#![cfg_attr(not(feature = "std"), no_std)]
#![cfg_attr(nightly, feature(async_fn_in_trait, impl_trait_projections))]
#![cfg_attr(nightly, allow(stable_features, unknown_lints))]
#![allow(async_fn_in_trait)]
#![warn(missing_docs)]
#![doc = include_str!("../README.md")]

#[cfg(not(any(feature = "proto-ipv4", feature = "proto-ipv6")))]
compile_error!("You must enable at least one of the following features: proto-ipv4, proto-ipv6");

// This mod MUST go first, so that the others see its macros.
pub(crate) mod fmt;

mod device;
#[cfg(feature = "dns")]
pub mod dns;
#[cfg(feature = "tcp")]
pub mod tcp;
mod time;
#[cfg(feature = "udp")]
pub mod udp;

use core::cell::RefCell;
use core::future::{poll_fn, Future};
use core::task::{Context, Poll};

pub use embassy_net_driver as driver;
use embassy_net_driver::{Driver, LinkState};
use embassy_sync::waitqueue::WakerRegistration;
use embassy_time::{Instant, Timer};
use futures::pin_mut;
#[allow(unused_imports)]
use heapless::Vec;
#[cfg(feature = "igmp")]
pub use smoltcp::iface::MulticastError;
#[allow(unused_imports)]
use smoltcp::iface::{Interface, SocketHandle, SocketSet, SocketStorage};
use smoltcp::phy::Medium;
#[cfg(feature = "dhcpv4")]
use smoltcp::socket::dhcpv4::{self, RetryConfig};
#[cfg(feature = "medium-ethernet")]
pub use smoltcp::wire::EthernetAddress;
#[cfg(any(feature = "medium-ethernet", feature = "medium-ieee802154", feature = "medium-ip"))]
pub use smoltcp::wire::HardwareAddress;
#[cfg(any(feature = "udp", feature = "tcp"))]
pub use smoltcp::wire::IpListenEndpoint;
#[cfg(feature = "medium-ieee802154")]
pub use smoltcp::wire::{Ieee802154Address, Ieee802154Frame};
pub use smoltcp::wire::{IpAddress, IpCidr, IpEndpoint};
#[cfg(feature = "proto-ipv4")]
pub use smoltcp::wire::{Ipv4Address, Ipv4Cidr};
#[cfg(feature = "proto-ipv6")]
pub use smoltcp::wire::{Ipv6Address, Ipv6Cidr};

use crate::device::DriverAdapter;
use crate::time::{instant_from_smoltcp, instant_to_smoltcp};

const LOCAL_PORT_MIN: u16 = 1025;
const LOCAL_PORT_MAX: u16 = 65535;
#[cfg(feature = "dns")]
const MAX_QUERIES: usize = 4;
#[cfg(feature = "dhcpv4-hostname")]
const MAX_HOSTNAME_LEN: usize = 32;

/// Memory resources needed for a network stack.
pub struct StackResources<const SOCK: usize> {
    sockets: [SocketStorage<'static>; SOCK],
    #[cfg(feature = "dns")]
    queries: [Option<dns::DnsQuery>; MAX_QUERIES],
    #[cfg(feature = "dhcpv4-hostname")]
    hostname: core::cell::UnsafeCell<HostnameResources>,
}

#[cfg(feature = "dhcpv4-hostname")]
struct HostnameResources {
    option: smoltcp::wire::DhcpOption<'static>,
    data: [u8; MAX_HOSTNAME_LEN],
}

impl<const SOCK: usize> StackResources<SOCK> {
    /// Create a new set of stack resources.
    pub const fn new() -> Self {
        #[cfg(feature = "dns")]
        const INIT: Option<dns::DnsQuery> = None;
        Self {
            sockets: [SocketStorage::EMPTY; SOCK],
            #[cfg(feature = "dns")]
            queries: [INIT; MAX_QUERIES],
            #[cfg(feature = "dhcpv4-hostname")]
            hostname: core::cell::UnsafeCell::new(HostnameResources {
                option: smoltcp::wire::DhcpOption { kind: 0, data: &[] },
                data: [0; MAX_HOSTNAME_LEN],
            }),
        }
    }
}

