use crate::random::Random;
use crate::protocol::*;
use crate::protocol::ast::ProcedureDefinitionId;
use crate::protocol::eval::{
    PortId as EvalPortId, Prompt,
    ValueGroup, Value,
    EvalContinuation, EvalResult, EvalError
};

use crate::runtime2::scheduler::SchedulerCtx;
use crate::runtime2::communication::*;

use super::component::*;
use super::component_context::*;
use super::control_layer::*;
use super::consensus::Consensus;

pub enum ExecStmt {
    CreatedChannel((Value, Value)),
    PerformedPut,
    PerformedGet(ValueGroup),
    PerformedSelectWait(u32),
    None,
}

impl ExecStmt {
    fn take(&mut self) -> ExecStmt {
        let mut value = ExecStmt::None;
        std::mem::swap(self, &mut value);
        return value;
    }

    fn is_none(&self) -> bool {
        match self {
            ExecStmt::None => return true,
            _ => return false,
        }
    }
}

pub struct ExecCtx {
    stmt: ExecStmt,
}

impl RunContext for ExecCtx {
    fn performed_put(&mut self, _port: EvalPortId) -> bool {
        match self.stmt.take() {
            ExecStmt::None => return false,
            ExecStmt::PerformedPut => return true,
            _ => 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!(),
        }
    }

    fn performed_select_wait(&mut self) -> Option<u32> {
        match self.stmt.take() {
            ExecStmt::None => return None,
            ExecStmt::PerformedSelectWait(selected_case) => Some(selected_case),
            _v => 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
    SyncEnd, // awaiting a solution, i.e. encountered the end of the sync block
    BlockedGet, // blocked because we need to receive a message on a particular port
    BlockedPut, // component is blocked because the port is blocked
    BlockedSelect, // waiting on message to complete the select statement
    StartExit, // temporary state: if encountered then we start the shutdown process
    BusyExit, // temporary state: waiting for Acks for all the closed ports
    Exit, // exiting: shutdown process started, now waiting until the reference count drops to 0
}

impl Mode {
    fn is_in_sync_block(&self) -> bool {
        use Mode::*;

        match self {
            Sync | SyncEnd | BlockedGet | BlockedPut | BlockedSelect => true,
            NonSync | StartExit | BusyExit | Exit => false,
        }
    }
}

struct SelectCase {
    involved_ports: Vec<LocalPortHandle>,
}

// TODO: @Optimize, flatten cases into single array, have index-pointers to next case
struct SelectState {
    cases: Vec<SelectCase>,
    next_case: u32,
    num_cases: u32,
    random: Random,
    candidates_workspace: Vec<usize>,
}

enum SelectDecision {
    None,
    Case(u32), // contains case index, should be passed along to PDL code
}

type InboxMain = Vec<Option<DataMessage>>;

impl SelectState {
    fn new() -> Self {
        return Self{
            cases: Vec::new(),
            next_case: 0,
            num_cases: 0,
            random: Random::new(),
            candidates_workspace: Vec::new(),
        }
    }

    fn handle_select_start(&mut self, num_cases: u32) {
        self.cases.clear();
        self.next_case = 0;
        self.num_cases = num_cases;
    }

    /// Register a port as belonging to a particular case. As for correctness of
    /// PDL code one cannot register the same port twice, this function might
    /// return an error
    fn register_select_case_port(&mut self, comp_ctx: &CompCtx, case_index: u32, _port_index: u32, port_id: PortId) -> Result<(), PortId> {
        // Retrieve case and port handle
        self.ensure_at_case(case_index);
        let cur_case = &mut self.cases[case_index as usize];
        let port_handle = comp_ctx.get_port_handle(port_id);
        debug_assert_eq!(cur_case.involved_ports.len(), _port_index as usize);

        // Make sure port wasn't added before, we disallow having the same port
        // in the same select guard twice.
        if cur_case.involved_ports.contains(&port_handle) {
            return Err(port_id);
        }

        cur_case.involved_ports.push(port_handle);
        return Ok(());
    }

    /// Notification that all ports have been registered and we should now wait
    /// until the appropriate messages have come in.
    fn handle_select_waiting_point(&mut self, inbox: &InboxMain, comp_ctx: &CompCtx) -> SelectDecision {
        if self.num_cases != self.next_case {
            // This happens when there are >=1 select cases written at the end
            // of the select block.
            self.ensure_at_case(self.num_cases - 1);
        }

        return self.has_decision(inbox, comp_ctx);
    }

    fn handle_updated_inbox(&mut self, inbox: &InboxMain, comp_ctx: &CompCtx) -> SelectDecision {
        return self.has_decision(inbox, comp_ctx);
    }

