package vl2

import (
	"encoding/binary"
	"fmt"
	"net"
	"sync"
)

const (
	MinFrameSize    = 14
	MaxFrameSize    = 65535
	EtherTypeIPv4   = 0x0800
	EtherTypeARP    = 0x0806
	EtherTypeIPv6   = 0x86DD
)

type EthernetFrame struct {
	DstMAC   net.HardwareAddr
	SrcMAC   net.HardwareAddr
	EtherType uint16
	Payload  []byte
}

func ParseEthernetFrame(data []byte) (*EthernetFrame, error) {
	if len(data) < MinFrameSize {
		return nil, fmt.Errorf("frame too short: %d < %d", len(data), MinFrameSize)
	}
	return &EthernetFrame{
		DstMAC:   net.HardwareAddr(data[0:6]),
		SrcMAC:   net.HardwareAddr(data[6:12]),
		EtherType: binary.BigEndian.Uint16(data[12:14]),
		Payload:  data[14:],
	}, nil
}

func (f *EthernetFrame) Encode() []byte {
	buf := make([]byte, MinFrameSize+len(f.Payload))
	copy(buf[0:6], f.DstMAC)
	copy(buf[6:12], f.SrcMAC)
	binary.BigEndian.PutUint16(buf[12:14], f.EtherType)
	copy(buf[14:], f.Payload)
	return buf
}

func (f *EthernetFrame) IsBroadcast() bool {
	for _, b := range f.DstMAC {
		if b != 0xff {
			return false
		}
	}
	return true
}

func (f *EthernetFrame) IsMulticast() bool {
	return len(f.DstMAC) > 0 && f.DstMAC[0]&0x01 == 0x01 && !f.IsBroadcast()
}

func (f *EthernetFrame) IsARP() bool {
	return f.EtherType == EtherTypeARP
}

func (f *EthernetFrame) IsIPv4() bool {
	return f.EtherType == EtherTypeIPv4
}

func (f *EthernetFrame) IsIPv6() bool {
	return f.EtherType == EtherTypeIPv6
}

type MACKey [6]byte

func MACToKey(mac net.HardwareAddr) MACKey {
	var key MACKey
	copy(key[:], mac)
	return key
}

var frameBufPool = sync.Pool{
	New: func() interface{} {
		buf := make([]byte, MaxFrameSize)
		return &buf
	},
}

func GetFrameBuf() *[]byte {
	return frameBufPool.Get().(*[]byte)
}

func PutFrameBuf(buf *[]byte) {
	frameBufPool.Put(buf)
}