package main

import (
    "fmt"
    "log"
)

// Request 是我們要在鏈中傳遞的請(qǐng)求對(duì)象
type Request struct {
    Type    string
    Payload string
    Handled bool // 標(biāo)記請(qǐng)求是否已被處理
}

// Handler 接口定義了處理者必須實(shí)現(xiàn)的方法
type Handler interface {
    SetNext(handler Handler) // 設(shè)置下一個(gè)處理者
    Handle(req *Request)     // 處理請(qǐng)求
}

// BaseHandler 提供了責(zé)任鏈的基礎(chǔ)實(shí)現(xiàn)，可以嵌入到具體的處理者中
type BaseHandler struct {
    next Handler
}

// SetNext 設(shè)置鏈中的下一個(gè)處理者
func (b *BaseHandler) SetNext(handler Handler) {
    b.next = handler
}

// PassToNext 如果有下一個(gè)處理者，則將請(qǐng)求傳遞下去
func (b *BaseHandler) PassToNext(req *Request) {
    if b.next != nil {
        b.next.Handle(req)
    } else {
        // 如果沒(méi)有下一個(gè)處理者，并且請(qǐng)求未被處理，可以記錄或拋出錯(cuò)誤
        if !req.Handled {
            log.Printf("Warning: Request type '%s' not handled by any handler in the chain.", req.Type)
        }
    }
}

// --- 具體處理者實(shí)現(xiàn) ---

// AuthenticationHandler 認(rèn)證處理者
type AuthenticationHandler struct {
    BaseHandler
}

func (h *AuthenticationHandler) Handle(req *Request) {
    if req.Type == "auth" {
        fmt.Printf("AuthenticationHandler: Handling authentication request for payload '%s'\n", req.Payload)
        req.Handled = true
    } else {
        fmt.Printf("AuthenticationHandler: Cannot handle type '%s', passing to next.\n", req.Type)
        h.PassToNext(req)
    }
}

// ValidationHandler 校驗(yàn)處理者
type ValidationHandler struct {
    BaseHandler
}

func (h *ValidationHandler) Handle(req *Request) {
    if req.Type == "validate" {
        fmt.Printf("ValidationHandler: Handling validation request for payload '%s'\n", req.Payload)
        req.Handled = true
    } else {
        fmt.Printf("ValidationHandler: Cannot handle type '%s', passing to next.\n", req.Type)
        h.PassToNext(req)
    }
}

// LoggingHandler 日志處理者 (通常在鏈的末端或作為通用前置處理)
type LoggingHandler struct {
    BaseHandler
}

func (h *LoggingHandler) Handle(req *Request) {
    fmt.Printf("LoggingHandler: Logging request type '%s' with payload '%s'\n", req.Type, req.Payload)
    // 日志處理者通常不會(huì)“消費(fèi)”請(qǐng)求，而是繼續(xù)傳遞
    h.PassToNext(req)
}

// DefaultHandler 默認(rèn)處理者，如果前面都沒(méi)有處理，它來(lái)兜底
type DefaultHandler struct {
    BaseHandler
}

func (h *DefaultHandler) Handle(req *Request) {
    if !req.Handled { // 只有在前面都沒(méi)處理的情況下才執(zhí)行
        fmt.Printf("DefaultHandler: No specific handler found for type '%s', handling as default.\n", req.Type)
        req.Handled = true
    }
    // DefaultHandler 是鏈的末端，通常不會(huì)再傳遞
}


func main() {
    // 構(gòu)造責(zé)任鏈
    authHandler := &AuthenticationHandler{}
    validationHandler := &ValidationHandler{}
    loggingHandler := &LoggingHandler{}
    defaultHandler := &DefaultHandler{}

    loggingHandler.SetNext(authHandler)
    authHandler.SetNext(validationHandler)
    validationHandler.SetNext(defaultHandler) // 確保鏈有終點(diǎn)

    fmt.Println("--- Sending Auth Request ---")
    req1 := &Request{Type: "auth", Payload: "user:pass"}
    loggingHandler.Handle(req1) // 從鏈的起點(diǎn)開(kāi)始處理

    fmt.Println("\n--- Sending Validation Request ---")
    req2 := &Request{Type: "validate", Payload: "data:123"}
    loggingHandler.Handle(req2)

    fmt.Println("\n--- Sending Unknown Request ---")
    req3 := &Request{Type: "unknown", Payload: "some_data"}
    loggingHandler.Handle(req3)

    fmt.Println("\n--- Sending Another Auth Request (demonstrating early exit) ---")
    req4 := &Request{Type: "auth", Payload: "admin:secret"}
    loggingHandler.Handle(req4)
}

BaseHandler

PassToNext

Handler

BaseHandler

SetNext

PassToNext