using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.Caching;
using System.Text.RegularExpressions;

namespace ConsoleAppNET_Framework
{
    /// <summary>
    /// MemoryCache快取
    /// </summary>
    /// <remarks>2018-9-27 15:28:32 wanghaoli 新增</remarks>
    public class MemoryCacheProvider
    {
        private static readonly Object _locker = new object(), _locker2 = new object();

        /// <summary>
        /// 取快取項，如果不存在則返回空
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="key"></param>
        /// <returns></returns>
        public static T GetCacheItem<T>(String key)
        {
            try
            {
                return (T)MemoryCache.Default[key];
            }
            catch
            {
                return default(T);
            }
        }

        /// <summary>
        /// 是否包含指定鍵的快取項
        /// </summary>
        /// <param name="key"></param>
        /// <returns></returns>
        public static bool Contains(string key)
        {
            return MemoryCache.Default.Contains(key);
        }
        /// <summary>
        ///  使用鍵和值將某個快取項插入快取中，並指定基於時間的過期詳細資訊
        /// </summary>
        /// <param name="key"></param>
        /// <param name="value"></param>
        /// <param name="absoluteExpiration"> 快取項的固定的過期日期和時間。</param>
        public static void Set(string key, object value, DateTimeOffset absoluteExpiration)
        {
            MemoryCache.Default.Set(key, value, absoluteExpiration);
        }

        /// <summary>
        /// 取快取項,如果不存在則新增快取項
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="key"></param>
        /// <param name="cachePopulate"></param>
        /// <param name="slidingExpiration"></param>
        /// <param name="absoluteExpiration"></param>
        /// <returns></returns>
        public static T GetOrAddCacheItem<T>(String key, Func<T> cachePopulate, TimeSpan? slidingExpiration = null, DateTime? absoluteExpiration = null)
        {
            if (String.IsNullOrWhiteSpace(key)) throw new ArgumentException("Invalid cache key");
            if (cachePopulate == null) throw new ArgumentNullException("cachePopulate");
            if (slidingExpiration == null && absoluteExpiration == null) throw new ArgumentException("Either a sliding expiration or absolute must be provided");

            if (MemoryCache.Default[key] == null)
            {
                lock (_locker)
                {
                    if (MemoryCache.Default[key] == null)
                    {
                        T cacheValue = cachePopulate();
                        if (!typeof(T).IsValueType && ((object)cacheValue) == null) //如果是引用型別且為NULL則不存快取
                        {
                            return cacheValue;
                        }
                        var item = new CacheItem(key, cacheValue);
                        var policy = CreatePolicy(slidingExpiration, absoluteExpiration);
                        MemoryCache.Default.Add(item, policy);
                    }
                }
            }
            return (T)MemoryCache.Default[key];
        }

        /// <summary>
        /// 取快取項,如果不存在則新增快取項
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="key"></param>
        /// <param name="cachePopulate"></param>
        /// <param name="dependencyFilePath"></param>
        /// <returns></returns>
        public static T GetOrAddCacheItem<T>(String key, Func<T> cachePopulate, string dependencyFilePath)
        {
            if (String.IsNullOrWhiteSpace(key)) throw new ArgumentException("Invalid cache key");
            if (cachePopulate == null) throw new ArgumentNullException("cachePopulate");

            if (MemoryCache.Default[key] == null)
            {
                lock (_locker2)
                {
                    if (MemoryCache.Default[key] == null)
                    {
                        T cacheValue = cachePopulate();
                        if (!typeof(T).IsValueType && ((object)cacheValue) == null) //如果是引用型別且為NULL則不存快取
                        {
                            return cacheValue;
                        }

                        var item = new CacheItem(key, cacheValue);
                        var policy = CreatePolicy(dependencyFilePath);

                        MemoryCache.Default.Add(item, policy);
                    }
                }
            }

            return (T)MemoryCache.Default[key];
        }

        /// <summary>
        /// 移除指定鍵的快取項
        /// </summary>
        /// <param name="key"></param>
        public static void Remove(string key)
        {
            try
            {
                MemoryCache.Default.Remove(key);
            }
            catch
            { }
        }

        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;
        }

        private static CacheItemPolicy CreatePolicy(string filePath)
        {
            CacheItemPolicy policy = new CacheItemPolicy();
            policy.ChangeMonitors.Add(new HostFileChangeMonitor(new List<string>() { filePath }));
            policy.Priority = CacheItemPriority.Default;
            return policy;
        }
    }
}