_ => unreachable!(),

        }

    }

    fn performed_get(&mut self, _port: EvalPortId) -> Option<ValueGroup> {

        match self.stmt.take() {

            ExecStmt::None => return None,

            ExecStmt::PerformedGet(value) => return Some(value),

            _ => unreachable!(),

        }

    }

    fn fires(&mut self, _port: EvalPortId) -> Option<Value> {

        todo!("remove fires")

    }

    fn performed_fork(&mut self) -> Option<bool> {

        todo!("remove fork")

    }

    fn created_channel(&mut self) -> Option<(Value, Value)> {

        match self.stmt.take() {

            ExecStmt::None => return None,

            ExecStmt::CreatedChannel(ports) => return Some(ports),

            _ => unreachable!(),

        }

    }

}

#[derive(Debug, Copy, Clone, PartialEq, Eq)]

pub(crate) enum Mode {

    NonSync, // not in sync mode

    Sync, // in sync mode, can interact with other components

    SyncFail, // something went wrong during sync mode (deadlocked, error, whatever)

    SyncEnd, // awaiting a solution, i.e. encountered the end of the sync block

    BlockedGet,

    BlockedPut,

    Exit,

}

impl Mode {

    fn can_run(&self) -> bool {

        match self {

            Mode::NonSync | Mode::Sync =>

                return true,

            Mode::SyncFail | Mode::SyncEnd | Mode::BlockedGet | Mode::BlockedPut | Mode::Exit =>

                return false,

        }

    }

}

pub(crate) struct CompPDL {

    pub mode: Mode,

    pub mode_port: PortId, // when blocked on a port

    pub mode_value: ValueGroup, // when blocked on a put

    pub prompt: Prompt,

    pub control: ControlLayer,

    pub consensus: Consensus,

    pub sync_counter: u32,

    pub exec_ctx: ExecCtx,

    // TODO: Temporary field, simulates future plans of having one storage place

    //  reserved per port.

    // Should be same length as the number of ports. Corresponding indices imply

    // message is intended for that port.

    pub inbox_main: Vec<Option<DataMessage>>,

    pub inbox_backup: Vec<DataMessage>,

}

impl CompPDL {

    pub(crate) fn new(initial_state: Prompt, num_ports: usize) -> Self {

        let mut inbox_main = Vec::new();

        inbox_main.reserve(num_ports);

        for _ in 0..num_ports {

            inbox_main.push(None);

        }

        return Self{

            mode: Mode::NonSync,

            mode_port: PortId::new_invalid(),

            mode_value: ValueGroup::default(),

            prompt: initial_state,

            control: ControlLayer::default(),

            consensus: Consensus::new(),

            sync_counter: 0,

            exec_ctx: ExecCtx{

                stmt: ExecStmt::None,

            },

            inbox_main,

            inbox_backup: Vec::new(),

        }

    }

    pub(crate) fn handle_message(&mut self, sched_ctx: &mut SchedulerCtx, comp_ctx: &mut CompCtx, message: Message) {

        sched_ctx.log(&format!("handling message: {:?}", message));

        if let Some(new_target) = self.control.should_reroute(&message) {

            let mut target = sched_ctx.runtime.get_component_public(new_target);

            let _should_remove = target.decrement_users();

            debug_assert!(!_should_remove);

            return;

        }

        match message {

            Message::Data(message) => {

                self.handle_incoming_data_message(sched_ctx, comp_ctx, message);

            },

            Message::Control(message) => {

                self.handle_incoming_control_message(sched_ctx, comp_ctx, message);

            },

            Message::Sync(message) => {

                self.handle_incoming_sync_message(sched_ctx, comp_ctx, message);

            }

        }

    }

    // -------------------------------------------------------------------------

    // Running component and handling changes in global component state

    // -------------------------------------------------------------------------

    pub(crate) fn run(&mut self, sched_ctx: &mut SchedulerCtx, comp_ctx: &mut CompCtx) -> Result<CompScheduling, EvalError> {

        use EvalContinuation as EC;

        let can_run = self.mode.can_run();

        sched_ctx.log(&format!("Running component (mode: {:?}, can run: {})", self.mode, can_run));

        if !can_run {

            return Ok(CompScheduling::Sleep);