/// Static IP address configuration.
#[cfg(feature = "proto-ipv4")]
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct StaticConfigV4 {
    /// IP address and subnet mask.
    pub address: Ipv4Cidr,
    /// Default gateway.
    pub gateway: Option<Ipv4Address>,
    /// DNS servers.
    pub dns_servers: Vec<Ipv4Address, 3>,
}

/// Static IPv6 address configuration
#[cfg(feature = "proto-ipv6")]
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct StaticConfigV6 {
    /// IP address and subnet mask.
    pub address: Ipv6Cidr,
    /// Default gateway.
    pub gateway: Option<Ipv6Address>,
    /// DNS servers.
    pub dns_servers: Vec<Ipv6Address, 3>,
}

/// DHCP configuration.
#[cfg(feature = "dhcpv4")]
#[derive(Debug, Clone, PartialEq, Eq)]
#[non_exhaustive]
pub struct DhcpConfig {
    /// Maximum lease duration.
    ///
    /// If not set, the lease duration specified by the server will be used.
    /// If set, the lease duration will be capped at this value.
    pub max_lease_duration: Option<embassy_time::Duration>,
    /// Retry configuration.
    pub retry_config: RetryConfig,
    /// Ignore NAKs from DHCP servers.
    ///
    /// This is not compliant with the DHCP RFCs, since theoretically we must stop using the assigned IP when receiving a NAK. This can increase reliability on broken networks with buggy routers or rogue DHCP servers, however.
    pub ignore_naks: bool,
    /// Server port. This is almost always 67. Do not change unless you know what you're doing.
    pub server_port: u16,
    /// Client port. This is almost always 68. Do not change unless you know what you're doing.
    pub client_port: u16,
    /// Our hostname. This will be sent to the DHCP server as Option 12.
    #[cfg(feature = "dhcpv4-hostname")]
    pub hostname: Option<heapless::String<MAX_HOSTNAME_LEN>>,
}

#[cfg(feature = "dhcpv4")]
impl Default for DhcpConfig {
    fn default() -> Self {
        Self {
            max_lease_duration: Default::default(),
            retry_config: Default::default(),
            ignore_naks: Default::default(),
            server_port: smoltcp::wire::DHCP_SERVER_PORT,
            client_port: smoltcp::wire::DHCP_CLIENT_PORT,
            #[cfg(feature = "dhcpv4-hostname")]
            hostname: None,
        }
    }
}

/// Network stack configuration.
#[derive(Debug, Clone, Default)]
#[non_exhaustive]
pub struct Config {
    /// IPv4 configuration
    #[cfg(feature = "proto-ipv4")]
    pub ipv4: ConfigV4,
    /// IPv6 configuration
    #[cfg(feature = "proto-ipv6")]
    pub ipv6: ConfigV6,
}

impl Config {
    /// IPv4 configuration with static addressing.
    #[cfg(feature = "proto-ipv4")]
    pub fn ipv4_static(config: StaticConfigV4) -> Self {
        Self {
            ipv4: ConfigV4::Static(config),
            #[cfg(feature = "proto-ipv6")]
            ipv6: ConfigV6::None,
        }
    }

    /// IPv6 configuration with static addressing.
    #[cfg(feature = "proto-ipv6")]
    pub fn ipv6_static(config: StaticConfigV6) -> Self {
        Self {
            #[cfg(feature = "proto-ipv4")]
            ipv4: ConfigV4::None,
            ipv6: ConfigV6::Static(config),
        }
    }

