use std::{
    fmt::Debug,
    io,
    pin::Pin,
    task::{Context, Poll},
};

use futures::{
    channel::mpsc::{UnboundedReceiver, UnboundedSender},
    Future,
    Sink,
    Stream,
};
use log::{error, warn};
use netlink_packet_core::{
    NetlinkDeserializable,
    NetlinkMessage,
    NetlinkPayload,
    NetlinkSerializable,
};

use crate::{
    codecs::NetlinkCodec,
    framed::NetlinkFramed,
    sys::{Socket, SocketAddr},
    Protocol,
    Request,
    Response,
};

/// Connection to a Netlink socket, running in the background.
///
/// [`ConnectionHandle`](struct.ConnectionHandle.html) are used to pass new requests to the
/// `Connection`, that in turn, sends them through the netlink socket.
pub struct Connection<T>
where
    T: Debug + Clone + PartialEq + Eq + NetlinkSerializable<T> + NetlinkDeserializable<T>,
{
    socket: NetlinkFramed<NetlinkCodec<NetlinkMessage<T>>>,

    protocol: Protocol<T, UnboundedSender<NetlinkMessage<T>>>,

    /// Channel used by the user to pass requests to the connection.
    requests_rx: Option<UnboundedReceiver<Request<T>>>,

    /// Channel used to transmit to the ConnectionHandle the unsolicited messages received from the
    /// socket (multicast messages for instance).
    unsolicited_messages_tx: Option<UnboundedSender<(NetlinkMessage<T>, SocketAddr)>>,

    socket_closed: bool,
}

impl<T> Connection<T>
where
    T: Debug + Clone + PartialEq + Eq + NetlinkSerializable<T> + NetlinkDeserializable<T> + Unpin,
{
    pub(crate) fn new(
        requests_rx: UnboundedReceiver<Request<T>>,
        unsolicited_messages_tx: UnboundedSender<(NetlinkMessage<T>, SocketAddr)>,
        protocol: isize,
    ) -> io::Result<Self> {
        let socket = Socket::new(protocol)?;
        Ok(Connection {
            socket: NetlinkFramed::new(socket, NetlinkCodec::<NetlinkMessage<T>>::new()),
            protocol: Protocol::new(),
            requests_rx: Some(requests_rx),
            unsolicited_messages_tx: Some(unsolicited_messages_tx),
            socket_closed: false,
        })
    }

    pub fn socket_mut(&mut self) -> &mut Socket {
        self.socket.get_mut()
    }

    pub fn poll_send_messages(&mut self, cx: &mut Context) {
        trace!("poll_send_messages called");
        let Connection {
            ref mut socket,
            ref mut protocol,
            ..
        } = self;
        let mut socket = Pin::new(socket);

        while !protocol.outgoing_messages.is_empty() {
            trace!("found outgoing message to send checking if socket is ready");
            if let Poll::Ready(Err(e)) = Pin::as_mut(&mut socket).poll_ready(cx) {
                // Sink errors are usually not recoverable. The socket
                // probably shut down.
                warn!("netlink socket shut down: {:?}", e);
                self.socket_closed = true;
                return;
            }

            let (mut message, addr) = protocol.outgoing_messages.pop_front().unwrap();
            message.finalize();

            trace!("sending outgoing message");
            if let Err(e) = Pin::as_mut(&mut socket).start_send((message, addr)) {
                error!("failed to send message: {:?}", e);
                self.socket_closed = true;
                return;
            }
        }

        trace!("poll_send_messages done");
        self.poll_flush(cx)
    }

    pub fn poll_flush(&mut self, cx: &mut Context) {
        trace!("poll_flush called");
        if let Poll::Ready(Err(e)) = Pin::new(&mut self.socket).poll_flush(cx) {
            warn!("error flushing netlink socket: {:?}", e);
            self.socket_closed = true;
        }
    }

    pub fn poll_read_messages(&mut self, cx: &mut Context) {
        trace!("poll_read_messages called");
        let mut socket = Pin::new(&mut self.socket);

        loop {
            trace!("polling socket");
            match socket.as_mut().poll_next(cx) {
                Poll::Ready(Some((message, addr))) => {
                    trace!("read datagram from socket");
                    self.protocol.handle_message(message, addr);
                }
                Poll::Ready(None) => {
                    warn!("netlink socket stream shut down");
                    self.socket_closed = true;
                    return;
                }
                Poll::Pending => {
                    trace!("no datagram read from socket");
                    return;
                }
            }
        }
    }

