pub struct PortId(pub(crate) Id);

    NewChannel,

    BlockFires(PortId),

    BlockGet(PortId),

    Put(PortId, Value),

    /// Big 'ol function right here. Didn't want to break it up unnecessarily.

    /// It consists of, in sequence: executing any expressions that should be

    /// executed before the next statement can be evaluated, then a section that

    /// performs debug printing, and finally a section that takes the next

    /// statement and executes it. If the statement requires any expressions to

    /// be evaluated, then they will be added such that the next time `step` is

    /// called, all of these expressions are indeed evaluated.

    pub(crate) fn step(&mut self, types: &TypeTable, heap: &Heap, modules: &[Module], ctx: &mut impl RunContext) -> EvalResult {

                                    let port_id = if let Value::Input(port_id) = value {

                                        port_id

                                    } else {

                                        unreachable!("executor calling 'get' on value {:?}", value)

                                    };

                                    match ctx.get(port_id, &mut self.store) {

                                            // We have the result

                                            // Don't have the result yet, prepare the expression to

                                            // get run again after we've received a message.

                                            return Ok(EvalContinuation::BlockGet(port_id));

                                    let port_id = if let Value::Output(port_id) = deref_port_value {

                                        port_id

                                    } else {

                                        unreachable!("executor calling 'put' on value {:?}", deref_port_value)

                                    };

                                    if ctx.did_put(port_id) {

                                        return Ok(EvalContinuation::Put(port_id, deref_msg_value));

                                    let port_id = match port_value_deref {

                                        Value::Input(port_id) => port_id,

                                        Value::Output(port_id) => port_id,

                                        _ => unreachable!("executor calling 'fires' on value {:?}", value),

                                    };

                                    match ctx.fires(port_id) {

                                            return Ok(EvalContinuation::BlockFires(port_id));

                        Ok(EvalContinuation::Stepping)

                        // Need to create a new channel by requesting it from

                        // the runtime.

                        match ctx.get_channel() {

                            None => {

                                // No channel is pending. So request one

                                Ok(EvalContinuation::NewChannel)

                            },

                            Some((put_port, get_port)) => {

                                self.store.write(ValueId::Stack(heap[stmt.from].unique_id_in_scope as u32), put_port);

                                self.store.write(ValueId::Stack(heap[stmt.to].unique_id_in_scope as u32), get_port);

                                cur_frame.position = stmt.next;

                                Ok(EvalContinuation::Stepping)

                            }

                        }

    pub(crate) modules: Vec<Module>,

    pub(crate) heap: Heap,

    pub(crate) types: TypeTable,

    pub(crate) pool: Mutex<StringPool>,

    pub(crate) prompt: Prompt,

        // TODO: Check for polymorph

// TODO: @temp Should just become a concrete thing that is passed in

pub trait RunContext {

    fn did_put(&self, port: PortId) -> bool;

    fn get(&self, port: PortId) -> Option<Value>; // None if still waiting on message

    fn fires(&self, port: PortId) -> Option<Value>; // None if not yet branched

    fn get_channel(&self) -> Option<(Value, Value)>; // None if not yet prepared

}

#[derive(Debug)]

pub enum RunResult {

    // Can only occur outside sync blocks

    ComponentTerminated, // component has exited its procedure

    ComponentAtSyncStart,

    NewComponent(DefinitionId, i32, ValueGroup), // should also be possible inside sync

    NewChannel, // should also be possible inside sync

    // Can only occur inside sync blocks

    BranchInconsistent, // branch has inconsistent behaviour

    BranchMissingPortState(PortId), // branch doesn't know about port firing

    BranchMissingPortValue(PortId), // branch hasn't received message on input port yet

    BranchAtSyncEnd,

    BranchPut(PortId, ValueGroup),

}

impl ComponentState {

    pub(crate) fn run(&mut self, ctx: &mut impl RunContext, pd: &ProtocolDescription) -> RunResult {

        use EvalContinuation as EC;

        use RunResult as RR;

        loop {

            let step_result = self.prompt.step(&pd.types, &pd.heap, &pd.modules, ctx);

            match step_result {

                Err(reason) => {

                    // TODO: @temp

                    println!("Evaluation error:\n{}", reason);

                    todo!("proper error handling/bubbling up");