    /// IPv4 configuration with dynamic addressing.
    ///
    /// # Example
    /// ```rust
    /// # use embassy_net::Config;
    /// let _cfg = Config::dhcpv4(Default::default());
    /// ```
    #[cfg(feature = "dhcpv4")]
    pub fn dhcpv4(config: DhcpConfig) -> Self {
        Self {
            ipv4: ConfigV4::Dhcp(config),
            #[cfg(feature = "proto-ipv6")]
            ipv6: ConfigV6::None,
        }
    }
}

/// Network stack IPv4 configuration.
#[cfg(feature = "proto-ipv4")]
#[derive(Debug, Clone, Default)]
pub enum ConfigV4 {
    /// Do not configure IPv4.
    #[default]
    None,
    /// Use a static IPv4 address configuration.
    Static(StaticConfigV4),
    /// Use DHCP to obtain an IP address configuration.
    #[cfg(feature = "dhcpv4")]
    Dhcp(DhcpConfig),
}

/// Network stack IPv6 configuration.
#[cfg(feature = "proto-ipv6")]
#[derive(Debug, Clone, Default)]
pub enum ConfigV6 {
    /// Do not configure IPv6.
    #[default]
    None,
    /// Use a static IPv6 address configuration.
    Static(StaticConfigV6),
}

/// A network stack.
///
/// This is the main entry point for the network stack.
pub struct Stack<D: Driver> {
    pub(crate) socket: RefCell<SocketStack>,
    inner: RefCell<Inner<D>>,
}

struct Inner<D: Driver> {
    device: D,
    link_up: bool,
    #[cfg(feature = "proto-ipv4")]
    static_v4: Option<StaticConfigV4>,
    #[cfg(feature = "proto-ipv6")]
    static_v6: Option<StaticConfigV6>,
    #[cfg(feature = "dhcpv4")]
    dhcp_socket: Option<SocketHandle>,
    config_waker: WakerRegistration,
    #[cfg(feature = "dns")]
    dns_socket: SocketHandle,
    #[cfg(feature = "dns")]
    dns_waker: WakerRegistration,
    #[cfg(feature = "dhcpv4-hostname")]
    hostname: &'static mut core::cell::UnsafeCell<HostnameResources>,
}

pub(crate) struct SocketStack {
    pub(crate) sockets: SocketSet<'static>,
    pub(crate) iface: Interface,
    pub(crate) waker: WakerRegistration,
    next_local_port: u16,
}

fn to_smoltcp_hardware_address(addr: driver::HardwareAddress) -> (HardwareAddress, Medium) {
    match addr {
        #[cfg(feature = "medium-ethernet")]
        driver::HardwareAddress::Ethernet(eth) => (HardwareAddress::Ethernet(EthernetAddress(eth)), Medium::Ethernet),
        #[cfg(feature = "medium-ieee802154")]
        driver::HardwareAddress::Ieee802154(ieee) => (
            HardwareAddress::Ieee802154(Ieee802154Address::Extended(ieee)),
            Medium::Ieee802154,
        ),
        #[cfg(feature = "medium-ip")]
        driver::HardwareAddress::Ip => (HardwareAddress::Ip, Medium::Ip),

        #[allow(unreachable_patterns)]
        _ => panic!(
            "Unsupported medium {:?}. Make sure to enable the right medium feature in embassy-net's Cargo features.",
            addr
        ),
    }
}

impl<D: Driver> Stack<D> {
    /// Create a new network stack.
    pub fn new<const SOCK: usize>(
        mut device: D,
        config: Config,
        resources: &'static mut StackResources<SOCK>,
        random_seed: u64,
    ) -> Self {
        let (hardware_addr, medium) = to_smoltcp_hardware_address(device.hardware_address());
        let mut iface_cfg = smoltcp::iface::Config::new(hardware_addr);
        iface_cfg.random_seed = random_seed;

        let iface = Interface::new(
            iface_cfg,
            &mut DriverAdapter {
                inner: &mut device,
                cx: None,
                medium,
            },
            instant_to_smoltcp(Instant::now()),
        );

        let sockets = SocketSet::new(&mut resources.sockets[..]);

        let next_local_port = (random_seed % (LOCAL_PORT_MAX - LOCAL_PORT_MIN) as u64) as u16 + LOCAL_PORT_MIN;

