rumqttc-v4-next 0.33.1

use crate::notice::{
    PublishNoticeTx, PublishResult, SubscribeNoticeTx, TrackedNoticeTx, UnsubscribeNoticeTx,
};
use crate::{Event, Incoming, NoticeFailureReason, Outgoing, PublishNoticeError, Request};

use crate::mqttbytes::v4::{
    Packet, PubAck, PubComp, PubRec, PubRel, Publish, SubAck, Subscribe, UnsubAck, Unsubscribe,
};
use crate::mqttbytes::{self, QoS};
use fixedbitset::FixedBitSet;
use std::collections::{BTreeMap, VecDeque};
use std::{io, time::Instant};

/// Errors during state handling
#[derive(Debug, thiserror::Error)]
pub enum StateError {
    /// Io Error while state is passed to network
    #[error("Io error: {0:?}")]
    Io(#[from] io::Error),
    /// Invalid state for a given operation
    #[error("Invalid state for a given operation")]
    InvalidState,
    /// Received a packet (ack) which isn't asked for
    #[error("Received unsolicited ack pkid: {0}")]
    Unsolicited(u16),
    /// Last pingreq isn't acked
    #[error("Last pingreq isn't acked")]
    AwaitPingResp,
    /// Received a wrong packet while waiting for another packet
    #[error("Received a wrong packet while waiting for another packet")]
    WrongPacket,
    #[error("Timeout while waiting to resolve collision")]
    CollisionTimeout,
    #[error("A Subscribe packet must contain atleast one filter")]
    EmptySubscription,
    #[error("Mqtt serialization/deserialization error: {0}")]
    Deserialization(#[from] mqttbytes::Error),
    #[error("Connection closed by peer abruptly")]
    ConnectionAborted,
}

/// State of the mqtt connection.
// Design: Methods will just modify the state of the object without doing any network operations
// Design: All inflight queues are maintained in a pkid-indexed vec/bitset structure.
// This is done for 2 reasons
// Bad acks or out of order acks aren't O(n) causing cpu spikes
// Any missing acks from the broker are detected during the next recycled use of packet ids
#[derive(Debug)]
pub struct MqttState {
    /// Status of last ping
    pub await_pingresp: bool,
    /// Collision ping count. Collisions stop user requests
    /// which inturn trigger pings. Multiple pings without
    /// resolving collisions will result in error
    pub collision_ping_count: usize,
    /// Last incoming packet time
    last_incoming: Instant,
    /// Last outgoing packet time
    last_outgoing: Instant,
    /// Packet id of the last outgoing packet
    pub(crate) last_pkid: u16,
    /// Packet id of the last acked publish
    pub(crate) last_puback: u16,
    /// Number of outgoing inflight publishes
    pub(crate) inflight: u16,
    /// Maximum number of allowed inflight
    pub(crate) max_inflight: u16,
    /// Outgoing `QoS` 1, 2 publishes which aren't acked yet
    pub(crate) outgoing_pub: Vec<Option<Publish>>,
    /// Notice handles for outgoing `QoS` 1, 2 publishes
    pub(crate) outgoing_pub_notice: Vec<Option<PublishNoticeTx>>,
    /// Packet ids acked by broker while waiting to advance last contiguous ack boundary
    pub(crate) outgoing_pub_ack: FixedBitSet,
    /// Packet ids of released `QoS` 2 publishes
    pub(crate) outgoing_rel: FixedBitSet,
    /// Notice handles for outgoing `QoS` 2 pubrels
    pub(crate) outgoing_rel_notice: Vec<Option<PublishNoticeTx>>,
    /// Packet ids on incoming `QoS` 2 publishes
    pub(crate) incoming_pub: FixedBitSet,
    /// Last collision due to broker not acking in order
    pub collision: Option<Publish>,
    /// Notice handle for the collision publish
    pub(crate) collision_notice: Option<PublishNoticeTx>,
    /// Tracked subscribe requests waiting for `SubAck`
    pub(crate) tracked_subscribe: BTreeMap<u16, (Subscribe, SubscribeNoticeTx)>,
    /// Tracked unsubscribe requests waiting for `UnsubAck`
    pub(crate) tracked_unsubscribe: BTreeMap<u16, (Unsubscribe, UnsubscribeNoticeTx)>,
    /// Buffered incoming packets
    pub events: VecDeque<Event>,
    /// Indicates if acknowledgements should be send immediately
    pub manual_acks: bool,
}

/// Builder for low-level MQTT 3.1.1 protocol state.
///
/// Most users should configure clients through [`crate::MqttOptions`] and
/// construct them with [`crate::Client::builder`] or [`crate::AsyncClient::builder`].
/// This builder is intended for users driving [`MqttState`] directly.
#[derive(Debug)]
pub struct MqttStateBuilder {
    max_inflight: u16,
    manual_acks: bool,
}

impl MqttStateBuilder {
    /// Create a new [`MqttState`] builder.
    #[must_use]
    pub const fn new(max_inflight: u16) -> Self {
        Self {
            max_inflight,
            manual_acks: false,
        }
    }

    /// Set whether incoming publish acknowledgements should be sent manually.
    #[must_use]
    pub const fn manual_acks(mut self, manual_acks: bool) -> Self {
        self.manual_acks = manual_acks;
        self
    }

    /// Build the configured [`MqttState`].
    #[must_use]
    pub fn build(self) -> MqttState {
        MqttState::new_internal(self.max_inflight, self.manual_acks)
    }
}

impl MqttState {
    const WARM_TRACKING_SLOTS: usize = 32;

    const fn initial_events_capacity() -> usize {
        128
    }

    const fn outgoing_tracking_len(max_inflight: u16) -> usize {
        max_inflight as usize + 1
    }

    const fn warm_tracking_len(max_inflight: u16) -> usize {
        let full_len = Self::outgoing_tracking_len(max_inflight);
        let warm_len = Self::WARM_TRACKING_SLOTS + 1;
        if full_len < warm_len {
            full_len
        } else {
            warm_len
        }
    }

    fn new_notice_slots_with_len(len: usize) -> Vec<Option<PublishNoticeTx>> {
        std::iter::repeat_with(|| None).take(len).collect()
    }

    fn ensure_outgoing_tracking_capacity(&mut self, target_len: usize) {
        if self.outgoing_pub.len() < target_len {
            self.outgoing_pub.resize_with(target_len, || None);
        }

        if self.outgoing_pub_notice.len() < target_len {
            self.outgoing_pub_notice.resize_with(target_len, || None);
        }

        if self.outgoing_rel_notice.len() < target_len {
            self.outgoing_rel_notice.resize_with(target_len, || None);
        }

        if self.outgoing_pub_ack.len() < target_len {
            self.outgoing_pub_ack.grow(target_len);
        }

        if self.outgoing_rel.len() < target_len {
            self.outgoing_rel.grow(target_len);
        }
    }

    pub(crate) fn outbound_requests_drained(&self) -> bool {
        self.inflight == 0
            && self.collision.is_none()
            && self.collision_notice.is_none()
            && self.tracked_subscribe.is_empty()
            && self.tracked_unsubscribe.is_empty()
            && self.outgoing_pub.iter().all(Option::is_none)
            && self.outgoing_pub_notice.iter().all(Option::is_none)
            && self.outgoing_rel_notice.iter().all(Option::is_none)
            && self.outgoing_pub_ack.ones().next().is_none()
            && self.outgoing_rel.ones().next().is_none()
    }

    fn maybe_shrink_outgoing_tracking_capacity(&mut self) {
        let target_len = Self::warm_tracking_len(self.max_inflight);
        if self.outgoing_pub.len() <= target_len || !self.outbound_requests_drained() {
            return;
        }

        self.outgoing_pub.truncate(target_len);
        self.outgoing_pub_notice.truncate(target_len);
        self.outgoing_rel_notice.truncate(target_len);
        self.outgoing_pub_ack = FixedBitSet::with_capacity(target_len);
        self.outgoing_rel = FixedBitSet::with_capacity(target_len);
        self.last_pkid = 0;
        self.last_puback = 0;
    }

    const fn validate_outgoing_pkid_bound(&self, pkid: u16) -> Result<(), StateError> {
        if pkid == 0 || pkid > self.max_inflight {
            return Err(StateError::Unsolicited(pkid));
        }