    /// Internal helper, pushes empty cases inbetween last case and provided new
    /// case index.
    fn ensure_at_case(&mut self, new_case_index: u32) {
        // Push an empty case for all intermediate cases that were not
        // registered with a port.
        debug_assert!(new_case_index >= self.next_case && new_case_index < self.num_cases);
        for _ in self.next_case..new_case_index + 1 {
            self.cases.push(SelectCase{ involved_ports: Vec::new() });
        }
        self.next_case = new_case_index + 1;
    }

    /// Checks if a decision can be reached
    fn has_decision(&mut self, inbox: &InboxMain, comp_ctx: &CompCtx) -> SelectDecision {
        self.candidates_workspace.clear();
        if self.cases.is_empty() {
            // If there are no cases then we can immediately reach a "bogus
            // decision".
            return SelectDecision::Case(0);
        }

        // Need to check for valid case
        'case_loop: for (case_index, case) in self.cases.iter().enumerate() {
            for port_handle in case.involved_ports.iter().copied() {
                let port_index = comp_ctx.get_port_index(port_handle);
                if inbox[port_index].is_none() {
                    // Condition not satisfied
                    continue 'case_loop;
                }
            }

            // If here then the case guard is satisfied
            self.candidates_workspace.push(case_index);
        }

        if self.candidates_workspace.is_empty() {
            return SelectDecision::None;
        } else {
            let candidate_index = self.random.get_u64() as usize % self.candidates_workspace.len();
            return SelectDecision::Case(self.candidates_workspace[candidate_index] as u32);
        }
    }
}

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
    select: SelectState,
    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: InboxMain,
    pub inbox_backup: Vec<DataMessage>,
}

impl Component for CompPDL {
    fn adopt_message(&mut self, comp_ctx: &mut CompCtx, message: DataMessage) {
        let port_handle = comp_ctx.get_port_handle(message.data_header.target_port);
        let port_index = comp_ctx.get_port_index(port_handle);
        if self.inbox_main[port_index].is_none() {
            self.inbox_main[port_index] = Some(message);
        } else {
            self.inbox_backup.push(message);
        }
    }

    fn handle_message(&mut self, sched_ctx: &mut SchedulerCtx, comp_ctx: &mut CompCtx, mut message: Message) {
        sched_ctx.log(&format!("handling message: {:#?}", message));
        if let Some(new_target) = self.control.should_reroute(&mut message) {
            let mut target = sched_ctx.runtime.get_component_public(new_target);
            target.send_message(sched_ctx, message, false); // not waking up: we schedule once we've received all PortPeerChanged Acks
            let _should_remove = target.decrement_users();
            debug_assert!(_should_remove.is_none());
            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);
            }
        }
    }

    fn run(&mut self, sched_ctx: &mut SchedulerCtx, comp_ctx: &mut CompCtx) -> Result<CompScheduling, EvalError> {
        use EvalContinuation as EC;

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

        // Depending on the mode don't do anything at all, take some special
        // actions, or fall through and run the PDL code.
        match self.mode {
            Mode::NonSync | Mode::Sync => {
                // continue and run PDL code
            },
            Mode::SyncEnd | Mode::BlockedGet | Mode::BlockedPut | Mode::BlockedSelect => {
                return Ok(CompScheduling::Sleep);
            }
            Mode::StartExit => {
                self.handle_component_exit(sched_ctx, comp_ctx);
                return Ok(CompScheduling::Immediate);
            },
            Mode::BusyExit => {
                if self.control.has_acks_remaining() {
                    return Ok(CompScheduling::Sleep);
                } else {
                    self.mode = Mode::Exit;
                    return Ok(CompScheduling::Exit);
                }
            },
            Mode::Exit => {
                return Ok(CompScheduling::Exit);
            }
        }

        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_handle = comp_ctx.get_port_handle(port_id);
                let port_index = comp_ctx.get_port_index(port_handle);
                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.handle_received_data_message(sched_ctx, comp_ctx, port_handle);

