using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Security.Cryptography;
using System.Collections.Concurrent;
using System.Runtime.Caching;
using System.Timers;

namespace WebSRM.Utility
{
    public class MemoryCacheHelper
    {
        /// <summary>
        /// 获取缓存
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="key"></param>
        /// <returns></returns>
        public static string GetCache(string key)
        {
            if (MemoryCache.Default == null || MemoryCache.Default[key] == null)
            {
                return null;
            }
            return MemoryCache.Default[key].ToString();
        }

        /// <summary>
        /// 创建缓存
        /// </summary>
        /// <param name="key"></param>
        /// <param name="val"></param>
        /// <param name="slidingExpiration">失效时间范围</param>
        /// <param name="absoluteExpiration">失效的绝对时间</param>
        /// <returns></returns>
        public static void SetCache(string key, string val, DateTime? absoluteExpiration = null, TimeSpan? slidingExpiration = null )
        {
            try
            {
                if (absoluteExpiration == null)
                {
                    //默认设置为2小时之后
                    absoluteExpiration = DateTime.Now.AddHours(2);
                }

                var policy = CreatePolicy(slidingExpiration, absoluteExpiration);
                MemoryCache.Default.Set(key, val, policy);
            }
            catch (Exception ex)
            {
                throw;
            }
        }


        /// <summary>
        /// 清空缓存
        /// </summary>
        public static void ClearCache()
        {
            List<string> cacheKeys = MemoryCache.Default.Select(kvp => kvp.Key).ToList();
            foreach (string cacheKey in cacheKeys)
            {
                MemoryCache.Default.Remove(cacheKey);
            }
        }


        private static CacheItemPolicy CreatePolicy(TimeSpan? slidingExpiration, DateTime? absoluteExpiration)
        {
            var policy = new CacheItemPolicy();

            if (absoluteExpiration.HasValue)
            {
                policy.AbsoluteExpiration = absoluteExpiration.Value;
            }
            else if (slidingExpiration.HasValue)
            {
                policy.SlidingExpiration = slidingExpiration.Value;
            }

            policy.Priority = CacheItemPriority.Default;

            return policy;
        }

    }
}