        Ok(())
    }

    const fn next_publish_pkid_after(&self, pkid: u16) -> u16 {
        if pkid >= self.max_inflight {
            1
        } else {
            pkid + 1
        }
    }

    fn packet_identifier_in_use(&self, pkid: u16) -> bool {
        let index = usize::from(pkid);
        self.outgoing_pub.get(index).is_some_and(Option::is_some)
            || self.outgoing_rel.contains(index)
            || self.tracked_subscribe.contains_key(&pkid)
            || self.tracked_unsubscribe.contains_key(&pkid)
    }

    pub(crate) fn can_send_publish(&self, publish: &Publish) -> bool {
        if publish.qos == QoS::AtMostOnce {
            return true;
        }

        if self.inflight >= self.max_inflight || self.collision.is_some() {
            return false;
        }

        if publish.pkid == 0 {
            return self.next_publish_pkid().is_some();
        }

        self.validate_outgoing_pkid_bound(publish.pkid).is_ok()
            && !self.packet_identifier_in_use(publish.pkid)
    }

    pub(crate) fn control_packet_identifier_available(&self) -> bool {
        (1..=u16::MAX).any(|pkid| !self.packet_identifier_in_use(pkid))
    }

    fn clean_pending_capacity(&self) -> usize {
        self.outgoing_pub
            .iter()
            .filter(|publish| publish.is_some())
            .count()
            + self.outgoing_rel.ones().count()
            + self.tracked_subscribe.len()
            + self.tracked_unsubscribe.len()
    }

    /// Create a builder for low-level MQTT 3.1.1 protocol state.
    #[must_use]
    pub const fn builder(max_inflight: u16) -> MqttStateBuilder {
        MqttStateBuilder::new(max_inflight)
    }

    /// Creates new mqtt state. Same state should be used during a
    /// connection for persistent sessions while new state should
    /// instantiated for clean sessions.
    #[must_use]
    pub(crate) fn new_internal(max_inflight: u16, manual_acks: bool) -> Self {
        let tracking_len = Self::warm_tracking_len(max_inflight);
        Self {
            await_pingresp: false,
            collision_ping_count: 0,
            last_incoming: Instant::now(),
            last_outgoing: Instant::now(),
            last_pkid: 0,
            last_puback: 0,
            inflight: 0,
            max_inflight,
            // index 0 is wasted as 0 is not a valid packet id
            outgoing_pub: std::iter::repeat_with(|| None).take(tracking_len).collect(),
            outgoing_pub_notice: Self::new_notice_slots_with_len(tracking_len),
            outgoing_pub_ack: FixedBitSet::with_capacity(tracking_len),
            outgoing_rel: FixedBitSet::with_capacity(tracking_len),
            outgoing_rel_notice: Self::new_notice_slots_with_len(tracking_len),
            incoming_pub: FixedBitSet::with_capacity(u16::MAX as usize + 1),
            collision: None,
            collision_notice: None,
            tracked_subscribe: BTreeMap::new(),
            tracked_unsubscribe: BTreeMap::new(),
            events: VecDeque::with_capacity(Self::initial_events_capacity()),
            manual_acks,
        }
    }

    pub(crate) fn clean_with_notices(&mut self) -> Vec<(Request, Option<TrackedNoticeTx>)> {
        let mut pending = Vec::with_capacity(self.clean_pending_capacity());
        let (first_half, second_half) = self
            .outgoing_pub
            .split_at_mut(self.last_puback as usize + 1);
        let (notice_first_half, notice_second_half) = self
            .outgoing_pub_notice
            .split_at_mut(self.last_puback as usize + 1);

        for (publish, notice) in second_half
            .iter_mut()
            .zip(notice_second_half.iter_mut())
            .chain(first_half.iter_mut().zip(notice_first_half.iter_mut()))
        {
            if let Some(publish) = publish.take() {
                let request = Request::Publish(publish);
                pending.push((request, notice.take().map(TrackedNoticeTx::Publish)));
            } else {
                _ = notice.take();
            }
        }

        // remove and collect pending releases
        for pkid in self.outgoing_rel.ones() {
            let pkid = u16::try_from(pkid).expect("fixedbitset index always fits in u16");
            let request = Request::PubRel(PubRel::new(pkid));
            pending.push((
                request,
                self.outgoing_rel_notice[pkid as usize]
                    .take()
                    .map(TrackedNoticeTx::Publish),
            ));
        }
        self.outgoing_rel.clear();
        self.outgoing_pub_ack.clear();

        for (pkid, (mut subscribe, notice)) in std::mem::take(&mut self.tracked_subscribe) {
            subscribe.pkid = pkid;
            pending.push((
                Request::Subscribe(subscribe),
                Some(TrackedNoticeTx::Subscribe(notice)),
            ));
        }

        for (pkid, (mut unsubscribe, notice)) in std::mem::take(&mut self.tracked_unsubscribe) {
            unsubscribe.pkid = pkid;
            pending.push((
                Request::Unsubscribe(unsubscribe),
                Some(TrackedNoticeTx::Unsubscribe(notice)),
            ));
        }

        // remove packet ids of incoming qos2 publishes
        self.incoming_pub.clear();

        self.await_pingresp = false;
        self.collision_ping_count = 0;
        self.inflight = 0;
        if pending.is_empty() {
            self.maybe_shrink_outgoing_tracking_capacity();
        }
        pending
    }

    /// Returns inflight outgoing packets and clears internal queues
    pub fn clean(&mut self) -> Vec<Request> {
        self.clean_with_notices()
            .into_iter()
            .map(|(request, _)| request)
            .collect()
    }

    pub const fn inflight(&self) -> u16 {
        self.inflight
    }

    pub fn tracked_subscribe_len(&self) -> usize {
        self.tracked_subscribe.len()
    }

    pub fn tracked_unsubscribe_len(&self) -> usize {
        self.tracked_unsubscribe.len()
    }

    pub fn tracked_requests_is_empty(&self) -> bool {
        self.tracked_subscribe.is_empty() && self.tracked_unsubscribe.is_empty()
    }

    pub fn drain_tracked_requests_as_failed(&mut self, reason: NoticeFailureReason) -> usize {
        let mut drained = 0;
        for (_, (_, notice)) in std::mem::take(&mut self.tracked_subscribe) {
            drained += 1;
            notice.error(reason.subscribe_error());
        }
        for (_, (_, notice)) in std::mem::take(&mut self.tracked_unsubscribe) {
            drained += 1;
            notice.error(reason.unsubscribe_error());
        }

        self.maybe_shrink_outgoing_tracking_capacity();
        drained
    }

    pub(crate) fn fail_pending_notices(&mut self) {
        for notice in &mut self.outgoing_pub_notice {
            if let Some(tx) = notice.take() {
                tx.error(PublishNoticeError::SessionReset);
            }
        }

        for notice in &mut self.outgoing_rel_notice {
            if let Some(tx) = notice.take() {
                tx.error(PublishNoticeError::SessionReset);
            }
        }

        if let Some(tx) = self.collision_notice.take() {
            tx.error(PublishNoticeError::SessionReset);
        }

        self.drain_tracked_requests_as_failed(NoticeFailureReason::SessionReset);
        self.clear_collision();
        self.maybe_shrink_outgoing_tracking_capacity();
    }

    /// Consolidates handling of all outgoing mqtt packet logic. Returns a packet which should
    /// be put on to the network by the eventloop
    ///
    /// # Errors
    ///
    /// Returns an error if the outgoing request is invalid for the current
    /// client state.
    pub fn handle_outgoing_packet(
        &mut self,
        request: Request,
    ) -> Result<Option<Packet>, StateError> {
        let (packet, flush_notice) = self.handle_outgoing_packet_with_notice(request, None)?;
        if let Some(tx) = flush_notice {
            tx.success(PublishResult::Qos0Flushed);
        }

        self.last_outgoing = Instant::now();
        Ok(packet)
    }

    pub(crate) fn handle_outgoing_packet_with_notice(
        &mut self,
        request: Request,
        notice: Option<TrackedNoticeTx>,
    ) -> Result<(Option<Packet>, Option<PublishNoticeTx>), StateError> {
        let result =
            match request {
                Request::Publish(publish) => {
                    let publish_notice = match notice {
                        Some(TrackedNoticeTx::Publish(notice)) => Some(notice),
                        Some(TrackedNoticeTx::Subscribe(_) | TrackedNoticeTx::Unsubscribe(_))
                        | None => None,
                    };
                    self.outgoing_publish_with_notice(publish, publish_notice)?
                }
                Request::PubRel(pubrel) => {
                    let publish_notice = match notice {
                        Some(TrackedNoticeTx::Publish(notice)) => Some(notice),
                        Some(TrackedNoticeTx::Subscribe(_) | TrackedNoticeTx::Unsubscribe(_))
                        | None => None,
                    };
                    self.outgoing_pubrel_with_notice(pubrel, publish_notice)?
                }
                Request::Subscribe(subscribe) => {
                    let request_notice = match notice {
                        Some(TrackedNoticeTx::Subscribe(notice)) => Some(notice),
                        Some(TrackedNoticeTx::Publish(_) | TrackedNoticeTx::Unsubscribe(_))
                        | None => None,
                    };
                    (self.outgoing_subscribe(subscribe, request_notice)?, None)
                }
                Request::Unsubscribe(unsubscribe) => {
                    let request_notice = match notice {
                        Some(TrackedNoticeTx::Unsubscribe(notice)) => Some(notice),
                        Some(TrackedNoticeTx::Publish(_) | TrackedNoticeTx::Subscribe(_))
                        | None => None,
                    };
                    (
                        Some(self.outgoing_unsubscribe(unsubscribe, request_notice)?),
                        None,
                    )
                }
                Request::PingReq(_) => (self.outgoing_ping()?, None),
                Request::Disconnect(_) | Request::DisconnectWithTimeout(_, _) => {
                    unreachable!("graceful disconnect requests are handled by the event loop")
                }
                Request::DisconnectNow(_) => (Some(self.outgoing_disconnect()), None),
                Request::PubAck(puback) => (Some(self.outgoing_puback(puback)), None),
                Request::PubRec(pubrec) => (Some(self.outgoing_pubrec(pubrec)), None),
                _ => unimplemented!(),
            };