                        self.exec_ctx.stmt = ExecStmt::PerformedGet(message.content);
                        return Ok(CompScheduling::Immediate);
                    } else {
                        todo!("handle sync failure due to message deadlock");
                        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);
                sched_ctx.log(&format!("Putting value {:?}", value));
                let port_id = port_id_from_eval(port_id);
                let port_handle = comp_ctx.get_port_handle(port_id);
                let port_info = comp_ctx.get_port(port_handle);
                if port_info.state.is_blocked() {
                    self.mode = Mode::BlockedPut;
                    self.mode_port = port_id;
                    self.mode_value = value;
                    self.exec_ctx.stmt = ExecStmt::PerformedPut; // prepare for when we become unblocked
                    return Ok(CompScheduling::Sleep);
                } else {
                    self.send_data_message_and_wake_up(sched_ctx, comp_ctx, port_handle, value);
                    self.exec_ctx.stmt = ExecStmt::PerformedPut;
                    return Ok(CompScheduling::Immediate);
                }
            },
            EC::SelectStart(num_cases, _num_ports) => {
                debug_assert_eq!(self.mode, Mode::Sync);
                self.select.handle_select_start(num_cases);
                return Ok(CompScheduling::Requeue);
            },
            EC::SelectRegisterPort(case_index, port_index, port_id) => {
                debug_assert_eq!(self.mode, Mode::Sync);
                let port_id = port_id_from_eval(port_id);
                if let Err(_err) = self.select.register_select_case_port(comp_ctx, case_index, port_index, port_id) {
                    todo!("handle registering a port multiple times");
                }
                return Ok(CompScheduling::Immediate);
            },
            EC::SelectWait => {
                debug_assert_eq!(self.mode, Mode::Sync);
                let select_decision = self.select.handle_select_waiting_point(&self.inbox_main, comp_ctx);
                if let SelectDecision::Case(case_index) = select_decision {
                    // Reached a conclusion, so we can continue immediately
                    self.exec_ctx.stmt = ExecStmt::PerformedSelectWait(case_index);
                    self.mode = Mode::Sync;
                    return Ok(CompScheduling::Immediate);
                } else {
                    // No decision yet
                    self.mode = Mode::BlockedSelect;
                    return Ok(CompScheduling::Sleep);
                }
            },
            // Results that can be returned outside of sync mode
            EC::ComponentTerminated => {
                self.mode = Mode::StartExit; // next call we'll take care of the exit
                return Ok(CompScheduling::Immediate);
            },
            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, type_id, arguments) => {
                debug_assert_eq!(self.mode, Mode::NonSync);
                self.create_component_and_transfer_ports(
                    sched_ctx, comp_ctx,
                    definition_id, type_id, arguments
                );
                return Ok(CompScheduling::Requeue);
            },
            EC::NewChannel => {
                debug_assert_eq!(self.mode, Mode::NonSync);
                debug_assert!(self.exec_ctx.stmt.is_none());
                let channel = comp_ctx.create_channel();
                self.exec_ctx.stmt = ExecStmt::CreatedChannel((
                    Value::Output(port_id_to_eval(channel.putter_id)),
                    Value::Input(port_id_to_eval(channel.getter_id))
                ));
                self.inbox_main.push(None);
                self.inbox_main.push(None);
                return Ok(CompScheduling::Immediate);
            }
        }
    }
}

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(),
            select: SelectState::new(),
            prompt: initial_state,
            control: ControlLayer::default(),
            consensus: Consensus::new(),
            sync_counter: 0,
            exec_ctx: ExecCtx{
                stmt: ExecStmt::None,
            },
            inbox_main,
            inbox_backup: Vec::new(),
        }
    }

    // -------------------------------------------------------------------------
    // Running component and handling changes in global component state
    // -------------------------------------------------------------------------

    fn execute_prompt(&mut self, sched_ctx: &SchedulerCtx) -> EvalResult {
        let mut step_result = EvalContinuation::Stepping;
        while let EvalContinuation::Stepping = step_result {
            step_result = self.prompt.step(
                &sched_ctx.runtime.protocol.types, &sched_ctx.runtime.protocol.heap,
                &sched_ctx.runtime.protocol.modules, &mut self.exec_ctx,
            )?;
        }

        return Ok(step_result)
    }

    fn handle_sync_start(&mut self, sched_ctx: &SchedulerCtx, comp_ctx: &mut CompCtx) {
        sched_ctx.log("Component starting sync mode");
        self.consensus.notify_sync_start(comp_ctx);
        for message in self.inbox_main.iter() {
            if let Some(message) = message {
                self.consensus.handle_new_data_message(comp_ctx, message);
            }
        }
        debug_assert_eq!(self.mode, Mode::NonSync);
        self.mode = Mode::Sync;
    }

