using CC.Yi.Model;
using Microsoft.EntityFrameworkCore;
using System.Collections.Concurrent;
using System.Threading;


namespace CC.Yi.DAL
{
    public class DbContentFactory
    {
        private static DataContext Webcontext;
        public static void Initialize(DataContext webContext)
        {
            Webcontext = webContext;
        }
        public static DataContext GetCurrentDbContent()
        {
            //return new DataModelContainer();
            //一次请求共用一个上下文实例
            //每一次http请求都会开启一个新的线程，保证在一个线程中,DbContext是唯一的
            //CallContext：是线程内部唯一的数据槽（一块内存空间/容器）,相当于一个键值对数据容器，通过key获取value了,需要引入System.Runtime.Remoting.Messaging;命名空间
            DataContext db = CallContext.GetData("DbContext") as DataContext;
            //从 CallContext 中检索具有指定key“DbContext”的对象，并强转为DbContext
            if (db == null)//线程在数据槽里面没有此上下文
            {
                db = Webcontext;
                CallContext.SetData("DbContext", db);//放到数据槽中去,DbContext是key，db是value
            }
            return db;
        }

        private static class CallContext
        {
            static ConcurrentDictionary<string, AsyncLocal<object>> state = new ConcurrentDictionary<string, AsyncLocal<object>>();

            public static void SetData(string name, object data) =>
                state.GetOrAdd(name, _ => new AsyncLocal<object>()).Value = data;

            public static object GetData(string name) =>
                state.TryGetValue(name, out AsyncLocal<object> data) ? data.Value : null;
        }
    }
}