        self.last_outgoing = Instant::now();
        Ok(result)
    }

    /// Consolidates handling of all incoming mqtt packets. Returns a `Notification` which for the
    /// user to consume and `Packet` which for the eventloop to put on the network
    /// E.g For incoming `QoS1` publish packet, this method returns (Publish, Puback). Publish packet will
    /// be forwarded to user and Pubck packet will be written to network
    ///
    /// # Errors
    ///
    /// Returns an error if the incoming packet is invalid for the current
    /// client state.
    pub fn handle_incoming_packet(
        &mut self,
        packet: Incoming,
    ) -> Result<Option<Packet>, StateError> {
        let events_len_before = self.events.len();
        let outgoing = match &packet {
            Incoming::PingResp => Ok(self.handle_incoming_pingresp()),
            Incoming::Publish(publish) => Ok(self.handle_incoming_publish(publish)),
            Incoming::SubAck(suback) => Ok(self.handle_incoming_suback(suback)),
            Incoming::UnsubAck(unsuback) => Ok(self.handle_incoming_unsuback(unsuback)),
            Incoming::PubAck(puback) => self.handle_incoming_puback(puback),
            Incoming::PubRec(pubrec) => self.handle_incoming_pubrec(pubrec),
            Incoming::PubRel(pubrel) => self.handle_incoming_pubrel(pubrel),
            Incoming::PubComp(pubcomp) => self.handle_incoming_pubcomp(pubcomp),
            _ => {
                error!("Invalid incoming packet = {packet:?}");
                Err(StateError::WrongPacket)
            }
        };

        // Preserve original event ordering (Incoming first, derived Outgoing next)
        // without cloning the incoming packet.
        self.events
            .insert(events_len_before, Event::Incoming(packet));
        let outgoing = outgoing?;
        self.last_incoming = Instant::now();

        Ok(outgoing)
    }

    pub fn clear_collision(&mut self) {
        self.collision = None;
        self.collision_notice = None;
        self.collision_ping_count = 0;
    }

    fn handle_incoming_suback(&mut self, suback: &SubAck) -> Option<Packet> {
        if let Some((_, notice)) = self.tracked_subscribe.remove(&suback.pkid) {
            notice.success(suback.clone());
        }
        None
    }

    fn handle_incoming_unsuback(&mut self, unsuback: &UnsubAck) -> Option<Packet> {
        if let Some((_, notice)) = self.tracked_unsubscribe.remove(&unsuback.pkid) {
            notice.success(unsuback.clone());
        }
        None
    }

    /// Results in a publish notification in all the `QoS` cases. Replys with an ack
    /// in case of `QoS1` and Replys rec in case of `QoS` while also storing the message
    fn handle_incoming_publish(&mut self, publish: &Publish) -> Option<Packet> {
        let qos = publish.qos;

        match qos {
            QoS::AtMostOnce => None,
            QoS::AtLeastOnce => {
                if !self.manual_acks {
                    let puback = PubAck::new(publish.pkid);
                    return Some(self.outgoing_puback(puback));
                }
                None
            }
            QoS::ExactlyOnce => {
                let pkid = publish.pkid;
                self.incoming_pub.insert(pkid as usize);

                if !self.manual_acks {
                    let pubrec = PubRec::new(pkid);
                    return Some(self.outgoing_pubrec(pubrec));
                }
                None
            }
        }
    }

    fn handle_incoming_puback(&mut self, puback: &PubAck) -> Result<Option<Packet>, StateError> {
        let publish = self
            .outgoing_pub
            .get_mut(puback.pkid as usize)
            .ok_or(StateError::Unsolicited(puback.pkid))?;

        if publish.take().is_none() {
            error!("Unsolicited puback packet: {:?}", puback.pkid);
            return Err(StateError::Unsolicited(puback.pkid));
        }
        self.mark_outgoing_packet_id_complete(puback.pkid);

        if let Some(tx) = self.outgoing_pub_notice[puback.pkid as usize].take() {
            tx.success(PublishResult::Qos1(puback.clone()));
        }

        self.inflight -= 1;
        let packet = self.replay_collision_publish(puback.pkid);
        if packet.is_none() {
            self.maybe_shrink_outgoing_tracking_capacity();
        }

        Ok(packet)
    }

    fn handle_incoming_pubrec(&mut self, pubrec: &PubRec) -> Result<Option<Packet>, StateError> {
        let publish = self
            .outgoing_pub
            .get_mut(pubrec.pkid as usize)
            .ok_or(StateError::Unsolicited(pubrec.pkid))?;

        if publish.take().is_none() {
            error!("Unsolicited pubrec packet: {:?}", pubrec.pkid);
            return Err(StateError::Unsolicited(pubrec.pkid));
        }

        let notice = self.outgoing_pub_notice[pubrec.pkid as usize].take();
        // NOTE: Inflight - 1 for qos2 in comp
        self.outgoing_rel.insert(pubrec.pkid as usize);
        self.outgoing_rel_notice[pubrec.pkid as usize] = notice;
        let release = PubRel { pkid: pubrec.pkid };
        let event = Event::Outgoing(Outgoing::PubRel(pubrec.pkid));
        self.events.push_back(event);

        Ok(Some(Packet::PubRel(release)))
    }

    fn handle_incoming_pubrel(&mut self, pubrel: &PubRel) -> Result<Option<Packet>, StateError> {
        if !self.incoming_pub.contains(pubrel.pkid as usize) {
            error!("Unsolicited pubrel packet: {:?}", pubrel.pkid);
            return Err(StateError::Unsolicited(pubrel.pkid));
        }

        self.incoming_pub.set(pubrel.pkid as usize, false);
        let event = Event::Outgoing(Outgoing::PubComp(pubrel.pkid));
        let pubcomp = PubComp { pkid: pubrel.pkid };
        self.events.push_back(event);

        Ok(Some(Packet::PubComp(pubcomp)))
    }

    fn handle_incoming_pubcomp(&mut self, pubcomp: &PubComp) -> Result<Option<Packet>, StateError> {
        if !self.outgoing_rel.contains(pubcomp.pkid as usize) {
            error!("Unsolicited pubcomp packet: {:?}", pubcomp.pkid);
            return Err(StateError::Unsolicited(pubcomp.pkid));
        }

        self.outgoing_rel.set(pubcomp.pkid as usize, false);
        self.mark_outgoing_packet_id_complete(pubcomp.pkid);
        if let Some(tx) = self.outgoing_rel_notice[pubcomp.pkid as usize].take() {
            tx.success(PublishResult::Qos2Completed(pubcomp.clone()));
        }
        self.inflight -= 1;
        let packet = self.replay_collision_publish(pubcomp.pkid);
        if packet.is_none() {
            self.maybe_shrink_outgoing_tracking_capacity();
        }

        Ok(packet)
    }

    const fn handle_incoming_pingresp(&mut self) -> Option<Packet> {
        self.await_pingresp = false;

        None
    }

    /// Adds next packet identifier to `QoS` 1 and 2 publish packets and returns
    /// it by wrapping the publish in a packet.
    #[cfg(test)]
    fn outgoing_publish(&mut self, publish: Publish) -> Result<Option<Packet>, StateError> {
        let (packet, flush_notice) = self.outgoing_publish_with_notice(publish, None)?;
        if let Some(tx) = flush_notice {
            tx.success(PublishResult::Qos0Flushed);
        }
        Ok(packet)
    }

    fn outgoing_publish_with_notice(
        &mut self,
        mut publish: Publish,
        notice: Option<PublishNoticeTx>,
    ) -> Result<(Option<Packet>, Option<PublishNoticeTx>), StateError> {
        let mut notice = notice;
        if publish.qos != QoS::AtMostOnce {
            if publish.pkid == 0 {
                publish.pkid = self.next_pkid();
            }

            let pkid = publish.pkid;
            self.validate_outgoing_pkid_bound(pkid)?;
            self.ensure_outgoing_tracking_capacity(pkid as usize + 1);
            if self
                .outgoing_pub
                .get(publish.pkid as usize)
                .ok_or(StateError::Unsolicited(publish.pkid))?
                .is_some()
            {
                info!("Collision on packet id = {:?}", publish.pkid);
                self.collision = Some(publish);
                self.collision_notice = notice.take();
                let event = Event::Outgoing(Outgoing::AwaitAck(pkid));
                self.events.push_back(event);
                return Ok((None, None));
            }