    /// Handles end of sync. The conclusion to the sync round might arise
    /// immediately (and be handled immediately), or might come later through
    /// messaging. In any case the component should be scheduled again
    /// immediately
    fn handle_sync_end(&mut self, sched_ctx: &SchedulerCtx, comp_ctx: &mut CompCtx) {
        sched_ctx.log("Component ending sync mode (now waiting for solution)");
        let decision = self.consensus.notify_sync_end(sched_ctx, comp_ctx);
        self.mode = Mode::SyncEnd;
        self.handle_sync_decision(sched_ctx, comp_ctx, decision);
    }

    /// Handles decision from the consensus round. This will cause a change in
    /// the internal `Mode`, such that the next call to `run` can take the
    /// appropriate next steps.
    fn handle_sync_decision(&mut self, sched_ctx: &SchedulerCtx, _comp_ctx: &mut CompCtx, decision: SyncRoundDecision) {
        sched_ctx.log(&format!("Handling sync decision: {:?} (in mode {:?})", decision, self.mode));
        let is_success = match decision {
            SyncRoundDecision::None => {
                // No decision yet
                return;
            },
            SyncRoundDecision::Solution => true,
            SyncRoundDecision::Failure => false,
        };

        // If here then we've reached a decision
        debug_assert_eq!(self.mode, Mode::SyncEnd);
        if is_success {
            self.mode = Mode::NonSync;
            self.consensus.notify_sync_decision(decision);
        } else {
            self.mode = Mode::StartExit;
        }
    }

    fn handle_component_exit(&mut self, sched_ctx: &SchedulerCtx, comp_ctx: &mut CompCtx) {
        sched_ctx.log("Component exiting");
        debug_assert_eq!(self.mode, Mode::StartExit);
        self.mode = Mode::BusyExit;

        // Doing this by index, then retrieving the handle is a bit rediculous,
        // but Rust is being Rust with its borrowing rules.
        for port_index in 0..comp_ctx.num_ports() {
            let port = comp_ctx.get_port_by_index_mut(port_index);
            if port.state == PortState::Closed {
                // Already closed, or in the process of being closed
                continue;
            }

            // Mark as closed
            let port_id = port.self_id;
            port.state = PortState::Closed;

            // Notify peer of closing
            let port_handle = comp_ctx.get_port_handle(port_id);
            let (peer, message) = self.control.initiate_port_closing(port_handle, comp_ctx);
            let peer_info = comp_ctx.get_peer(peer);
            peer_info.handle.send_message(sched_ctx, Message::Control(message), true);
        }
    }

    // -------------------------------------------------------------------------
    // Handling messages
    // -------------------------------------------------------------------------

    fn send_data_message_and_wake_up(&mut self, sched_ctx: &SchedulerCtx, comp_ctx: &CompCtx, source_port_handle: LocalPortHandle, value: ValueGroup) {
        let port_info = comp_ctx.get_port(source_port_handle);
        let peer_handle = comp_ctx.get_peer_handle(port_info.peer_comp_id);
        let peer_info = comp_ctx.get_peer(peer_handle);
        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) {
        // Whatever we do, glean information from headers in message
        if self.mode.is_in_sync_block() {
            self.consensus.handle_new_data_message(comp_ctx, &message);
        }

        // 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_handle = comp_ctx.get_port_handle(target_port_id);
        let port_index = comp_ctx.get_port_index(port_handle);
        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!(!comp_ctx.get_port(port_handle).state.is_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();
            } else if self.mode == Mode::BlockedSelect {
                let select_decision = self.select.handle_updated_inbox(&self.inbox_main, comp_ctx);
                if let SelectDecision::Case(case_index) = select_decision {
                    self.exec_ctx.stmt = ExecStmt::PerformedSelectWait(case_index);
                    self.mode = Mode::Sync;
                }
            }
            
            return;
        }

        // The direct inbox is full, so the port will become (or was already) blocked
        let port_info = comp_ctx.get_port_mut(port_handle);
        debug_assert!(port_info.state == PortState::Open || port_info.state.is_blocked());

        if port_info.state == PortState::Open {
            comp_ctx.set_port_state(port_handle, PortState::BlockedDueToFullBuffers);
            let (peer_handle, message) =
                self.control.initiate_port_blocking(comp_ctx, port_handle);

            let peer = comp_ctx.get_peer(peer_handle);
            peer.handle.send_message(sched_ctx, Message::Control(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_handle: LocalPortHandle) {
        let port_index = comp_ctx.get_port_index(port_handle);
        debug_assert!(self.inbox_main[port_index].is_none()); // this function should be called after the message is taken out

