using Application.Abstractions.Data;
using Application.Abstractions.Paper;
using Application.Helpers;
using StackExchange.Redis;

namespace Infrastructure.Paper;

/// <summary>
/// Redis Sorted Set 기반 모의투자 리더보드 캐시 (d4 M3 리더보드 백엔드 구현) — RedisChatLeaderboard 패턴 복제.
/// (sort, period) 조합별 키. TTL 25h — 만료 시 다음 호출이 DB 지표 산출 후 재시드.
/// return/winrate 는 ZREVRANGE(내림차순 = 높을수록 상위), mdd 는 ZRANGE(오름차순 = 낮을수록 상위).
/// </summary>
internal sealed class PaperLeaderboardCache(IConnectionMultiplexer redis) : IPaperLeaderboardCache
{
    private static readonly TimeSpan CacheTtl = TimeSpan.FromHours(25);

    private static string Key(PaperLeaderboardSort sort, PaperLeaderboardPeriod period)
    {
        var s = sort switch
        {
            PaperLeaderboardSort.Return => "return",
            PaperLeaderboardSort.WinRate => "winrate",
            PaperLeaderboardSort.Mdd => "mdd",
            _ => "return"
        };

        var p = period switch
        {
            PaperLeaderboardPeriod.Week => "week",
            PaperLeaderboardPeriod.Month => "month",
            PaperLeaderboardPeriod.All => "all",
            _ => "all"
        };

        return $"paper-lb:{s}:{p}";
    }

    public async Task<IReadOnlyList<PaperLeaderboardRow>> GetPageAsync(
        PaperLeaderboardSort sort,
        PaperLeaderboardPeriod period,
        int offset,
        int count,
        IAppDbContext db,
        int minFillsForRank,
        CancellationToken ct = default)
    {
        var r = redis.GetDatabase();
        var key = Key(sort, period);

        await EnsureSeededAsync(r, key, sort, period, db, minFillsForRank, ct);

        var ascending = PaperLeaderboardMetrics.IsAscending(sort);
        var order = ascending ? Order.Ascending : Order.Descending;

        var stop = offset + count - 1;
        var entries = await r.SortedSetRangeByRankWithScoresAsync(key, offset, stop, order);

        var rows = new List<PaperLeaderboardRow>(entries.Length);

        for (var i = 0; i < entries.Length; i++)
        {
            if (int.TryParse((string?)entries[i].Element, out var memberID))
            {
                rows.Add(new PaperLeaderboardRow(memberID, (int)entries[i].Score, offset + i));
            }
        }

        return rows;
    }

    public async Task<PaperLeaderboardMyRank?> GetMyRankAsync(
        PaperLeaderboardSort sort,
        PaperLeaderboardPeriod period,
        int memberID,
        IAppDbContext db,
        int minFillsForRank,
        CancellationToken ct = default)
    {
        var r = redis.GetDatabase();
        var key = Key(sort, period);

        await EnsureSeededAsync(r, key, sort, period, db, minFillsForRank, ct);

        var member = (RedisValue)memberID.ToString();
        var score = await r.SortedSetScoreAsync(key, member);

        if (!score.HasValue)
        {
            return null;
        }

        var ascending = PaperLeaderboardMetrics.IsAscending(sort);
        var order = ascending ? Order.Ascending : Order.Descending;

        var rank = await r.SortedSetRankAsync(key, member, order);
        var total = await r.SortedSetLengthAsync(key);

        if (!rank.HasValue)
        {
            return null;
        }

        return new PaperLeaderboardMyRank(rank.Value, (int)score.Value, total);
    }

    /// <summary>캐시 미스 → DB 지표 산출 후 ZADD 재시드. TTL 동안 후속 호출은 Redis only.</summary>
    private static async Task EnsureSeededAsync(
        IDatabase r,
        string key,
        PaperLeaderboardSort sort,
        PaperLeaderboardPeriod period,
        IAppDbContext db,
        int minFillsForRank,
        CancellationToken ct)
    {
        if (await r.KeyExistsAsync(key))
        {
            return;
        }

        var metrics = await PaperLeaderboardMetrics.ComputeAllAsync(db, period, minFillsForRank, ct);

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

        var entries = metrics
            .Select(c => new SortedSetEntry(c.MemberID.ToString(), PaperLeaderboardMetrics.Score(c, sort)))
            .ToArray();

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