            // if there is an existing publish at this pkid, this implies that broker hasn't acked this
            // packet yet. This error is possible only when broker isn't acking sequentially
            self.outgoing_pub[pkid as usize] = Some(publish.clone());
            self.outgoing_pub_notice[pkid as usize] = notice.take();
            self.outgoing_pub_ack.set(pkid as usize, false);
            self.inflight += 1;
        }

        debug!(
            "Publish. Topic = {}, Pkid = {:?}, Payload Size = {:?}",
            String::from_utf8_lossy(&publish.topic),
            publish.pkid,
            publish.payload.len()
        );

        let event = Event::Outgoing(Outgoing::Publish(publish.pkid));
        self.events.push_back(event);

        if publish.qos == QoS::AtMostOnce {
            Ok((Some(Packet::Publish(publish)), notice.take()))
        } else {
            Ok((Some(Packet::Publish(publish)), None))
        }
    }

    fn outgoing_pubrel_with_notice(
        &mut self,
        pubrel: PubRel,
        notice: Option<PublishNoticeTx>,
    ) -> Result<(Option<Packet>, Option<PublishNoticeTx>), StateError> {
        let pubrel = self.save_pubrel_with_notice(pubrel, notice)?;

        debug!("Pubrel. Pkid = {}", pubrel.pkid);
        let event = Event::Outgoing(Outgoing::PubRel(pubrel.pkid));
        self.events.push_back(event);

        Ok((Some(Packet::PubRel(pubrel)), None))
    }

    fn outgoing_puback(&mut self, puback: PubAck) -> Packet {
        let event = Event::Outgoing(Outgoing::PubAck(puback.pkid));
        self.events.push_back(event);

        Packet::PubAck(puback)
    }

    fn outgoing_pubrec(&mut self, pubrec: PubRec) -> Packet {
        let event = Event::Outgoing(Outgoing::PubRec(pubrec.pkid));
        self.events.push_back(event);

        Packet::PubRec(pubrec)
    }

    /// check when the last control packet/pingreq packet is received and return
    /// the status which tells if keep alive time has exceeded
    /// NOTE: status will be checked for zero keepalive times also
    fn outgoing_ping(&mut self) -> Result<Option<Packet>, StateError> {
        let elapsed_in = self.last_incoming.elapsed();
        let elapsed_out = self.last_outgoing.elapsed();

        if self.collision.is_some() {
            self.collision_ping_count += 1;
            if self.collision_ping_count >= 2 {
                return Err(StateError::CollisionTimeout);
            }
        }

        // raise error if last ping didn't receive ack
        if self.await_pingresp {
            return Err(StateError::AwaitPingResp);
        }

        self.await_pingresp = true;

        debug!(
            "Pingreq,
            last incoming packet before {} millisecs,
            last outgoing request before {} millisecs",
            elapsed_in.as_millis(),
            elapsed_out.as_millis()
        );

        let event = Event::Outgoing(Outgoing::PingReq);
        self.events.push_back(event);

        Ok(Some(Packet::PingReq))
    }

    fn outgoing_subscribe(
        &mut self,
        mut subscription: Subscribe,
        notice: Option<SubscribeNoticeTx>,
    ) -> Result<Option<Packet>, StateError> {
        if subscription.filters.is_empty() {
            return Err(StateError::EmptySubscription);
        }

        let pkid = self.next_control_pkid()?;
        subscription.pkid = pkid;

        debug!(
            "Subscribe. Topics = {:?}, Pkid = {:?}",
            subscription.filters, subscription.pkid
        );

        let event = Event::Outgoing(Outgoing::Subscribe(subscription.pkid));
        self.events.push_back(event);
        if let Some(notice) = notice {
            self.tracked_subscribe
                .insert(subscription.pkid, (subscription.clone(), notice));
        }

        Ok(Some(Packet::Subscribe(subscription)))
    }

    fn outgoing_unsubscribe(
        &mut self,
        mut unsub: Unsubscribe,
        notice: Option<UnsubscribeNoticeTx>,
    ) -> Result<Packet, StateError> {
        let pkid = self.next_control_pkid()?;
        unsub.pkid = pkid;

        debug!(
            "Unsubscribe. Topics = {:?}, Pkid = {:?}",
            unsub.topics, unsub.pkid
        );

        let event = Event::Outgoing(Outgoing::Unsubscribe(unsub.pkid));
        self.events.push_back(event);
        if let Some(notice) = notice {
            self.tracked_unsubscribe
                .insert(unsub.pkid, (unsub.clone(), notice));
        }

        Ok(Packet::Unsubscribe(unsub))
    }

    fn outgoing_disconnect(&mut self) -> Packet {
        debug!("Disconnect");

        let event = Event::Outgoing(Outgoing::Disconnect);
        self.events.push_back(event);

        Packet::Disconnect
    }

    fn check_collision(&mut self, pkid: u16) -> Option<(Publish, Option<PublishNoticeTx>)> {
        if let Some(publish) = &self.collision
            && publish.pkid == pkid
        {
            return self
                .collision
                .take()
                .map(|publish| (publish, self.collision_notice.take()));
        }

        None
    }

    fn save_pubrel_with_notice(
        &mut self,
        mut pubrel: PubRel,
        notice: Option<PublishNoticeTx>,
    ) -> Result<PubRel, StateError> {
        let pubrel = match pubrel.pkid {
            // consider PacketIdentifier(0) as uninitialized packets
            0 => {
                pubrel.pkid = self.next_pkid();
                pubrel
            }
            _ => pubrel,
        };

        self.validate_outgoing_pkid_bound(pubrel.pkid)?;
        self.ensure_outgoing_tracking_capacity(pubrel.pkid as usize + 1);
        self.outgoing_rel.insert(pubrel.pkid as usize);
        self.outgoing_rel_notice[pubrel.pkid as usize] = notice;
        self.inflight += 1;
        Ok(pubrel)
    }

    fn replay_collision_publish(&mut self, pkid: u16) -> Option<Packet> {
        self.check_collision(pkid).map(|(publish, notice)| {
            let publish_pkid = publish.pkid;
            self.ensure_outgoing_tracking_capacity(publish_pkid as usize + 1);
            self.outgoing_pub[publish_pkid as usize] = Some(publish.clone());
            self.outgoing_pub_notice[publish_pkid as usize] = notice;
            self.inflight += 1;

            let event = Event::Outgoing(Outgoing::Publish(publish_pkid));
            self.events.push_back(event);
            self.collision_ping_count = 0;

            Packet::Publish(publish)
        })
    }

    fn mark_outgoing_packet_id_complete(&mut self, pkid: u16) {
        self.outgoing_pub_ack.set(pkid as usize, true);
        self.advance_last_puback_frontier();
    }

    fn advance_last_puback_frontier(&mut self) {
        let mut next = self.next_puback_boundary_pkid(self.last_puback);
        while next != 0 && self.outgoing_pub_ack.contains(next as usize) {
            self.outgoing_pub_ack.set(next as usize, false);
            self.last_puback = next;
            next = self.next_puback_boundary_pkid(self.last_puback);
        }
    }

    const fn next_puback_boundary_pkid(&self, pkid: u16) -> u16 {
        if self.max_inflight == 0 {
            return 0;
        }

        if pkid >= self.max_inflight {
            1
        } else {
            pkid + 1
        }
    }

    /// <http://stackoverflow.com/questions/11115364/mqtt-messageid-practical-implementation>
    /// Packet ids are incremented till maximum set inflight messages and reset to 1 after that.
    ///
    fn next_publish_pkid(&self) -> Option<u16> {
        let mut pkid = self.next_publish_pkid_after(self.last_pkid);
        for _ in 0..usize::from(self.max_inflight) {
            if !self.packet_identifier_in_use(pkid) {
                return Some(pkid);
            }
            pkid = self.next_publish_pkid_after(pkid);
        }

        None
    }

    fn next_pkid(&mut self) -> u16 {
        let pkid = self
            .next_publish_pkid()
            .unwrap_or_else(|| self.next_publish_pkid_after(self.last_pkid));
        if pkid == self.max_inflight {
            self.last_pkid = 0;
        } else {
            self.last_pkid = pkid;
        }

        pkid
    }

    fn next_control_pkid(&mut self) -> Result<u16, StateError> {
        for offset in 1..=u16::MAX {
            let pkid = self.last_pkid.wrapping_add(offset);
            if pkid != 0 && !self.packet_identifier_in_use(pkid) {
                self.last_pkid = pkid;
                return Ok(pkid);
            }
        }

