flutter: Prompt at the end of move list

src/ui/flutter_app/lib/l10n/intl_en.arb

@@ -903,5 +903,9 @@
   "autoReplay": "Auto replay moves",
   "@autoReplay": {
     "description": "Auto replay moves"
+  },
+  "atEnd": "At the end of move list.",
+  "@atEnd": {
+    "description": "At the end of move list."
   }
 }

src/ui/flutter_app/lib/l10n/intl_zh.arb

@@ -225,5 +225,6 @@
   "boardTop": "棋盘和上边缘的间距",
   "notAIsTurn": "现在不是轮到电脑行棋",
   "aiIsNotThinking": "电脑并非正在思考中",
-  "autoReplay": "自动回放"
+  "autoReplay": "自动回放",
+  "atEnd": "已经到底了"
 }

src/ui/flutter_app/lib/mill/position.dart

@@ -1035,16 +1035,23 @@ class Position {
 
 ///////////////////////////////////////////////////////////////////////////////
 
-  void _gotoHistory(int moveIndex) async {
+  Future<bool> _gotoHistory(int moveIndex) async {
+    bool ret = false;
+
     if (recorder == null) {
       print("[goto] recorder is null.");
-      return;
+      return false;
     }
 
     var history = recorder!.getHistory();
     if (moveIndex < -1 || history.length <= moveIndex) {
       print("[goto] moveIndex is out of range.");
-      return;
+      return false;
+    }
+
+    if (recorder!.cur == moveIndex) {
+      print("[goto] cur is equal to moveIndex.");
+      return false;
     }
 
     // Backup context
@@ -1057,8 +1064,13 @@ class Position {
 
     await Game.instance.newGame();
 
+    if (moveIndex == -1) {
+      ret = true;
+    }
+
     for (var i = 0; i <= moveIndex; i++) {
       Game.instance.doMove(history[i].move);
+      ret = true;
       //await Future.delayed(Duration(seconds: 1));
       //setState(() {});
     }
@@ -1068,22 +1080,24 @@ class Position {
     Game.instance.setWhoIsAi(engineTypeBackup);
     recorder!.setHistory(historyBack);
     recorder!.cur = moveIndex;
+
+    return ret;
   }
 
-  void takeBack() async {
-    _gotoHistory(recorder!.cur - 1);
+  Future<bool> takeBack() async {
+    return _gotoHistory(recorder!.cur - 1);
   }
 
-  void stepForward() async {
-    _gotoHistory(recorder!.cur + 1);
+  Future<bool> stepForward() async {
+    return _gotoHistory(recorder!.cur + 1);
   }
 
-  void takeBackAll() async {
-    _gotoHistory(-1);
+  Future<bool> takeBackAll() async {
+    return _gotoHistory(-1);
   }
 
-  void stepForwardAll() async {
-    _gotoHistory(recorder!.getHistory().length - 1);
+  Future<bool> stepForwardAll() async {
+    return _gotoHistory(recorder!.getHistory().length - 1);
   }
 
   String movesSinceLastRemove() {

src/ui/flutter_app/lib/widgets/game_page.dart

@@ -601,7 +601,11 @@ class _GamePageState extends State<GamePage> with RouteAware {
     }
 
     isGoingToHistory = true;
-    await func;
+
+    if (await func == false) {
+      showSnackBar(S.of(context).atEnd);
+    }
+
     isGoingToHistory = false;
 
     if (mounted) {