@RestController
@RequestMapping("/api")
public class OrderController {
    @Autowired
    private StringRedisTemplate redisTemplate;
    private static final String TOKEN_PREFIX = "idempotent:token:";
    private static final long EXPIRE_SECONDS = 60;
    // 獲取冪等令牌
    @GetMapping("/token")
    public ResponseEntity<String> getToken() {
        String token = UUID.randomUUID().toString();
        String key = TOKEN_PREFIX + token;
        redisTemplate.opsForValue().set(key, "1", Duration.ofSeconds(EXPIRE_SECONDS));
        return ResponseEntity.ok(token);
    }
    // 提交訂單（冪等）
    @PostMapping("/order")
    public ResponseEntity<String> createOrder(@RequestBody OrderRequest request,
                                             @RequestHeader("Idempotent-Token") String token) {
        if (token == null || token.isEmpty()) {
            return ResponseEntity.badRequest().body("缺少冪等令牌");
        }
        String key = TOKEN_PREFIX + token;
        Boolean exists = redisTemplate.opsForValue().getOperations().hasKey(key);
        if (!exists) {
            return ResponseEntity.badRequest().body("請勿重復(fù)提交");
        }
        // 使用 Lua 腳本保證原子性：先get再del
        String script = "if redis.call('get', KEYS[1]) then return redis.call('del', KEYS[1]) else return 0 end";
        Long result = (Long) redisTemplate.execute(
            new DefaultRedisScript<>(script, Long.class),
            Collections.singletonList(key)
        );
        if (result == 0L) {
            return ResponseEntity.badRequest().body("操作已執(zhí)行，請勿重復(fù)提交");
        }
        // 正式處理業(yè)務(wù)邏輯（下單）
        processOrder(request);
        return ResponseEntity.ok("下單成功");
    }
    private void processOrder(OrderRequest request) {
        // 模擬下單邏輯
        System.out.println("創(chuàng)建訂單: " + request.getProductId());
    }
}

// ? 危險！存在并發(fā)漏洞
Boolean exists = redisTemplate.hasKey(key);
if (exists) {
    redisTemplate.delete(key); // 此時可能已被其他線程刪掉
    // 繼續(xù)執(zhí)行 → 可能被重復(fù)執(zhí)行
}

CREATE TABLE user_sign_in (
    id BIGINT PRIMARY KEY AUTO_INCREMENT,
    user_id BIGINT NOT NULL,
    sign_date DATE NOT NULL,
    created_at DATETIME,
    UNIQUE KEY uk_user_date (user_id, sign_date)
);

@Service
public class SignInService {
    @Autowired
    private UserSignInMapper mapper;
    @Transactional
    public void signIn(Long userId) {
        UserSignIn record = new UserSignIn();
        record.setUserId(userId);
        record.setSignDate(LocalDate.now());
        record.setCreatedAt(new Date());
        try {
            mapper.insert(record);
            System.out.println("簽到成功");
        } catch (DuplicateKeyException e) {
            System.out.println("今天已簽到，無需重復(fù)操作");
        }
    }
}

@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Idempotent {
    String key() default ""; // 支持 SpEL 表達(dá)式
    int expireTime() default 60; // 過期時間（秒）
}

@Aspect
@Component
@Slf4j
public class IdempotentAspect {
    @Autowired
    private StringRedisTemplate redisTemplate;
    @Around("@annotation(idempotent)")
    public Object handleIdempotent(ProceedingJoinPoint joinPoint, Idempotent idempotent) throws Throwable {
        String key = generateKey(joinPoint, idempotent.key());
        Boolean lock = redisTemplate.opsForValue().setIfAbsent(key, "1", Duration.ofSeconds(idempotent.expireTime()));
        if (!lock) {
            throw new RuntimeException("請勿重復(fù)請求");
        }
        try {
            return joinPoint.proceed();
        } catch (Exception e) {
            // 出現(xiàn)異常時釋放鎖？看業(yè)務(wù)需求
            redisTemplate.delete(key);
            throw e;
        }
    }
    private String generateKey(ProceedingJoinPoint joinPoint, String spELKey) {
        MethodSignature signature = (MethodSignature) joinPoint.getSignature();
        Method method = signature.getMethod();
        Object[] args = joinPoint.getArgs();
        EvaluationContext context = new StandardEvaluationContext();
        String[] paramNames = new DefaultParameterNameDiscoverer().getParameterNames(method);
        if (paramNames != null) {
            for (int i = 0; i < paramNames.length; i++) {
                context.setVariable(paramNames[i], args[i]);
            }
        }
        ExpressionParser parser = new SpelExpressionParser();
        String finalKey = parser.parseExpression(spELKey).getValue(context, String.class);
        return "idempotent:" + finalKey;
    }
}

@PostMapping("/pay/callback")
@Idempotent(key = "#request.orderId", expireTime = 300)
public ResponseEntity<String> handlePayCallback(@RequestBody PayCallbackRequest request) {
    // 處理支付回調(diào)邏輯
    log.info("處理支付回調(diào): {}", request.getOrderId());
    return ResponseEntity.ok("success");
}

private String generateFingerprint(HttpServletRequest request, String userId) throws IOException {
    StringBuilder sb = new StringBuilder();
    sb.append(request.getRequestURI())
      .append("_")
      .append(userId)
      .append("_");
    // 計算請求體的 MD5（注意：流只能讀一次，需緩存）
    String body = IOUtils.toString(request.getInputStream(), StandardCharsets.UTF_8);
    sb.append(DigestUtils.md5DigestAsHex(body.getBytes()));
    return sb.toString();
}