        Err(StateError::InvalidState)
    }
}

impl Clone for MqttState {
    fn clone(&self) -> Self {
        let tracking_len = self.outgoing_pub_notice.len();
        Self {
            await_pingresp: self.await_pingresp,
            collision_ping_count: self.collision_ping_count,
            last_incoming: self.last_incoming,
            last_outgoing: self.last_outgoing,
            last_pkid: self.last_pkid,
            last_puback: self.last_puback,
            inflight: self.inflight,
            max_inflight: self.max_inflight,
            outgoing_pub: self.outgoing_pub.clone(),
            outgoing_pub_notice: Self::new_notice_slots_with_len(tracking_len),
            outgoing_pub_ack: self.outgoing_pub_ack.clone(),
            outgoing_rel: self.outgoing_rel.clone(),
            outgoing_rel_notice: Self::new_notice_slots_with_len(self.outgoing_rel_notice.len()),
            incoming_pub: self.incoming_pub.clone(),
            collision: self.collision.clone(),
            collision_notice: None,
            tracked_subscribe: BTreeMap::new(),
            tracked_unsubscribe: BTreeMap::new(),
            events: self.events.clone(),
            manual_acks: self.manual_acks,
        }
    }
}

#[cfg(test)]
mod test {
    use super::{MqttState, StateError};
    use crate::mqttbytes::v4::*;
    use crate::mqttbytes::*;
    use crate::notice::{
        PublishNoticeTx, PublishResult, SubscribeNoticeError, SubscribeNoticeTx,
        UnsubscribeNoticeError, UnsubscribeNoticeTx,
    };
    use crate::{Event, Incoming, NoticeFailureReason, Outgoing, Request};
    use bytes::Bytes;

    fn build_outgoing_publish(qos: QoS) -> Publish {
        let topic = "hello/world".to_owned();
        let payload = vec![1, 2, 3];

        let mut publish = Publish::new(topic, QoS::AtLeastOnce, payload);
        publish.qos = qos;
        publish
    }

    fn build_incoming_publish(qos: QoS, pkid: u16) -> Publish {
        let topic = "hello/world".to_owned();
        let payload = vec![1, 2, 3];

        let mut publish = Publish::new(topic, QoS::AtLeastOnce, payload);
        publish.pkid = pkid;
        publish.qos = qos;
        publish
    }

    fn build_mqttstate() -> MqttState {
        MqttState::builder(100).build()
    }

    fn queue_publish_with_notice(mqtt: &mut MqttState, publish: Publish) -> crate::PublishNotice {
        let (tx, notice) = PublishNoticeTx::new();
        let (packet, flush_notice) = mqtt
            .outgoing_publish_with_notice(publish, Some(tx))
            .unwrap();
        assert!(packet.is_some());
        assert!(flush_notice.is_none());
        notice
    }

    #[test]
    fn new_state_preallocates_event_queue_for_read_batch_bursts() {
        let mqtt = MqttState::builder(10).build();
        assert!(mqtt.events.capacity() >= MqttState::initial_events_capacity());
    }

    #[test]
    fn new_state_uses_warm_tracking_floor() {
        let mqtt = MqttState::builder(100).build();

        assert_eq!(mqtt.outgoing_pub.len(), 33);
        assert_eq!(mqtt.outgoing_pub_notice.len(), 33);
        assert_eq!(mqtt.outgoing_rel_notice.len(), 33);
        assert_eq!(mqtt.outgoing_pub_ack.len(), 33);
        assert_eq!(mqtt.outgoing_rel.len(), 33);
    }

    #[test]
    fn new_state_uses_full_tracking_len_when_max_inflight_is_below_warm_floor() {
        let mqtt = MqttState::builder(10).build();

        assert_eq!(mqtt.outgoing_pub.len(), 11);
        assert_eq!(mqtt.outgoing_pub_notice.len(), 11);
        assert_eq!(mqtt.outgoing_rel_notice.len(), 11);
        assert_eq!(mqtt.outgoing_pub_ack.len(), 11);
        assert_eq!(mqtt.outgoing_rel.len(), 11);
    }

    #[test]
    fn clean_pending_capacity_counts_publish_rel_and_tracked_requests() {
        let mut mqtt = MqttState::builder(10).build();
        mqtt.outgoing_pub[1] = Some(build_outgoing_publish(QoS::AtLeastOnce));
        mqtt.outgoing_pub[2] = Some(build_outgoing_publish(QoS::ExactlyOnce));
        mqtt.outgoing_rel.insert(3);
        mqtt.outgoing_rel.insert(4);

        let (sub_notice, _) = SubscribeNoticeTx::new();
        mqtt.tracked_subscribe
            .insert(5, (Subscribe::new("a/b", QoS::AtMostOnce), sub_notice));

        let (unsub_notice, _) = UnsubscribeNoticeTx::new();
        mqtt.tracked_unsubscribe
            .insert(6, (Unsubscribe::new("a/b"), unsub_notice));

        assert_eq!(mqtt.clean_pending_capacity(), 6);
    }

    #[test]
    fn tracked_request_len_helpers_report_counts() {
        let mut mqtt = MqttState::builder(10).build();
        let (sub_notice, _) = SubscribeNoticeTx::new();
        mqtt.tracked_subscribe
            .insert(5, (Subscribe::new("a/b", QoS::AtMostOnce), sub_notice));
        let (unsub_notice, _) = UnsubscribeNoticeTx::new();
        mqtt.tracked_unsubscribe
            .insert(6, (Unsubscribe::new("a/b"), unsub_notice));

        assert_eq!(mqtt.tracked_subscribe_len(), 1);
        assert_eq!(mqtt.tracked_unsubscribe_len(), 1);
        assert!(!mqtt.tracked_requests_is_empty());

        mqtt.drain_tracked_requests_as_failed(NoticeFailureReason::SessionReset);
        assert!(mqtt.tracked_requests_is_empty());
    }

    #[test]
    fn drain_tracked_requests_as_failed_reports_session_reset_and_returns_count() {
        let mut mqtt = MqttState::builder(10).build();
        let (sub_notice_tx, sub_notice) = SubscribeNoticeTx::new();
        mqtt.tracked_subscribe
            .insert(5, (Subscribe::new("a/b", QoS::AtMostOnce), sub_notice_tx));
        let (unsub_notice_tx, unsub_notice) = UnsubscribeNoticeTx::new();
        mqtt.tracked_unsubscribe
            .insert(6, (Unsubscribe::new("a/b"), unsub_notice_tx));

        let drained = mqtt.drain_tracked_requests_as_failed(NoticeFailureReason::SessionReset);

        assert_eq!(drained, 2);
        assert!(mqtt.tracked_requests_is_empty());
        assert_eq!(
            sub_notice.wait().unwrap_err(),
            SubscribeNoticeError::SessionReset
        );
        assert_eq!(
            unsub_notice.wait().unwrap_err(),
            UnsubscribeNoticeError::SessionReset
        );
    }

    #[test]
    fn drain_tracked_requests_as_failed_is_noop_when_empty() {
        let mut mqtt = MqttState::builder(10).build();
        let drained = mqtt.drain_tracked_requests_as_failed(NoticeFailureReason::SessionReset);

        assert_eq!(drained, 0);
        assert!(mqtt.tracked_requests_is_empty());
    }

    #[test]
    fn tracked_puback_returns_ack_and_preserves_incoming_event() {
        let mut mqtt = build_mqttstate();
        let notice = queue_publish_with_notice(&mut mqtt, build_outgoing_publish(QoS::AtLeastOnce));
        mqtt.events.clear();

        let puback = PubAck::new(1);
        assert!(
            mqtt.handle_incoming_packet(Incoming::PubAck(puback.clone()))
                .unwrap()
                .is_none()
        );

        assert_eq!(notice.wait(), Ok(PublishResult::Qos1(puback.clone())));
        assert_eq!(
            mqtt.events.pop_front(),
            Some(Event::Incoming(Packet::PubAck(puback)))
        );
    }

    #[test]
    fn tracked_suback_returns_ack_and_preserves_incoming_event() {
        let mut mqtt = build_mqttstate();
        let (tx, notice) = SubscribeNoticeTx::new();
        mqtt.outgoing_subscribe(Subscribe::new("a/b", QoS::AtMostOnce), Some(tx))
            .unwrap();
        mqtt.events.clear();

        let suback = SubAck::new(1, vec![SubscribeReasonCode::Failure]);
        assert!(
            mqtt.handle_incoming_packet(Incoming::SubAck(suback.clone()))
                .unwrap()
                .is_none()
        );

        assert_eq!(notice.wait(), Ok(suback.clone()));
        assert_eq!(
            mqtt.events.pop_front(),
            Some(Event::Incoming(Packet::SubAck(suback)))
        );
    }

