ANTOOZA-BACKEND/Application/Features/Api/Paper/GetLeaderboard/Handler.cs

using Application.Abstractions.Data;
using Application.Abstractions.Messaging;
using Application.Abstractions.Paper;
using Application.Helpers;
using Microsoft.EntityFrameworkCore;

namespace Application.Features.Api.Paper.GetLeaderboard;

/// <summary>
/// 모의투자 리더보드 (익명 허용) — Redis 캐시로 순위 페이지 조회 후 회원(SID/닉네임/썸네일)·지표 결합 (d4 M3 리더보드 백엔드 구현).
/// </summary>
internal sealed class Handler(IAppDbContext db, IPaperLeaderboardCache cache) : IQueryHandler<Query, Response>
{
    private const int PageSize = 50;

    public async Task<Response> Handle(Query request, CancellationToken ct)
    {
        var sort = PaperLeaderboardMetrics.ParseSort(request.Sort);
        var period = PaperLeaderboardMetrics.ParsePeriod(request.Period);
        var page = request.Page < 1 ? 1 : request.Page;

        var minFillsForRank = await db.Config.AsNoTracking().OrderByDescending(c => c.ID).Select(c => c.Paper.MinFillsForRank).FirstOrDefaultAsync(ct);

        if (minFillsForRank <= 0)
        {
            minFillsForRank = 3;
        }

        var offset = (page - 1) * PageSize;
        var pageRows = await cache.GetPageAsync(sort, period, offset, PageSize, db, minFillsForRank, ct);

        if (pageRows.Count == 0)
        {
            return new Response(PaperLeaderboardMetrics.SortToString(sort), PaperLeaderboardMetrics.PeriodToString(period), page, PageSize, []);
        }

        // 전체 지표 산출 후 memberID 로 매핑 (배치 리더보드 규모 소량 가정)
        var metrics = await PaperLeaderboardMetrics.ComputeAllAsync(db, period, minFillsForRank, ct);
        var metricByMember = metrics.ToDictionary(c => c.MemberID);

        var memberIDs = pageRows.Select(c => c.MemberID).ToList();

        var members = await db.Member.AsNoTracking()
            .Where(c => memberIDs.Contains(c.ID))
            .Select(c => new { c.ID, c.SID, c.Name, c.Thumb })
            .ToListAsync(ct);

        var memberByID = members.ToDictionary(c => c.ID);

        var rows = new List<Row>(pageRows.Count);

        foreach (var pr in pageRows)
        {
            if (!memberByID.TryGetValue(pr.MemberID, out var m))
            {
                continue;
            }

            metricByMember.TryGetValue(pr.MemberID, out var metric);

            rows.Add(new Row(
                pr.Rank + 1,
                m.SID,
                m.Name,
                m.Thumb,
                metric?.ReturnBp ?? 0,
                metric?.WinRateBp ?? 0,
                metric?.MddBp ?? 0,
                metric?.FillCount ?? 0));
        }

        return new Response(PaperLeaderboardMetrics.SortToString(sort), PaperLeaderboardMetrics.PeriodToString(period), page, PageSize, rows);
    }
}