C# 디자인 패턴의 전략 패턴에 대한 심층적인 이해 및 역할별 사례 공유

namespace StragetyPattern

public abstract class Tax {

    protected decimal TaxRate = 0;

    protected decimal QuickDeduction = 0;

    public virtual decimal Calculate(decimal income) {
        return income * TaxRate - QuickDeduction;
    }

}

public class Level0 : Tax {

    public Level0() {
        TaxRate = 0.00m;
        QuickDeduction = 0;
    }

}

public class Level1 : Tax {

    public Level1() {
        TaxRate = 0.03m;
        QuickDeduction = 0;
    }

}

public class Level2 : Tax {

    public Level2() {
        TaxRate = 0.10m;
        QuickDeduction = 105;
    }

}

public class Level3 : Tax {

    public Level3() {
        TaxRate = 0.20m;
        QuickDeduction = 555;
    }

}

public class Level4 : Tax {

    public Level4() {
        TaxRate = 0.25m;
        QuickDeduction = 1005;
    }

}

public class Level5 : Tax {

    public Level5() {
        TaxRate = 0.30m;
        QuickDeduction = 2755;
    }

}

public class Level6 : Tax {

    public Level6() {
        TaxRate = 0.35m;
        QuickDeduction = 5505;
    }

}

public class Level7 : Tax {

    public Level7() {
        TaxRate = 0.45m;
        QuickDeduction = 13505;
    }

}

public class Context {

    private Tax _tax = null;

    private const decimal EXEMPTION_VALUE = 3500m;

    private List<decimal> _taxLevel = new List<decimal>{
        0,
        1500,
        4500,
        9000,
        35000,
        55000,
        80000,
        decimal.MaxValue
    };

    private List<Type> _levels = new List<Type>();

    private void GetLevels() {
        _levels = AppDomain.CurrentDomain.GetAssemblies()
                           .SelectMany(tp => tp.GetTypes()
                           .Where(t => t.BaseType == typeof(Tax)))
                           .ToList();
    }

    public Context() {
        GetLevels();
    }

    public Context Calculate(decimal income) {
        _tax = new Level0();
        var result = income - EXEMPTION_VALUE;
        for(int i = 1; i <= _taxLevel.Count - 1; i++) {
            if(result > _taxLevel[i - 1] && result <= _taxLevel[i]) {
                _tax = (Tax)Activator.CreateInstance(_levels[i]);
            }
        }
        Console.WriteLine($"Income = {income}," + $"tax = {_tax.Calculate(result)}!");
        return this;
    }

}

public class Program {

    private static Context _context = new Context();

    public static void Main(string[] args) {
        _context.Calculate(2500.00m)
                .Calculate(4900.00m)
                .Calculate(5500.00m)
                .Calculate(7000.00m)
                .Calculate(10000.00m)
                .Calculate(16000.00m)
                .Calculate(43000.00m)
                .Calculate(70000.00m)
                .Calculate(100000.00m)
                .Calculate(4500.00m)
                .Calculate(1986.00m);

        Console.ReadKey();
    }

}

Income = 2500.00,tax = 0.0000!
Income = 4900.00,tax = 42.0000!
Income = 5500.00,tax = 95.0000!
Income = 7000.00,tax = 245.0000!
Income = 10000.00,tax = 745.0000!
Income = 16000.00,tax = 2120.0000!
Income = 43000.00,tax = 9095.0000!
Income = 70000.00,tax = 17770.0000!
Income = 100000.00,tax = 29920.0000!
Income = 4500.00,tax = 30.0000!
Income = 1986.00,tax = 0.0000!