// +build !darwin

package main

import (
	"bytes"
	"encoding/binary"
	"errors"
	"fmt"
	"strings"
	"syscall"
	"time"

	"go.fuchsia.dev/fuchsia/tools/net/netboot"
	devicePkg "go.fuchsia.dev/infra/devices"
	"golang.org/x/sys/unix"
)

const (
	// broadcastRetryTimeout defines how long we can retry broadcast packet reads.
	broadcastRetryTimeout = 10 * time.Second
)

// netbootHeader is the netboot protocol message header.
type netbootHeader struct {
	Magic  uint32
	Cookie uint32
	Cmd    uint32
	Arg    uint32
}

// netbootMessage is the netboot protocol message.
type netbootMessage struct {
	Header netbootHeader
	Data   [1024]byte
}

func netbootString(bs []byte) (string, error) {
	for i, b := range bs {
		if b == 0 {
			return string(bs[:i]), nil
		}
	}
	return "", errors.New("no null terminated string found")
}

// checkBroadcasting ensures that broadcast packets are being sent by the device
// is a no-op on NUCs
func checkBroadcasting(n *netboot.Client, device *devicePkg.DeviceTarget) error {
	if device.Type() == "nuc" {
		return nil
	}

	// Create a socket.
	socket, err := syscall.Socket(syscall.AF_INET6, syscall.SOCK_DGRAM, syscall.IPPROTO_UDP)
	if err != nil {
		return err
	}

	// Set reuseport on the socket so that multiple invocations do not
	// trample each other.
	if err := syscall.SetsockoptInt(socket, syscall.SOL_SOCKET, unix.SO_REUSEPORT, 1); err != nil {
		return err
	}

	// Set a timeout so we don't block forever.
	timeout := &syscall.Timeval{
		Sec: 10,
	}
	if err := syscall.SetsockoptTimeval(socket, syscall.SOL_SOCKET, syscall.SO_RCVTIMEO, timeout); err != nil {
		return err
	}

	// Set bind to device to only check for this device.
	if err := syscall.SetsockoptString(socket, syscall.SOL_SOCKET, syscall.SO_BINDTODEVICE, device.Interface()); err != nil {
		return err
	}

	// Bind to the advertisement port.
	var addr [16]byte
	sockAddr := &syscall.SockaddrInet6{
		Port: n.AdvertPort,
		Addr: addr,
	}
	if err := syscall.Bind(socket, sockAddr); err != nil {
		return err
	}

	// Read a packet in from the socket.
	b := make([]byte, 4096)
	startTime := time.Now()
	for {
		if _, err := syscall.Read(socket, b); err != nil {
			if err != syscall.EINTR {
				return err
			}
		} else {
			break
		}
		if time.Now().Sub(startTime) >= broadcastRetryTimeout {
			return errors.New("failed to read broadcast packets")
		}
	}

	r := bytes.NewReader(b)
	var res netbootMessage
	if err := binary.Read(r, binary.LittleEndian, &res); err != nil {
		return err
	}

	data, err := netbootString(res.Data[:])
	if err != nil {
		return err
	}
	// The query packet payload contains fields separated by ;.
	for _, f := range strings.Split(string(data[:]), ";") {
		// The field has a key=value format.
		vars := strings.SplitN(f, "=", 2)
		// The field with the "nodename" key contains the name of the device.
		if vars[0] == "nodename" && vars[1] == device.Nodename() {
			return nil
		}
	}
	if err := syscall.Close(socket); err != nil {
		return err
	}
	return fmt.Errorf("device %s is not broadcasting", device.Nodename())
}