//go:build darwin || freebsd

package arpdb

import (
	"bufio"
	"net"
	"net/netip"
	"strings"
	"sync"

	"github.com/AdguardTeam/golibs/log"
)

func newARPDB() (arp *cmdARPDB) {
	return &cmdARPDB{
		parse: parseArpA,
		ns: &neighs{
			mu: &sync.RWMutex{},
			ns: make([]Neighbor, 0),
		},
		cmd: "arp",
		// Use -n flag to avoid resolving the hostnames of the neighbors.  By
		// default ARP attempts to resolve the hostnames via DNS.  See man 8
		// arp.
		//
		// See also https://github.com/AdguardTeam/AdGuardHome/issues/3157.
		args: []string{"-a", "-n"},
	}
}

// parseArpA parses the output of the "arp -a -n" command on macOS and FreeBSD.
// The expected input format:
//
//	host.name (192.168.0.1) at ff:ff:ff:ff:ff:ff on en0 ifscope [ethernet]
func parseArpA(sc *bufio.Scanner, lenHint int) (ns []Neighbor) {
	ns = make([]Neighbor, 0, lenHint)
	for sc.Scan() {
		ln := sc.Text()

		fields := strings.Fields(ln)
		if len(fields) < 4 {
			continue
		}

		ipStr := fields[1]
		if len(ipStr) < 2 {
			continue
		}

		ip, err := netip.ParseAddr(ipStr[1 : len(ipStr)-1])
		if err != nil {
			log.Debug("arpdb: parsing arp output: ip: %s", err)

			continue
		}

		hwStr := fields[3]
		mac, err := net.ParseMAC(hwStr)
		if err != nil {
			log.Debug("arpdb: parsing arp output: mac: %s", err)

			continue
		}

		ns = append(ns, Neighbor{
			IP:   ip,
			MAC:  mac,
			Name: validatedHostname(fields[0]),
		})
	}

	return ns
}