ANTOOZA-BACKEND/Infrastructure/Hubs/PresenceTracker.cs

using Application.Abstractions.Cache;
using Application.Abstractions.Hub;
using StackExchange.Redis;

namespace Infrastructure.Hubs;

/// <summary>
/// SignalR 멤버 접속 추적 (Redis 기반).
/// `member:connections:{memberID}` set에 connectionId 저장 → refcount 패턴.
/// 첫 connection 진입 시 `member:online` set에 추가, 마지막 disconnect 시 제거.
/// </summary>
internal sealed class PresenceTracker(IConnectionMultiplexer redis) : IPresenceTracker
{
    public async Task<bool> AddConnectionAsync(int memberID, string connectionId)
    {
        var db = redis.GetDatabase();
        var key = CacheKeys.MemberConnections(memberID);

        var added = await db.SetAddAsync(key, connectionId);

        if (!added)
        {
            // 동일 connectionId 중복 등록 — 변화 없음
            return false;
        }

        // 항상 MemberOnlineSet 반영. SADD 의 set semantics 로 idempotent.
        // 이전 버전은 totalConnections==1 가드를 두었으나, Web.Api 비정상 종료로 남은
        // 고아 connectionId 가 set 에 있을 때 신규 connection 이 와도 online set 에 반영되지 않는 버그가 있었음.
        var wasNewlyOnline = await db.SetAddAsync(CacheKeys.MemberOnlineSet, memberID);

        return wasNewlyOnline; // true = 0→1 전환 (online set 에 새로 추가됨)
    }

    public async Task ClearAllAsync()
    {
        // Web.Api 재시작 시 stale presence 데이터 정리. 모든 client 는 reconnect 시 OnConnected 로 재등록됨.
        var db = redis.GetDatabase();
        var endpoints = redis.GetEndPoints();

        foreach (var endpoint in endpoints)
        {
            var server = redis.GetServer(endpoint);
            if (!server.IsConnected || server.IsReplica)
            {
                continue;
            }

            // member:connections:* 패턴 일괄 삭제
            await foreach (var key in server.KeysAsync(database: db.Database, pattern: "member:connections:*"))
            {
                await db.KeyDeleteAsync(key);
            }
        }

        // member:online set 전체 삭제
        await db.KeyDeleteAsync(CacheKeys.MemberOnlineSet);
    }

    public async Task<bool> RemoveConnectionAsync(int memberID, string connectionId)
    {
        var db = redis.GetDatabase();
        var key = CacheKeys.MemberConnections(memberID);

        var removed = await db.SetRemoveAsync(key, connectionId);

        if (!removed)
        {
            return false;
        }

        // 마지막 connection이면 online set에서 제거 + 빈 set 삭제
        var remaining = await db.SetLengthAsync(key);
        if (remaining == 0)
        {
            await db.KeyDeleteAsync(key);
            await db.SetRemoveAsync(CacheKeys.MemberOnlineSet, memberID);
            return true; // 1→0 전환
        }

        return false;
    }

    public async Task<bool> IsOnlineAsync(int memberID)
    {
        var db = redis.GetDatabase();
        return await db.SetContainsAsync(CacheKeys.MemberOnlineSet, memberID);
    }

    public async Task<HashSet<int>> GetOnlineMembersAsync(IEnumerable<int> memberIDs)
    {
        var ids = memberIDs.Distinct().ToArray();

        if (ids.Length == 0)
        {
            return [];
        }

        var db = redis.GetDatabase();
        var values = ids.Select(id => (RedisValue)id).ToArray();
        var results = await db.SetContainsAsync(CacheKeys.MemberOnlineSet, values);

        var online = new HashSet<int>();
        for (int i = 0; i < ids.Length; i++)
        {
            if (results[i])
            {
                online.Add(ids[i]);
            }
        }

        return online;
    }
}