package ripv2

import (
	"bytes"
	"encoding/binary"
	"errors"
	"fmt"
	"net"
)

func New() Message {
	return Message{}
}

func (m *Message) MParse(b *[]byte, n int) error {
	if n == 0 {
		return errors.New("can't parse empty data")
	}

	if (n-4)/20 > 25 {
		return errors.New("rip table exceeds limit")
	}

	m.Command = Command((*b)[0])
	m.Version = Version((*b)[1])

	if m.Version > RIPv2 {
		return errors.New("unknown version")
	}

	var indexA, indexB = 4, 25
	ripentry := (*b)[indexA:indexB]
	switch m.Command {
	case REQUEST:
		return nil
	case RESPONSE:
		for i := 0; i < (n-4)/20; i++ {
			m.RIP[i].AFI = binary.BigEndian.Uint16(ripentry[0:2])
			m.RIP[i].RouteTag = binary.BigEndian.Uint16(ripentry[2:4])
			m.RIP[i].Addr = binary.BigEndian.Uint32(ripentry[4:8])      //net.IPv4(ripentry[4], ripentry[5], ripentry[6], ripentry[7])
			m.RIP[i].Subnet = binary.BigEndian.Uint32(ripentry[8:12])   //net.IPv4Mask(ripentry[8], ripentry[9], ripentry[10], ripentry[11])
			m.RIP[i].Nexthop = binary.BigEndian.Uint32(ripentry[12:16]) //net.IPv4(ripentry[12], ripentry[13], ripentry[14], ripentry[15])
			m.RIP[i].Metric = binary.BigEndian.Uint32(ripentry[16:20])
			indexA += 20
			indexB += 20
			ripentry = (*b)[indexA:indexB]
		}
	default:
		return errors.New("unknown command type")
	}

	return nil
}

/* Basic parsing */
func (m *Message) Parse(b *[]byte) error {
	if len(*b) == 0 {
		return fmt.Errorf("can't parse empty data")
	}

	bytes := bytes.NewBuffer(*b)

	if err := binary.Read(bytes, binary.BigEndian, m); err != nil {
		return err
	}

	if m.Version != 2 {
		return fmt.Errorf("version: %d", m.Version)
	}

	return nil
}

func (m *Message) Request(conn *net.UDPConn) ([]byte, error) {
	var buffer = make([]byte, 24)
	m.Command = REQUEST
	m.Version = 2
	m.RIP[0].Metric = 16
	buff := bytes.NewBuffer(buffer)
	buff.Reset()
	if err := binary.Write(buff, binary.BigEndian, m); err != nil {
		return []byte{}, err
	}

	return buffer, nil
}