using System;
using NewLife.Data;
using NewLife.Reflection;

namespace NewLife.Messaging
{
    /// <summary>标准消息SRMP</summary>
    /// <remarks>
    /// 标准网络封包协议：1 Flag + 1 Sequence + 2 Length + N Payload
    /// 1个字节标识位，标识请求、响应、错误、加密、压缩等；
    /// 1个字节序列号，用于请求响应包配对；
    /// 2个字节数据长度N，小端，指示后续负载数据长度（不包含头部4个字节），解决粘包问题；
    /// N个字节负载数据，数据内容完全由业务决定，最大长度65535=64k。
    /// 如：
    /// Open => OK
    /// 01-01-04-00-"Open" => 81-01-02-00-"OK"
    /// </remarks>
    public class DefaultMessage : Message
    {
        #region 属性
        /// <summary>标记位</summary>
        public Byte Flag { get; set; } = 1;

        /// <summary>序列号，匹配请求和响应</summary>
        public Byte Sequence { get; set; }
        #endregion

        #region 方法
        /// <summary>根据请求创建配对的响应消息</summary>
        /// <returns></returns>
        public override IMessage CreateReply()
        {
            if (Reply) throw new Exception("不能根据响应消息创建响应消息");

            var type = GetType();
            var msg = type == typeof(DefaultMessage) ? new DefaultMessage() : type.CreateInstance() as DefaultMessage;
            msg.Flag = Flag;
            msg.Reply = true;
            msg.Sequence = Sequence;

            return msg;
        }

        /// <summary>从数据包中读取消息</summary>
        /// <param name="pk"></param>
        /// <returns>是否成功</returns>
        public override Boolean Read(Packet pk)
        {
            if (pk.Count < 4) throw new ArgumentOutOfRangeException(nameof(pk), "数据包头部长度不足4字节");

            var size = 4;
            var buf = pk.ReadBytes(0, size);

            Flag = (Byte)(buf[0] & 0b0011_1111);
            var mode = buf[0] >> 6;
            switch (mode)
            {
                case 0: Reply = false; break;
                case 1: OneWay = true; break;
                case 2: Reply = true; break;
                case 3: Reply = true; Error = true; break;
                default:
                    break;
            }

            Sequence = buf[1];

            var len = (buf[3] << 8) | buf[2];
            if (size + len > pk.Count) throw new ArgumentOutOfRangeException(nameof(pk), "数据包长度{0}不足{1}字节".F(pk.Count, size + len));

            // 支持超过64k的超大包
            if (len == 0xFFFF)
            {
                size += 4;
                if (pk.Count < size) throw new ArgumentOutOfRangeException(nameof(pk), "数据包头部长度不足8字节");

                len = pk.ReadBytes(size - 4, 4).ToInt();
                if (size + len > pk.Count) throw new ArgumentOutOfRangeException(nameof(pk), "数据包长度{0}不足{1}字节".F(pk.Count, size + len));
            }

            Payload = new Packet(pk.Data, pk.Offset + size, len);

            return true;
        }

        /// <summary>把消息转为封包</summary>
        /// <returns></returns>
        public override Packet ToPacket()
        {
            var pk = Payload;
            var len = 0;
            if (pk != null) len = pk.Total;

            // 增加4字节头部
            var size = len < 0xFFFF ? 4 : 8;
            if (pk.Offset >= size)
                pk = new Packet(pk.Data, pk.Offset - size, pk.Count + size) { Next = pk.Next };
            else
                pk = new Packet(new Byte[size]) { Next = pk };

            // 标记位
            var b = Flag & 0b0011_1111;
            if (Reply) b |= 0x80;
            if (Error || OneWay) b |= 0x40;
            pk[0] = (Byte)b;

            // 序列号
            pk[1] = Sequence;

            if (len < 0xFFFF)
            {
                // 2字节长度，小端字节序
                pk[2] = (Byte)(len & 0xFF);
                pk[3] = (Byte)(len >> 8);
            }
            // 支持64k以上超大包
            else
            {
                pk[2] = 0xFF;
                pk[3] = 0xFF;

                // 再来4字节写长度
                pk.Data.Write((UInt32)len, pk.Offset + 4, true);
            }

            return pk;
        }
        #endregion

        #region 辅助
        /// <summary>获取数据包长度</summary>
        /// <param name="pk"></param>
        /// <returns></returns>
        public static Int32 GetLength(Packet pk)
        {
            if (pk.Total < 4) return 0;

            // 小于64k，直接返回
            var len = pk.Data.ToUInt16(pk.Offset + 2);
            if (len < 0xFFFF) return 4 + len;

            // 超过64k的超大数据包，再来4个字节
            if (pk.Total < 8) return 0;

            return 8 + (Int32)pk.Data.ToUInt32(pk.Offset + 2 + 2);
        }

        /// <summary>消息摘要</summary>
        /// <returns></returns>
        public override String ToString() => $"{Flag:X2} Seq={Sequence} {Payload}";
        #endregion
    }
}