    #[test]
    fn tracked_unsuback_returns_ack_and_preserves_incoming_event() {
        let mut mqtt = build_mqttstate();
        let (tx, notice) = UnsubscribeNoticeTx::new();
        mqtt.outgoing_unsubscribe(Unsubscribe::new("a/b"), Some(tx))
            .unwrap();
        mqtt.events.clear();

        let unsuback = UnsubAck::new(1);
        assert!(
            mqtt.handle_incoming_packet(Incoming::UnsubAck(unsuback.clone()))
                .unwrap()
                .is_none()
        );

        assert_eq!(notice.wait(), Ok(unsuback.clone()));
        assert_eq!(
            mqtt.events.pop_front(),
            Some(Event::Incoming(Packet::UnsubAck(unsuback)))
        );
    }

    #[test]
    fn outgoing_publish_grows_tracking_capacity_on_demand() {
        let mut mqtt = build_mqttstate();
        mqtt.last_pkid = 32;

        mqtt.outgoing_publish(build_outgoing_publish(QoS::AtLeastOnce))
            .unwrap();

        assert_eq!(mqtt.outgoing_pub.len(), 34);
        assert_eq!(mqtt.outgoing_pub_notice.len(), 34);
        assert_eq!(mqtt.outgoing_rel_notice.len(), 34);
        assert_eq!(mqtt.outgoing_pub_ack.len(), 34);
        assert_eq!(mqtt.outgoing_rel.len(), 34);
        assert!(mqtt.outgoing_pub[33].is_some());
    }

    #[test]
    fn incoming_puback_shrinks_tracking_when_state_becomes_empty() {
        let mut mqtt = build_mqttstate();
        mqtt.last_pkid = 32;
        mqtt.last_puback = 32;

        mqtt.outgoing_publish(build_outgoing_publish(QoS::AtLeastOnce))
            .unwrap();
        assert_eq!(mqtt.outgoing_pub.len(), 34);

        mqtt.handle_incoming_puback(&PubAck::new(33)).unwrap();

        assert_eq!(mqtt.outgoing_pub.len(), 33);
        assert_eq!(mqtt.outgoing_pub_notice.len(), 33);
        assert_eq!(mqtt.outgoing_rel_notice.len(), 33);
        assert_eq!(mqtt.outgoing_pub_ack.len(), 33);
        assert_eq!(mqtt.outgoing_rel.len(), 33);
        assert_eq!(mqtt.last_pkid, 0);
        assert_eq!(mqtt.last_puback, 0);
    }

    #[test]
    fn incoming_puback_does_not_shrink_tracking_when_state_is_non_empty() {
        let mut mqtt = build_mqttstate();
        mqtt.last_pkid = 32;
        mqtt.last_puback = 32;

        mqtt.outgoing_publish(build_outgoing_publish(QoS::AtLeastOnce))
            .unwrap();
        mqtt.outgoing_publish(build_outgoing_publish(QoS::AtLeastOnce))
            .unwrap();
        assert_eq!(mqtt.outgoing_pub.len(), 35);

        mqtt.handle_incoming_puback(&PubAck::new(33)).unwrap();

        assert_eq!(mqtt.outgoing_pub.len(), 35);
        assert_eq!(mqtt.inflight, 1);
    }

    #[test]
    fn clean_preserves_packet_id_frontier_when_pending_state_is_exported() {
        let mut mqtt = build_mqttstate();
        mqtt.outgoing_publish(build_outgoing_publish(QoS::AtLeastOnce))
            .unwrap();
        mqtt.outgoing_publish(build_outgoing_publish(QoS::AtLeastOnce))
            .unwrap();
        assert_eq!(mqtt.last_pkid, 2);

        let pending = mqtt.clean();
        assert_eq!(pending.len(), 2);
        assert_eq!(mqtt.last_pkid, 2);
        assert_eq!(mqtt.last_puback, 0);

        for request in pending {
            let packet = mqtt.handle_outgoing_packet(request).unwrap().unwrap();
            match packet {
                Packet::Publish(publish) => assert!(matches!(publish.pkid, 1 | 2)),
                packet => panic!("Unexpected replay packet: {packet:?}"),
            }
        }

        let packet = mqtt
            .handle_outgoing_packet(Request::Publish(build_outgoing_publish(QoS::AtLeastOnce)))
            .unwrap()
            .unwrap();
        match packet {
            Packet::Publish(publish) => assert_eq!(publish.pkid, 3),
            packet => panic!("Unexpected fresh packet after replay: {packet:?}"),
        }

        assert!(mqtt.collision.is_none());
    }

    #[test]
    fn clone_preserves_current_tracking_lengths_after_shrink() {
        let mut mqtt = build_mqttstate();
        mqtt.last_pkid = 32;
        mqtt.last_puback = 32;

        mqtt.outgoing_publish(build_outgoing_publish(QoS::AtLeastOnce))
            .unwrap();
        mqtt.handle_incoming_puback(&PubAck::new(33)).unwrap();

        let cloned = mqtt.clone();
        assert_eq!(cloned.outgoing_pub.len(), 33);
        assert_eq!(cloned.outgoing_pub_notice.len(), 33);
        assert_eq!(cloned.outgoing_rel_notice.len(), 33);
        assert_eq!(cloned.outgoing_pub_ack.len(), 33);
        assert_eq!(cloned.outgoing_rel.len(), 33);
    }

    #[test]
    fn next_pkid_increments_as_expected() {
        let mut mqtt = build_mqttstate();

        for i in 1..=100 {
            let pkid = mqtt.next_pkid();

            // loops between 0-99. % 100 == 0 implies border
            let expected = i % 100;
            if expected == 0 {
                break;
            }

            assert_eq!(expected, pkid);
        }
    }

    #[test]
    fn can_send_publish_searches_free_pkid_after_control_ids_pass_inflight_limit() {
        let mut mqtt = MqttState::builder(4).build();
        let mut active_publish = build_outgoing_publish(QoS::AtLeastOnce);
        active_publish.pkid = 1;
        mqtt.outgoing_pub[1] = Some(active_publish);
        mqtt.inflight = 1;
        mqtt.last_pkid = 5;

        assert!(mqtt.can_send_publish(&build_outgoing_publish(QoS::AtLeastOnce)));

        let packet = mqtt
            .outgoing_publish(build_outgoing_publish(QoS::AtLeastOnce))
            .unwrap()
            .unwrap();
        match packet {
            Packet::Publish(publish) => assert_eq!(publish.pkid, 2),
            packet => panic!("Unexpected packet: {packet:?}"),
        }
    }

    #[test]
    fn outgoing_publish_should_set_pkid_and_add_publish_to_queue() {
        let mut mqtt = build_mqttstate();

        // QoS0 Publish
        let publish = build_outgoing_publish(QoS::AtMostOnce);

        // QoS 0 publish shouldn't be saved in queue
        mqtt.outgoing_publish(publish).unwrap();
        assert_eq!(mqtt.last_pkid, 0);
        assert_eq!(mqtt.inflight, 0);

        // QoS1 Publish
        let publish = build_outgoing_publish(QoS::AtLeastOnce);

        // Packet id should be set and publish should be saved in queue
        mqtt.outgoing_publish(publish.clone()).unwrap();
        assert_eq!(mqtt.last_pkid, 1);
        assert_eq!(mqtt.inflight, 1);

        // Packet id should be incremented and publish should be saved in queue
        mqtt.outgoing_publish(publish).unwrap();
        assert_eq!(mqtt.last_pkid, 2);
        assert_eq!(mqtt.inflight, 2);

        // QoS1 Publish
        let publish = build_outgoing_publish(QoS::ExactlyOnce);

        // Packet id should be set and publish should be saved in queue
        mqtt.outgoing_publish(publish.clone()).unwrap();
        assert_eq!(mqtt.last_pkid, 3);
        assert_eq!(mqtt.inflight, 3);

        // Packet id should be incremented and publish should be saved in queue
        mqtt.outgoing_publish(publish).unwrap();
        assert_eq!(mqtt.last_pkid, 4);
        assert_eq!(mqtt.inflight, 4);
    }

    #[test]
    fn incoming_publish_should_be_added_to_queue_correctly() {
        let mut mqtt = build_mqttstate();

        // QoS0, 1, 2 Publishes
        let publish1 = build_incoming_publish(QoS::AtMostOnce, 1);
        let publish2 = build_incoming_publish(QoS::AtLeastOnce, 2);
        let publish3 = build_incoming_publish(QoS::ExactlyOnce, 3);

        let _ = mqtt.handle_incoming_publish(&publish1);
        let _ = mqtt.handle_incoming_publish(&publish2);
        let _ = mqtt.handle_incoming_publish(&publish3);

