package main

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"net/http"
	"os"

	"inet.af/netaddr"
)

type device struct {
	Hostname  string   `json:"hostname"`
	ID        string   `json:"id"`
	Addresses []string `json:"addresses"`
}

const (
	TS_NAME       = "franck.cuny@gmail.com"
	TS_API_DOMAIN = "api.tailscale.com"
)

func getTsDevice(ctx context.Context, deviceName string) (*device, error) {
	apiKey, found := os.LookupEnv("TS_API_KEY")
	if !found {
		return nil, errors.New("the environment variable TS_API_KEY is not set")
	}

	url := fmt.Sprintf("https://%s/api/v2/tailnet/%s/devices", TS_API_DOMAIN, TS_NAME)
	req, err := http.NewRequestWithContext(ctx, "GET", url, nil)
	if err != nil {
		return nil, err
	}

	req.SetBasicAuth(apiKey, "")
	resp, err := http.DefaultClient.Do(req)
	if err != nil {
		return nil, err
	}

	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("non-ok status code %d returned from tailscale api: %s", resp.StatusCode, resp.Status)
	}
	var buf struct {
		Devices []device `json:"devices"`
	}
	if err := json.NewDecoder(resp.Body).Decode(&buf); err != nil {
		return nil, err
	}

	for _, d := range buf.Devices {
		if d.Hostname == deviceName {
			return &d, nil
		}
	}
	return nil, fmt.Errorf("could not find the tailscale device named %s", deviceName)
}

// Get the Tailscale IPv4 and IPv6 addresses associated with the given device.
func getTsIpsDevice(ctx context.Context, device string) ([]string, []string, error) {
	ts_device, err := getTsDevice(ctx, device)
	if err != nil {
		return nil, nil, fmt.Errorf("failed to get Tailscale device information: %v", err)
	}

	var (
		tsIpV4Addresses = []string{}
		tsIpV6Addresses = []string{}
	)
	for _, ipString := range ts_device.Addresses {
		// we convert the string to a netaddr.IP so we can check if
		// it's an IP v4 or v6. We need to know what's the version in
		// order to use it properly when creating/updating the
		// record. Then we convert it back as a string, since this is
		// what the DNS API expect.
		ip := netaddr.MustParseIP(ipString)
		if ip.Is4() {
			tsIpV4Addresses = append(tsIpV4Addresses, ip.String())
		} else {
			tsIpV6Addresses = append(tsIpV6Addresses, ip.String())
		}
	}

	return tsIpV4Addresses, tsIpV6Addresses, nil
}