public class HostedReturnBookService : IHostedService
    {
        private readonly IServiceProvider serviceProvider;
        private Timer timer;

        public HostedReturnBookService(IServiceProvider serviceProvider)
        {
            this.serviceProvider = serviceProvider;
        }

        public Task StartAsync(CancellationToken cancellationToken)
        {
            this.timer = new Timer(ReturnBook, null, TimeSpan.FromDays(1),
                TimeSpan.FromDays(1));

            return Task.CompletedTask;
        }

        private async void ReturnBook(object state)
        {
            using (var scope = this.serviceProvider.CreateScope())
            {
                var checkoutService = scope.ServiceProvider.GetRequiredService<ICheckoutService>();

                await checkoutService.CheckForExpiredCheckoutsAsync();
            }
        }

        public Task StopAsync(CancellationToken cancellationToken)
        {
            this.timer?.Change(Timeout.Infinite, 0);

            return Task.CompletedTask;
        }
    }


//GOES IN STARTUP DI REGISTRATION
            services.AddHostedService<HostedReturnBookService>();