                },

                Ok(continuation) => match continuation {

                    // TODO: Probably want to remove this translation

                    EC::Stepping => continue,

                    EC::Inconsistent => return RR::BranchInconsistent,

                    EC::Terminal => return RR::ComponentTerminated,

                    EC::SyncBlockStart => return RR::ComponentAtSyncStart,

                    EC::SyncBlockEnd => return RR::BranchAtSyncEnd,

                    EC::NewComponent(definition_id, monomorph_idx, args) =>

                        return RR::NewComponent(definition_id, monomorph_idx, arg),

                    EC::NewChannel =>

                        return RR::NewChannel,

                    EC::BlockFires(port_id) => return RR::BranchMissingPortState(port_id),

                    EC::BlockGet(port_id) => return RR::BranchMissingPortValue(port_id),

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

                        let value_group = ValueGroup::from_store(&self.prompt.store, &[value]);

                        return RR::BranchPut(port_id, value_group);

                    },

                }

            }

        }

    }

}

// TODO: @remove the old stuff

                        return SyncBlocker::PutMsg(port, payload);

mod runtime;

use std::collections::{HashMap, VecDeque};

use std::collections::hash_map::{Entry};

use crate::{Polarity, PortId};

use crate::common::Id;

struct PortDesc {

    id: u32,

    peer_id: u32,

    owning_connector_id: Option<u32>,

    is_getter: bool, // otherwise one can only call `put`

}

// Message received from some kind of peer

struct BufferedMessage {

    // If in inbox, then sender is the connector's peer. If in the outbox, then

    // the sender is the connector itself.

    sending_port: PortId,

    receiving_port: PortId,

    peer_prev_branch_id: Option<u32>, // of the sender

    peer_cur_branch_id: u32, // of the sender

    message: ValueGroup,

}

struct ConnectorDesc {

    id: u32,

    in_sync: bool,

    branches: Vec<BranchDesc>, // first one is always non-speculative one

    branch_id_counter: u32,

    spec_branches_active: VecDeque<u32>, // branches that can be run immediately

    spec_branches_pending_receive: HashMap<PortId, u32>, // from port_id to branch index

    global_inbox: HashMap<(PortId, u32), BufferedMessage>,

    global_outbox: HashMap<(PortId, u32), BufferedMessage>,

}

impl ConnectorDesc {

    /// Creates a new connector description. Implicit assumption is that there

    /// is one (non-sync) branch that can be immediately executed.

    fn new(id: u32, component_state: ComponentState, owned_ports: Vec<u32>) -> Self {

        let mut branches_active = VecDeque::new();

        branches_active.push_back(0);

        Self{

            id,

            in_sync: false,

            branches: vec![BranchDesc::new_non_sync(component_state, owned_ports)],

            branch_id_counter: 1,

            spec_branches_active: branches_active,

            spec_branches_pending_receive: HashMap::new(),

            global_inbox: HashMap::new(),

            global_outbox: HashMap::new(),

        }

    }

}

enum BranchState {

    RunningNonSync, // regular running non-speculative branch

    RunningSync, // regular running speculative branch

    BranchPoint, // branch which ended up being a branching point

    ReachedEndSync, // branch that successfully reached the end-sync point, is a possible local solution

    Failed, // branch that became inconsistent

}

struct BranchPortDesc {

    last_registered_identifier: Option<u32>, // if putter, then last sent branch ID, if getter, then last received branch ID

    num_times_fired: u32, // number of puts/gets on this port

}

struct BranchDesc {

    index: u32,

    parent_index: Option<u32>,

    identifier: u32,

    code_state: ComponentState,

    branch_state: BranchState,

    owned_ports: Vec<u32>,

    message_inbox: HashMap<(PortId, u32), ValueGroup>, // from (port id, 1-based recv index) to received value

    port_mapping: HashMap<PortId, BranchPortDesc>,

}

impl BranchDesc {

    /// Creates the first non-sync branch of a connector

    fn new_non_sync(component_state: ComponentState, owned_ports: Vec<u32>) -> Self {