        #[cfg_attr(feature = "medium-ieee802154", allow(unused_mut))]
        let mut socket = SocketStack {
            sockets,
            iface,
            waker: WakerRegistration::new(),
            next_local_port,
        };

        let mut inner = Inner {
            device,
            link_up: false,
            #[cfg(feature = "proto-ipv4")]
            static_v4: None,
            #[cfg(feature = "proto-ipv6")]
            static_v6: None,
            #[cfg(feature = "dhcpv4")]
            dhcp_socket: None,
            config_waker: WakerRegistration::new(),
            #[cfg(feature = "dns")]
            dns_socket: socket.sockets.add(dns::Socket::new(
                &[],
                managed::ManagedSlice::Borrowed(&mut resources.queries),
            )),
            #[cfg(feature = "dns")]
            dns_waker: WakerRegistration::new(),
            #[cfg(feature = "dhcpv4-hostname")]
            hostname: &mut resources.hostname,
        };

        #[cfg(feature = "proto-ipv4")]
        inner.set_config_v4(&mut socket, config.ipv4);
        #[cfg(feature = "proto-ipv6")]
        inner.set_config_v6(&mut socket, config.ipv6);
        inner.apply_static_config(&mut socket);

        Self {
            socket: RefCell::new(socket),
            inner: RefCell::new(inner),
        }
    }

    fn with<R>(&self, f: impl FnOnce(&SocketStack, &Inner<D>) -> R) -> R {
        f(&*self.socket.borrow(), &*self.inner.borrow())
    }

    fn with_mut<R>(&self, f: impl FnOnce(&mut SocketStack, &mut Inner<D>) -> R) -> R {
        f(&mut *self.socket.borrow_mut(), &mut *self.inner.borrow_mut())
    }

    /// Get the hardware address of the network interface.
    pub fn hardware_address(&self) -> HardwareAddress {
        self.with(|_s, i| to_smoltcp_hardware_address(i.device.hardware_address()).0)
    }

    /// Get whether the link is up.
    pub fn is_link_up(&self) -> bool {
        self.with(|_s, i| i.link_up)
    }

    /// Get whether the network stack has a valid IP configuration.
    /// This is true if the network stack has a static IP configuration or if DHCP has completed
    pub fn is_config_up(&self) -> bool {
        let v4_up;
        let v6_up;

        #[cfg(feature = "proto-ipv4")]
        {
            v4_up = self.config_v4().is_some();
        }
        #[cfg(not(feature = "proto-ipv4"))]
        {
            v4_up = false;
        }

        #[cfg(feature = "proto-ipv6")]
        {
            v6_up = self.config_v6().is_some();
        }
        #[cfg(not(feature = "proto-ipv6"))]
        {
            v6_up = false;
        }

        v4_up || v6_up
    }

    /// Wait for the network stack to obtain a valid IP configuration.
    ///
    /// ## Notes:
    /// - Ensure [`Stack::run`] has been called before using this function.
    ///
    /// - This function may never return (e.g. if no configuration is obtained through DHCP).
    /// The caller is supposed to handle a timeout for this case.
    ///
    /// ## Example
    /// ```ignore
    /// let config = embassy_net::Config::dhcpv4(Default::default());
    ///// Init network stack
    /// let stack = &*make_static!(embassy_net::Stack::new(
    ///    device,
    ///    config,
    ///    make_static!(embassy_net::StackResources::<2>::new()),
    ///    seed
    /// ));
    /// // Launch network task that runs `stack.run().await`
    /// spawner.spawn(net_task(stack)).unwrap();
    /// // Wait for DHCP config
    /// stack.wait_config_up().await;
    /// // use the network stack
    /// // ...
    /// ```
    pub async fn wait_config_up(&self) {
        // If the config is up already, we can return immediately.
        if self.is_config_up() {
            return;
        }

        poll_fn(|cx| {
            if self.is_config_up() {
                Poll::Ready(())
            } else {
                // If the config is not up, we register a waker that is woken up
                // when a config is applied (static or DHCP).
                trace!("Waiting for config up");

                self.with_mut(|_, i| {
                    i.config_waker.register(cx.waker());
                });

