Add takeback button

src/game/game-instance.ts

@@ -7,7 +7,7 @@ export class GomokuGame {
   public currentPlayerColor: null | PlayerColor;
   public status: GameStatus;
   public winnerColor: null | PlayerColor | 'draw';
-  public history: { row: number, col: number }[];
+  public history: { row: number; col: number }[];
 
   private readonly boardSize = 15;
   private moveCount = 0;
@@ -82,6 +82,24 @@ export class GomokuGame {
     this.currentPlayerColor = null;
   }
 
+  public undoMove() {
+    if (this.history.length === 0) {
+      return;
+    }
+
+    const lastMove = this.history.pop();
+    if (lastMove) {
+      this.board[lastMove.row][lastMove.col] = null;
+      this.moveCount--;
+      this.currentPlayerColor =
+        this.currentPlayerColor === 'black' ? 'white' : 'black';
+      if (this.status === 'finished') {
+        this.status = 'playing';
+        this.winnerColor = null;
+      }
+    }
+  }
+
   private checkWin(row: number, col: number, color: PlayerColor): boolean {
     const directions = [
       [1, 0], // vertical