Module.PremiumArea/Server/Services/PremiumService.cs

using System;
using SZUAbsolventenverein.Module.PremiumArea.Models;
using SZUAbsolventenverein.Module.PremiumArea.Repository;
using Oqtane.Infrastructure;
using Oqtane.Shared;
using Oqtane.Modules;
using Oqtane.Enums;

namespace SZUAbsolventenverein.Module.PremiumArea.Services
{
    public interface IPremiumService
    {
        bool IsPremium(int userId);
        DateTime? GetPremiumUntil(int userId);
        void GrantPremium(int userId, int durationMonths, string source, string referenceId = null);
    }

    public class PremiumService : IPremiumService, ITransientService
    {
        private readonly IUserPremiumRepository _userPremiumRepository;
        private readonly ILogManager _logger;

        public PremiumService(IUserPremiumRepository userPremiumRepository, ILogManager logger)
        {
            _userPremiumRepository = userPremiumRepository;
            _logger = logger;
        }

        public bool IsPremium(int userId)
        {
            var premium = _userPremiumRepository.GetUserPremium(userId);
            return premium != null && premium.PremiumUntil.HasValue && premium.PremiumUntil.Value > DateTime.UtcNow;
        }

        public DateTime? GetPremiumUntil(int userId)
        {
            var premium = _userPremiumRepository.GetUserPremium(userId);
            return premium?.PremiumUntil;
        }

        public void GrantPremium(int userId, int durationMonths, string source, string referenceId = null)
        {
            var current = _userPremiumRepository.GetUserPremium(userId);
            var now = DateTime.UtcNow;
            
            DateTime startBase = now;
            if (current != null && current.PremiumUntil.HasValue && current.PremiumUntil.Value > now)
            {
                startBase = current.PremiumUntil.Value;
            }

            var newUntil = startBase.AddMonths(durationMonths);

            // delta days for audit
            int deltaDays = (newUntil - (current?.PremiumUntil ?? now)).Days;
            // correction: actually we want to know how many days we ADDED to the existing flow.
            // If they had 0 days separately, we added durationMonths * 30 approx.
            // If they had existing time, we added durationMonths. 
            // Audit Log usually tracks "What did this action add?". It added 1 year. 
            // But let's calculate days added relative to "previous state".
            // If expired: Added (NewUntil - Now) days.
            // If active: Added (NewUntil - OldUntil) = durationMonths roughly.
            
            // Simpler: Just store the DurationMonths converted to days roughly, or the stored delta.
            int addedDays = (newUntil - startBase).Days; 

            if (current == null)
            {
                current = new UserPremium
                {
                    UserId = userId,
                    CreatedOn = now,
                    ModifiedOn = now
                };
            }
            
            current.PremiumUntil = newUntil;
            current.Source = source;
            current.ModifiedOn = now;

            _userPremiumRepository.SaveUserPremium(current);

            // Audit
            var audit = new PremiumEvent
            {
                UserId = userId,
                DeltaDays = addedDays,
                Source = source,
                ReferenceId = referenceId,
                CreatedOn = now,
                ModifiedOn = now
            };
            _userPremiumRepository.AddPremiumEvent(audit);
            
            _logger.Log(LogLevel.Information, this, LogFunction.Update, "Granted Premium for User {UserId} until {Until}", userId, newUntil);
        }
    }
}