// 在program.cs中加入这句，加入缓存支持
builder.Services.AddMemoryCache();

    public class Book
    {
        public int Id { get; init; }
        public string Title { get; init; }

        public Book(int id, string title)
        {
            Id = id;
            Title = title;
        }

        public override string ToString()
        {
            return $"book:{Id}, {Title}";
        }
    }

    public class BookDbContext
    {
        public Task<Book?> GetBookByIdAsync(int id)
        {
            Book? book = null;

            switch (id)
            {
                case 1:
                    book = new Book(1, "book1");
                    break;

                case 2:
                    book = new Book(2, "book2");
                    break;

                case 3:
                    book = new Book(3, "book3");
                    break;
            }

            return Task.FromResult(book);
        }
    }

    [ApiController]
    [Route("api/[controller]")]
    public class CacheTestController : ControllerBase
    {
        private IMemoryCache MemoryCache { get; init; }
        private ILogger<CacheTestController> Logger { get; set; }

        public CacheTestController(IMemoryCache memoryCache, ILogger<CacheTestController> logger)
        {
            MemoryCache = memoryCache;
            Logger = logger;
        }

        [HttpGet("book")]
        public async Task<ActionResult<Book?>> GetBookById(int id)
        {
            Logger.LogInformation($"enter GetBookById, id={id}");

            // 尽量使用GetOrCreateAsync，而不是Get/Set。
            // 因为GetOrCreateAsync可以把null也作为缓存值，这样就可以避免缓存穿透。
            Book? book = await MemoryCache.GetOrCreateAsync($"book_{id}", (e) =>
            {
                Logger.LogInformation($"not found in cache, search in BookDbContext.");

                // 混用SlidingExpiration和AbsoluteExpirationRelativeToNow，这样滑动超时或绝对超时后，缓存都会失效， 
                e.SlidingExpiration = TimeSpan.FromSeconds(5);
                // 使用随机数作为超时值，避免缓存雪崩
                e.AbsoluteExpirationRelativeToNow = TimeSpan.FromSeconds(Random.Shared.Next(10, 50));
                return new BookDbContext().GetBookByIdAsync(id);
            });
            Logger.LogInformation($"GetOrCreateAsync returns {book}");

            if (book == null)
                return NotFound($"cannot find bood with id:{id}");

            return book;
        }


        [ResponseCache(Duration = 10)]  // 浏览器缓存支持，在响应头里加入cache-control: public,max-age=10
        [HttpGet("Now")]
        public DateTime Now()
        {
            return DateTime.Now;
        }
    }