        }

        let run_result = self.execute_prompt(&sched_ctx)?;

        match run_result {

            EC::Stepping => unreachable!(), // execute_prompt runs until this is no longer returned

            EC::BranchInconsistent | EC::NewFork | EC::BlockFires(_) => todo!("remove these"),

            // Results that can be returned in sync mode

            EC::SyncBlockEnd => {

                debug_assert_eq!(self.mode, Mode::Sync);

                self.handle_sync_end(sched_ctx, comp_ctx);

                return Ok(CompScheduling::Immediate);

            },

            EC::BlockGet(port_id) => {

                debug_assert_eq!(self.mode, Mode::Sync);

                debug_assert!(self.exec_ctx.stmt.is_none());

                let port_id = port_id_from_eval(port_id);

                let port_index = comp_ctx.get_port_index(port_id).unwrap();

                if let Some(message) = &self.inbox_main[port_index] {

                    // Check if we can actually receive the message

                    if self.consensus.try_receive_data_message(sched_ctx, comp_ctx, message) {

                        // Message was received. Make sure any blocked peers and

                        // pending messages are handled.

                        let message = self.inbox_main[port_index].take().unwrap();

                        self.exec_ctx.stmt = ExecStmt::PerformedGet(message.content);

                        return Ok(CompScheduling::Immediate);

                    } else {

                        self.mode = Mode::SyncFail;

                        return Ok(CompScheduling::Sleep);

                    }

                } else {

                    // We need to wait

                    self.mode = Mode::BlockedGet;

                    self.mode_port = port_id;

                    return Ok(CompScheduling::Sleep);

                }

            },

            EC::Put(port_id, value) => {

                debug_assert_eq!(self.mode, Mode::Sync);

                let port_id = port_id_from_eval(port_id);

                let port_info = comp_ctx.get_port(port_id);

                if port_info.state == PortState::Blocked {

                    todo!("handle blocked port");

                }

                self.send_data_message_and_wake_up(sched_ctx, comp_ctx, port_id, value);

                self.exec_ctx.stmt = ExecStmt::PerformedPut;

                return Ok(CompScheduling::Immediate);

            },

            // Results that can be returned outside of sync mode

            EC::ComponentTerminated => {

                self.handle_component_exit(sched_ctx, comp_ctx);

                return Ok(CompScheduling::Exit);

            },

            EC::SyncBlockStart => {

                debug_assert_eq!(self.mode, Mode::NonSync);

                self.handle_sync_start(sched_ctx, comp_ctx);

                return Ok(CompScheduling::Immediate);

            },

            EC::NewComponent(definition_id, monomorph_idx, arguments) => {

                debug_assert_eq!(self.mode, Mode::NonSync);

                let mut ports = Vec::new(); // TODO: Optimize

                let protocol = &sched_ctx.runtime.protocol;

                find_ports_in_value_group(&arguments, &mut ports);

                let prompt = Prompt::new(

        self.consensus.notify_sync_end(sched_ctx, comp_ctx);

        debug_assert_eq!(self.mode, Mode::Sync);

        self.mode = Mode::SyncEnd;

    }

    fn handle_component_exit(&mut self, sched_ctx: &SchedulerCtx, comp_ctx: &mut CompCtx) {

        debug_assert_eq!(self.mode, Mode::NonSync); // not a perfect assert, but just to remind myself: cannot exit while in sync

        // Note: for now we have that the scheduler handles exiting. I don't

        // know if that is a good idea, we'll see

        self.mode = Mode::Exit;

    }

    // -------------------------------------------------------------------------

    // Handling messages

    // -------------------------------------------------------------------------

    fn send_data_message_and_wake_up(&mut self, sched_ctx: &SchedulerCtx, comp_ctx: &CompCtx, source_port_id: PortId, value: ValueGroup) {

        let port_info = comp_ctx.get_port(source_port_id);

        let peer_info = comp_ctx.get_peer(port_info.peer_comp_id);

        let annotated_message = self.consensus.annotate_data_message(comp_ctx, port_info, value);

        peer_info.handle.send_message(sched_ctx, Message::Data(annotated_message), true);

    }

    /// Handles a message that came in through the public inbox. This function

    /// will handle putting it in the correct place, and potentially blocking

    /// the port in case too many messages are being received.