        // only qos2 publish should be add to queue
        assert!(mqtt.incoming_pub.contains(3));
    }

    #[test]
    fn incoming_publish_should_be_acked() {
        let mut mqtt = build_mqttstate();

        // QoS0, 1, 2 Publishes
        let publish1 = build_incoming_publish(QoS::AtMostOnce, 1);
        let publish2 = build_incoming_publish(QoS::AtLeastOnce, 2);
        let publish3 = build_incoming_publish(QoS::ExactlyOnce, 3);

        assert!(mqtt.handle_incoming_publish(&publish1).is_none());

        let packet = mqtt.handle_incoming_publish(&publish2).unwrap();
        if let Packet::PubAck(puback) = packet {
            let pkid = puback.pkid;
            assert_eq!(pkid, 2);
        } else {
            panic!("missing puback");
        }

        let packet = mqtt.handle_incoming_publish(&publish3).unwrap();
        if let Packet::PubRec(pubrec) = packet {
            let pkid = pubrec.pkid;
            assert_eq!(pkid, 3);
        } else {
            panic!("missing PubRec");
        }
    }

    #[test]
    fn incoming_publish_should_not_be_acked_with_manual_acks() {
        let mut mqtt = build_mqttstate();
        mqtt.manual_acks = true;

        // QoS0, 1, 2 Publishes
        let publish1 = build_incoming_publish(QoS::AtMostOnce, 1);
        let publish2 = build_incoming_publish(QoS::AtLeastOnce, 2);
        let publish3 = build_incoming_publish(QoS::ExactlyOnce, 3);

        assert!(mqtt.handle_incoming_publish(&publish1).is_none());
        assert!(mqtt.handle_incoming_publish(&publish2).is_none());
        assert!(mqtt.handle_incoming_publish(&publish3).is_none());

        assert!(mqtt.incoming_pub.contains(3));

        assert!(mqtt.events.is_empty());
    }

    #[test]
    fn handle_incoming_packet_should_emit_incoming_before_derived_qos1_ack() {
        let mut mqtt = build_mqttstate();
        let publish = build_incoming_publish(QoS::AtLeastOnce, 42);

        mqtt.handle_incoming_packet(Incoming::Publish(publish.clone()))
            .unwrap();

        assert_eq!(mqtt.events.len(), 2);
        assert_eq!(mqtt.events[0], Event::Incoming(Incoming::Publish(publish)));
        assert_eq!(mqtt.events[1], Event::Outgoing(Outgoing::PubAck(42)));
    }

    #[test]
    fn handle_incoming_packet_should_emit_incoming_before_derived_qos2_ack() {
        let mut mqtt = build_mqttstate();
        let publish = build_incoming_publish(QoS::ExactlyOnce, 43);

        mqtt.handle_incoming_packet(Incoming::Publish(publish.clone()))
            .unwrap();

        assert_eq!(mqtt.events.len(), 2);
        assert_eq!(mqtt.events[0], Event::Incoming(Incoming::Publish(publish)));
        assert_eq!(mqtt.events[1], Event::Outgoing(Outgoing::PubRec(43)));
    }

    #[test]
    fn incoming_qos2_publish_should_send_rec_to_network_and_publish_to_user() {
        let mut mqtt = build_mqttstate();
        let publish = build_incoming_publish(QoS::ExactlyOnce, 1);

        let packet = mqtt.handle_incoming_publish(&publish).unwrap();
        match packet {
            Packet::PubRec(pubrec) => assert_eq!(pubrec.pkid, 1),
            _ => panic!("Invalid network request: {packet:?}"),
        }
    }

    #[test]
    fn incoming_puback_should_remove_correct_publish_from_queue() {
        let mut mqtt = build_mqttstate();

        let publish1 = build_outgoing_publish(QoS::AtLeastOnce);
        let publish2 = build_outgoing_publish(QoS::ExactlyOnce);

        mqtt.outgoing_publish(publish1).unwrap();
        mqtt.outgoing_publish(publish2).unwrap();
        assert_eq!(mqtt.inflight, 2);

        mqtt.handle_incoming_puback(&PubAck::new(1)).unwrap();
        assert_eq!(mqtt.inflight, 1);

        mqtt.handle_incoming_puback(&PubAck::new(2)).unwrap();
        assert_eq!(mqtt.inflight, 0);

        assert!(mqtt.outgoing_pub[1].is_none());
        assert!(mqtt.outgoing_pub[2].is_none());
    }

    #[test]
    fn incoming_puback_advances_last_puback_only_on_contiguous_boundary() {
        let mut mqtt = build_mqttstate();

        mqtt.outgoing_publish(build_outgoing_publish(QoS::AtLeastOnce))
            .unwrap();
        mqtt.outgoing_publish(build_outgoing_publish(QoS::AtLeastOnce))
            .unwrap();
        mqtt.outgoing_publish(build_outgoing_publish(QoS::AtLeastOnce))
            .unwrap();
        assert_eq!(mqtt.last_puback, 0);

        mqtt.handle_incoming_puback(&PubAck::new(2)).unwrap();
        assert_eq!(mqtt.last_puback, 0);

        mqtt.handle_incoming_puback(&PubAck::new(1)).unwrap();
        assert_eq!(mqtt.last_puback, 2);

        mqtt.handle_incoming_puback(&PubAck::new(3)).unwrap();
        assert_eq!(mqtt.last_puback, 3);
    }

    #[test]
    fn mixed_qos_completion_clears_outbound_drain_state() {
        let mut mqtt = build_mqttstate();

        mqtt.outgoing_publish(build_outgoing_publish(QoS::ExactlyOnce))
            .unwrap();
        mqtt.outgoing_publish(build_outgoing_publish(QoS::AtLeastOnce))
            .unwrap();
        mqtt.outgoing_publish(build_outgoing_publish(QoS::AtLeastOnce))
            .unwrap();
        mqtt.outgoing_publish(build_outgoing_publish(QoS::ExactlyOnce))
            .unwrap();

        mqtt.handle_incoming_pubrec(&PubRec::new(1)).unwrap();
        mqtt.handle_incoming_puback(&PubAck::new(2)).unwrap();
        mqtt.handle_incoming_puback(&PubAck::new(3)).unwrap();
        mqtt.handle_incoming_pubcomp(&PubComp::new(1)).unwrap();
        mqtt.handle_incoming_pubrec(&PubRec::new(4)).unwrap();
        mqtt.handle_incoming_pubcomp(&PubComp::new(4)).unwrap();

        assert_eq!(mqtt.inflight, 0);
        assert!(mqtt.outbound_requests_drained());
        assert!(mqtt.outgoing_pub_ack.ones().next().is_none());
        assert!(mqtt.outgoing_rel.ones().next().is_none());
    }

    #[test]
    fn incoming_puback_with_pkid_greater_than_max_inflight_should_be_handled_gracefully() {
        let mut mqtt = build_mqttstate();

        let got = mqtt.handle_incoming_puback(&PubAck::new(101)).unwrap_err();

        match got {
            StateError::Unsolicited(pkid) => assert_eq!(pkid, 101),
            e => panic!("Unexpected error: {e}"),
        }
    }

    #[test]
    fn incoming_puback_with_pkid_beyond_allocated_tracking_is_unsolicited() {
        let mut mqtt = build_mqttstate();

        let got = mqtt.handle_incoming_puback(&PubAck::new(50)).unwrap_err();

        match got {
            StateError::Unsolicited(pkid) => assert_eq!(pkid, 50),
            e => panic!("Unexpected error: {e}"),
        }
    }

    #[test]
    fn outgoing_publish_with_pkid_above_max_inflight_is_unsolicited_and_does_not_grow_tracking() {
        let mut mqtt = MqttState::builder(10).build();
        let mut publish = build_outgoing_publish(QoS::AtLeastOnce);
        publish.pkid = 50;

        let got = mqtt
            .handle_outgoing_packet(Request::Publish(publish))
            .unwrap_err();

        match got {
            StateError::Unsolicited(pkid) => assert_eq!(pkid, 50),
            e => panic!("Unexpected error: {e}"),
        }
        assert_eq!(mqtt.outgoing_pub.len(), 11);
        assert_eq!(mqtt.outgoing_pub_notice.len(), 11);
        assert_eq!(mqtt.outgoing_rel_notice.len(), 11);
        assert_eq!(mqtt.inflight, 0);
    }

    #[test]
    fn outgoing_pubrel_with_pkid_above_max_inflight_is_unsolicited_and_does_not_grow_tracking() {
        let mut mqtt = MqttState::builder(10).build();

        let got = mqtt
            .handle_outgoing_packet(Request::PubRel(PubRel::new(50)))
            .unwrap_err();

        match got {
            StateError::Unsolicited(pkid) => assert_eq!(pkid, 50),
            e => panic!("Unexpected error: {e}"),
        }
        assert_eq!(mqtt.outgoing_pub.len(), 11);
        assert_eq!(mqtt.outgoing_pub_notice.len(), 11);
        assert_eq!(mqtt.outgoing_rel_notice.len(), 11);
        assert_eq!(mqtt.inflight, 0);
    }

