// reconfig computes the correct wireguard config and calls the engine.Reconfig
// with the config we have.  It is not intended for this to be called outside of
// the updateLoop()
func (c *configMaps) reconfig(nm *netmap.NetworkMap) {
	cfg, err := nmcfg.WGCfg(nm, Logger(c.logger.Named("net.wgconfig")), netmap.AllowSingleHosts, "")
	if err != nil {
		// WGCfg never returns an error at the time this code was written.  If it starts, returning
		// errors if/when we upgrade tailscale, we'll need to deal.
		c.logger.Critical(context.Background(), "update wireguard config failed", slog.Error(err))
		return
	}

	addrs := append([]netip.Prefix{}, nm.Addresses...)
	rc := &router.Config{
		LocalAddrs: addrs,
		Routes:     []netip.Prefix{ServicePrefix},
	}
	err = c.engine.Reconfig(cfg, rc, &dns.Config{
		Routes: map[dnsname.FQDN][]*dnstype.Resolver{
			"coderlan.": nil,
		},
		Hosts: map[dnsname.FQDN][]netip.Addr{
			"dogfood2.coderlan.": {netip.MustParseAddr("fd7a:115c:a1e0:4280:a0ad:1919:6552:9fe3")},
		},
		OnlyIPv6: true,
	}, &tailcfg.Debug{})
	if err != nil {
		if errors.Is(err, wgengine.ErrNoChanges) {
			return
		}
		c.logger.Error(context.Background(), "failed to reconfigure wireguard engine", slog.Error(err))
	}
}