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

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

namespace Application.Features.Api.Ranking.GetRising;

/// <summary>
/// 최근 7일 vs 이전 7일 후원 증가율 기준 급상승 크리에이터.
/// 집계는 실시간 Donation 테이블로 계산 (최근성이 중요하므로 스냅샷 아님).
/// </summary>
internal sealed class Handler(IAppDbContext db) : IQueryHandler<Query, Response>
{
    public async Task<Response> Handle(Query request, CancellationToken ct)
    {
        var limit = request.Limit is < 1 or > 100 ? 20 : request.Limit;

        var now = DateTime.UtcNow;
        var recent7End = now;
        var recent7Start = now.AddDays(-7);
        var prev7Start = now.AddDays(-14);

        // 최근 7일 집계
        var recent = await db.Donation.AsNoTracking()
            .Where(d => d.CreatedAt >= recent7Start && d.CreatedAt < recent7End && !d.IsTest)
            .GroupBy(d => d.ReceiverMemberID)
            .Select(g => new
            {
                MemberID = g.Key,
                Amount = g.Sum(d => (long)d.NetAmount),
                DonorCount = g.Select(d => d.SponsorMemberID).Distinct().Count()
            })
            .ToListAsync(ct);

        if (recent.Count == 0)
        {
            return new Response([], now);
        }

        // 이전 7일 집계
        var memberIds = recent.Select(r => r.MemberID).ToList();
        var previous = await db.Donation.AsNoTracking()
            .Where(d => d.CreatedAt >= prev7Start && d.CreatedAt < recent7Start && !d.IsTest && memberIds.Contains(d.ReceiverMemberID))
            .GroupBy(d => d.ReceiverMemberID)
            .Select(g => new { MemberID = g.Key, Amount = g.Sum(d => (long)d.NetAmount) })
            .ToDictionaryAsync(g => g.MemberID, g => g.Amount, ct);

        var rising = recent.Select(r => {
            var prevAmount = previous.GetValueOrDefault(r.MemberID);
            double rate;

            if (prevAmount <= 0)
            {
                rate = r.Amount > 0 ? 1000.0 : 0.0; // 신규 유입 — 1000% 취급
            }
            else
            {
                rate = ((double)(r.Amount - prevAmount) / prevAmount) * 100.0;
            }

            return new { r.MemberID, r.Amount, r.DonorCount, PreviousAmount = prevAmount, Rate = rate };
        })
        .Where(r => r.Rate > 0)
        .OrderByDescending(r => r.Rate).ThenByDescending(r => r.Amount)
        .Take(limit)
        .ToList();

        var memberInfo = await db.Member.AsNoTracking()
            .Where(m => rising.Select(r => r.MemberID).Contains(m.ID))
            .Select(m => new { m.ID, m.Name, m.Thumb })
            .ToListAsync(ct);

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

        var channels = await db.Channel.AsNoTracking()
            .Where(c => rising.Select(r => r.MemberID).Contains(c.MemberID))
            .Select(c => new
            {
                c.MemberID,
                c.Name,
                c.ThumbnailUrl
            })
            .ToListAsync(ct);

        var channelDict = channels.GroupBy(c => c.MemberID).ToDictionary(g => g.Key, g => g.First());

        var entries = rising.Select(r => {
            var m = memberDict.GetValueOrDefault(r.MemberID);
            var ch = channelDict.GetValueOrDefault(r.MemberID);

            // Member.Thumb 우선, 없으면 Channel.ThumbnailUrl(YouTube 채널 썸네일) 폴백
            return new RisingEntry(
                r.MemberID,
                m?.Name ?? "",
                m?.Thumb ?? ch?.ThumbnailUrl,
                ch?.Name,
                r.Amount,
                r.PreviousAmount,
                r.Rate,
                r.DonorCount
            );
        }).ToList();

        return new Response(entries, now);
    }
}