    #[test]
    fn clean_keeps_oldest_unacked_publish_first_after_out_of_order_puback() {
        let mut mqtt = build_mqttstate();

        mqtt.outgoing_publish(build_outgoing_publish(QoS::AtLeastOnce))
            .unwrap();
        mqtt.outgoing_publish(build_outgoing_publish(QoS::AtLeastOnce))
            .unwrap();
        mqtt.outgoing_publish(build_outgoing_publish(QoS::AtLeastOnce))
            .unwrap();

        mqtt.handle_incoming_puback(&PubAck::new(2)).unwrap();
        let requests = mqtt.clean();

        let pending_pkids: Vec<u16> = requests
            .iter()
            .map(|req| match req {
                Request::Publish(publish) => publish.pkid,
                req => panic!("Unexpected request while cleaning: {req:?}"),
            })
            .collect();

        assert_eq!(pending_pkids, vec![1, 3]);
    }

    #[test]
    fn incoming_pubrec_should_release_publish_from_queue_and_add_relid_to_rel_queue() {
        let mut mqtt = build_mqttstate();

        let publish1 = build_outgoing_publish(QoS::AtLeastOnce);
        let publish2 = build_outgoing_publish(QoS::ExactlyOnce);

        let _publish_out = mqtt.outgoing_publish(publish1);
        let _publish_out = mqtt.outgoing_publish(publish2);

        mqtt.handle_incoming_pubrec(&PubRec::new(2)).unwrap();
        assert_eq!(mqtt.inflight, 2);

        // check if the remaining element's pkid is 1
        let backup = mqtt.outgoing_pub[1].clone();
        assert_eq!(backup.unwrap().pkid, 1);

        // check if the qos2 element's release pkid is 2
        assert!(mqtt.outgoing_rel.contains(2));
    }

    #[test]
    fn incoming_pubrec_should_send_release_to_network_and_nothing_to_user() {
        let mut mqtt = build_mqttstate();

        let publish = build_outgoing_publish(QoS::ExactlyOnce);
        let packet = mqtt.outgoing_publish(publish).unwrap().unwrap();
        match packet {
            Packet::Publish(publish) => assert_eq!(publish.pkid, 1),
            packet => panic!("Invalid network request: {packet:?}"),
        }

        let packet = mqtt
            .handle_incoming_pubrec(&PubRec::new(1))
            .unwrap()
            .unwrap();
        match packet {
            Packet::PubRel(pubrel) => assert_eq!(pubrel.pkid, 1),
            packet => panic!("Invalid network request: {packet:?}"),
        }
    }

    #[test]
    fn incoming_pubrel_should_send_comp_to_network_and_nothing_to_user() {
        let mut mqtt = build_mqttstate();
        let publish = build_incoming_publish(QoS::ExactlyOnce, 1);

        let packet = mqtt.handle_incoming_publish(&publish).unwrap();
        match packet {
            Packet::PubRec(pubrec) => assert_eq!(pubrec.pkid, 1),
            packet => panic!("Invalid network request: {packet:?}"),
        }

        let packet = mqtt
            .handle_incoming_pubrel(&PubRel::new(1))
            .unwrap()
            .unwrap();
        match packet {
            Packet::PubComp(pubcomp) => assert_eq!(pubcomp.pkid, 1),
            packet => panic!("Invalid network request: {packet:?}"),
        }
    }

    #[test]
    fn incoming_pubcomp_should_release_correct_pkid_from_release_queue() {
        let mut mqtt = build_mqttstate();
        let publish = build_outgoing_publish(QoS::ExactlyOnce);

        mqtt.outgoing_publish(publish).unwrap();
        mqtt.handle_incoming_pubrec(&PubRec::new(1)).unwrap();

        mqtt.handle_incoming_pubcomp(&PubComp::new(1)).unwrap();
        assert_eq!(mqtt.inflight, 0);
    }

    #[test]
    fn incoming_pubcomp_collision_replay_should_restore_qos2_tracking() {
        let mut mqtt = build_mqttstate();
        let publish = build_outgoing_publish(QoS::ExactlyOnce);
        mqtt.outgoing_publish(publish).unwrap();

        let mut collided = build_outgoing_publish(QoS::ExactlyOnce);
        collided.pkid = 1;
        assert!(mqtt.outgoing_publish(collided).unwrap().is_none());
        assert!(mqtt.collision.is_some());

        mqtt.handle_incoming_pubrec(&PubRec::new(1)).unwrap();
        let packet = mqtt
            .handle_incoming_pubcomp(&PubComp::new(1))
            .unwrap()
            .unwrap();
        match packet {
            Packet::Publish(publish) => assert_eq!(publish.pkid, 1),
            packet => panic!("Invalid network request: {packet:?}"),
        }

        assert!(mqtt.outgoing_pub[1].is_some());
        assert_eq!(mqtt.inflight, 1);

        let packet = mqtt
            .handle_incoming_pubrec(&PubRec::new(1))
            .unwrap()
            .unwrap();
        match packet {
            Packet::PubRel(pubrel) => assert_eq!(pubrel.pkid, 1),
            packet => panic!("Invalid network request: {packet:?}"),
        }
    }

    #[test]
    fn outgoing_ping_handle_should_throw_errors_for_no_pingresp() {
        let mut mqtt = build_mqttstate();
        mqtt.outgoing_ping().unwrap();

        // network activity other than pingresp
        let publish = build_outgoing_publish(QoS::AtLeastOnce);
        mqtt.handle_outgoing_packet(Request::Publish(publish))
            .unwrap();
        mqtt.handle_incoming_packet(Incoming::PubAck(PubAck::new(1)))
            .unwrap();

        // should throw error because we didn't get pingresp for previous ping
        match mqtt.outgoing_ping() {
            Ok(_) => panic!("Should throw pingresp await error"),
            Err(StateError::AwaitPingResp) => (),
            Err(e) => panic!("Should throw pingresp await error. Error = {e:?}"),
        }
    }

    #[test]
    fn outgoing_ping_handle_should_succeed_if_pingresp_is_received() {
        let mut mqtt = build_mqttstate();

        // should ping
        mqtt.outgoing_ping().unwrap();
        mqtt.handle_incoming_packet(Incoming::PingResp).unwrap();

        // should ping
        mqtt.outgoing_ping().unwrap();
    }

    #[test]
    fn clean_is_calculating_pending_correctly() {
        fn build_outgoing_pub() -> Vec<Option<Publish>> {
            vec![
                None,
                Some(Publish {
                    dup: false,
                    qos: QoS::AtMostOnce,
                    retain: false,
                    topic: Bytes::from_static(b"test"),
                    pkid: 1,
                    payload: "".into(),
                }),
                Some(Publish {
                    dup: false,
                    qos: QoS::AtMostOnce,
                    retain: false,
                    topic: Bytes::from_static(b"test"),
                    pkid: 2,
                    payload: "".into(),
                }),
                Some(Publish {
                    dup: false,
                    qos: QoS::AtMostOnce,
                    retain: false,
                    topic: Bytes::from_static(b"test"),
                    pkid: 3,
                    payload: "".into(),
                }),
                None,
                None,
                Some(Publish {
                    dup: false,
                    qos: QoS::AtMostOnce,
                    retain: false,
                    topic: Bytes::from_static(b"test"),
                    pkid: 6,
                    payload: "".into(),
                }),
            ]
        }

        let mut mqtt = build_mqttstate();
        mqtt.outgoing_pub = build_outgoing_pub();
        mqtt.last_puback = 3;
        let requests = mqtt.clean();
        let res = vec![6, 1, 2, 3];
        for (req, idx) in requests.iter().zip(res) {
            if let Request::Publish(publish) = req {
                assert_eq!(publish.pkid, idx);
            } else {
                unreachable!()
            }
        }

        mqtt.outgoing_pub = build_outgoing_pub();
        mqtt.last_puback = 0;
        let requests = mqtt.clean();
        let res = vec![1, 2, 3, 6];
        for (req, idx) in requests.iter().zip(res) {
            if let Request::Publish(publish) = req {
                assert_eq!(publish.pkid, idx);
            } else {
                unreachable!()
            }
        }

        mqtt.outgoing_pub = build_outgoing_pub();
        mqtt.last_puback = 6;
        let requests = mqtt.clean();
        let res = vec![1, 2, 3, 6];
        for (req, idx) in requests.iter().zip(res) {
            if let Request::Publish(publish) = req {
                assert_eq!(publish.pkid, idx);
            } else {
                unreachable!()
            }
        }
    }
}