package main

import (
	"errors"
	"fmt"
	"io"
	"os"
	"strconv"
	"strings"
)

var (
	ErrInvalidPCIFormat = errors.New("Invalid PCI address format")
	ErrInvalidUSBFormat = errors.New("Invalid USB address format")
	ErrParseMac         = errors.New("Failed to parse MAC address")
)

var SYSFS = "/sys"

// Sourced from include/uapi/linux/netdevice.h
// as of v6.8
const (
	NET_NAME_UNKNOWN     = 0 /* unknown origin (not exposed to userspace) */
	NET_NAME_ENUM        = 1 /* enumerated by kernel */
	NET_NAME_PREDICTABLE = 2 /* predictably named by the kernel */
	NET_NAME_USER        = 3 /* provided by user-space */
	NET_NAME_RENAMED     = 4 /* renamed by user-space */
)

type IfNameType int
type IfNameList map[IfNameType]string

const (
	IfNameKern IfNameType = iota
	IfNameMAC
	IfNameLoc
)

type iface struct {
	pfx     string
	netpath string
	names   IfNameList
}

func New(ifname string) (i iface, err error) {
	if strings.HasPrefix(ifname, "eth") {
		i.pfx = "en"
	} else {
		// Fall back to first 2 characters
		i.pfx = ifname[0:2]
	}

	i.names = make(IfNameList)
	i.names[IfNameKern] = ifname
	i.netpath = strings.Join([]string{SYSFS, "class/net", i.names[IfNameKern]}, "/")
	return
}

func (i iface) shouldRun() (should bool, err error) {
	ifname_assign_type := strings.Join([]string{i.netpath, "name_assign_type"}, "/")
	should = true

	var (
		file     *os.File
		contents []byte
	)

	if file, err = os.Open(ifname_assign_type); err != nil {
		err = fmt.Errorf("Failed to open interface rename property: %w", err)
		return
	}

	defer file.Close()
	if contents, err = io.ReadAll(file); err != nil {
		err = fmt.Errorf("Failed to read interface rename property: %w", err)
		return
	}
	num, _ := strings.CutSuffix(string(contents), "\n")

	var res int
	if res, err = strconv.Atoi(num); err != nil {
		err = fmt.Errorf("Failed to interpret interface rename property as number: %w", err)
		return
	}

	if res != NET_NAME_ENUM {
		should = false
		return
	}
	return
}