Implemented methods and test for winner

lib/data/dao/game_dao.dart

@@ -253,4 +253,49 @@ class GameDao extends DatabaseAccessor<AppDatabase> with _$GameDaoMixin {
     final rowsAffected = await query.go();
     return rowsAffected > 0;
   }
+
+  /// Sets the winner of the game with the given [gameId] to the player with
+  /// the given [winnerId].
+  /// Returns `true` if more than 0 rows were affected, otherwise `false`.
+  Future<bool> setWinner({
+    required String gameId,
+    required String winnerId,
+  }) async {
+    final query = update(gameTable)..where((g) => g.id.equals(gameId));
+    final rowsAffected = await query.write(
+      GameTableCompanion(winnerId: Value(winnerId)),
+    );
+    return rowsAffected > 0;
+  }
+
+  /// Retrieves the winner of the game with the given [gameId].
+  /// Returns the [Player] who won the game, or `null` if no winner is set.
+  Future<Player?> getWinner({required String gameId}) async {
+    final query = select(gameTable)..where((g) => g.id.equals(gameId));
+    final result = await query.getSingleOrNull();
+    if (result == null || result.winnerId == null) {
+      return null;
+    }
+    final winner = await db.playerDao.getPlayerById(playerId: result.winnerId!);
+    return winner;
+  }
+
+  /// Removes the winner of the game with the given [gameId].
+  /// Returns `true` if more than 0 rows were affected, otherwise `false`.
+  Future<bool> removeWinner({required String gameId}) async {
+    final query = update(gameTable)..where((g) => g.id.equals(gameId));
+    final rowsAffected = await query.write(
+      const GameTableCompanion(winnerId: Value(null)),
+    );
+    return rowsAffected > 0;
+  }
+
+  /// Checks if the game with the given [gameId] has a winner set.
+  /// Returns `true` if a winner is set, otherwise `false`.
+  Future<bool> hasWinner({required String gameId}) async {
+    final query = select(gameTable)
+      ..where((g) => g.id.equals(gameId) & g.winnerId.isNotNull());
+    final result = await query.getSingleOrNull();
+    return result != null;
+  }
 }

test/db_tests/game_test.dart

@@ -234,5 +234,79 @@ void main() {
       gameCount = await database.gameDao.getGameCount();
       expect(gameCount, 0);
     });
+
+    test('Checking if game has winner works correclty', () async {
+      await database.gameDao.addGame(game: testGame1);
+      await database.gameDao.addGame(game: testGameOnlyGroup);
+
+      var hasWinner = await database.gameDao.hasWinner(gameId: testGame1.id);
+      expect(hasWinner, true);
+
+      hasWinner = await database.gameDao.hasWinner(
+        gameId: testGameOnlyGroup.id,
+      );
+      expect(hasWinner, false);
+    });
+
+    test('Fetching the winner of a game works correctly', () async {
+      await database.gameDao.addGame(game: testGame1);
+
+      final winner = await database.gameDao.getWinner(gameId: testGame1.id);
+      if (winner == null) {
+        fail('Winner is null');
+      } else {
+        expect(winner.id, testGame1.winner!.id);
+        expect(winner.name, testGame1.winner!.name);
+        expect(winner.createdAt, testGame1.winner!.createdAt);
+      }
+    });
+
+    test('Updating the winner of a game works correctly', () async {
+      await database.gameDao.addGame(game: testGame1);
+
+      final winner = await database.gameDao.getWinner(gameId: testGame1.id);
+      if (winner == null) {
+        fail('Winner is null');
+      } else {
+        expect(winner.id, testGame1.winner!.id);
+        expect(winner.name, testGame1.winner!.name);
+        expect(winner.createdAt, testGame1.winner!.createdAt);
+        expect(winner.id, testPlayer4.id);
+        expect(winner.id != testPlayer5.id, true);
+      }
+
+      await database.gameDao.setWinner(
+        gameId: testGame1.id,
+        winnerId: testPlayer5.id,
+      );
+
+      final newWinner = await database.gameDao.getWinner(gameId: testGame1.id);
+
+      if (newWinner == null) {
+        fail('New winner is null');
+      } else {
+        expect(newWinner.id, testPlayer5.id);
+        expect(newWinner.name, testPlayer5.name);
+        expect(newWinner.createdAt, testPlayer5.createdAt);
+      }
+    });
+
+    test('Removing a winner works correctly', () async {
+      await database.gameDao.addGame(game: testGame2);
+
+      var hasWinner = await database.gameDao.hasWinner(gameId: testGame2.id);
+      expect(hasWinner, true);
+
+      await database.gameDao.removeWinner(gameId: testGame2.id);
+
+      hasWinner = await database.gameDao.hasWinner(gameId: testGame2.id);
+      expect(hasWinner, false);
+
+      final removedWinner = await database.gameDao.getWinner(
+        gameId: testGame2.id,
+      );
+
+      expect(removedWinner, null);
+    });
   });
 }