                Poll::Pending
            }
        })
        .await;
    }

    /// Get the current IPv4 configuration.
    ///
    /// If using DHCP, this will be None if DHCP hasn't been able to
    /// acquire an IP address, or Some if it has.
    #[cfg(feature = "proto-ipv4")]
    pub fn config_v4(&self) -> Option<StaticConfigV4> {
        self.with(|_, i| i.static_v4.clone())
    }

    /// Get the current IPv6 configuration.
    #[cfg(feature = "proto-ipv6")]
    pub fn config_v6(&self) -> Option<StaticConfigV6> {
        self.with(|_, i| i.static_v6.clone())
    }

    /// Set the IPv4 configuration.
    #[cfg(feature = "proto-ipv4")]
    pub fn set_config_v4(&self, config: ConfigV4) {
        self.with_mut(|s, i| {
            i.set_config_v4(s, config);
            i.apply_static_config(s);
        })
    }

    /// Set the IPv6 configuration.
    #[cfg(feature = "proto-ipv6")]
    pub fn set_config_v6(&self, config: ConfigV6) {
        self.with_mut(|s, i| {
            i.set_config_v6(s, config);
            i.apply_static_config(s);
        })
    }

    /// Run the network stack.
    ///
    /// You must call this in a background task, to process network events.
    pub async fn run(&self) -> ! {
        poll_fn(|cx| {
            self.with_mut(|s, i| i.poll(cx, s));
            Poll::<()>::Pending
        })
        .await;
        unreachable!()
    }

    /// Make a query for a given name and return the corresponding IP addresses.
    #[cfg(feature = "dns")]
    pub async fn dns_query(
        &self,
        name: &str,
        qtype: dns::DnsQueryType,
    ) -> Result<Vec<IpAddress, { smoltcp::config::DNS_MAX_RESULT_COUNT }>, dns::Error> {
        // For A and AAAA queries we try detect whether `name` is just an IP address
        match qtype {
            #[cfg(feature = "proto-ipv4")]
            dns::DnsQueryType::A => {
                if let Ok(ip) = name.parse().map(IpAddress::Ipv4) {
                    return Ok([ip].into_iter().collect());
                }
            }
            #[cfg(feature = "proto-ipv6")]
            dns::DnsQueryType::Aaaa => {
                if let Ok(ip) = name.parse().map(IpAddress::Ipv6) {
                    return Ok([ip].into_iter().collect());
                }
            }
            _ => {}
        }

        let query = poll_fn(|cx| {
            self.with_mut(|s, i| {
                let socket = s.sockets.get_mut::<dns::Socket>(i.dns_socket);
                match socket.start_query(s.iface.context(), name, qtype) {
                    Ok(handle) => {
                        s.waker.wake();
                        Poll::Ready(Ok(handle))
                    }
                    Err(dns::StartQueryError::NoFreeSlot) => {
                        i.dns_waker.register(cx.waker());
                        Poll::Pending
                    }
                    Err(e) => Poll::Ready(Err(e)),
                }
            })
        })
        .await?;

        #[must_use = "to delay the drop handler invocation to the end of the scope"]
        struct OnDrop<F: FnOnce()> {
            f: core::mem::MaybeUninit<F>,
        }

        impl<F: FnOnce()> OnDrop<F> {
            fn new(f: F) -> Self {
                Self {
                    f: core::mem::MaybeUninit::new(f),
                }
            }

            fn defuse(self) {
                core::mem::forget(self)
            }
        }

        impl<F: FnOnce()> Drop for OnDrop<F> {
            fn drop(&mut self) {
                unsafe { self.f.as_ptr().read()() }
            }
        }