        // Check for any more messages
        let port_info = comp_ctx.get_port(port_handle);
        for message_index in 0..self.inbox_backup.len() {
            let message = &self.inbox_backup[message_index];
            if message.data_header.target_port == port_info.self_id {
                // One more message for this port
                let message = self.inbox_backup.remove(message_index);
                debug_assert!(comp_ctx.get_port(port_handle).state.is_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.
        if port_info.state == PortState::BlockedDueToFullBuffers {
            comp_ctx.set_port_state(port_handle, PortState::Open);
            let (peer_handle, message) = self.control.cancel_port_blocking(comp_ctx, port_handle);
            let peer_info = comp_ctx.get_peer(peer_handle);
            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) {
        // Little local utility to send an Ack
        fn send_control_ack_message(sched_ctx: &SchedulerCtx, comp_ctx: &CompCtx, causer_id: ControlId, peer_handle: LocalPeerHandle) {
            let peer_info = comp_ctx.get_peer(peer_handle);
            peer_info.handle.send_message(sched_ctx, Message::Control(ControlMessage{
                id: causer_id,
                sender_comp_id: comp_ctx.id,
                target_port_id: None,
                content: ControlMessageContent::Ack,
            }), true);
        }

        // Handle the content of the control message, and optionally Ack it
        match message.content {
            ControlMessageContent::Ack => {
                self.handle_ack(sched_ctx, comp_ctx, message.id);
            },
            ControlMessageContent::BlockPort(port_id) => {
                // On of our messages was accepted, but the port should be
                // blocked.
                let port_handle = comp_ctx.get_port_handle(port_id);
                let port_info = comp_ctx.get_port(port_handle);
                debug_assert_eq!(port_info.kind, PortKind::Putter);
                if port_info.state == PortState::Open {
                    // only when open: we don't do this when closed, and we we don't do this if we're blocked due to peer changes
                    comp_ctx.set_port_state(port_handle, PortState::BlockedDueToFullBuffers);
                }
            },
            ControlMessageContent::ClosePort(port_id) => {
                // Request to close the port. We immediately comply and remove
                // the component handle as well
                let port_handle = comp_ctx.get_port_handle(port_id);
                let peer_comp_id = comp_ctx.get_port(port_handle).peer_comp_id;
                let peer_handle = comp_ctx.get_peer_handle(peer_comp_id);

                // One exception to sending an `Ack` is if we just closed the
                // port ourselves, meaning that the `ClosePort` messages got
                // sent to one another.
                if let Some(control_id) = self.control.has_close_port_entry(port_handle, comp_ctx) {
                    self.handle_ack(sched_ctx, comp_ctx, control_id);
                } else {
                    send_control_ack_message(sched_ctx, comp_ctx, message.id, peer_handle);
                    comp_ctx.remove_peer(sched_ctx, port_handle, peer_comp_id, false); // do not remove if closed
                    comp_ctx.set_port_state(port_handle, PortState::Closed); // now set to closed
                }
            },
            ControlMessageContent::UnblockPort(port_id) => {
                // We were previously blocked (or already closed)
                let port_handle = comp_ctx.get_port_handle(port_id);
                let port_info = comp_ctx.get_port(port_handle);
                debug_assert_eq!(port_info.kind, PortKind::Putter);
                if port_info.state == PortState::BlockedDueToFullBuffers {
                    self.handle_unblock_port_instruction(sched_ctx, comp_ctx, port_handle);
                }
            },
            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_handle = comp_ctx.get_port_handle(port_id);
                comp_ctx.set_port_state(port_handle, PortState::BlockedDueToPeerChange);

                let port_info = comp_ctx.get_port(port_handle);
                let peer_handle = comp_ctx.get_peer_handle(port_info.peer_comp_id);

                send_control_ack_message(sched_ctx, comp_ctx, message.id, peer_handle);
            },
            ControlMessageContent::PortPeerChangedUnblock(new_port_id, new_comp_id) => {
                let port_handle = comp_ctx.get_port_handle(message.target_port_id.unwrap());
                let port_info = comp_ctx.get_port(port_handle);
                debug_assert!(port_info.state == PortState::BlockedDueToPeerChange);
                let old_peer_id = port_info.peer_comp_id;

                comp_ctx.remove_peer(sched_ctx, port_handle, old_peer_id, false);

                let port_info = comp_ctx.get_port_mut(port_handle);
                port_info.peer_comp_id = new_comp_id;
                port_info.peer_port_id = new_port_id;
                comp_ctx.add_peer(port_handle, sched_ctx, new_comp_id, None);
                self.handle_unblock_port_instruction(sched_ctx, comp_ctx, port_handle);
            }
        }
    }

    fn handle_incoming_sync_message(&mut self, sched_ctx: &SchedulerCtx, comp_ctx: &mut CompCtx, message: SyncMessage) {
        let decision = self.consensus.receive_sync_message(sched_ctx, comp_ctx, message);
        self.handle_sync_decision(sched_ctx, comp_ctx, decision);
    }

