package arp

import (
	"bufio"
	"net"
	"os"
	"strings"
)

func lookup() (map[string]net.HardwareAddr, error) {
	f, err := os.Open("/proc/net/arp")
	if err != nil {
		return nil, err
	}
	defer func() { _ = f.Close() }()

	t := make(map[string]net.HardwareAddr)
	s := bufio.NewScanner(f)
	for i := 0; s.Scan(); i++ {
		if i == 0 {
			continue
		}
		line := strings.Fields(s.Text())
		if len(line) < 4 {
			continue
		}
		if mac, err := net.ParseMAC(line[3]); err == nil {
			t[line[0]] = mac
		}
	}
	return t, nil
}