ANTOOZA-BACKEND/Application/Features/Api/Member/GetLevel/Handler.cs

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

namespace Application.Features.Api.Member.GetLevel;

internal sealed class Handler(IAppDbContext db) : IQueryHandler<Query, Result<Response>>
{
    public async Task<Result<Response>> Handle(Query request, CancellationToken ct)
    {
        var member = await db.Member.AsNoTracking()
            .Where(c => c.ID == request.MemberID)
            .Select(c => new { c.ID, c.MemberGradeID })
            .FirstOrDefaultAsync(ct);

        if (member is null)
        {
            return Result.Failure<Response>(Error.NotFound("Member.NotFound", "회원 정보를 찾을 수 없습니다."));
        }

        var exp = await db.MemberStats.AsNoTracking()
            .Where(c => c.MemberID == request.MemberID)
            .Select(c => (long?)c.Exp)
            .FirstOrDefaultAsync(ct) ?? 0;

        // 활성 등급을 RequiredExp 오름차순으로 로드 (소량)
        var grades = await db.MemberGrade.AsNoTracking()
            .Where(c => c.IsActive)
            .OrderBy(c => c.RequiredExp)
            .Select(c => new { c.ID, c.KorName, c.RequiredExp, c.Image, c.TextColor })
            .ToListAsync(ct);

        // 현재 등급 = 회원 등급 스냅샷 (없으면 충족하는 최고 등급으로 추정)
        var current = member.MemberGradeID is int gid
            ? grades.FirstOrDefault(c => c.ID == gid)
            : grades.LastOrDefault(c => c.RequiredExp <= exp);

        // 다음 등급 = 현재 RequiredExp 초과 첫 등급
        var currentRequired = current?.RequiredExp ?? -1;
        var next = grades.FirstOrDefault(c => c.RequiredExp > currentRequired);

        long? expToNext = next is not null ? Math.Max(0, next.RequiredExp - exp) : null;

        return Result.Success(new Response(
            exp,
            current?.ID,
            current?.KorName,
            current?.Image,
            current?.TextColor,
            next?.ID,
            next?.KorName,
            next?.RequiredExp,
            expToNext
        ));
    }
}