        let drop = OnDrop::new(|| {
            self.with_mut(|s, i| {
                let socket = s.sockets.get_mut::<dns::Socket>(i.dns_socket);
                socket.cancel_query(query);
                s.waker.wake();
                i.dns_waker.wake();
            })
        });

        let res = poll_fn(|cx| {
            self.with_mut(|s, i| {
                let socket = s.sockets.get_mut::<dns::Socket>(i.dns_socket);
                match socket.get_query_result(query) {
                    Ok(addrs) => {
                        i.dns_waker.wake();
                        Poll::Ready(Ok(addrs))
                    }
                    Err(dns::GetQueryResultError::Pending) => {
                        socket.register_query_waker(query, cx.waker());
                        Poll::Pending
                    }
                    Err(e) => {
                        i.dns_waker.wake();
                        Poll::Ready(Err(e.into()))
                    }
                }
            })
        })
        .await;

        drop.defuse();

        res
    }
}

#[cfg(feature = "igmp")]
impl<D: Driver> Stack<D> {
    /// Join a multicast group.
    pub async fn join_multicast_group<T>(&self, addr: T) -> Result<bool, MulticastError>
    where
        T: Into<IpAddress>,
    {
        let addr = addr.into();

        poll_fn(move |cx| self.poll_join_multicast_group(addr, cx)).await
    }

    /// Join a multicast group.
    ///
    /// When the send queue is full, this method will return `Poll::Pending`
    /// and register the current task to be notified when the queue has space available.
    pub fn poll_join_multicast_group<T>(&self, addr: T, cx: &mut Context<'_>) -> Poll<Result<bool, MulticastError>>
    where
        T: Into<IpAddress>,
    {
        let addr = addr.into();

        self.with_mut(|s, i| {
            let (_hardware_addr, medium) = to_smoltcp_hardware_address(i.device.hardware_address());
            let mut smoldev = DriverAdapter {
                cx: Some(cx),
                inner: &mut i.device,
                medium,
            };

            match s
                .iface
                .join_multicast_group(&mut smoldev, addr, instant_to_smoltcp(Instant::now()))
            {
                Ok(announce_sent) => Poll::Ready(Ok(announce_sent)),
                Err(MulticastError::Exhausted) => Poll::Pending,
                Err(other) => Poll::Ready(Err(other)),
            }
        })
    }

    /// Leave a multicast group.
    pub async fn leave_multicast_group<T>(&self, addr: T) -> Result<bool, MulticastError>
    where
        T: Into<IpAddress>,
    {
        let addr = addr.into();

        poll_fn(move |cx| self.poll_leave_multicast_group(addr, cx)).await
    }

    /// Leave a multicast group.
    ///
    /// When the send queue is full, this method will return `Poll::Pending`
    /// and register the current task to be notified when the queue has space available.
    pub fn poll_leave_multicast_group<T>(&self, addr: T, cx: &mut Context<'_>) -> Poll<Result<bool, MulticastError>>
    where
        T: Into<IpAddress>,
    {
        let addr = addr.into();

        self.with_mut(|s, i| {
            let (_hardware_addr, medium) = to_smoltcp_hardware_address(i.device.hardware_address());
            let mut smoldev = DriverAdapter {
                cx: Some(cx),
                inner: &mut i.device,
                medium,
            };

            match s
                .iface
                .leave_multicast_group(&mut smoldev, addr, instant_to_smoltcp(Instant::now()))
            {
                Ok(leave_sent) => Poll::Ready(Ok(leave_sent)),
                Err(MulticastError::Exhausted) => Poll::Pending,
                Err(other) => Poll::Ready(Err(other)),
            }
        })
    }

