19.状态者模式(State Pattern)

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

namespace ConsoleApplication2
{
    class Program
    {
        //每个对象都有其对应的状态，而每个状态又对应一些相应的行为，如果某个对象有多个状态时，
        //那么就会对应很多的行为。那么对这些状态的判断和根据状态完成的行为，就会导致多重条件语句，
        //并且如果添加一种新的状态时，需要更改之前现有的代码。这样的设计显然违背了开闭原则。
        //状态模式正是用来解决这样的问题的。状态模式将每种状态对应的行为抽象出来成为单独新的对象，
        //这样状态的变化不再依赖于对象内部的行为。
        //Account类：维护一个State类的一个实例，该实例标识着当前对象的状态。
        //State类：抽象状态类，定义了一个具体状态类需要实现的行为约定。
        //SilveStater、GoldState和RedState类：具体状态类，实现抽象状态类的每个行为。
        static void Main(string[] args)
        {
            // 开一个新的账户
            Account account = new Account("Learning Hard");

            // 进行交易
            // 存钱
            account.Deposit(1000.0);
            account.Deposit(200.0);
            account.Deposit(600.0);

            // 付利息
            account.PayInterest();

            // 取钱
            account.Withdraw(2000.00);
            account.Withdraw(500.00);

            // 等待用户输入
            Console.ReadKey();
        }
    }

    /// <summary>
    /// 账户
    /// </summary>
    public class Account
    {
        public State State { get; set; }
        public string Owner { get; set; }
        public Account(string owner)
        {
            this.Owner = owner;
            this.State = new SilverState(0.0, this);
        }

        public double Balance { get { return State.Balance; } } // 余额
        // 存钱
        public void Deposit(double amount)
        {
            State.Deposit(amount);
            Console.WriteLine("存款金额为 {0:C}——", amount);
            Console.WriteLine("账户余额为 =:{0:C}", this.Balance);
            Console.WriteLine("账户状态为: {0}", this.State.GetType().Name);
            Console.WriteLine();
        }

        // 取钱
        public void Withdraw(double amount)
        {
            State.Withdraw(amount);
            Console.WriteLine("取款金额为 {0:C}——", amount);
            Console.WriteLine("账户余额为 =:{0:C}", this.Balance);
            Console.WriteLine("账户状态为: {0}", this.State.GetType().Name);
            Console.WriteLine();
        }

        // 获得利息
        public void PayInterest()
        {
            State.PayInterest();
            Console.WriteLine("Interest Paid --- ");
            Console.WriteLine("账户余额为 =:{0:C}", this.Balance);
            Console.WriteLine("账户状态为: {0}", this.State.GetType().Name);
            Console.WriteLine();
        }
    }

    // 抽象状态类
    public abstract class State
    {
        // Properties
        public Account Account { get; set; }
        public double Balance { get; set; } // 余额
        public double Interest { get; set; } // 利率
        public double LowerLimit { get; set; } // 下限
        public double UpperLimit { get; set; } // 上限

        public abstract void Deposit(double amount); // 存款
        public abstract void Withdraw(double amount); // 取钱
        public abstract void PayInterest(); // 获得的利息
    }

    // Red State意味着Account透支了
    public class RedState : State
    {
        public RedState(State state)
        {
            // Initialize
            this.Balance = state.Balance;
            this.Account = state.Account;
            Interest = 0.00;
            LowerLimit = -100.00;
            UpperLimit = 0.00;
        }

        // 存款
        public override void Deposit(double amount)
        {
            Balance += amount;
            StateChangeCheck();
        }
        // 取钱
        public override void Withdraw(double amount)
        {
            Console.WriteLine("没有钱可以取了！");
        }

        public override void PayInterest()
        {
            // 没有利息
        }

        private void StateChangeCheck()
        {
            if (Balance > UpperLimit)
            {
                Account.State = new SilverState(this);
            }
        }
    }

    // Silver State意味着没有利息得
    public class SilverState : State
    {
        public SilverState(State state)
            : this(state.Balance, state.Account)
        {
        }

        public SilverState(double balance, Account account)
        {
            this.Balance = balance;
            this.Account = account;
            Interest = 0.00;
            LowerLimit = 0.00;
            UpperLimit = 1000.00;
        }

        public override void Deposit(double amount)
        {
            Balance += amount;
            StateChangeCheck();
        }
        public override void Withdraw(double amount)
        {
            Balance -= amount;
            StateChangeCheck();
        }

        public override void PayInterest()
        {
            Balance += Interest * Balance;
            StateChangeCheck();
        }

        private void StateChangeCheck()
        {
            if (Balance < LowerLimit)
            {
                Account.State = new RedState(this);
            }
            else if (Balance > UpperLimit)
            {
                Account.State = new GoldState(this);
            }
        }
    }

    // Gold State意味着有利息状态
    public class GoldState : State
    {
        public GoldState(State state)
        {
            this.Balance = state.Balance;
            this.Account = state.Account;
            Interest = 0.05;
            LowerLimit = 1000.00;
            UpperLimit = 1000000.00;
        }
        // 存钱
        public override void Deposit(double amount)
        {
            Balance += amount;
            StateChangeCheck();
        }
        // 取钱
        public override void Withdraw(double amount)
        {
            Balance -= amount;
            StateChangeCheck();
        }
        public override void PayInterest()
        {
            Balance += Interest * Balance;
            StateChangeCheck();
        }

        private void StateChangeCheck()
        {
            if (Balance < 0.0)
            {
                Account.State = new RedState(this);
            }
            else if (Balance < LowerLimit)
            {
                Account.State = new SilverState(this);
            }
        }
    }
}