using System;

​

interface IInvoiceProcessor

{

    void ProcessInvoice(decimal amount);

}

​

class DomesticInvoiceProcessor: IInvoiceProcessor

{

    public void ProcessInvoice(decimal amount)

    {

        Console.WriteLine($"国内請求処理: {amount} 円");

    }

}

​

//↓国外請求処理を追加する場合の追加実装↓

class InternationalInvoiceProcessor: IInvoiceProcessor

{

    public void ProcessInvoice(decimal amount)

    {

        Console.WriteLine($"国外請求処理: {amount} 円");

    }

}

//↑国外請求処理を追加する場合の追加実装↑

​

class AccountingSystem

{

    private IInvoiceProcessor _invoiceProcessor;

​

    public AccountingSystem(IInvoiceProcessor invoiceProcessor)

    {

        _invoiceProcessor = invoiceProcessor;

    }

​

    public void Run()

    {

        _invoiceProcessor.ProcessInvoice(10000);

    }

}

​

class Program

{

    static void Main()

    {

        //国内請求処理

        IInvoiceProcessor domesticInvoiceProcessor = new DomesticInvoiceProcessor();

        AccountingSystem domesticsystem = new AccountingSystem(domesticInvoiceProcessor);

        domesticsystem.Run();

        //↓国外請求処理を追加する場合の追加実装↓

        IInvoiceProcessor internationalInvoiceProcessor = new InternationalInvoiceProcessor();

        AccountingSystem internationalsystem = new AccountingSystem(internationalInvoiceProcessor);　　//AccountingSystemの引数(コンストラクタの引数)を変更するだけで、国外請求処理が実行できる。

        //↑国外請求処理を追加する場合の追加実装↑

        internationalsystem.Run();

    }

}