@Service
public class UserServiceCacheAside {
    
    @Autowired
    private RedisTemplate<String, User> redisTemplate;
    
    @Autowired
    private UserRepository userRepository;
    
    private static final String CACHE_KEY_PREFIX = "user:";
    private static final long CACHE_EXPIRATION = 30; // 緩存過(guò)期時(shí)間（分鐘）
    
    public User getUserById(Long userId) {
        String cacheKey = CACHE_KEY_PREFIX + userId;
        
        // 1. 查詢(xún)緩存
        User user = redisTemplate.opsForValue().get(cacheKey);
        
        // 2. 緩存命中，直接返回
        if (user != null) {
            return user;
        }
        
        // 3. 緩存未命中，查詢(xún)數(shù)據(jù)庫(kù)
        user = userRepository.findById(userId).orElse(null);
        
        // 4. 將數(shù)據(jù)庫(kù)結(jié)果寫(xiě)入緩存（設(shè)置過(guò)期時(shí)間）
        if (user != null) {
            redisTemplate.opsForValue().set(cacheKey, user, CACHE_EXPIRATION, TimeUnit.MINUTES);
        }
        
        return user;
    }
    
    public void updateUser(User user) {
        // 1. 先更新數(shù)據(jù)庫(kù)
        userRepository.save(user);
        
        // 2. 再刪除緩存
        String cacheKey = CACHE_KEY_PREFIX + user.getId();
        redisTemplate.delete(cacheKey);
        
        // 或者選擇更新緩存
        // redisTemplate.opsForValue().set(cacheKey, user, CACHE_EXPIRATION, TimeUnit.MINUTES);
    }
}

public interface CacheLoader<K, V> {
    V load(K key);
}

@Component
public class ReadThroughCacheManager<K, V> {
    
    @Autowired
    private RedisTemplate<String, V> redisTemplate;
    
    private final ConcurrentHashMap<String, CacheLoader<K, V>> loaders = new ConcurrentHashMap<>();
    
    public void registerLoader(String cachePrefix, CacheLoader<K, V> loader) {
        loaders.put(cachePrefix, loader);
    }
    
    public V get(String cachePrefix, K key, long expiration, TimeUnit timeUnit) {
        String cacheKey = cachePrefix + key;
        
        // 1. 查詢(xún)緩存
        V value = redisTemplate.opsForValue().get(cacheKey);
        
        // 2. 緩存命中，直接返回
        if (value != null) {
            return value;
        }
        
        // 3. 緩存未命中，通過(guò)加載器獲取數(shù)據(jù)
        CacheLoader<K, V> loader = loaders.get(cachePrefix);
        if (loader == null) {
            throw new IllegalStateException("No cache loader registered for prefix: " + cachePrefix);
        }
        
        // 使用加載器從數(shù)據(jù)源加載數(shù)據(jù)
        value = loader.load(key);
        
        // 4. 將加載的數(shù)據(jù)存入緩存
        if (value != null) {
            redisTemplate.opsForValue().set(cacheKey, value, expiration, timeUnit);
        }
        
        return value;
    }
}

@Service
public class UserServiceReadThrough {
    
    private static final String CACHE_PREFIX = "user:";
    private static final long CACHE_EXPIRATION = 30;
    
    @Autowired
    private ReadThroughCacheManager<Long, User> cacheManager;
    
    @Autowired
    private UserRepository userRepository;
    
    @PostConstruct
    public void init() {
        // 注冊(cè)用戶(hù)數(shù)據(jù)加載器
        cacheManager.registerLoader(CACHE_PREFIX, this::loadUserFromDb);
    }
    
    private User loadUserFromDb(Long userId) {
        return userRepository.findById(userId).orElse(null);
    }
    
    public User getUserById(Long userId) {
        // 直接通過(guò)緩存管理器獲取數(shù)據(jù)，緩存邏輯由管理器處理
        return cacheManager.get(CACHE_PREFIX, userId, CACHE_EXPIRATION, TimeUnit.MINUTES);
    }
}

public interface CacheWriter<K, V> {
    void write(K key, V value);
}

@Component
public class WriteThroughCacheManager<K, V> {
    
    @Autowired
    private RedisTemplate<String, V> redisTemplate;
    
    private final ConcurrentHashMap<String, CacheWriter<K, V>> writers = new ConcurrentHashMap<>();
    
    public void registerWriter(String cachePrefix, CacheWriter<K, V> writer) {
        writers.put(cachePrefix, writer);
    }
    
    public void put(String cachePrefix, K key, V value, long expiration, TimeUnit timeUnit) {
        String cacheKey = cachePrefix + key;
        