    /// Get whether the network stack has joined the given multicast group.
    pub fn has_multicast_group<T: Into<IpAddress>>(&self, addr: T) -> bool {
        self.socket.borrow().iface.has_multicast_group(addr)
    }
}

impl SocketStack {
    #[allow(clippy::absurd_extreme_comparisons, dead_code)]
    pub fn get_local_port(&mut self) -> u16 {
        let res = self.next_local_port;
        self.next_local_port = if res >= LOCAL_PORT_MAX { LOCAL_PORT_MIN } else { res + 1 };
        res
    }
}

impl<D: Driver> Inner<D> {
    #[cfg(feature = "proto-ipv4")]
    pub fn set_config_v4(&mut self, _s: &mut SocketStack, config: ConfigV4) {
        // Handle static config.
        self.static_v4 = match config.clone() {
            ConfigV4::None => None,
            #[cfg(feature = "dhcpv4")]
            ConfigV4::Dhcp(_) => None,
            ConfigV4::Static(c) => Some(c),
        };

        // Handle DHCP config.
        #[cfg(feature = "dhcpv4")]
        match config {
            ConfigV4::Dhcp(c) => {
                // Create the socket if it doesn't exist.
                if self.dhcp_socket.is_none() {
                    let socket = smoltcp::socket::dhcpv4::Socket::new();
                    let handle = _s.sockets.add(socket);
                    self.dhcp_socket = Some(handle);
                }

                // Configure it
                let socket = _s.sockets.get_mut::<dhcpv4::Socket>(unwrap!(self.dhcp_socket));
                socket.set_ignore_naks(c.ignore_naks);
                socket.set_max_lease_duration(c.max_lease_duration.map(crate::time::duration_to_smoltcp));
                socket.set_ports(c.server_port, c.client_port);
                socket.set_retry_config(c.retry_config);

                socket.set_outgoing_options(&[]);
                #[cfg(feature = "dhcpv4-hostname")]
                if let Some(h) = c.hostname {
                    // safety: we just did set_outgoing_options([]) so we know the socket is no longer holding a reference.
                    let hostname = unsafe { &mut *self.hostname.get() };

                    // create data
                    // safety: we know the buffer lives forever, new borrows the StackResources for 'static.
                    // also we won't modify it until next call to this function.
                    hostname.data[..h.len()].copy_from_slice(h.as_bytes());
                    let data: &[u8] = &hostname.data[..h.len()];
                    let data: &'static [u8] = unsafe { core::mem::transmute(data) };

                    // set the option.
                    hostname.option = smoltcp::wire::DhcpOption { data, kind: 12 };
                    socket.set_outgoing_options(core::slice::from_ref(&hostname.option));
                }

                socket.reset();
            }
            _ => {
                // Remove DHCP socket if any.
                if let Some(socket) = self.dhcp_socket {
                    _s.sockets.remove(socket);
                    self.dhcp_socket = None;
                }
            }
        }
    }

    #[cfg(feature = "proto-ipv6")]
    pub fn set_config_v6(&mut self, _s: &mut SocketStack, config: ConfigV6) {
        self.static_v6 = match config {
            ConfigV6::None => None,
            ConfigV6::Static(c) => Some(c),
        };
    }

    fn apply_static_config(&mut self, s: &mut SocketStack) {
        let mut addrs = Vec::new();
        #[cfg(feature = "dns")]
        let mut dns_servers: Vec<_, 6> = Vec::new();
        #[cfg(feature = "proto-ipv4")]
        let mut gateway_v4 = None;
        #[cfg(feature = "proto-ipv6")]
        let mut gateway_v6 = None;

        #[cfg(feature = "proto-ipv4")]
        if let Some(config) = &self.static_v4 {
            debug!("IPv4: UP");
            debug!("   IP address:      {:?}", config.address);
            debug!("   Default gateway: {:?}", config.gateway);

            unwrap!(addrs.push(IpCidr::Ipv4(config.address)).ok());
            gateway_v4 = config.gateway.into();
            #[cfg(feature = "dns")]
            for s in &config.dns_servers {
                debug!("   DNS server:      {:?}", s);
                unwrap!(dns_servers.push(s.clone().into()).ok());
            }
        } else {
            info!("IPv4: DOWN");
        }

