ANTOOZA-BACKEND/Infrastructure/Stocks/RedisStockBoardTrendingCache.cs

using Application.Abstractions.Data;
using Application.Abstractions.Stocks;
using Microsoft.EntityFrameworkCore;
using StackExchange.Redis;

namespace Infrastructure.Stocks;

/// <summary>
/// Redis Sorted Set 기반 종목 트렌딩 캐시 (d2 §④·§⑥) — RedisChatLeaderboard/PaperLeaderboardCache 패턴 복제.
/// 점수 = 최근 24h PostStockTag 언급량 × RecentWeight + StockBoardStats.Posts(총 글 수, tie-breaker).
/// TTL 10분 — 만료 시 다음 호출이 DB 집계 1회 후 재시드. StockMentionAggregator 배치가 없을 때도 lazy 로 동작.
/// </summary>
internal sealed class RedisStockBoardTrendingCache(IConnectionMultiplexer redis) : IStockBoardTrendingCache
{
    private static readonly TimeSpan CacheTtl = TimeSpan.FromMinutes(10);

    // 최근성 가중 — 24h 언급 1건이 총 글 10건과 동일 가중.
    private const int RecentWeight = 10;

    private const string Key = "stock-trending";

    public async Task<IReadOnlyList<StockTrendingEntry>> GetTopAsync(int count, IAppDbContext db, CancellationToken ct = default)
    {
        if (count <= 0)
        {
            return [];
        }

        var r = redis.GetDatabase();

        await EnsureSeededAsync(r, db, ct);

        var entries = await r.SortedSetRangeByRankWithScoresAsync(Key, 0, count - 1, Order.Descending);

        var rows = new List<StockTrendingEntry>(entries.Length);
        foreach (var entry in entries)
        {
            var code = (string?)entry.Element;
            if (!string.IsNullOrEmpty(code))
            {
                rows.Add(new StockTrendingEntry(code, (int)entry.Score));
            }
        }

        return rows;
    }

    public async Task InvalidateAsync(CancellationToken ct = default)
    {
        var r = redis.GetDatabase();
        await r.KeyDeleteAsync(Key);
    }

    /// <summary>캐시 미스 → DB 집계 후 ZADD 재시드. TTL 동안 후속 호출은 Redis only.</summary>
    private static async Task EnsureSeededAsync(IDatabase r, IAppDbContext db, CancellationToken ct)
    {
        if (await r.KeyExistsAsync(Key))
        {
            return;
        }

        var since = DateTime.UtcNow.AddHours(-24);

        // 최근 24h 언급량 (코드별 count)
        var recentMentions = await db.PostStockTag.AsNoTracking()
            .Where(c => c.CreatedAt >= since)
            .GroupBy(c => c.StockCode)
            .Select(g => new { Code = g.Key, Count = g.Count() })
            .ToListAsync(ct);

        // 총 글 수 (StockBoardStats 파티션)
        var totals = await db.StockBoardStats.AsNoTracking()
            .Select(c => new { c.StockCode, c.Posts })
            .ToListAsync(ct);

        var scores = new Dictionary<string, int>(StringComparer.Ordinal);

        foreach (var t in totals)
        {
            scores[t.StockCode] = t.Posts;
        }

        foreach (var m in recentMentions)
        {
            scores.TryGetValue(m.Code, out var baseScore);
            scores[m.Code] = baseScore + (m.Count * RecentWeight);
        }

        if (scores.Count == 0)
        {
            return;
        }

        var entries = scores
            .Where(kv => kv.Value > 0)
            .Select(kv => new SortedSetEntry(kv.Key, kv.Value))
            .ToArray();

        if (entries.Length == 0)
        {
            return;
        }

        await r.SortedSetAddAsync(Key, entries);
        await r.KeyExpireAsync(Key, CacheTtl);
    }
}