        // 1. 獲取對(duì)應(yīng)的緩存寫(xiě)入器
        CacheWriter<K, V> writer = writers.get(cachePrefix);
        if (writer == null) {
            throw new IllegalStateException("No cache writer registered for prefix: " + cachePrefix);
        }
        
        // 2. 同步寫(xiě)入數(shù)據(jù)庫(kù)
        writer.write(key, value);
        
        // 3. 更新緩存
        redisTemplate.opsForValue().set(cacheKey, value, expiration, timeUnit);
    }
}

@Service
public class UserServiceWriteThrough {
    
    private static final String CACHE_PREFIX = "user:";
    private static final long CACHE_EXPIRATION = 30;
    
    @Autowired
    private WriteThroughCacheManager<Long, User> cacheManager;
    
    @Autowired
    private UserRepository userRepository;
    
    @PostConstruct
    public void init() {
        // 注冊(cè)用戶(hù)數(shù)據(jù)寫(xiě)入器
        cacheManager.registerWriter(CACHE_PREFIX, this::saveUserToDb);
    }
    
    private void saveUserToDb(Long userId, User user) {
        userRepository.save(user);
    }
    
    public void updateUser(User user) {
        // 通過(guò)緩存管理器更新數(shù)據(jù)，會(huì)同步更新數(shù)據(jù)庫(kù)和緩存
        cacheManager.put(CACHE_PREFIX, user.getId(), user, CACHE_EXPIRATION, TimeUnit.MINUTES);
    }
}

@Component
public class WriteBehindCacheManager<K, V> {
    
    @Autowired
    private RedisTemplate<String, V> redisTemplate;
    
    private final BlockingQueue<CacheUpdate<K, V>> updateQueue = new LinkedBlockingQueue<>();
    private final ConcurrentHashMap<String, CacheWriter<K, V>> writers = new ConcurrentHashMap<>();
    
    public void registerWriter(String cachePrefix, CacheWriter<K, V> writer) {
        writers.put(cachePrefix, writer);
    }
    
    @PostConstruct
    public void init() {
        // 啟動(dòng)異步寫(xiě)入線(xiàn)程
        Thread writerThread = new Thread(this::processWriteBehindQueue);
        writerThread.setDaemon(true);
        writerThread.start();
    }
    
    public void put(String cachePrefix, K key, V value, long expiration, TimeUnit timeUnit) {
        String cacheKey = cachePrefix + key;
        
        // 1. 更新緩存
        redisTemplate.opsForValue().set(cacheKey, value, expiration, timeUnit);
        
        // 2. 將更新放入隊(duì)列，等待異步寫(xiě)入數(shù)據(jù)庫(kù)
        updateQueue.offer(new CacheUpdate<>(cachePrefix, key, value));
    }
    
    private void processWriteBehindQueue() {
        List<CacheUpdate<K, V>> batch = new ArrayList<>(100);
        
        while (true) {
            try {
                // 獲取隊(duì)列中的更新，最多等待100ms
                CacheUpdate<K, V> update = updateQueue.poll(100, TimeUnit.MILLISECONDS);
                
                if (update != null) {
                    batch.add(update);
                }
                
                // 繼續(xù)收集隊(duì)列中可用的更新，最多收集100個(gè)或等待200ms
                updateQueue.drainTo(batch, 100 - batch.size());
                
                if (!batch.isEmpty()) {
                    // 按緩存前綴分組批量處理
                    Map<String, List<CacheUpdate<K, V>>> groupedUpdates = batch.stream()
                            .collect(Collectors.groupingBy(CacheUpdate::getCachePrefix));
                    
                    for (Map.Entry<String, List<CacheUpdate<K, V>>> entry : groupedUpdates.entrySet()) {
                        String cachePrefix = entry.getKey();
                        List<CacheUpdate<K, V>> updates = entry.getValue();
                        
                        CacheWriter<K, V> writer = writers.get(cachePrefix);
                        if (writer != null) {
                            // 批量寫(xiě)入數(shù)據(jù)庫(kù)
                            for (CacheUpdate<K, V> u : updates) {
                                try {
                                    writer.write(u.getKey(), u.getValue());
                                } catch (Exception e) {
                                    // 處理異常，可以重試或記錄日志
                                    log.error("Failed to write-behind for key {}: {}", u.getKey(), e.getMessage());
                                }
                            }
                        }
                    }
                    
                    batch.clear();
                }
                
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt();
                break;
            } catch (Exception e) {
                log.error("Error in write-behind process", e);
            }
        }
    }
    
    @Data
    @AllArgsConstructor
    private static class CacheUpdate<K, V> {
        private String cachePrefix;
        private K key;
        private V value;
    }
}