    fn handle_incoming_data_message(&mut self, sched_ctx: &SchedulerCtx, comp_ctx: &mut CompCtx, message: DataMessage) {

        // Check if we can insert it directly into the storage associated with

        // the port

        let target_port_id = message.data_header.target_port;

        let port_index = comp_ctx.get_port_index(target_port_id).unwrap();

        if self.inbox_main[port_index].is_none() {

            self.inbox_main[port_index] = Some(message);

            // After direct insertion, check if this component's execution is 

            // blocked on receiving a message on that port

            debug_assert_ne!(comp_ctx.ports[port_index].state, PortState::Blocked); // because we could insert directly

            if self.mode == Mode::BlockedGet && self.mode_port == target_port_id {

                // We were indeed blocked

                self.mode = Mode::Sync;

                self.mode_port = PortId::new_invalid();

            }

            return;

        }

        // The direct inbox is full, so the port will become (or was already) blocked

        let port_info = &mut comp_ctx.ports[port_index];

        debug_assert!(port_info.state == PortState::Open || port_info.state == PortState::Blocked);

        let _peer_comp_id = port_info.peer_comp_id;

        if port_info.state == PortState::Open {

            let (target_comp_id, block_message) =

                self.control.set_port_and_peer_blocked(target_port_id, comp_ctx);

            debug_assert_eq!(_peer_comp_id, target_comp_id);

            let peer = comp_ctx.get_peer(target_comp_id);

            peer.handle.send_message(sched_ctx, Message::Control(block_message), true);

        }

        // But we still need to remember the message, so:

        self.inbox_backup.push(message);

    }

    /// Handles when a message has been handed off from the inbox to the PDL

    /// code. We check to see if there are more messages waiting and, if not,

    /// then we handle the case where the port might have been blocked

    /// previously.

    fn handle_received_data_message(&mut self, sched_ctx: &SchedulerCtx, comp_ctx: &mut CompCtx, port_id: PortId) {

        let port_index = comp_ctx.get_port_index(port_id).unwrap();

        debug_assert!(self.inbox_main[port_index].is_none()); // because we just received it

        // Check for any more messages

        for message_index in 0..self.inbox_backup.len() {

            let message = &self.inbox_backup[message_index];

            if message.data_header.target_port == port_id {

                // One more message for this port

                let message = self.inbox_backup.remove(message_index);

                debug_assert_eq!(comp_ctx.get_port(port_id).state, PortState::Blocked); // since we had >1 message on the port

                self.inbox_main[port_index] = Some(message);

                return;

            }

        }

        // Did not have any more messages. So if we were blocked, then we need

        // to send the "unblock" message.

        let port_info = &comp_ctx.ports[port_index];

        if port_info.state == PortState::Blocked {

            let (peer_comp_id, message) = self.control.set_port_and_peer_unblocked(port_id, comp_ctx);

            let peer_info = comp_ctx.get_peer(peer_comp_id);

            peer_info.handle.send_message(sched_ctx, Message::Control(message), true);

        }

    }

    fn handle_incoming_control_message(&mut self, sched_ctx: &SchedulerCtx, comp_ctx: &mut CompCtx, message: ControlMessage) {

        match message.content {

            ControlMessageContent::Ack => {

                let mut to_ack = message.id;

                loop {

                    let action = self.control.handle_ack(to_ack, sched_ctx, comp_ctx);

                    match action {

                        AckAction::SendMessageAndAck(target_comp, message, new_to_ack) => {

                            // FIX @NoDirectHandle

                            handle.send_message(sched_ctx, Message::Control(message), true);

                            to_ack = new_to_ack;

                        },

                        AckAction::ScheduleComponent(to_schedule) => {

                            // FIX @NoDirectHandle

                            wake_up_if_sleeping(sched_ctx, to_schedule, &handle);

                            break;

                        },

                        AckAction::None => {

                            break;

                        }

                    }

                }

            },

            ControlMessageContent::BlockPort(port_id) => {

                // On of our messages was accepted, but the port should be

                // blocked.

                let port_info = comp_ctx.get_port_mut(port_id);

                debug_assert_eq!(port_info.kind, PortKind::Putter);

                if port_info.state != PortState::Closed {

                    debug_assert_ne!(port_info.state, PortState::Blocked); // implies unnecessary messages

                    port_info.state = PortState::Blocked;

