ANTOOZA-BACKEND/Application/Features/Api/Ranking/GetHallOfFame/Handler.cs

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

namespace Application.Features.Api.Ranking.GetHallOfFame;

/// <summary>
/// 후원자(Donor) 누적 후원 명예의 전당. Donation.SponsorMemberID GROUP BY 실시간 집계.
/// 비공개 동의(IsRankingPublic=false) 회원은 익명 처리 — 개인정보 보호.
/// </summary>
internal sealed class Handler(IAppDbContext db) : IQueryHandler<Query, Response>
{
    private const string AnonymousName = "비공개 사용자";

    public async Task<Response> Handle(Query request, CancellationToken ct)
    {
        var limit = request.Limit is < 1 or > 500 ? 100 : request.Limit;
        var period = HallPeriod.ValidPeriods.Contains(request.Period) ? request.Period : HallPeriod.All;

        var (periodStart, periodEnd) = BuildPeriodRange(period);

        var donationQuery = db.Donation.AsNoTracking().Where(d => !d.IsTest);

        if (periodStart.HasValue)
        {
            donationQuery = donationQuery.Where(d => d.CreatedAt >= periodStart.Value);
        }

        if (periodEnd.HasValue)
        {
            donationQuery = donationQuery.Where(d => d.CreatedAt <= periodEnd.Value);
        }

        // 후원자별 누적 금액 — 단순 GROUP BY → Sum (EF Core 가 SQL 로 안전하게 변환 가능)
        // 주의: GroupBy 안에서 g.Select(...).Distinct().Count() nested aggregate 는 EF Core 가 변환 못 함
        // → distinct receiver count 는 별도 쿼리로 분리.
        var sums = await donationQuery
            .GroupBy(d => d.SponsorMemberID)
            .Select(g => new { MemberID = g.Key, Amount = g.Sum(d => (long)d.NetAmount) })
            .OrderByDescending(g => g.Amount)
            .Take(limit)
            .ToListAsync(ct);

        if (sums.Count == 0)
        {
            return new Response([], periodStart, periodEnd);
        }

        var memberIds = sums.Select(s => s.MemberID).ToList();

        // Top N 후원자별 distinct (sponsor, receiver) pair → 메모리에서 sponsor 별로 count
        // SQL: SELECT DISTINCT SponsorMemberID, ReceiverMemberID FROM Donation WHERE ... AND SponsorMemberID IN (...)
        var pairs = await donationQuery
            .Where(d => memberIds.Contains(d.SponsorMemberID))
            .Select(d => new { d.SponsorMemberID, d.ReceiverMemberID })
            .Distinct()
            .ToListAsync(ct);

        var peerCounts = pairs.GroupBy(p => p.SponsorMemberID).ToDictionary(g => g.Key, g => g.Count());

        var aggregate = sums.Select(s => new AggregateRow(s.MemberID, s.Amount, peerCounts.GetValueOrDefault(s.MemberID, 0))).ToList();

        var members = await db.Member.AsNoTracking()
            .Where(m => memberIds.Contains(m.ID))
            .Select(m => new MemberRow(
                m.ID,
                m.Name,
                m.Thumb,
                m.MemberGradeID,
                m.MemberGrade != null ? m.MemberGrade.KorName : null,
                m.MemberGrade != null ? m.MemberGrade.Image : null,
                m.MemberGrade != null ? m.MemberGrade.TextColor : null,
                m.MemberApprove != null && m.MemberApprove.IsRankingPublic
            ))
            .ToListAsync(ct);

        var memberDict = members.ToDictionary(m => m.ID, m => m);

        var top100 = aggregate.Select((row, i) => {
            var m = memberDict.GetValueOrDefault(row.MemberID);

            // 비공개 동의 회원 익명 처리 (개인정보 보호)
            var anonymize = m is not null && !m.IsRankingPublic;

            return new HallEntry(
                i + 1,
                row.MemberID,
                anonymize ? AnonymousName : (m?.Name ?? ""),
                anonymize ? null : m?.Thumb,
                null, // donor는 channel 컨텍스트 없음
                row.Amount,
                row.PeerCount,
                anonymize ? null : m?.MemberGradeID,
                anonymize ? null : m?.GradeKorName,
                anonymize ? null : m?.GradeImage,
                anonymize ? null : m?.GradeTextColor,
                anonymize
            );
        }).ToList();

        return new Response(top100, periodStart, periodEnd);
    }

    /// <summary>
    /// 기간 키워드 → UTC 롤링 윈도우 (start, end). All 은 (null, null).
    /// </summary>
    private static (DateTime? start, DateTime? end) BuildPeriodRange(string period)
    {
        var now = DateTime.UtcNow;

        return period switch
        {
            HallPeriod.Today => (now.Date, now),
            HallPeriod.Week => (now.AddDays(-7), now),
            HallPeriod.Month => (now.AddMonths(-1), now),
            HallPeriod.Quarter => (now.AddMonths(-3), now),
            HallPeriod.Half => (now.AddMonths(-6), now),
            _ => (null, null)
        };
    }

    private sealed record AggregateRow(int MemberID, long Amount, int PeerCount);

    private sealed record MemberRow(
        int ID,
        string? Name,
        string? Thumb,
        int? MemberGradeID,
        string? GradeKorName,
        string? GradeImage,
        string? GradeTextColor,
        bool IsRankingPublic
    );
}