@Service
public class UserServiceWriteBehind {
    
    private static final String CACHE_PREFIX = "user:";
    private static final long CACHE_EXPIRATION = 30;
    
    @Autowired
    private WriteBehindCacheManager<Long, User> cacheManager;
    
    @Autowired
    private UserRepository userRepository;
    
    @PostConstruct
    public void init() {
        // 注冊(cè)用戶(hù)數(shù)據(jù)寫(xiě)入器
        cacheManager.registerWriter(CACHE_PREFIX, this::saveUserToDb);
    }
    
    private void saveUserToDb(Long userId, User user) {
        userRepository.save(user);
    }
    
    public void updateUser(User user) {
        // 更新僅寫(xiě)入緩存，異步寫(xiě)入數(shù)據(jù)庫(kù)
        cacheManager.put(CACHE_PREFIX, user.getId(), user, CACHE_EXPIRATION, TimeUnit.MINUTES);
    }
}

@Component
public class RefreshAheadCacheManager<K, V> {
    
    @Autowired
    private RedisTemplate<String, Object> redisTemplate;
    
    @Autowired
    private ThreadPoolTaskExecutor refreshExecutor;
    
    private final ConcurrentHashMap<String, CacheLoader<K, V>> loaders = new ConcurrentHashMap<>();
    
    // 刷新閾值，當(dāng)過(guò)期時(shí)間剩余不足閾值比例時(shí)觸發(fā)刷新
    private final double refreshThreshold = 0.75; // 75%
    
    public void registerLoader(String cachePrefix, CacheLoader<K, V> loader) {
        loaders.put(cachePrefix, loader);
    }
    
    @SuppressWarnings("unchecked")
    public V get(String cachePrefix, K key, long expiration, TimeUnit timeUnit) {
        String cacheKey = cachePrefix + key;
        
        // 1. 獲取緩存項(xiàng)和其TTL
        V value = (V) redisTemplate.opsForValue().get(cacheKey);
        Long ttl = redisTemplate.getExpire(cacheKey, TimeUnit.MILLISECONDS);
        
        if (value != null) {
            // 2. 如果緩存存在但接近過(guò)期，觸發(fā)異步刷新
            if (ttl != null && ttl > 0) {
                long expirationMs = timeUnit.toMillis(expiration);
                if (ttl < expirationMs * (1 - refreshThreshold)) {
                    refreshAsync(cachePrefix, key, cacheKey, expiration, timeUnit);
                }
            }
            return value;
        }
        
        // 3. 緩存不存在，同步加載
        return loadAndCache(cachePrefix, key, cacheKey, expiration, timeUnit);
    }
    
    private void refreshAsync(String cachePrefix, K key, String cacheKey, long expiration, TimeUnit timeUnit) {
        refreshExecutor.execute(() -> {
            try {
                loadAndCache(cachePrefix, key, cacheKey, expiration, timeUnit);
            } catch (Exception e) {
                // 異步刷新失敗，記錄日志但不影響當(dāng)前請(qǐng)求
                log.error("Failed to refresh cache for key {}: {}", cacheKey, e.getMessage());
            }
        });
    }
    
    private V loadAndCache(String cachePrefix, K key, String cacheKey, long expiration, TimeUnit timeUnit) {
        CacheLoader<K, V> loader = loaders.get(cachePrefix);
        if (loader == null) {
            throw new IllegalStateException("No cache loader registered for prefix: " + cachePrefix);
        }
        
        // 從數(shù)據(jù)源加載
        V value = loader.load(key);
        
        // 更新緩存
        if (value != null) {
            redisTemplate.opsForValue().set(cacheKey, value, expiration, timeUnit);
        }
        
        return value;
    }
}

@Service
public class ProductServiceRefreshAhead {
    
    private static final String CACHE_PREFIX = "product:";
    private static final long CACHE_EXPIRATION = 60; // 1小時(shí)
    
    @Autowired
    private RefreshAheadCacheManager<String, Product> cacheManager;
    
    @Autowired
    private ProductRepository productRepository;
    
    @PostConstruct
    public void init() {
        // 注冊(cè)產(chǎn)品數(shù)據(jù)加載器
        cacheManager.registerLoader(CACHE_PREFIX, this::loadProductFromDb);
    }
    
    private Product loadProductFromDb(String productId) {
        return productRepository.findById(productId).orElse(null);
    }
    
    public Product getProduct(String productId) {
        return cacheManager.get(CACHE_PREFIX, productId, CACHE_EXPIRATION, TimeUnit.MINUTES);
    }
}