                }

            },

            ControlMessageContent::ClosePort(port_id) => {

                // Request to close the port. We immediately comply and remove

                // the component handle as well

                let port_index = comp_ctx.get_port_index(port_id).unwrap();

                let port_info = &mut comp_ctx.ports[port_index];

                let peer_comp_id = port_info.peer_comp_id;

                port_info.state = PortState::Closed;

                let peer_index = comp_ctx.get_peer_index(peer_comp_id).unwrap();

                let peer_info = &mut comp_ctx.peers[peer_index];

                peer_info.num_associated_ports -= 1;

                if peer_info.num_associated_ports == 0 {

                    // TODO: @Refactor clean up all these uses of "num_associated_ports"

                    let should_remove = peer_info.handle.decrement_users();

                    if should_remove {

                        let comp_key = unsafe{ peer_info.id.upgrade() };

                        sched_ctx.runtime.destroy_component(comp_key);

                    }

                    comp_ctx.peers.remove(peer_index);

                }

            }

            ControlMessageContent::UnblockPort(port_id) => {

                // We were previously blocked (or already closed)

                let port_info = comp_ctx.get_port(port_id);

                debug_assert_eq!(port_info.kind, PortKind::Putter);

                debug_assert!(port_info.state == PortState::Blocked || port_info.state == PortState::Closed);

                if port_info.state == PortState::Blocked {

                    self.unblock_local_port(sched_ctx, comp_ctx, port_id);

                }

            },

            ControlMessageContent::PortPeerChangedBlock(port_id) => {

                // The peer of our port has just changed. So we are asked to

                // temporarily block the port (while our original recipient is

                // potentially rerouting some of the in-flight messages) and

                // Ack. Then we wait for the `unblock` call.

                debug_assert_eq!(message.target_port_id, Some(port_id));

                let port_info = comp_ctx.get_port_mut(port_id);

                debug_assert!(port_info.state == PortState::Open || port_info.state == PortState::Blocked);

                if port_info.state == PortState::Open {

                    port_info.state = PortState::Blocked;

                }

            },

            ControlMessageContent::PortPeerChangedUnblock(port_id, new_comp_id) => {

                debug_assert_eq!(message.target_port_id, Some(port_id));

                let port_info = comp_ctx.get_port_mut(port_id);

                debug_assert!(port_info.state == PortState::Blocked);

                port_info.peer_comp_id = new_comp_id;

                self.unblock_local_port(sched_ctx, comp_ctx, port_id);

            }

        }

    }

    fn handle_incoming_sync_message(&mut self, sched_ctx: &SchedulerCtx, comp_ctx: &mut CompCtx, message: SyncMessage) -> Option<CompScheduling> {

        let decision = self.consensus.receive_sync_message(sched_ctx, comp_ctx, message);

        let is_success = match decision {

            SyncRoundDecision::None => {

                // No decision yet

                return None;

            },

            SyncRoundDecision::Solution => true,

            SyncRoundDecision::Failure => false,

        };

        // If here then we've reached a conclusion

        debug_assert_eq!(self.mode, Mode::SyncEnd);

        self.mode = Mode::NonSync;

        if is_success {

            // We can simply continue executing. So we do nothing extra!

        } else {

            todo!("handle this better, show some kind of error");

            self.handle_component_exit(sched_ctx, comp_ctx);

            return Some(CompScheduling::Exit);

        }

        return None;

    }

    // -------------------------------------------------------------------------

    // Handling ports

    // -------------------------------------------------------------------------

    /// Marks the local port as being unblocked. If the execution was blocked on

    /// sending a message over this port, then execution will continue and the

    /// message will be sent.

    fn unblock_local_port(&mut self, sched_ctx: &SchedulerCtx, comp_ctx: &mut CompCtx, port_id: PortId) {

        let port_info = comp_ctx.get_port_mut(port_id);

        debug_assert_eq!(port_info.state, PortState::Blocked);

        port_info.state = PortState::Open;

        if self.mode == Mode::BlockedPut && port_id == self.mode_port {

            // We were blocked on the port that just became unblocked, so

            // send the message.