    /// Little helper that notifies the control layer of an `Ack`, and takes the
    /// appropriate subsequent action
    fn handle_ack(&mut self, sched_ctx: &SchedulerCtx, comp_ctx: &mut CompCtx, control_id: ControlId) {
        let mut to_ack = control_id;
        loop {
            let (action, new_to_ack) = self.control.handle_ack(to_ack, sched_ctx, comp_ctx);
            match action {
                AckAction::SendMessage(target_comp, message) => {
                    // FIX @NoDirectHandle
                    let mut handle = sched_ctx.runtime.get_component_public(target_comp);
                    handle.send_message(sched_ctx, Message::Control(message), true);
                    let _should_remove = handle.decrement_users();
                    debug_assert!(_should_remove.is_none());
                },
                AckAction::ScheduleComponent(to_schedule) => {
                    // FIX @NoDirectHandle
                    let mut handle = sched_ctx.runtime.get_component_public(to_schedule);

                    // Note that the component is intentionally not
                    // sleeping, so we just wake it up
                    debug_assert!(!handle.sleeping.load(std::sync::atomic::Ordering::Acquire));
                    let key = unsafe{ to_schedule.upgrade() };
                    sched_ctx.runtime.enqueue_work(key);
                    let _should_remove = handle.decrement_users();
                    debug_assert!(_should_remove.is_none());
                },
                AckAction::None => {}
            }

            match new_to_ack {
                Some(new_to_ack) => to_ack = new_to_ack,
                None => break,
            }
        }
    }

    // -------------------------------------------------------------------------
    // Handling ports
    // -------------------------------------------------------------------------

    /// Unblocks a port, potentially continuing execution of the component, in
    /// response to a message that told us to unblock a previously blocked
    fn handle_unblock_port_instruction(&mut self, sched_ctx: &SchedulerCtx, comp_ctx: &mut CompCtx, port_handle: LocalPortHandle) {
        let port_info = comp_ctx.get_port_mut(port_handle);
        let port_id = port_info.self_id;
        debug_assert!(port_info.state.is_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_handle, 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,
        definition_id: ProcedureDefinitionId, type_id: TypeId, mut arguments: ValueGroup
    ) {
        struct PortPair{
            creator_handle: LocalPortHandle,
            creator_id: PortId,
            created_handle: LocalPortHandle,
            created_id: PortId,
        }
        let mut port_id_pairs = Vec::new();

        let reservation = sched_ctx.runtime.start_create_pdl_component();
        let mut created_ctx = CompCtx::new(&reservation);

        // Take all the ports ID that are in the `args` (and currently belong to
        // the creator component) and translate them into new IDs that are
        // associated with the component we're about to create
        let mut arg_iter = ValueGroupPortIter::new(&mut arguments);
        while let Some(port_reference) = arg_iter.next() {
            // Create port entry for new component
            let creator_port_id = port_reference.id;
            let creator_port_handle = creator_ctx.get_port_handle(creator_port_id);
            let creator_port = creator_ctx.get_port(creator_port_handle);
            let created_port_handle = created_ctx.add_port(
                creator_port.peer_comp_id, creator_port.peer_port_id,
                creator_port.kind, creator_port.state
            );
            let created_port = created_ctx.get_port(created_port_handle);
            let created_port_id = created_port.self_id;

            port_id_pairs.push(PortPair{
                creator_handle: creator_port_handle,
                creator_id: creator_port_id,
                created_handle: created_port_handle,
                created_id: created_port_id,
            });

            // Modify value in arguments (bit dirty, but double vec in ValueGroup causes lifetime issues)
            let arg_value = if let Some(heap_pos) = port_reference.heap_pos {
                &mut arg_iter.group.regions[heap_pos][port_reference.index]
            } else {
                &mut arg_iter.group.values[port_reference.index]
            };
            match arg_value {
                Value::Input(id) => *id = port_id_to_eval(created_port_id),
                Value::Output(id) => *id = port_id_to_eval(created_port_id),
                _ => unreachable!(),
            }
        }

