r := gin.Default()
v1 := r.Group("/api/v1")
{
    v1.GET("/users", getUsers)
    v1.POST("/users", createUser)
}
v2 := r.Group("/api/v2")
{
    v2.GET("/users", getUsersV2)
}

r.GET("/users/:id", func(c *gin.Context) {
    id := c.Param("id")
    c.String(200, "User ID: %s", id)
})

r.GET("/files/*filepath", func(c *gin.Context) {
    fp := c.Param("filepath")
    c.String(200, "Path: %s", fp)
})

func Logger() gin.HandlerFunc {
    return func(c *gin.Context) {
        t := time.Now()
        c.Next()
        latency := time.Since(t)
        log.Printf("[%s] %s", c.Request.Method, latency)
    }
}
r := gin.New()
r.Use(Logger())

auth := r.Group("/admin")
auth.Use(AuthMiddleware())
{
    auth.GET("/dashboard", dashboardHandler)
}

type RegisterForm struct {
    Username string `json:"username" binding:"required,min=3"`
    Email    string `json:"email" binding:"required,email"`
    Age      int    `json:"age" binding:"gte=18,lte=60"`
}
func RegisterHandler(c *gin.Context) {
    var form RegisterForm
    if err := c.ShouldBindJSON(&form); err != nil {
        c.JSON(400, gin.H{"error": err.Error()})
        return
    }
    c.JSON(200, gin.H{"message": "Register success"})
}

var validate *validator.Validate
func main() {
    validate = validator.New()
    validate.RegisterValidation("username_available", checkUsernameAvailable)
}
func checkUsernameAvailable(fl validator.FieldLevel) bool {
    username := fl.Field().String()
    // 檢查用戶(hù)名是否已存在（偽代碼）
    return !isUserExist(username)
}

func ErrorHandler() gin.HandlerFunc {
    return func(c *gin.Context) {
        c.Next()
        if len(c.Errors) > 0 {
            c.JSON(-1, gin.H{"error": c.Errors[0].Error()})
        }
    }
}