        #[cfg(feature = "proto-ipv6")]
        if let Some(config) = &self.static_v6 {
            debug!("IPv6: UP");
            debug!("   IP address:      {:?}", config.address);
            debug!("   Default gateway: {:?}", config.gateway);

            unwrap!(addrs.push(IpCidr::Ipv6(config.address)).ok());
            gateway_v6 = config.gateway.into();
            #[cfg(feature = "dns")]
            for s in &config.dns_servers {
                debug!("   DNS server:      {:?}", s);
                unwrap!(dns_servers.push(s.clone().into()).ok());
            }
        } else {
            info!("IPv6: DOWN");
        }

        // Apply addresses
        s.iface.update_ip_addrs(|a| *a = addrs);

        // Apply gateways
        #[cfg(feature = "proto-ipv4")]
        if let Some(gateway) = gateway_v4 {
            unwrap!(s.iface.routes_mut().add_default_ipv4_route(gateway));
        } else {
            s.iface.routes_mut().remove_default_ipv4_route();
        }
        #[cfg(feature = "proto-ipv6")]
        if let Some(gateway) = gateway_v6 {
            unwrap!(s.iface.routes_mut().add_default_ipv6_route(gateway));
        } else {
            s.iface.routes_mut().remove_default_ipv6_route();
        }

        // Apply DNS servers
        #[cfg(feature = "dns")]
        s.sockets
            .get_mut::<smoltcp::socket::dns::Socket>(self.dns_socket)
            .update_servers(&dns_servers[..]);

        self.config_waker.wake();
    }

    fn poll(&mut self, cx: &mut Context<'_>, s: &mut SocketStack) {
        s.waker.register(cx.waker());

        let (_hardware_addr, medium) = to_smoltcp_hardware_address(self.device.hardware_address());

        #[cfg(any(feature = "medium-ethernet", feature = "medium-ieee802154"))]
        {
            let do_set = match medium {
                #[cfg(feature = "medium-ethernet")]
                Medium::Ethernet => true,
                #[cfg(feature = "medium-ieee802154")]
                Medium::Ieee802154 => true,
                #[allow(unreachable_patterns)]
                _ => false,
            };
            if do_set {
                s.iface.set_hardware_addr(_hardware_addr);
            }
        }

        let timestamp = instant_to_smoltcp(Instant::now());
        let mut smoldev = DriverAdapter {
            cx: Some(cx),
            inner: &mut self.device,
            medium,
        };
        s.iface.poll(timestamp, &mut smoldev, &mut s.sockets);

        // Update link up
        let old_link_up = self.link_up;
        self.link_up = self.device.link_state(cx) == LinkState::Up;

        // Print when changed
        if old_link_up != self.link_up {
            info!("link_up = {:?}", self.link_up);
        }

        #[allow(unused_mut)]
        let mut apply_config = false;

        #[cfg(feature = "dhcpv4")]
        if let Some(dhcp_handle) = self.dhcp_socket {
            let socket = s.sockets.get_mut::<dhcpv4::Socket>(dhcp_handle);

            if self.link_up {
                if old_link_up != self.link_up {
                    socket.reset();
                }
                match socket.poll() {
                    None => {}
                    Some(dhcpv4::Event::Deconfigured) => {
                        self.static_v4 = None;
                        apply_config = true;
                    }
                    Some(dhcpv4::Event::Configured(config)) => {
                        self.static_v4 = Some(StaticConfigV4 {
                            address: config.address,
                            gateway: config.router,
                            dns_servers: config.dns_servers,
                        });
                        apply_config = true;
                    }
                }
            } else if old_link_up {
                socket.reset();
                self.static_v4 = None;
                apply_config = true;
            }
        }

        if apply_config {
            self.apply_static_config(s);
        }

        if let Some(poll_at) = s.iface.poll_at(timestamp, &mut s.sockets) {
            let t = Timer::at(instant_from_smoltcp(poll_at));
            pin_mut!(t);
            if t.poll(cx).is_ready() {
                cx.waker().wake_by_ref();
            }
        }
    }
}
