#附近的人（LBS）系统

@Service
public class LBSService {

    @Autowired
    private RedisTemplate<String, String> redisTemplate;

    /**
     * 上报用户位置
     */
    public void updateLocation(Long userId, double longitude, double latitude) {
        String key = "geo:user:location";
        redisTemplate.opsForGeo().add(key, new Point(longitude, latitude), "user_" + userId);
    }

    /**
     * 搜索附近的人
     */
    public List<NearByUser> searchNearBy(Long userId, double longitude,
                                          double latitude, double radiusKm, int limit) {
        String key = "geo:user:location";

        // 查询附近的人（返回距离）
        Distance distance = new Distance(radiusKm, Metrics.KILOMETERS);
        Circle circle = new Circle(new Point(longitude, latitude), distance);

        GeoResults<RedisGeoCommands.GeoLocation<String>> results =
            redisTemplate.opsForGeo().radius(key,
                GeoRedisCommands.GeoRadiusCommandArgs.newGeoRadiusArgs()
                    .includeDistance()  // 返回距离
                    .sortAscending()    // 按距离升序
                    .limit(limit)       // 限制数量
            );

        // 转换为业务对象
        return results.getContent().stream()
            .map(r -> {
                String redisMember = r.getContent().getName();
                Long nearByUserId = Long.parseLong(redisMember.replace("user_", ""));
                return new NearByUser(nearByUserId, r.getDistance().getValue());
            })
            .filter(u -> !u.getUserId().equals(userId))  // 排除自己
            .collect(Collectors.toList());
    }
}

public List<NearByUser> searchNearByMultiPrecision(
        double longitude, double latitude, double radiusKm, int limit) {

    // 获取当前精度的Geohash及其周边格子
    String currentHash = Geohash.encode(latitude, longitude, 7);
    List<String> neighborHashes = getNeighborHashes(currentHash);  // 9个格子

    Set<Long> userIds = new LinkedHashSet<>();
    List<NearByUser> results = new ArrayList<>();

    for (String hash : neighborHashes) {
        // 搜索每个格子
        List<NearByUser> users = searchByGeohash(hash, longitude, latitude, radiusKm);
        for (NearByUser user : users) {
            if (!userIds.contains(user.getUserId())) {
                userIds.add(user.getUserId());
                results.add(user);
                if (results.size() >= limit) {
                    return results;
                }
            }
        }
    }

    return results;
}

// 按城市分片
public String getGeoKey(Long userId) {
    Long cityId = userDAO.selectCityId(userId);
    return "geo:user:location:city_" + cityId;
}

// 按Geohash前缀分片
public String getGeoKeyByHash(double longitude, double latitude) {
    String hash = Geohash.encode(latitude, longitude, 5);  // 5位精度
    String shardKey = hash.substring(0, 2);  // 取前2位作为分片key
    return "geo:user:location:shard_" + shardKey;
}