using System;

using System.Threading; 

using System.Threading.Tasks;   

​

public class Program

{

    public static void Main()

    {       

        //以下程式設計有某種「瑕疵」，執行10次，有很高機率會出現錢包金額產生「負數」的案例

        //請用想得到的機制去改善此問題，如何避免錢包餘額出現負數

        ICSBankService service = new ICSBankService();

        //開10個執行緒，短時間連續請求提款行為 (請想像成使用者短時間內連續點擊提款按紐10次)

        var tasks = new Task[10];

        for (int i = 0; i < tasks.Length; i++)

        {

            tasks[i] = Task.Run(() => RandomlyWithdrawalAmount(service));

        }

        Task.WaitAll(tasks);

    }

    static void RandomlyWithdrawalAmount(ICSBankService account)

    {

        int rnd_Amount = GenerateRandomAmount(); //產生隨機提款金額

        account.WithdrawalMyMoney(rnd_Amount);

    }

    private static int GenerateRandomAmount()

    {

        var rnd = new Random(Guid.NewGuid().GetHashCode());

        var amount = rnd.Next(25, 100);

        return amount;

    }

}

​

public class ICSBankService 

{

    int _totalMoney = 100;

    public void WithdrawalMyMoney(int amount)

    {   

        bool isMoneyEnough = _totalMoney > 0 && (_totalMoney - amount) > 0;

        //餘額不足

        if(!isMoneyEnough)

        {

            Console.WriteLine(string.Format("本次提款:{0}，餘額不足僅剩:{1}" , amount, _totalMoney));

        }else{

            //餘額足，嘗試夠扣除錢包金額

            if(!ReduceMyMoney(amount)){

                Console.WriteLine(string.Format("本次提款:{0}，餘額不足僅剩:{1}" , amount, _totalMoney));

            }else{

                Console.WriteLine(string.Format("本次提款:{0}，餘額剩下:{1}" , amount, _totalMoney));

            }

        }

​

    }

    public int GetMyMoney()

    {   

        //此查詢較慢，會約150毫秒才回應

        Thread.Sleep(50);

        return _totalMoney;

    }

    public bool ReduceMyMoney(int withdrawalAmount)

    {   

        int amount = _totalMoney - withdrawalAmount;

        if(amount > 0) {

            _totalMoney =amount;

            return true;

        }else{

            return false;

        }

    }

}