile(t, filepath.Join(dir, "rooms", "2.yaml"), `name: Room Two
+exits:
+  south: 1
+`)
+	issues := validateExitReciprocity(newSource(dir))
+	if !containsMsg(issues, "not the expected opposite direction") {
+		t.Errorf("expected mismatch warning, got: %+v", issues)
+	}
+}
+
+func TestValidateExitReciprocityOneWay(t *testing.T) {
+	dir := t.TempDir()
+	writeFile(t, filepath.Join(dir, "rooms", "1.yaml"), `name: Room One
+exits:
+  east: 2
+`)
+	writeFile(t, filepath.Join(dir, "rooms", "2.yaml"), `name: Room Two
+`)
+	issues := validateExitReciprocity(newSource(dir))
+	if len(issues) != 0 {
+		t.Errorf("expected no issues for one-way exit, got: %+v", issues)
+	}
+}
+
 func TestValidateRoomsPartialNameSiblingsOK(t *testing.T) {
 	dir := t.TempDir()
 	writeFile(t, filepath.Join(dir, "rooms", "1.yaml"), `name: Test Room
diff --git a/internal/validate/validate.go b/internal/validate/validate.go
index 56de6f1..6558216 100644
--- a/internal/validate/validate.go
+++ b/internal/validate/validate.go
@@ -81,6 +81,7 @@ func Run(s Source) []Issue {
 	issues = append(issues, validateTechs(s)...)
 	issues = append(issues, validateRoomWiring(s)...)
 	issues = append(issues, validateRoomGrid(s)...)
+	issues = append(issues, validateExitReciprocity(s)...)
 
 	return issues
 }