        // For each transferred port pair set their peer components to the
        // correct values. This will only change the values for the ports of
        // the new component.
        let mut created_component_has_remote_peers = false;

        for pair in port_id_pairs.iter() {
            let creator_port_info = creator_ctx.get_port(pair.creator_handle);
            let created_port_info = created_ctx.get_port_mut(pair.created_handle);

            if created_port_info.peer_comp_id == creator_ctx.id {
                // Port peer is owned by the creator as well
                let created_peer_port_index = port_id_pairs
                    .iter()
                    .position(|v| v.creator_id == creator_port_info.peer_port_id);
                match created_peer_port_index {
                    Some(created_peer_port_index) => {
                        // Peer port moved to the new component as well. So
                        // adjust IDs appropriately.
                        let peer_pair = &port_id_pairs[created_peer_port_index];
                        created_port_info.peer_port_id = peer_pair.created_id;
                        created_port_info.peer_comp_id = reservation.id();
                        todo!("either add 'self peer', or remove that idea from Ctx altogether")
                    },
                    None => {
                        // Peer port remains with creator component.
                        created_port_info.peer_comp_id = creator_ctx.id;
                        created_ctx.add_peer(pair.created_handle, sched_ctx, creator_ctx.id, None);
                    }
                }
            } else {
                // Peer is a different component. We'll deal with sending the
                // appropriate messages later
                let peer_handle = creator_ctx.get_peer_handle(created_port_info.peer_comp_id);
                let peer_info = creator_ctx.get_peer(peer_handle);
                created_ctx.add_peer(pair.created_handle, sched_ctx, peer_info.id, Some(&peer_info.handle));
                created_component_has_remote_peers = true;
            }
        }

        // We'll now actually turn our reservation for a new component into an
        // actual component. Note that we initialize it as "not sleeping" as
        // its initial scheduling might be performed based on `Ack`s in response
        // to message exchanges between remote peers.
        let prompt = Prompt::new(
            &sched_ctx.runtime.protocol.types, &sched_ctx.runtime.protocol.heap,
            definition_id, type_id, arguments,
        );
        let component = CompPDL::new(prompt, port_id_pairs.len());
        let (created_key, component) = sched_ctx.runtime.finish_create_pdl_component(
            reservation, component, created_ctx, false,
        );

        // Now modify the creator's ports: remove every transferred port and
        // potentially remove the peer component.
        for pair in port_id_pairs.iter() {
            // Remove peer if appropriate
            let creator_port_info = creator_ctx.get_port(pair.creator_handle);
            let creator_port_index = creator_ctx.get_port_index(pair.creator_handle);
            let creator_peer_comp_id = creator_port_info.peer_comp_id;
            creator_ctx.remove_peer(sched_ctx, pair.creator_handle, creator_peer_comp_id, false);
            creator_ctx.remove_port(pair.creator_handle);

            // Transfer any messages
            if let Some(mut message) = self.inbox_main.remove(creator_port_index) {
                message.data_header.target_port = pair.created_id;
                component.component.adopt_message(&mut component.ctx, message)
            }

            let mut message_index = 0;
            while message_index < self.inbox_backup.len() {
                let message = &self.inbox_backup[message_index];
                if message.data_header.target_port == pair.creator_id {
                    // transfer message
                    let mut message = self.inbox_backup.remove(message_index);
                    message.data_header.target_port = pair.created_id;
                    component.component.adopt_message(&mut component.ctx, message);
                } else {
                    message_index += 1;
                }
            }

            // Handle potential channel between creator and created component
            let created_port_info = component.ctx.get_port(pair.created_handle);

            if created_port_info.peer_comp_id == creator_ctx.id {
                let peer_port_handle = creator_ctx.get_port_handle(created_port_info.peer_port_id);
                let peer_port_info = creator_ctx.get_port_mut(peer_port_handle);
                peer_port_info.peer_comp_id = component.ctx.id;
                peer_port_info.peer_port_id = created_port_info.self_id;
                creator_ctx.add_peer(peer_port_handle, sched_ctx, component.ctx.id, None);
            }
        }

