ReservationRepository.cs

private async Task<bool> IsSpaceAvailable(int spaceId, DateTime startTime, DateTime endTime)
        {
            var reservationList = await _context.Reservations
                                                .Where(reservation =>
                                                    reservation.ReservedSpaceId == spaceId &&
                                                    !reservation.IsDeleted &&
                                                    !reservation.IsCancelled
                                                )
                                                .ToListAsync();

            // 4 Edge cases
            foreach (var reservation in reservationList)
            {
                if (endTime > reservation.StartsAt && endTime < reservation.EndsAt)
                    return false;
                if (startTime <= reservation.StartsAt && endTime >= reservation.EndsAt)
                    return false;
                if (startTime > reservation.StartsAt && startTime <= reservation.EndsAt)
                    return false;
                if (startTime > reservation.StartsAt && endTime < reservation.EndsAt)
                    return false;
            }

            return true;
        }