ANTOOZA-BACKEND/Application/Features/Api/Stocks/Watch/IsWatching/Handler.cs

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

namespace Application.Features.Api.Stocks.Watch.IsWatching;

/// <summary>회원이 관심 등록한 코드 집합을 조회해 요청 코드별 true/false 맵을 반환 (IsFollowing 패턴).</summary>
internal sealed class Handler(IAppDbContext db) : IQueryHandler<Query, Response>
{
    // 방어적 상한 — 엔드포인트에서도 Take(100) 하지만 Handler 계층 자체도 무방비가 되지 않도록 (GetQuotes 패턴)
    public const int MaxCodes = 100;

    public async Task<Response> Handle(Query request, CancellationToken ct)
    {
        var codes = request.Codes.Select(c => c.Trim()).Where(c => c.Length > 0).Distinct().Take(MaxCodes).ToArray();

        if (codes.Length == 0)
        {
            return new Response { Map = new Dictionary<string, bool>() };
        }

        var watched = await db.StockWatch.AsNoTracking()
            .Where(w => w.MemberID == request.MemberID && codes.Contains(w.StockCode))
            .Select(w => w.StockCode)
            .ToListAsync(ct);

        var watchedSet = watched.ToHashSet();

        var map = codes.ToDictionary(c => c, c => watchedSet.Contains(c));

        return new Response { Map = map };
    }
}