Chain of Responsibilityパターン [C#]

## Chain of Responsibility
Chain-of-responsibility パターン, CoR パターンは、オブジェクト指向設計におけるデザインパターンの一つであり、一つの コマンドオブジェクトと一連の 処理オブジェクトから構成されます。

各処理オブジェクトは、処理できるコマンドオブジェクトの種類と、自身が処理できないコマンドオブジェクトをチェーン内の次の処理オブジェクトに渡す方法を記述する情報を保持します。

また、新たな処理オブジェクトをチェーンの最後に追加する機構を備えます。

## クラス図

![image.png](https://qiita-image-store.s3.amazonaws.com/0/293729/8270e8b2-f888-2427-fb3a-fb8524af4977.png)


## コード

``` cs
using System;

namespace ConsoleApp10
{
    public enum PRICE_MANAGER_APPROVE : int
    {
        MANAGER = 100000,
        DIRECTOR = 200000,
        PRESIDENT = 300000
    }

    class Program
    {
        static void Main(string[] args)
        {
            Purchase item1 = new Purchase(1, "PC", 100000);
            Purchase item2 = new Purchase(2, "High Spec PC", 200000);
            Purchase item3 = new Purchase(3, "Super High Spec PC", 300000);
            Purchase item4 = new Purchase(4, "Ultra High Spec PC", 400000);
            Authorizer manager = new GeneralManager("Ichiro");
            Authorizer director = new Director("Tom");
            Authorizer president = new President("Jerry");

            manager.SetNextApprove(director);
            director.SetNextApprove(president);
            president.SetNextApprove(null);

            // マネージャーにPC購入の承認を判定してもらう
            manager.JudgeApproveItem(item1);
            Console.WriteLine();

            // マネージャーにHigh Spec PC購入の承認を判定してもらう
            manager.JudgeApproveItem(item2);
            Console.WriteLine();

            // マネージャーにSuper High Spec PC購入の承認を判定してもらう
            manager.JudgeApproveItem(item3);
            Console.WriteLine();

            // マネージャーにUltra High Spec PC購入の承認を判定してもらう
            manager.JudgeApproveItem(item4);
        }
    }

    /// <summary>
    /// 承認者クラス
    /// </summary>
    public abstract class Authorizer
    {
        /// <summary>
        /// 承認者名
        /// </summary>
        public string Name { get; private set; }

        /// <summary>
        /// 次の承認者
        /// </summary>
        protected Authorizer next = null;

        /// <summary>
        /// コンストラクタ
        /// </summary>
        /// <param name="someName"></param>
        public Authorizer(string someName)
        {
            this.Name = someName;
        }

        /// <summary>
        /// 次の承認者をセットする
        /// </summary>
        /// <param name="someNext"></param>
        public abstract void SetNextApprove(Authorizer someNext);

        /// <summary>
        /// 購入物を承認するか判定する
        /// </summary>
        /// <param name="somePurchase"></param>
        public abstract void JudgeApproveItem(Purchase somePurchase);
    }

    /// <summary>
    /// 部長クラス
    /// </summary>
    public class GeneralManager : Authorizer
    {
        public GeneralManager(string someName) : base(someName) { }

        public override void SetNextApprove(Authorizer someNext)
        {
            this.next = someNext;
        }

        public override void JudgeApproveItem(Purchase somePurchase)
        {
            if (somePurchase.Price <= (int)PRICE_MANAGER_APPROVE.MANAGER)
            {
                Console.WriteLine("Manager has approved this item({0} : {1}yen)].", somePurchase.Name, somePurchase.Price);
            }
            else
            {
                Console.WriteLine("Manager can't judge this item({0} : {1}yen)].", somePurchase.Name, somePurchase.Price);
                next.JudgeApproveItem(somePurchase);
            }
        }
    }

    /// <summary>
    /// 取締役クラス
    /// </summary>
    public class Director : Authorizer
    {
        public Director(string someName) : base(someName) { }

        public override void SetNextApprove(Authorizer someNext)
        {
            this.next = someNext;
        }

        public override void JudgeApproveItem(Purchase somePurchase)
        {
            if (somePurchase.Price <= (int)PRICE_MANAGER_APPROVE.DIRECTOR)
            {
                Console.WriteLine("Director has approved this item({0} : {1}yen)].", somePurchase.Name, somePurchase.Price);
            }
            else
            {
                Console.WriteLine("Director can't judge this item({0} : {1}yen)].", somePurchase.Name, somePurchase.Price);
                next.JudgeApproveItem(somePurchase);
            }
        }
    }

    /// <summary>
    /// 社長クラス
    /// </summary>
    public class President : Authorizer
    {
        public President(string someName) : base(someName) { }

        public override void SetNextApprove(Authorizer someNext)
        {
            this.next = someNext;
        }


        public override void JudgeApproveItem(Purchase somePurchase)
        {
            if (somePurchase.Price <= (int)PRICE_MANAGER_APPROVE.PRESIDENT)
            {
                Console.WriteLine("President has approved this item({0} : {1}yen)].", somePurchase.Name, somePurchase.Price);
            }
            else
            {
                Console.WriteLine("President can't judge this item({0} : {1}yen)].", somePurchase.Name, somePurchase.Price);
            }
        }
    }

    /// <summary>
    /// 購入品クラス
    /// </summary>
    public class Purchase
    {
        public int Id { get; private set; } = 0;
        public string Name { get; private set; } = null;
        public int Price { get; private set; } = 0;

        public Purchase(int someId, string someName, int somePrice)
        {
            this.Id = someId;
            this.Name = someName;
            this.Price = somePrice;
        }
    }
}
```
#### 出力結果

```
Manager has approved this item(PC : 100000yen)].

Manager can't judge this item(High Spec PC : 200000yen)].
Director has approved this item(High Spec PC : 200000yen)].

Manager can't judge this item(Super High Spec PC : 300000yen)].
Director can't judge this item(Super High Spec PC : 300000yen)].
President has approved this item(Super High Spec PC : 300000yen)].

Manager can't judge this item(Ultra High Spec PC : 400000yen)].
Director can't judge this item(Ultra High Spec PC : 400000yen)].
President can't judge this item(Ultra High Spec PC : 400000yen)].
```

## 参考リンク
* デザインパターン ～Chain of Responsibility～
  - [https://qiita.com/i-tanaka730/items/073c106c58d7c74c1706]