        Self{

            index: 0,

            parent_index: None,

            identifier: 0,

            code_state: component_state,

            branch_state: BranchState::RunningNonSync,

            owned_ports,

            message_inbox: HashMap::new(),

            port_mapping: HashMap::new(),

        }

    }

    /// Creates a sync branch based on the supplied branch. This supplied branch

    /// is the branching point for the new one, i.e. the parent in the branching

    /// tree.

    fn new_sync_from(index: u32, identifier: u32, branch_state: &BranchDesc) -> Self {

        Self{

            index,

            parent_index: Some(branch_state.index),

            identifier,

            code_state: branch_state.code_state.clone(),

            branch_state: BranchState::RunningSync,

            owned_ports: branch_state.owned_ports.clone(),

            message_inbox: branch_state.message_inbox.clone(),

            port_mapping: branch_state.port_mapping.clone(),

        }

    }

}

// Separate from Runtime for borrowing reasons

struct Registry {

    ports: HashMap<u32, PortDesc>,

    port_counter: u32,

    connectors: HashMap<u32, ConnectorDesc>,

    connector_counter: u32,

}

impl Registry {

    fn new() -> Self {

        Self{

            ports: HashMap::new(),

            port_counter: 0,

            connectors: HashMap::new(),

            connector_counter: 0,

        }

    }

    /// Returns (putter_port, getter_port)

    pub fn add_channel(&mut self, owning_connector_id: Option<u32>) -> (u32, u32) {

        let get_id = self.generate_port_id();

        let put_id = self.generate_port_id();

        self.ports.insert(get_id, PortDesc{

            id: get_id,

            peer_id: put_id,

            owning_connector_id,

            is_getter: true,

        });

        self.ports.insert(put_id, PortDesc{

            id: put_id,

            peer_id: get_id,

            owning_connector_id,

            is_getter: false,

        });

        return (put_id, get_id);

    }

    fn generate_port_id(&mut self) -> u32 {

        let id = self.port_counter;

        self.port_counter += 1;

        return id;

    }

}

// TODO: @performance, use freelists+ids instead of HashMaps

    registry: Registry,

    connectors_active: VecDeque<u32>,

        Self{

            protocol: pd,

            registry: Registry::new(),

            connectors_active: VecDeque::new(),

        }

    }

    /// Creates a new channel that is not owned by any connector and returns its

    /// endpoints. The returned values are of the (putter port, getter port)

    /// respectively.

    pub fn add_channel(&mut self) -> (Value, Value) {

        let (put_id, get_id) = self.registry.add_channel(None);

        return (

            port_value_from_id(None, put_id, true),

            port_value_from_id(None, get_id, false)

        );

        use crate::runtime::error::AddComponentError as OldACE;

        // TODO: Remove this error enum translation. Note that for now this

        //  function forces port-only arguments

        let component_id = self.generate_connector_id();

        let ports = ports.into_iter().map(|v| v.0.u32_suffix).collect();

        self.registry.connectors.insert(component_id, ConnectorDesc::new(component_id, component_state, ports));

        self.connectors_active.push_back(component_id);

        Ok(())

    }

    pub fn run(&mut self) {

        // Go through all active connectors

        while !self.connectors_active.is_empty() {

            let next_id = self.connectors_active.pop_front().unwrap();

            self.run_connector(next_id);

        }

    }

    /// Runs a connector for as long as sensible, then returns `true` if the

    /// connector should be run again in the future, and return `false` if the

    /// connector has terminated. Note that a terminated connector still 

    /// requires cleanup.