    pub fn poll_requests(&mut self, cx: &mut Context) {
        trace!("poll_requests called");
        if let Some(mut stream) = self.requests_rx.as_mut() {
            loop {
                match Pin::new(&mut stream).poll_next(cx) {
                    Poll::Ready(Some(request)) => self.protocol.request(request),
                    Poll::Ready(None) => break,
                    Poll::Pending => return,
                }
            }
            let _ = self.requests_rx.take();
            trace!("no new requests to handle poll_requests done");
        }
    }

    pub fn forward_unsolicited_messages(&mut self) {
        if self.unsolicited_messages_tx.is_none() {
            while let Some((message, source)) = self.protocol.incoming_requests.pop_front() {
                warn!(
                    "ignoring unsolicited message {:?} from {:?}",
                    message, source
                );
            }
            return;
        }

        trace!("forward_unsolicited_messages called");
        let mut ready = false;

        let Connection {
            ref mut protocol,
            ref mut unsolicited_messages_tx,
            ..
        } = self;

        while let Some((message, source)) = protocol.incoming_requests.pop_front() {
            if unsolicited_messages_tx
                .as_mut()
                .unwrap()
                .unbounded_send((message, source))
                .is_err()
            {
                // The channel is unbounded so the only error that can
                // occur is that the channel is closed because the
                // receiver was dropped
                warn!("failed to forward message to connection handle: channel closed");
                ready = true;
                break;
            }
        }

        if ready {
            // The channel is closed so we can drop the sender.
            let _ = self.unsolicited_messages_tx.take();
            // purge `protocol.incoming_requests`
            self.forward_unsolicited_messages();
        }

        trace!("forward_unsolicited_messages done");
    }

    pub fn forward_responses(&mut self) {
        trace!("forward_responses called");
        let protocol = &mut self.protocol;

        while let Some(response) = protocol.incoming_responses.pop_front() {
            let Response {
                message,
                done,
                metadata: tx,
            } = response;
            if done {
                use NetlinkPayload::*;
                match &message.payload {
                    // Since `self.protocol` set the `done` flag here,
                    // we know it has already dropped the request and
                    // its associated metadata, ie the UnboundedSender
                    // used to forward messages back to the
                    // ConnectionHandle. By just continuing we're
                    // dropping the last instance of that sender,
                    // hence closing the channel and signaling the
                    // handle that no more messages are expected.
                    Noop | Done | Ack(_) => {
                        trace!("not forwarding Ack/Done message to the handle");
                        continue;
                    }
                    // I'm not sure how we should handle overrun messages
                    Overrun(_) => unimplemented!("overrun is not handled yet"),
                    // We need to forward error messages and messages
                    // that are part of the netlink subprotocol,
                    // because only the user knows how they want to
                    // handle them.
                    Error(_) | InnerMessage(_) => {}
                }
            }

            trace!("forwarding response to the handle");
            if tx.unbounded_send(message).is_err() {
                // With an unboundedsender, an error can
                // only happen if the receiver is closed.
                warn!("failed to forward response back to the handle");
            }
        }
        trace!("forward_responses done");
    }

    pub fn should_shut_down(&self) -> bool {
        self.socket_closed || (self.unsolicited_messages_tx.is_none() && self.requests_rx.is_none())
    }
}

impl<T> Future for Connection<T>
where
    T: Debug + Clone + PartialEq + Eq + NetlinkSerializable<T> + NetlinkDeserializable<T> + Unpin,
{
    type Output = ();

    fn poll(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Self::Output> {
        trace!("polling Connection");
        let pinned = self.get_mut();

        debug!("reading incoming messages");
        pinned.poll_read_messages(cx);

        debug!("forwarding unsolicited messages to the connection handle");
        pinned.forward_unsolicited_messages();

        debug!("forwaring responses to previous requests to the connection handle");
        pinned.forward_responses();

        debug!("handling requests");
        pinned.poll_requests(cx);

        debug!("sending messages");
        pinned.poll_send_messages(cx);

        trace!("done polling Connection");

        if pinned.should_shut_down() {
            Poll::Ready(())
        } else {
            Poll::Pending
        }
    }
}