ANTOOZA-BACKEND/Application/Helpers/ExpBoostService.cs

using Application.Abstractions.Data;
using Domain.Entities.Store.ValueObject;
using Microsoft.EntityFrameworkCore;

namespace Application.Helpers;

/// <summary>
/// 경험치 부스터(ExpBooster) 활성 시 획득 XP 를 2배로. 모든 XP 지급처가 공유하는 공용 헬퍼.
/// (현 시점 적용처: 출석. 향후 글/댓글 보상엔진 도입 시 동일 헬퍼 경유.)
/// </summary>
public static class ExpBoostService
{
    public const int Multiplier = 2;

    public static async Task<bool> IsActiveAsync(IAppDbContext db, int memberID, DateTime nowUtc, CancellationToken ct)
    {
        var boosters = await db.MemberItem.AsNoTracking()
            .Where(x => x.MemberID == memberID && x.Kind == ItemKind.ExpBooster && x.UsedAt != null && x.RevokedAt == null)
            .Select(x => new { x.UsedAt, x.DurationDays })
            .ToListAsync(ct);

        return boosters.Any(b => b.UsedAt!.Value.AddDays(b.DurationDays) > nowUtc);
    }

    /// <summary>부스터 활성 시 baseExp × 2, 아니면 baseExp.</summary>
    public static async Task<int> ApplyAsync(IAppDbContext db, int memberID, int baseExp, DateTime nowUtc, CancellationToken ct)
    {
        if (baseExp <= 0)
        {
            return baseExp;
        }

        var active = await IsActiveAsync(db, memberID, nowUtc, ct);
        return active ? baseExp * Multiplier : baseExp;
    }
}