    pub fn run_connector(&mut self, id: u32) -> bool {

        let desc = self.registry.connectors.get_mut(&id).unwrap();

        let mut run_context = Context{

            connector_id: id,

            branch_id: None,

            pending_channel: None,

        };

        let mut call_again = false;

        while call_again {

            call_again = false; // bit of a silly pattern, maybe revise

            if desc.in_sync {

                // Running in synchronous mode, so run all branches until their

                // blocking point

                debug_assert!(!desc.spec_branches_active.is_empty());

                let branch_index = desc.spec_branches_active.pop_front().unwrap();

                let branch = &mut desc.branches[branch_index as usize];

                let run_result = branch.code_state.run(&mut run_context, &self.protocol);

                match run_result {

                    RunResult::BranchInconsistent => {

                        // Speculative branch became inconsistent. So we don't

                        // run it again

                        branch.branch_state = BranchState::Failed;

                    },

                    RunResult::BranchMissingPortState(port_id) => {

                        // Branch called `fires()` on a port that did not have a

                        // value assigned yet. So branch and keep running

                        debug_assert!(branch.owned_ports.contains(&port_id.0.u32_suffix));

                        debug_assert!(branch.port_mapping.get(&port_id).is_none());

                        let copied_index = Self::duplicate_branch(desc, branch_index);

                        // Need to re-borrow to assign changed port state

                        let original_branch = &mut desc.branches[branch_index as usize];

                        original_branch.port_mapping.insert(port_id, BranchPortDesc{

                            last_registered_identifier: None,

                            num_times_fired: 0,

                        });

                        let copied_branch = &mut desc.branches[copied_index as usize];

                        copied_branch.port_mapping.insert(port_id, BranchPortDesc{

                            last_registered_identifier: None,

                            num_times_fired: 1,

                        });

                        // Run both again

                        desc.spec_branches_active.push_back(branch_index);

                        desc.spec_branches_active.push_back(copied_index);

                    },

                    RunResult::BranchMissingPortValue(port_id) => {

                        // Branch just performed a `get()` on a port that did

                        // not yet receive a value.

                        // First check if a port value is assigned to the

                        // current branch. If so, check if it is consistent.

                        debug_assert!(branch.owned_ports.contains(&port_id.0.u32_suffix));

                        match branch.port_mapping.entry(port_id) {

                            Entry::Vacant(entry) => {

                                // No entry yet, so force to firing

                                entry.insert(BranchPortDesc{

                                    last_registered_identifier: None,

                                    num_times_fired: 1,

                                });

                                branch.branch_state = BranchState::BranchPoint;

                                desc.spec_branches_pending_receive.insert(port_id, branch_index);

                            },

                            Entry::Occupied(entry) => {

                                // Have an entry, check if it is consistent

                                let entry = entry.get();

                                if entry.num_times_fired == 0 {

                                    // Inconsistent

                                    branch.branch_state = BranchState::Failed;

                                } else {

                                    // Perfectly fine, add to queue

                                    branch.branch_state = BranchState::BranchPoint;

                                    desc.spec_branches_pending_receive.insert(port_id, branch_index);

                                }

                            }

                        }

                    },

                    RunResult::BranchAtSyncEnd => {

                        branch.branch_state = BranchState::ReachedEndSync;

                        todo!("somehow propose solution");

                    },

                    RunResult::BranchPut(port_id, value_group) => {

                        debug_assert!(branch.owned_ports.contains(&port_id.0.u32_suffix));

                        debug_assert_eq!(value_group.values.len(), 1)

                    },

                    _ => unreachable!("got result '{:?}' from running component in sync mode", run_result),

                }

            } else {

                // Running in non-synchronous mode

                let branch = &mut desc.branches[0];

                let run_result = branch.code_state.run(&mut run_context, &self.protocol);

                match run_result {

                    RunResult::ComponentTerminated => return false,

                    RunResult::ComponentAtSyncStart => {

                        // Prepare for sync execution

                        Self::prepare_branch_for_sync(desc);

                        call_again = true;

                    },

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

                        // Generate a new connector with its own state

                        let new_component_id = self.generate_connector_id();

                        let new_component_state = ComponentState {

                            prompt: Prompt::new(&self.protocol.types, &self.protocol.heap, definition_id, monomorph_idx, arguments)

                        };

                        // Transfer the ownership of any ports to the new connector

                        let mut ports = Vec::with_capacity(arguments.values.len());

