package decoder

import (
	"bytes"
	"encoding/binary"
	"encoding/hex"
	"github.com/aceld/zinx/ziface"
	"github.com/aceld/zinx/zlog"
	"math"
)

//ffff 01 00999999 000a 68656c6c6f2074657374
// +---------------+---------------+--------------------+----------------+-------------------
// |    开始标志     |     type       |     秒时间戳       |  长度           |     消息体
// | 0xffff(2byte) |  uint8(1byte)  |     uint32(4byte) |  uint16(2byte) |    bytes(N byte)
// +---------------+---------------+--------------------+----------------+-------------------

const OmcMsgHeaderSize = 9 //表示OMC空包长度

type OmcDecoder struct {
	StartSign uint16
	MsgType   uint8
	TimeStamp uint32
	LenOfBody uint16
	Value     []byte
}

func NewOmcDecoder() ziface.IDecoder {
	return &OmcDecoder{}
}

func (omc *OmcDecoder) GetLengthField() *ziface.LengthField {
	return &ziface.LengthField{
		MaxFrameLength:      math.MaxUint16 + 9,
		LengthFieldOffset:   7,
		LengthFieldLength:   2,
		LengthAdjustment:    0,
		InitialBytesToStrip: 0,
		//注意现在默认是大端，使用小端需要指定编码方式
		Order: binary.BigEndian,
	}
}

func (omc *OmcDecoder) decode(data []byte) *OmcDecoder {
	ltvData := OmcDecoder{}
	ltvData.StartSign = binary.BigEndian.Uint16(data[0:2])
	ltvData.MsgType = data[2]
	ltvData.TimeStamp = binary.BigEndian.Uint32(data[3:7])
	ltvData.LenOfBody = binary.BigEndian.Uint16(data[7:9])
	//Determine the length of V. (确定V的长度)
	ltvData.Value = make([]byte, ltvData.LenOfBody)

	//5. Get V
	binary.Read(bytes.NewBuffer(data[OmcMsgHeaderSize:OmcMsgHeaderSize+ltvData.LenOfBody]), binary.BigEndian, ltvData.Value)

	return &ltvData
}

func (omc *OmcDecoder) Intercept(chain ziface.IChain) ziface.IcResp {
	//1. Get the IMessage of zinx
	iMessage := chain.GetIMessage()
	if iMessage == nil {
		// Go to the next layer in the chain of responsibility
		return chain.ProceedWithIMessage(iMessage, nil)
	}

	//2. Get Data
	data := iMessage.GetData()
	zlog.Ins().DebugF("omc-RawData size:%d data:%s\n", len(data), hex.EncodeToString(data))

	// (读取的数据不超过包头，直接进入下一层)
	if len(data) < OmcMsgHeaderSize {
		return chain.ProceedWithIMessage(iMessage, nil)
	}

	//4.  Decode
	ltvData := omc.decode(data)
	zlog.Ins().DebugF("omc-decode  %v", ltvData)

	// (将解码后的数据重新设置到IMessage中, Zinx的Router需要MsgID来寻址)
	iMessage.SetDataLen(uint32(ltvData.LenOfBody))
	iMessage.SetMsgID(uint32(ltvData.MsgType))
	iMessage.SetData(ltvData.Value)

	//6. Pass the decoded data to the next layer.
	// (将解码后的数据进入下一层)
	return chain.ProceedWithIMessage(iMessage, *ltvData)
}