ANTOOZA-BACKEND/Application/Features/Api/Note/SearchRecipient/Handler.cs

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

namespace Application.Features.Api.Note.SearchRecipient;

/// <summary>
/// 쪽지 수신자 검색 — 보안 정책상 본인이 팔로우한 회원/채널만 검색됨 (enumeration 차단).
/// 직접 진입 (프로필/채널 페이지 "쪽지 보내기" 버튼)은 별도 — 검색은 빠른 발송용.
/// </summary>
internal sealed class Handler(IAppDbContext db) : IQueryHandler<Query, Response>
{
    public async Task<Response> Handle(Query r, CancellationToken ct)
    {
        var kw = r.Keyword?.Trim() ?? string.Empty;

        if (kw.Length < 2)
        {
            return new Response([], false);
        }

        var offset = r.Offset < 0 ? 0 : r.Offset;
        var limit = r.Limit is < 1 or > 50 ? 20 : r.Limit;

        // 본인이 팔로우 중인 회원 IDs (보안 필터)
        var followingIDs = db.MemberFollow.AsNoTracking()
            .Where(f => f.FollowerMemberID == r.CurrentMemberID)
            .Select(f => f.FolloweeMemberID);

        // Member LEFT JOIN Channel — 닉네임/SID/채널명/핸들 OR 검색
        var rows = await (
            from m in db.Member.AsNoTracking()
            where !m.IsWithdraw && !m.IsDenied
                && m.ID != r.CurrentMemberID
                && followingIDs.Contains(m.ID)
            from c in db.Channel.AsNoTracking().Where(c => c.MemberID == m.ID).DefaultIfEmpty()
            where (m.Name != null && m.Name.Contains(kw))
                || m.SID.Contains(kw)
                || (c != null && c.Name.Contains(kw))
                || (c != null && c.Handle != null && c.Handle.Contains(kw))
            orderby m.ID descending
            select new
            {
                m.ID,
                MemberName = m.Name,
                m.SID,
                MemberThumb = m.Thumb,
                ChannelName = c != null ? c.Name : null,
                ChannelHandle = c != null ? c.Handle : null,
                ChannelThumbnail = c != null ? c.ThumbnailUrl : null
            }
        )
        .Skip(offset)
        .Take(limit + 1)
        .ToListAsync(ct);

        var hasMore = rows.Count > limit;
        var page = rows.Take(limit).ToList();

        // 채널 보유 여부와 무관하게 일관된 UI 데이터 — (썸네일, 이름, 부제)
        var list = page.Select(x => new RecipientItem(
            x.ID,
            x.ChannelName ?? x.MemberName ?? x.SID,
            x.ChannelHandle != null ? "@" + x.ChannelHandle : "@" + x.SID,
            x.ChannelThumbnail ?? x.MemberThumb
        )).ToList();

        return new Response(list, hasMore);
    }
}