            debug_assert_eq!(port_info.kind, PortKind::Putter);

            let mut replacement = ValueGroup::default();

            std::mem::swap(&mut replacement, &mut self.mode_value);

            self.send_data_message_and_wake_up(sched_ctx, comp_ctx, port_id, replacement);

            self.mode = Mode::Sync;

            self.mode_port = PortId::new_invalid();

        }

    }

    fn create_component_and_transfer_ports(&mut self, sched_ctx: &SchedulerCtx, creator_ctx: &mut CompCtx, prompt: Prompt, ports: &[PortId]) {

        let component = CompPDL::new(prompt, ports.len());

        let (comp_key, component) = sched_ctx.runtime.create_pdl_component(component, true);

        let created_ctx = &mut component.ctx;

        let mut has_reroute_entry = false;

        let schedule_entry_id = self.control.add_schedule_entry(created_ctx.id);

        for port_id in ports.iter().copied() {

            // Create temporary reroute entry if the peer is another component

            let port_info = creator_ctx.get_port(port_id);

            debug_assert_ne!(port_info.state, PortState::Blocked);

            if port_info.peer_comp_id == creator_ctx.id {

                // We own the peer port. So retrieve it and modify the peer directly

                let peer_port_id = port_info.peer_id;

                let port_info = creator_ctx.get_port_mut(peer_port_id);

                port_info.peer_comp_id = created_ctx.id;

                Self::add_peer_associated_port_to_component(sched_ctx, creator_ctx, created_ctx.id);

            } else {

                // We don't own the peer port, so send the appropriate messages

                // to the peer component and notify the control layer

                has_reroute_entry = true;

                let message = self.control.add_reroute_entry(

                    creator_ctx.id, port_info.peer_id, port_info.peer_comp_id,

                    port_info.self_id, created_ctx.id, schedule_entry_id

                );

                let peer_info = creator_ctx.get_peer(port_info.peer_comp_id);

                peer_info.handle.send_message(sched_ctx, message, true);

            }

            // Take out any potential messages for the peer

            let creator_port_index = creator_ctx.get_port_index(port_id).unwrap();

            let port_main_message = self.inbox_main[creator_port_index].take();

use crate::runtime2::component::*;

#[derive(Debug, PartialEq, Eq, Clone, Copy)]

pub(crate) struct ControlId(u32);

impl ControlId {

    /// Like other invalid IDs, this one doesn't care any significance, but is

    /// just set at u32::MAX to hopefully bring out bugs sooner.

    fn new_invalid() -> Self {

        return ControlId(u32::MAX);

    }

}

struct ControlEntry {

    id: ControlId,

    ack_countdown: u32,

    content: ControlContent,

}

enum ControlContent {

    PeerChange(ContentPeerChange),

    ScheduleComponent(CompId),

    BlockedPort(PortId),

    ClosedPort(PortId),

}

struct ContentPeerChange {

    source_port: PortId,

    source_comp: CompId,

    target_port: PortId,

    new_target_comp: CompId,

    schedule_entry_id: ControlId,

}

pub(crate) enum AckAction {

    None,

    SendMessageAndAck(CompId, ControlMessage, ControlId),

    ScheduleComponent(CompId),

}

/// Handling/sending control messages.

pub(crate) struct ControlLayer {

    id_counter: ControlId,

    entries: Vec<ControlEntry>,

}

impl ControlLayer {

    pub(crate) fn should_reroute(&self, message: &Message) -> Option<CompId> {

        // Safety note: rerouting should occur during the time when we're

        // notifying a peer of a new component. During this period that

        // component hasn't been executed yet, so cannot have died yet.

        // FIX @NoDirectHandle

        let target_port = message.target_port();

        if target_port.is_none() {

            return None;

        }

        let target_port = target_port.unwrap();

        for entry in &self.entries {

            if let ControlContent::PeerChange(entry) = &entry.content {

                if entry.target_port == target_port {

                    return Some(entry.new_target_comp);

                }

            }

        }

        return None;

    }

    pub(crate) fn handle_ack(&mut self, entry_id: ControlId, sched_ctx: &SchedulerCtx, comp_ctx: &mut CompCtx) -> AckAction {

        let entry_index = self.get_entry_index(entry_id).unwrap();

        let entry = &mut self.entries[entry_index];

        debug_assert!(entry.ack_countdown > 0);

        entry.ack_countdown -= 1;

        if entry.ack_countdown != 0 {

            return AckAction::None;

