OpenIsle/backend/src/main/java/com/openisle/config/ShardingStrategy.java

package com.openisle.config;

import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.atomic.AtomicLong;
import java.util.Map;
import java.util.stream.Collectors;

@Component
@Slf4j
public class ShardingStrategy {
    
    // 固定为16以匹配RabbitMQConfig中的十六进制分片逻辑
    private static final int QUEUE_COUNT = 16;
    
    // 分片分布统计
    private final Map<Integer, AtomicLong> shardCounts = new ConcurrentHashMap<>();
    
    /**
     * 根据用户名获取分片信息（基于哈希值首字符）
     */
    public ShardInfo getShardInfo(String username) {
        if (username == null || username.isEmpty()) {
            // 空用户名默认分到第0个分片
            return getShardInfoByIndex(0);
        }
        
        // 计算用户名的哈希值并转为十六进制字符串
        String hash = Integer.toHexString(Math.abs(username.hashCode()));
        
        // 取哈希值的第一个字符 (0-9, a-f)
        char firstChar = hash.charAt(0);
        
        // 十六进制字符映射到队列
        int shard = getShardFromHexChar(firstChar);
        recordShardUsage(shard);
        
        log.debug("Username '{}' -> hash '{}' -> firstChar '{}' -> shard {}", 
                 username, hash, firstChar, shard);
        
        return getShardInfoByIndex(shard);
    }
    
    /**
     * 将十六进制字符映射到分片索引
     */
    private int getShardFromHexChar(char hexChar) {
        int charValue;
        if (hexChar >= '0' && hexChar <= '9') {
            charValue = hexChar - '0'; // 0-9
        } else if (hexChar >= 'a' && hexChar <= 'f') {
            charValue = hexChar - 'a' + 10; // 10-15
        } else {
            // 异常情况，默认为0
            charValue = 0;
        }
        
        // 映射到队列数量范围内
        return charValue % QUEUE_COUNT;
    }
    
    /**
     * 根据分片索引获取分片信息
     */
    private ShardInfo getShardInfoByIndex(int shard) {
        String shardKey = Integer.toHexString(shard);
        return new ShardInfo(
            shard,
            "notifications-queue-" + shardKey,
            "notifications.shard." + shardKey
        );
    }
    
    /**
     * 记录分片使用统计
     */
    private void recordShardUsage(int shard) {
        shardCounts.computeIfAbsent(shard, k -> new AtomicLong(0)).incrementAndGet();
    }

}