// auth.js
import axios from 'axios';
// Base Axios 實例
const api = axios.create({
  baseURL: '/api',
});
// Token 存取
function getAccessToken() { return localStorage.getItem('access_token'); }
function getRefreshToken() { return localStorage.getItem('refresh_token'); }
function setTokens({ accessToken, refreshToken }) {
  localStorage.setItem('access_token', accessToken);
  localStorage.setItem('refresh_token', refreshToken);
}
// 請求攔截：自動附帶 Access Token
api.interceptors.request.use(config => {
  const token = getAccessToken();
  if (token) config.headers['Authorization'] = `Bearer ${token}`;
  return config;
});
// 響應攔截：遇到 401 刷新并重試
let isRefreshing = false;
let subscribers = [];
function onRefreshed(newToken) {
  subscribers.forEach(cb => cb(newToken));
  subscribers = [];
}
function addSubscriber(cb) {
  subscribers.push(cb);
}
api.interceptors.response.use(
  res => res,
  error => {
    const { config, response } = error;
    if (response && response.status === 401 && !config._retry) {
      if (isRefreshing) {
        // 正在刷新，加入隊列
        return new Promise(resolve => {
          addSubscriber(token => {
            config.headers['Authorization'] = `Bearer ${token}`;
            resolve(api(config));
          });
        });
      }
      config._retry = true;
      isRefreshing = true;
      // 調用刷新接口
      return api.post('/auth/refresh', { refreshToken: getRefreshToken() })
        .then(res => {
          const { accessToken, refreshToken } = res.data;
          setTokens({ accessToken, refreshToken });
          isRefreshing = false;
          onRefreshed(accessToken);
          // 重試原請求
          config.headers['Authorization'] = `Bearer ${accessToken}`;
          return api(config);
        })
        .catch(err => {
          // 刷新失敗，跳轉登錄
          isRefreshing = false;
          window.location.href = '/login';
          return Promise.reject(err);
        });
    }
    return Promise.reject(error);
  }
);
export default api;

<dependencies>
  <!-- Spring Boot Starter Web -->
  <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
  </dependency>
  <!-- MyBatis-Plus -->
  <dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>mybatis-plus-boot-starter</artifactId>
    <version>3.5.3.1</version>
  </dependency>
  <!-- MySQL 驅動 -->
  <dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
  </dependency>
  <!-- Redis -->
  <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-redis</artifactId>
  </dependency>
  <!-- JWT -->
  <dependency>
    <groupId>io.jsonwebtoken</groupId>
    <artifactId>jjwt-api</artifactId>
    <version>0.11.5</version>
  </dependency>
  <dependency>
    <groupId>io.jsonwebtoken</groupId>
    <artifactId>jjwt-impl</artifactId>
    <version>0.11.5</version>
    <scope>runtime</scope>
  </dependency>
  <dependency>
    <groupId>io.jsonwebtoken</groupId>
    <artifactId>jjwt-jackson</artifactId>
    <version>0.11.5</version>
    <scope>runtime</scope>
  </dependency>
</dependencies>

-- 用戶表（簡化）
CREATE TABLE user_account (
  id BIGINT PRIMARY KEY AUTO_INCREMENT,
  username VARCHAR(50) UNIQUE NOT NULL,
  password VARCHAR(255) NOT NULL
);

// JwtUtil.java
@Component
public class JwtUtil {
    @Value("${jwt.secret}") private String secret;
    @Value("${jwt.access.expire}") private long accessExpire;   // ms
    @Value("${jwt.refresh.expire}") private long refreshExpire; // ms
    // 生成 Access Token（短期）
    public String generateAccessToken(Long userId) {
        return Jwts.builder()
            .setSubject(userId.toString())
            .setIssuedAt(new Date())
            .setExpiration(new Date(System.currentTimeMillis() + accessExpire))
            .signWith(Keys.hmacShaKeyFor(secret.getBytes()))
            .compact();
    }
    // 生成 Refresh Token（長期）
    public String generateRefreshToken(Long userId) {
        return Jwts.builder()
            .setSubject(userId.toString())
            .setIssuedAt(new Date())
            .setExpiration(new Date(System.currentTimeMillis() + refreshExpire))
            .signWith(Keys.hmacShaKeyFor(secret.getBytes()))
            .compact();
    }
    // 解析 Token
    public Claims parseToken(String token) {
        return Jwts.parserBuilder()
            .setSigningKey(secret.getBytes())
            .build()
            .parseClaimsJws(token)
            .getBody();
    }
}

// AuthService.java
@Service
public class AuthService {
    @Autowired private JwtUtil jwtUtil;
    @Autowired private StringRedisTemplate redis;
    public Tokens login(String username, String password) {
        // 1. 驗證用戶名密碼（略，用 MyBatis-Plus 查詢）
        Long userId = /* ... */;
        // 2. 生成雙 Token
        String accessToken  = jwtUtil.generateAccessToken(userId);
        String refreshToken = jwtUtil.generateRefreshToken(userId);
        // 3. 保存到 Redis
        String key = "refresh:" + userId;
        redis.opsForValue().set(key, refreshToken, jwtUtil.getRefreshExpire(), TimeUnit.MILLISECONDS);
        return new Tokens(accessToken, refreshToken);
    }
    public Tokens refresh(String refreshToken) {
        // 1. 解析
        Claims claims = jwtUtil.parseToken(refreshToken);
        Long userId = Long.parseLong(claims.getSubject());
        // 2. Redis 校驗
        String key = "refresh:" + userId;
        String cached = redis.opsForValue().get(key);
        if (cached == null || !cached.equals(refreshToken)) {
            throw new RuntimeException("Refresh Token 無效或已過期");
        }
        // 3. 生成新 Token
        String newAccess  = jwtUtil.generateAccessToken(userId);
        String newRefresh = jwtUtil.generateRefreshToken(userId);
        // 4. 覆蓋 Redis
        redis.opsForValue().set(key, newRefresh, jwtUtil.getRefreshExpire(), TimeUnit.MILLISECONDS);
        return new Tokens(newAccess, newRefresh);
    }
}

// AuthController.java
@RestController
@RequestMapping("/api/auth")
public class AuthController {
    @Autowired private AuthService authService;
    @PostMapping("/login")
    public Tokens login(@RequestBody LoginReq req) {
        return authService.login(req.getUsername(), req.getPassword());
    }
    @PostMapping("/refresh")
    public Tokens refresh(@RequestBody Map<String,String> body) {
        return authService.refresh(body.get("refreshToken"));
    }
}
// DTOs
@Data
class LoginReq { private String username, password; }
@Data
@AllArgsConstructor
class Tokens { 
    private String accessToken; 
    private String refreshToken; 
}