@Configuration
public class ThreadPoolConfig {
    
    @Bean
    public ThreadPoolTaskExecutor refreshExecutor() {
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        executor.setCorePoolSize(5);
        executor.setMaxPoolSize(20);
        executor.setQueueCapacity(100);
        executor.setThreadNamePrefix("cache-refresh-");
        executor.setRejectedExecutionHandler(new ThreadPoolExecutor.CallerRunsPolicy());
        executor.initialize();
        return executor;
    }
}

@Data
@AllArgsConstructor
public class DataChangeEvent {
    private String entityType;
    private String entityId;
    private String operation; // CREATE, UPDATE, DELETE
    private String payload;   // JSON格式的實(shí)體數(shù)據(jù)
}

@Component
public class DataChangePublisher {
    
    @Autowired
    private KafkaTemplate<String, DataChangeEvent> kafkaTemplate;
    
    private static final String TOPIC = "data-changes";
    
    public void publishChange(String entityType, String entityId, String operation, Object entity) {
        try {
            // 將實(shí)體序列化為JSON
            String payload = new ObjectMapper().writeValueAsString(entity);
            
            // 創(chuàng)建事件
            DataChangeEvent event = new DataChangeEvent(entityType, entityId, operation, payload);
            
            // 發(fā)布到Kafka
            kafkaTemplate.send(TOPIC, entityId, event);
        } catch (Exception e) {
            log.error("Failed to publish data change event", e);
            throw new RuntimeException("Failed to publish event", e);
        }
    }
}

@Component
@Slf4j
public class CacheUpdateConsumer {
    
    @Autowired
    private RedisTemplate<String, Object> redisTemplate;
    
    private static final long CACHE_EXPIRATION = 30;
    
    @KafkaListener(topics = "data-changes")
    public void handleDataChangeEvent(DataChangeEvent event) {
        try {
            String cacheKey = buildCacheKey(event.getEntityType(), event.getEntityId());
            
            switch (event.getOperation()) {
                case "CREATE":
                case "UPDATE":
                    // 解析JSON數(shù)據(jù)
                    Object entity = parseEntity(event.getPayload(), event.getEntityType());
                    // 更新緩存
                    redisTemplate.opsForValue().set(
                            cacheKey, entity, CACHE_EXPIRATION, TimeUnit.MINUTES);
                    log.info("Updated cache for {}: {}", cacheKey, event.getOperation());
                    break;
                    
                case "DELETE":
                    // 刪除緩存
                    redisTemplate.delete(cacheKey);
                    log.info("Deleted cache for {}", cacheKey);
                    break;
                    
                default:
                    log.warn("Unknown operation: {}", event.getOperation());
            }
        } catch (Exception e) {
            log.error("Error handling data change event: {}", e.getMessage(), e);
            // 失敗處理：可以將失敗事件放入死信隊(duì)列等
        }
    }
    
    private String buildCacheKey(String entityType, String entityId) {
        return entityType.toLowerCase() + ":" + entityId;
    }
    
    private Object parseEntity(String payload, String entityType) throws JsonProcessingException {
        // 根據(jù)實(shí)體類(lèi)型選擇反序列化目標(biāo)類(lèi)
        Class<?> targetClass = getClassForEntityType(entityType);
        return new ObjectMapper().readValue(payload, targetClass);
    }
    
    private Class<?> getClassForEntityType(String entityType) {
        switch (entityType) {
            case "User": return User.class;
            case "Product": return Product.class;
            // 其他實(shí)體類(lèi)型
            default: throw new IllegalArgumentException("Unknown entity type: " + entityType);
        }
    }
}

@Service
@Transactional
public class UserServiceEventDriven {
    
    @Autowired
    private UserRepository userRepository;
    
    @Autowired
    private DataChangePublisher publisher;
    
    public User createUser(User user) {
        // 1. 保存用戶(hù)到數(shù)據(jù)庫(kù)
        User savedUser = userRepository.save(user);
        
        // 2. 發(fā)布創(chuàng)建事件
        publisher.publishChange("User", savedUser.getId().toString(), "CREATE", savedUser);
        
        return savedUser;
    }
    
    public User updateUser(User user) {
        // 1. 更新用戶(hù)到數(shù)據(jù)庫(kù)
        User updatedUser = userRepository.save(user);
        
        // 2. 發(fā)布更新事件
        publisher.publishChange("User", updatedUser.getId().toString(), "UPDATE", updatedUser);
        
        return updatedUser;
    }
    
    public void deleteUser(Long userId) {
        // 1. 從數(shù)據(jù)庫(kù)刪除用戶(hù)
        userRepository.deleteById(userId);
        
        // 2. 發(fā)布刪除事件
        publisher.publishChange("User", userId.toString(), "DELETE", null);
    }
}