package main

import (
    "crypto/hmac"
    "crypto/sha256"
    "encoding/hex"
    "fmt"
    "net/http"
    "strconv"
    "time"
)

const secretKey = "your-secret-key"

func validateSignature(timestamp, nonce, signature string) bool {
    data := timestamp + nonce
    mac := hmac.New(sha256.New, []byte(secretKey))
    mac.Write([]byte(data))
    expectedSignature := hex.EncodeToString(mac.Sum(nil))
    return hmac.Equal([]byte(signature), []byte(expectedSignature))
}

func handler(w http.ResponseWriter, r *http.Request) {
    timestamp := r.Header.Get("X-Timestamp")
    nonce := r.Header.Get("X-Nonce")
    signature := r.Header.Get("X-Signature")

    if!validateSignature(timestamp, nonce, signature) {
        http.Error(w, "Unauthorized", http.StatusUnauthorized)
        return
    }
    fmt.Fprintf(w, "Request is valid!")
}

func main() {
    http.HandleFunc("/api", handler)
    http.ListenAndServe(":8080", nil)
}

package main

import (
    "fmt"
    "log"
    "net/http"
    "sync"
)

// 模擬數據庫，保存用戶的 API 調用次數和剩余額度
var userQuota = map[string]int{
    "user1": 100, // 初始免費調用次數
}

var mu sync.Mutex

func recordCall(userID string) {
    mu.Lock()
    defer mu.Unlock()
    if quota, exists := userQuota[userID]; exists && quota > 0 {
        userQuota[userID]--
        log.Printf("User %s called the API. Remaining quota: %d\n", userID, userQuota[userID])
    } else {
        log.Printf("User %s has no quota left.\n", userID)
    }
}

func handler(w http.ResponseWriter, r *http.Request) {
    userID := r.Header.Get("X-User-ID")
    recordCall(userID)
    if userQuota[userID] <= 0 {
        http.Error(w, "Payment Required", http.StatusPaymentRequired)
        return
    }
    fmt.Fprintf(w, "API Call Recorded!")
}

func main() {
    http.HandleFunc("/api", handler)
    http.ListenAndServe(":8080", nil)
}

package main

import (
    "fmt"
    "log"
    "net/http"
    "sync"
)

var userBalance = map[string]float64{
    "user1": 50.00, // 用戶初始余額
}

var serviceCosts = map[string]float64{
    "/api/simple-test": 0.1, // 簡單功能費用
    "/api/advanced-test": 0.5, // 高級功能費用
}

var mu sync.Mutex

func recordCall(userID, endpoint string) bool {
    mu.Lock()
    defer mu.Unlock()
    cost, exists := serviceCosts[endpoint]
    if!exists {
        return false
    }
    if balance, exists := userBalance[userID]; exists && balance >= cost {
        userBalance[userID] -= cost
        log.Printf("User %s used %s. Remaining balance: %.2f\n", userID, endpoint, userBalance[userID])
        return true
    }
    return false
}

func handler(w http.ResponseWriter, r *http.Request) {
    userID := r.Header.Get("X-User-ID")
    endpoint := r.URL.Path
    if!recordCall(userID, endpoint) {
        http.Error(w, "Insufficient Funds", http.StatusPaymentRequired)
        return
    }
    fmt.Fprintf(w, "Service %s Called!", endpoint)
}

func main() {
    http.HandleFunc("/api/simple-test", handler)
    http.HandleFunc("/api/advanced-test", handler)
    http.ListenAndServe(":8080", nil)
}

package main

import (
    "fmt"
    "log"
    "net/http"
    "sync"
    "time"
)

type Subscription struct {
    Plan         string
    ExpiryDate   time.Time
    CallQuota    int
}

var userSubscriptions = map[string]Subscription{
    "user1": {
        Plan:       "monthly",
        ExpiryDate: time.Now().AddDate(0, 1, 0), // 有效期 1 個月

        CallQuota:  1000, // 每月調用額度
    },
}

var mu sync.Mutex

func checkSubscription(userID string) bool {
    mu.Lock()
    defer mu.Unlock()
    sub, exists := userSubscriptions[userID]
    if!exists || time.Now().After(sub.ExpiryDate) {
        return false
    }
    if sub.CallQuota > 0 {
        sub.CallQuota--
        userSubscriptions[userID] = sub
        log.Printf("User %s used API. Remaining quota: %d\n", userID, sub.CallQuota)
        return true
    }
    return false
}

func handler(w http.ResponseWriter, r *http.Request) {
    userID := r.Header.Get("X-User-ID")
    if!checkSubscription(userID) {
        http.Error(w, "Subscription Expired or Quota Exceeded", http.StatusPaymentRequired)
        return
    }
    fmt.Fprintf(w, "API Call within Subscription!")
}

func main() {
    http.HandleFunc("/api", handler)
    http.ListenAndServe(":8080", nil)
}

五、總結