type ErrorCode int

const (
    Success           ErrorCode = 0
    ErrInvalidParams  ErrorCode = 1001
    ErrUserNotFound   ErrorCode = 1002
    ErrUnauthorized   ErrorCode = 1003
    ErrInternalServer ErrorCode = 5001
)

type Error struct {
    Code    ErrorCode `json:"code"`
    Message string    `json:"message"`
    Detail  string    `json:"detail,omitempty"`
}

func (e *Error) Error() string {
    return e.Message
}

// 全局错误变量，便于复用
var (
    ErrInvalidParamsErr = &Error{Code: ErrInvalidParams, Message: "请求参数无效"}
    ErrUserNotFoundErr  = &Error{Code: ErrUserNotFound, Message: "用户不存在"}
)

func HTTPStatusFromErrorCode(code ErrorCode) int {
    switch code {
    case Success:
        return 200
    case ErrInvalidParams:
        return 400
    case ErrUnauthorized:
        return 401
    case ErrUserNotFound:
        return 404
    case ErrInternalServer:
        return 500
    default:
        return 500
    }
}

func GetUserHandler(w http.ResponseWriter, r *http.Request) {
    userId := r.URL.Query().Get("id")
    if userId == "" {
        respondWithError(w, ErrInvalidParamsErr)
        return
    }

    user, err := GetUserById(userId)
    if err != nil {
        if errors.Is(err, ErrUserNotFound) {
            respondWithError(w, ErrUserNotFoundErr)
            return
        }
        // 其他错误包装为内部错误
        log.Printf("get user failed: %v", err)
        respondWithError(w, &Error{Code: ErrInternalServer, Message: "服务器内部错误"})
        return
    }

    respondWithJSON(w, 200, map[string]interface{}{"data": user})
}

func respondWithError(w http.ResponseWriter, err *Error) {
    w.Header().Set("Content-Type", "application/json")
    status := HTTPStatusFromErrorCode(err.Code)
    respondWithJSON(w, status, err)
}

func respondWithJSON(w http.ResponseWriter, code int, payload interface{}) {
    w.WriteHeader(code)
    json.NewEncoder(w).Encode(payload)
}