                        find_ports_in_value_group(&arguments, &mut ports);

                        for port_id in &ports {

                            let port = self.registry.ports.get_mut(&port_id.0.u32_suffix).unwrap();

                            debug_assert_eq!(port.owning_connector_id.unwrap(), run_context.connector_id);

                            port.owning_connector_id = Some(new_component_id)

                        }

                        // Finally push the new connector into the registry

                        let ports = ports.into_iter().map(|v| v.0.u32_suffix).collect();

                        self.registry.connectors.insert(new_component_id, ConnectorDesc::new(new_component_id, new_component_state, ports));

                        self.connectors_active.push_back(new_component_id);

                    },

                    RunResult::NewChannel => {

                        // Prepare channel

                        debug_assert!(run_context.pending_channel.is_none());

                        let (put_id, get_id) = self.registry.add_channel(Some(run_context.connector_id));

                        run_context.pending_channel = Some((

                            port_value_from_id(Some(run_context.connector_id), put_id, true),

                            port_value_from_id(Some(run_context.connector_id), get_id, false)

                        ));

                        // Call again so it is retrieved from the context

                        call_again = true;

                    },

                    _ => unreachable!("got result '{:?}' from running component in non-sync mode", run_result),

                }

            }

        }

        return true;

    }

    fn generate_connector_id(&mut self) -> u32 {

        let id = self.registry.connector_counter;

        self.registry.connector_counter += 1;

        return id;

    }

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

    // Helpers for branch management

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

    /// Prepares a speculative branch for further execution from the connector's

    /// non-speculative base branch.

    fn prepare_branch_for_sync(desc: &mut ConnectorDesc) {

        // Ensure only one branch is active, the non-sync branch

        debug_assert!(!desc.in_sync);

        debug_assert_eq!(desc.branches.len(), 1);

        debug_assert!(desc.spec_branches_active.is_empty());

        let new_branch_index = 1;

        let new_branch_identifier = desc.branch_id_counter;

        desc.branch_id_counter += 1;

        // Push first speculative branch as active branch

        let new_branch = BranchDesc::new_sync_from(new_branch_index, new_branch_identifier, &desc.branches[0]);

        desc.branches.push(new_branch);

        desc.spec_branches_active.push_back(new_id);

        desc.in_sync = true;

    }

    /// Duplicates a particular (speculative) branch and returns its index.

    fn duplicate_branch(desc: &mut ConnectorDesc, original_branch_idx: u32) -> u32 {

        let original_branch = &desc.branches[original_branch_idx as usize];

        debug_assert!(desc.in_sync);

        let copied_index = desc.branches.len() as u32;

        let copied_id = desc.branch_id_counter;

        desc.branch_id_counter += 1;

        let copied_branch = BranchDesc::new_sync_from(copied_index, copied_id, original_branch);

        desc.branches.push(copied_branch);

        return copied_index;

    }

}

/// Context accessible by the code while being executed by the runtime. When the

/// code is being executed by the runtime it sometimes needs to interact with 

/// the runtime. This is achieved by the "code throwing an error code", after 

/// which the runtime modifies the appropriate variables and continues executing

/// the code again. 

struct Context<'a> {

    // Properties of currently running connector/branch

    connector_id: u32,

    branch_id: Option<u32>,

    // Resources ready to be retrieved by running code

    pending_channel: Option<(Value, Value)>, // (put, get) ports

}

impl<'a> crate::protocol::RunContext for Context<'a> {

    fn did_put(&self, port: PortId) -> bool {

        todo!()

    }

    fn get(&self, port: PortId) -> Option<Value> {

        todo!()

    }

    fn fires(&self, port: PortId) -> Option<Value> {

        todo!()

    }

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

        self.pending_channel.take()

    }

}

/// Recursively goes through the value group, attempting to find ports. 

/// Duplicates will only be added once.

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

                for prev_port in ports {

                    if prev_port == port_id {

                        // Already added

                        return;

                    }

                }

                ports.push(*port_id);

            },

            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);