        }

        // All `Ack`s received, take action based on the kind of entry

        match &entry.content {

            ControlContent::PeerChange(content) => {

                // If change of peer is ack'd. Then we are certain we have

                // rerouted all of the messages, and the sender's port can now

                // be unblocked again.

                let target_comp_id = content.source_comp;

                let message_to_send = ControlMessage{

                    id: ControlId::new_invalid(),

                    sender_comp_id: comp_ctx.id,

                    target_port_id: Some(content.source_port),

                    content: ControlMessageContent::PortPeerChangedUnblock(

                        content.source_port,

                        content.new_target_comp

                    )

                };

                let to_ack = content.schedule_entry_id;

                self.entries.remove(entry_index);

                return AckAction::SendMessageAndAck(target_comp_id, message_to_send, to_ack);

            },

            ControlContent::ScheduleComponent(to_schedule) => {

                // If all change-of-peers are `Ack`d, then we're ready to

                // schedule the component!

                return AckAction::ScheduleComponent(*to_schedule);

            },

            ControlContent::BlockedPort(_) => unreachable!(),

            ControlContent::ClosedPort(port_id) => {

                // If a closed port is Ack'd, then we remove the reference to

                // that component.

                let port_index = comp_ctx.get_port_index(*port_id).unwrap();

                debug_assert_eq!(comp_ctx.ports[port_index].state, PortState::Blocked);

                let peer_id = comp_ctx.ports[port_index].peer_comp_id;

                let peer_index = comp_ctx.get_peer_index(peer_id).unwrap();

                let peer_info = &mut comp_ctx.peers[peer_index];

                peer_info.num_associated_ports -= 1;

                if peer_info.num_associated_ports == 0 {

                    let should_remove = peer_info.handle.decrement_users();

                    if should_remove {

                        let comp_key = unsafe{ peer_info.id.upgrade() };

                        sched_ctx.runtime.destroy_component(comp_key);

                    }

                    comp_ctx.peers.remove(peer_index);

                }

                return AckAction::None;

            }

        }

    }

    // -------------------------------------------------------------------------

    // Port transfer (due to component creation)

    // -------------------------------------------------------------------------

    /// Adds an entry that, when completely ack'd, will schedule a component.

    pub(crate) fn add_schedule_entry(&mut self, to_schedule_id: CompId) -> ControlId {

        let entry_id = self.take_id();

        self.entries.push(ControlEntry{

            id: entry_id,

            ack_countdown: 0, // incremented by calls to `add_reroute_entry`

            content: ControlContent::ScheduleComponent(to_schedule_id),

        });

        return entry_id;

    }

    /// Removes a schedule entry. Only used if the caller preemptively called

    /// `add_schedule_entry`, but ended up not calling `add_reroute_entry`,

    /// hence the `ack_countdown` in the scheduling entry is at 0.

    pub(crate) fn remove_schedule_entry(&mut self, schedule_entry_id: ControlId) {

        let index = self.get_entry_index(schedule_entry_id).unwrap();

        debug_assert_eq!(self.entries[index].ack_countdown, 0);

        self.entries.remove(index);

    }

    pub(crate) fn add_reroute_entry(

        &mut self, creator_comp_id: CompId,

        source_port_id: PortId, source_comp_id: CompId,

        target_port_id: PortId, new_comp_id: CompId,

        schedule_entry_id: ControlId,

    ) -> Message {

        let entry_id = self.take_id();

        self.entries.push(ControlEntry{

            id: entry_id,

            ack_countdown: 1,

            content: ControlContent::PeerChange(ContentPeerChange{

                source_port: source_port_id,

                source_comp: source_comp_id,

                target_port: target_port_id,

                new_target_comp: new_comp_id,

                schedule_entry_id,

            }),

        });

        // increment counter on schedule entry

        for entry in &mut self.entries {

            if entry.id == schedule_entry_id {

                entry.ack_countdown += 1;

                break;

            }

        }

        return Message::Control(ControlMessage{

            id: entry_id,

            sender_comp_id: creator_comp_id,

            target_port_id: Some(source_port_id),

            content: ControlMessageContent::PortPeerChangedBlock(source_port_id)

        })

    }

    // -------------------------------------------------------------------------

    // Blocking, unblocking, and closing ports