namespace 简单工厂
{
    public class Operation
    {
        private double _leftNum;

        public double LeftNum
        {
            get { return _leftNum; }
            set { _leftNum = value; }
        }
        private double _rightNum;

        public double RightNum
        {
            get { return _rightNum; }
            set { _rightNum = value; }
        }

        public virtual double GetResule()
        {
            return 0.0;
        }
    }

    public class OperationAdd : Operation
    {
        public override double GetResule()
        {
            double result = 0;
            result = LeftNum + RightNum;
            return result;
        }
    }

    public class OperationSub : Operation
    {
        public override double GetResule()
        {
            double result = 0;
            result = LeftNum + RightNum;
            return result;
        }
    }

    public class OperationMul : Operation
    {
        public override double GetResule()
        {
            double result = 0;
            result = LeftNum * RightNum;
            return result;
        }
    }

    public class OperationDiv : Operation
    {
        public override double GetResule()
        {
            double result = 0;
            if (LeftNum == 0)
            {
                throw new Exception("除数不能为 0。");
            }
            result = LeftNum / RightNum;
            return result;
        }
    }

    public class OperationSqr : Operation
    {
        public override double  GetResule()
        {
            double result = 0;
            result = LeftNum * LeftNum;
            return result;
        }
    }

    public class OperationSqrt : Operation
    {
        public override double GetResule()
        {
            double result = 0;
            if (LeftNum == 0)
            {
                throw new Exception("负数不能开平方根。");
            }
            result = Math.Sqrt(LeftNum);
            return result;
        }
    }

    public class OperationReverse : Operation
    {
        public override double GetResule()
        {
            double result = 0;
            result = -LeftNum;
            return result;
        }
    }

    public class OperationFactory
    {
        public static Operation createOperate(string operate)
        {
            Operation op = null;
            switch (operate)
            {
                case "+":
                    {
                        op = new OperationAdd();
                        break;
                    }
                case "-":
                    {
                        op = new OperationSub();
                        break;
                    }
                case "*":
                    {
                        op = new OperationMul();
                        break;
                    }
                case "/":
                    {
                        op = new OperationDiv();
                        break;
                    }
                case "sqr":
                    {
                        op = new OperationSqr();
                        break;
                    }
                case "sqrt":
                    {
                        op = new OperationSqrt();
                        break;
                    }
                case "+/-":
                    {
                        op = new OperationReverse();
                        break;
                    }
            }

            return op;
        }
    }
}