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

using Application.Abstractions.Data;
using Application.Abstractions.Messaging;
using Domain.Entities.Members;
using Microsoft.EntityFrameworkCore;

namespace Application.Features.Api.TrackRecord.GetLeaderboard;

/// <summary>
/// 예측 적중률 리더보드 조회 (D2 M4). 필터 인덱스(IX_MemberTrackRecord_HitRate WHERE Predictions>=10)를 활용해
/// 채점 표본(Hits+Misses) 10+ 회원을 HitRate 내림차순으로 페이징한다. Redis 캐시는 v1 미사용(필터 인덱스로 충분).
/// </summary>
internal sealed class Handler(IAppDbContext db) : IQueryHandler<Query, Response>
{
    private const int PageSize = 50;

    /// <summary>리더보드 게이트 — 채점 표본(Hits+Misses) 최소치 (d2 §③ 표본 10+).</summary>
    private const int MinSample = TrackRecordTiers.MinSample;

    public async Task<Response> Handle(Query request, CancellationToken ct)
    {
        var page = request.Page < 1 ? 1 : request.Page;

        // 표본(채점 완료) = Hits + Misses. 필터 인덱스는 Predictions>=10 이지만 Void 가 껴 실제 표본이 10 미만일 수
        // 있어 Hits+Misses>=10 을 명시적으로 재확인한다(정확성 우선, 인덱스는 후보 축소).
        var query = db.MemberTrackRecord.AsNoTracking().Where(c => c.Hits + c.Misses >= MinSample);

        var total = await query.CountAsync(ct);

        var rows = await query
            .OrderByDescending(c => c.HitRate).ThenByDescending(c => c.Hits + c.Misses).ThenBy(c => c.MemberID)
            .Skip((page - 1) * PageSize)
            .Take(PageSize)
            .Select(c => new
            {
                c.Member.SID,
                c.Member.Name,
                c.Tier,
                c.HitRate,
                c.Predictions,
                c.Hits,
                c.Misses,
                c.BestStreak
            })
            .ToListAsync(ct);

        var baseRank = (page - 1) * PageSize;

        return new Response
        {
            Total = total,
            Period = "all",
            List = [..rows.Select((c, i) => new Response.Row
            {
                Rank = baseRank + i + 1,
                SID = c.SID,
                Name = c.Name ?? string.Empty,
                Tier = c.Tier.ToString(),
                TierCode = (byte)c.Tier,
                HitRate = c.HitRate,
                Predictions = c.Predictions,
                Hits = c.Hits,
                Misses = c.Misses,
                BestStreak = c.BestStreak
            })]
        };
    }
}