using System;
using System.Collections;
using System.Data;
using System.ServiceModel;
using System.ServiceModel.Channels;


namespace CSFrameworkV5.Core.SystemSecurity
{
    /// <summary>
    /// 用于检测非法攻击WCF的接口,用户连续访问的次数超过指定值抛出异常中断操作
    /// </summary>
    public static class AttackRecorder
    {
        //限制指定时间范围内，当前用户可以访问服务端的次数
        //此值不能太大，否则缓存表记录数较多，记录最后10次访问记录
        private const int LAST_VISIT_COUNT = 20;

        //与 LAST_VISIT_COUNT参数配合使用，比如限制用户3秒内只能访问30次后台的接口
        //时间间隔(秒)，大于此参数值，可能存在恶意攻击行为
        private const int LIMIT_SECONDS = 5;

        //记录访客IP信息及访问记录
        private static Hashtable _VisitorList;

        static AttackRecorder()
        {
            _VisitorList = new Hashtable();
        }

        /// <summary>
        /// 建立访问记录表
        /// </summary>
        /// <returns></returns>
        private static DataTable CreataTable()
        {
            var dt = new DataTable();
            dt.Columns.Add("IP", typeof(string)); //IP地址
            dt.Columns.Add("VisitTime", typeof(DateTime)); //访问时间
            return dt;
        }

        /// <summary>
        /// 取当前用户的IP(客户端)
        /// </summary>
        /// <returns></returns>
        public static string ClientIP
        {
            get
            {
                try
                {
                    var context = OperationContext.Current;
                    var properties = context.IncomingMessageProperties;
                    var endpoint =
                        properties[RemoteEndpointMessageProperty.Name] as
                            RemoteEndpointMessageProperty;
                    return endpoint.Address;
                }
                catch
                {
                    return "无法获取IP";
                }
            }
        }


        private static DateTime ToDateTimeEx(object o)
        {
            if (null == o) return DateTime.MinValue;
            try
            {
                var dt = Convert.ToDateTime(o.ToStringEx());
                if (dt < DateTime.Parse("1900-01-01"))
                    return DateTime.Parse("1900-01-01");
                else
                    return dt;
            }
            catch
            {
                return DateTime.MinValue;
            }
        }


        /// <summary>
        /// 检查用户访问量，如有恶意攻击行为抛出异常
        /// </summary>
        public static void IsAttack()
        {
            var IP = ClientIP; //取客户端IP

            if (_VisitorList.ContainsKey(IP)) //有登记访客
            {
                var dt = _VisitorList[IP] as DataTable;
                dt.Rows.Add(new object[] { IP, DateTime.Now }); //增加访问记录

                //按时间倒序排列，取当前用户最后N次的访问记录
                var rs = dt.Select("IP='" + IP + "'", "VisitTime DESC");
                if (rs.Length >= LAST_VISIT_COUNT)
                {
                    var maxTime = ToDateTimeEx(rs[0]["VisitTime"]); //最近一次访问时间
                    var minTime =
                        ToDateTimeEx(rs[LAST_VISIT_COUNT - 1]["VisitTime"]);
                    var ts = maxTime - minTime;
                    if (ts.TotalSeconds < LIMIT_SECONDS) //在指定时间内访问次数大于系统参数
                    {
                        throw new Exception("您的访问频率太高了，请休息下！");
                    }
                    else
                    {
                        //删除小于指定时间的访问记录
                        var filter = "IP='" + IP + "' AND VisitTime<'" +
                                     minTime.ToString("yyyy-MM-dd HH:mm:ss") +
                                     "'";
                        rs = dt.Select(filter);
                        for (var i = 0; i <= rs.Length - 1; i++)
                            dt.Rows.Remove(rs[i]);
                        dt.AcceptChanges();
                    }
                }
            }
            else //第一次访问服务端，记录IP及访问时间
            {
                var dt = CreataTable();
                dt.Rows.Add(new object[] { IP, DateTime.Now }); //增加访问记录
                dt.AcceptChanges();
                _VisitorList.Add(IP, dt);
            }
        }
    }
}