KoogleV4/GameHandler/GameService.cs

using GameModel;
using GameModel.Exceptions;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace GameHandler
{
    public class GameService
    {
        private bool _isStarted = false;
        private ThrowHandler _th;
        private BoardState _lastState;

        public BoardState Start()
        {
            if (_isStarted)
            {
                throw new InvalidGameStateExcpetion("Game already started");
            }    
            if (!_isStarted)
            {
                _isStarted = true;
            }

            _th = new ThrowHandler();

            _lastState = BoardState.Create(ThrowMode.Decrease);
            return _lastState;
        }

        public BoardState HandleThrow(PinThrow pinThrow) 
        {
            if (!_isStarted)
            {
                throw new InvalidGameStateExcpetion("Game not started");
            }

            _lastState = _th.Update(_lastState, pinThrow);
            return _lastState;
        }

        public void Stop()
        {
            if (!_isStarted)
            {
                throw new InvalidGameStateExcpetion("Game not started");
            }
            _isStarted = false;
        }
    }
}