flutter: rule50: Fix rule50 doesn't work

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

@@ -200,9 +200,9 @@
   "@loseReasonTimeOver": {
     "description": "Time Over"
   },
-  "drawReasonRule50": "Rule50",
+  "drawReasonRule50": "In moving phase, no piece has been removed in the last fifty moves.",
   "@drawReasonRule50": {
-    "description": "Rule50"
+    "description": "In moving phase, no piece has been removed in the last fifty moves."
   },
   "drawReasonBoardIsFull": "Draw, because the board is full",
   "@drawReasonBoardIsFull": {

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

@@ -50,7 +50,7 @@
   "loseReasonNoWay": "被闷杀。",
   "loseReasonBoardIsFull": "因棋盘摆满而无路可走。",
   "loseReasonTimeOver": "超时判负。",
-  "drawReasonRule50": "连续超过50步未吃子，判和。",
+  "drawReasonRule50": "走子阶段连续50步未吃子，判和。",
   "drawReasonBoardIsFull": "棋盘摆满，无路可走，判和。",
   "drawReasonThreefoldRepetition": "三次重复局面和。",
   "gameOverUnknownReason": "游戏结束，原因未知！",

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

@@ -27,7 +27,7 @@ import 'types.dart';
 import 'zobrist.dart';
 
 int repetition = 0;
-late List<int> posKeyHistory;
+List<int> posKeyHistory = [];
 
 class StateInfo {
   // Copied when making a move
@@ -334,6 +334,16 @@ class Position {
     ++gamePly;
     ++st.pliesFromNull;
 
+    if (record != null && record!.length > "-(1,2)".length) {
+      if (posKeyHistory.length == 0 ||
+          (posKeyHistory.length > 0 &&
+              st.key != posKeyHistory[posKeyHistory.length - 1])) {
+        posKeyHistory.add(st.key);
+      }
+    } else {
+      posKeyHistory.clear();
+    }
+
     this.move = m;
 
     recorder!.moveIn(m, this); // TODO: Is Right?
@@ -715,8 +725,8 @@ class Position {
       return true;
     }
 
-    // TOOD: cpp: posKeyHistory.size() > rule.maxStepsLedToDraw
-    if (rule.maxStepsLedToDraw > 0 && st.rule50 > rule.maxStepsLedToDraw) {
+    if (rule.maxStepsLedToDraw > 0 &&
+        posKeyHistory.length > rule.maxStepsLedToDraw) {
       setGameOver(PieceColor.draw, GameOverReason.drawReasonRule50);
       return true;
     }

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

@@ -26,6 +26,7 @@ import 'package:sanmill/engine/native_engine.dart';
 import 'package:sanmill/generated/l10n.dart';
 import 'package:sanmill/main.dart';
 import 'package:sanmill/mill/game.dart';
+import 'package:sanmill/mill/position.dart';
 import 'package:sanmill/mill/types.dart';
 import 'package:sanmill/services/audios.dart';
 import 'package:sanmill/style/app_theme.dart';
@@ -227,6 +228,16 @@ class _GamePageState extends State<GamePage> with RouteAware {
         ++position.st.rule50;
         ++position.st.pliesFromNull;
 
+        if (position.record.length > "-(1,2)".length) {
+          if (posKeyHistory.length == 0 ||
+              (posKeyHistory.length > 0 &&
+                  position.st.key != posKeyHistory[posKeyHistory.length - 1])) {
+            posKeyHistory.add(position.st.key);
+          }
+        } else {
+          posKeyHistory.clear();
+        }
+
         //position.move = m;
 
         Move m = Move(position.record);