        // By now all ports and messages have been transferred. If there are any
        // peers that need to be notified about this new component, then we
        // initiate the protocol that will notify everyone here.
        if created_component_has_remote_peers {
            let created_ctx = &component.ctx;
            let schedule_entry_id = self.control.add_schedule_entry(created_ctx.id);
            for pair in port_id_pairs.iter() {
                let port_info = created_ctx.get_port(pair.created_handle);
                if port_info.peer_comp_id != creator_ctx.id && port_info.peer_comp_id != created_ctx.id {
                    let message = self.control.add_reroute_entry(
                        creator_ctx.id, port_info.peer_port_id, port_info.peer_comp_id,
                        pair.creator_id, pair.created_id, created_ctx.id,
                        schedule_entry_id
                    );
                    let peer_handle = created_ctx.get_peer_handle(port_info.peer_comp_id);
                    let peer_info = created_ctx.get_peer(peer_handle);
                    peer_info.handle.send_message(sched_ctx, message, true);
                }
            }
        } else {
            // Peer can be scheduled immediately
            sched_ctx.runtime.enqueue_work(created_key);
        }
    }
}

#[inline]
fn port_id_from_eval(port_id: EvalPortId) -> PortId {
    return PortId(port_id.id);
}

#[inline]
fn port_id_to_eval(port_id: PortId) -> EvalPortId {
    return EvalPortId{ id: port_id.0 };
}

/// Recursively goes through the value group, attempting to find ports.
/// Duplicates will only be added once.
pub(crate) fn find_ports_in_value_group(value_group: &ValueGroup, ports: &mut Vec<PortId>) {
    // Helper to check a value for a port and recurse if needed.
    fn find_port_in_value(group: &ValueGroup, value: &Value, ports: &mut Vec<PortId>) {
        match value {
            Value::Input(port_id) | Value::Output(port_id) => {
                // This is an actual port
                let cur_port = PortId(port_id.id);
                for prev_port in ports.iter() {
                    if *prev_port == cur_port {
                        // Already added
                        return;
                    }
                }

                ports.push(cur_port);
            },
            Value::Array(heap_pos) |
            Value::Message(heap_pos) |
            Value::String(heap_pos) |
            Value::Struct(heap_pos) |
            Value::Union(_, heap_pos) => {
                // Reference to some dynamic thing which might contain ports,
                // so recurse
                let heap_region = &group.regions[*heap_pos as usize];
                for embedded_value in heap_region {
                    find_port_in_value(group, embedded_value, ports);
                }
            },
            _ => {}, // values we don't care about
        }
    }

    // Clear the ports, then scan all the available values
    ports.clear();
    for value in &value_group.values {
        find_port_in_value(value_group, value, ports);
    }
}

struct ValueGroupPortIter<'a> {
    group: &'a mut ValueGroup,
    heap_stack: Vec<(usize, usize)>,
    index: usize,
}

impl<'a> ValueGroupPortIter<'a> {
    fn new(group: &'a mut ValueGroup) -> Self {
        return Self{ group, heap_stack: Vec::new(), index: 0 }
    }
}

struct ValueGroupPortRef {
    id: PortId,
    heap_pos: Option<usize>, // otherwise: on stack
    index: usize,
}

impl<'a> Iterator for ValueGroupPortIter<'a> {
    type Item = ValueGroupPortRef;

    fn next(&mut self) -> Option<Self::Item> {
        // Enter loop that keeps iterating until a port is found
        loop {
            if let Some(pos) = self.heap_stack.last() {
                let (heap_pos, region_index) = *pos;
                if region_index >= self.group.regions[heap_pos].len() {
                    self.heap_stack.pop();
                    continue;
                }

                let value = &self.group.regions[heap_pos][region_index];
                self.heap_stack.last_mut().unwrap().1 += 1;

                match value {
                    Value::Input(id) | Value::Output(id) => {
                        let id = PortId(id.id);
                        return Some(ValueGroupPortRef{
                            id,
                            heap_pos: Some(heap_pos),
                            index: region_index,
                        });
                    },
                    _ => {},
                }

                if let Some(heap_pos) = value.get_heap_pos() {
                    self.heap_stack.push((heap_pos as usize, 0));
                }
            } else {
                if self.index >= self.group.values.len() {
                    return None;
                }

                let value = &mut self.group.values[self.index];
                self.index += 1;

                match value {
                    Value::Input(id) | Value::Output(id) => {
                        let id = PortId(id.id);
                        return Some(ValueGroupPortRef{
                            id,
                            heap_pos: None,
                            index: self.index - 1
                        });
                    },
                    _ => {},
                }

                // Not a port, check if we need to enter a heap region
                if let Some(heap_pos) = value.get_heap_pos() {
                    self.heap_stack.push((heap_pos as usize, 0));
                } // else: just consider the next value
            }
        }
    }
}