責任鏈模式 - Chain of Responsibility Pattern

用途

將責任分割、鏈結，一步一步處理請求

classDiagram
  Handler o-- Handler
  Handler <|-- ConcreteHandlerA
  Handler <|-- ConcreteHandlerB
  Handler <|-- ConcreteHandlerC
  Handler ..> Request
  ConcreteHandlerA <-- Client
  ConcreteHandlerB <-- Client
  ConcreteHandlerC <-- Client
  namespace ChainOfResponsibility {
    class Request{

    }
    class Handler{
      <<Abstract>>
      +SetNextHandler(Handler handler)
      +Process(Request request)*
    }
    class ConcreteHandlerA{
      +Process(Request request)
    }
    class ConcreteHandlerB{
      +Process(Request request)
    }
    class ConcreteHandlerC{
      +Process(Request request)
    }
  }
  class Client{
    +Operation()
  }

例子

當談到責任鏈模式（Chain of Responsibility Pattern）時，我們可以以一個請假申請的例子來解釋

假設你是一家公司的員工，你需要向你的上級提出請假申請
在公司中，有不同級別的管理人員，包括小組長、部門經理和總經理
每個管理人員都有不同的權限和批准請假的能力

使用責任鏈模式可以實現這樣的請假申請流程，讓請假申請依次經過不同級別的管理人員進行審批，直到找到可以批准請假的人為止

在範例中，請假申請先經過小組長的審批，如果小組長無法批准，則交給部門經理審批，如果部門經理也無法批准，則交給總經理審批

這樣，請假申請就會依次經過不同級別的管理人員進行審批，直到找到可以批准請假的人為止
這種方式可以實現彈性的審批流程，並且可以輕鬆地新增或更改管理人員的層級和權限

Request

// 請假申請類別
public class LeaveRequest
{
    public string EmployeeName { get; set; }
    public int LeaveDays { get; set; }
}

Handler

// 抽象處理者類別
public abstract class Approver
{
    protected Approver NextApprover;

    public void SetNextApprover(Approver nextApprover)
    {
        NextApprover = nextApprover;
    }

    public abstract void ProcessRequest(LeaveRequest request);
}

Concrete Handler

// 小組長類別
public class TeamLeader : Approver
{
    public override void ProcessRequest(LeaveRequest request)
    {
        if (request.LeaveDays <= 2)
        {
            Console.WriteLine($"小組長批准 {request.EmployeeName} 的請假申請");
        }
        else if (NextApprover != null)
        {
            NextApprover.ProcessRequest(request);
        }
    }
}

// 部門經理類別
public class DepartmentManager : Approver
{
    public override void ProcessRequest(LeaveRequest request)
    {
        if (request.LeaveDays <= 5)
        {
            Console.WriteLine($"部門經理批准 {request.EmployeeName} 的請假申請");
        }
        else if (NextApprover != null)
        {
            NextApprover.ProcessRequest(request);
        }
    }
}

// 總經理類別
public class GeneralManager : Approver
{
    public override void ProcessRequest(LeaveRequest request)
    {
        if (request.LeaveDays > 5)
        {
            Console.WriteLine($"總經理批准 {request.EmployeeName} 的請假申請");
        }
    }
}

Client

// 使用範例
LeaveRequest leaveRequest = new LeaveRequest
{
    EmployeeName = "John",
    LeaveDays = 4
};

Approver teamLeader = new TeamLeader();
Approver departmentManager = new DepartmentManager();
Approver generalManager = new GeneralManager();

teamLeader.SetNextApprover(departmentManager);
departmentManager.SetNextApprover(generalManager);

teamLeader.ProcessRequest(leaveRequest);

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