use std::fmt::{Display as FmtDisplay, Result as FmtResult, Formatter};

use crate::protocol::eval::{Prompt, EvalError, ValueGroup, Value, ValueId, PortId as EvalPortId};
use crate::protocol::*;
use crate::runtime2::*;
use crate::runtime2::communication::*;
use crate::runtime2::component::component_pdl::find_ports_in_value_group;

use super::{CompCtx, CompPDL, CompId};
use super::component_context::*;
use super::component_random::*;
use super::component_internet::*;
use super::control_layer::*;
use super::consensus::*;

pub enum CompScheduling {
    Immediate,
    Requeue,
    Sleep,
    Exit,
}

/// Potential error emitted by a component
pub enum CompError {
    /// Error originating from the code executor. Hence has an associated
    /// source location.
    Executor(EvalError),
    /// Error originating from a component, but not necessarily associated with
    /// a location in the source.
    Component(String), // TODO: Maybe a different embedded value in the future?
    /// Pure runtime error. Not necessarily originating from the component
    /// itself. Should be treated as a very severe runtime-compromising error.
    Runtime(RtError),
}

impl FmtDisplay for CompError {
    fn fmt(&self, f: &mut Formatter<'_>) -> FmtResult {
        match self {
            CompError::Executor(v) => v.fmt(f),
            CompError::Component(v) => v.fmt(f),
            CompError::Runtime(v) => v.fmt(f),
        }
    }
}

/// Generic representation of a component (as viewed by a scheduler).
pub(crate) trait Component {
    /// Called upon the creation of the component. Note that the scheduler
    /// context is officially running another component (the component that is
    /// creating the new component).
    fn on_creation(&mut self, comp_id: CompId, sched_ctx: &SchedulerCtx);

    /// Called when a component crashes or wishes to exit. So is not called
    /// right before destruction, other components may still hold a handle to
    /// the component and send it messages!
    fn on_shutdown(&mut self, sched_ctx: &SchedulerCtx);

    /// Called if the component is created by another component and the messages
    /// are being transferred between the two.
    fn adopt_message(&mut self, comp_ctx: &mut CompCtx, message: DataMessage);

    /// Called if the component receives a new message. The component is
    /// responsible for deciding where that messages goes.
    fn handle_message(&mut self, sched_ctx: &mut SchedulerCtx, comp_ctx: &mut CompCtx, message: Message);

    /// Called if the component's routine should be executed. The return value
    /// can be used to indicate when the routine should be run again.
    fn run(&mut self, sched_ctx: &mut SchedulerCtx, comp_ctx: &mut CompCtx) -> CompScheduling;
}

/// Representation of the generic operating mode of a component. Although not
/// every state may be used by every kind of (builtin) component, this allows
/// writing standard handlers for particular events in a component's lifetime.
#[derive(Debug, Copy, Clone, PartialEq, Eq)]
pub(crate) enum CompMode {
    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
    BlockedPutPorts,// blocked because we're waiting to send a data message containing ports
    StartExit, // temporary state: if encountered then we start the shutdown process.
    BusyExit, // temporary state: waiting for Acks for all the closed ports, potentially waiting for sync round to finish
    Exit, // exiting: shutdown process started, now waiting until the reference count drops to 0
}

impl CompMode {
    pub(crate) fn is_in_sync_block(&self) -> bool {
        use CompMode::*;

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

    pub(crate) fn is_busy_exiting(&self) -> bool {
        use CompMode::*;

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

#[derive(Debug)]
pub(crate) enum ExitReason {
    Termination, // regular termination of component
    ErrorInSync,
    ErrorNonSync,
}

impl ExitReason {
    pub(crate) fn is_in_sync(&self) -> bool {
        use ExitReason::*;

        match self {
            Termination | ErrorNonSync => false,
            ErrorInSync => true,
        }
    }

    pub(crate) fn is_error(&self) -> bool {
        use ExitReason::*;

        match self {
            Termination => false,
            ErrorInSync | ErrorNonSync => true,
        }
    }
}

/// Component execution state: the execution mode along with some descriptive
/// fields. Fields are public for ergonomic reasons, use member functions when
/// appropriate.
pub(crate) struct CompExecState {
    pub mode: CompMode,
    pub mode_port: PortId, // valid if blocked on a port (put/get)
    pub mode_value: ValueGroup, // valid if blocked on a put
    pub exit_reason: ExitReason, // valid if in StartExit/BusyExit/Exit mode
}

impl CompExecState {
    pub(crate) fn new() -> Self {
        return Self{
            mode: CompMode::NonSync,
            mode_port: PortId::new_invalid(),
            mode_value: ValueGroup::default(),
            exit_reason: ExitReason::Termination,
        }
    }

    pub(crate) fn set_as_start_exit(&mut self, reason: ExitReason) {
        self.mode = CompMode::StartExit;
        self.exit_reason = reason;
    }

    pub(crate) fn set_as_blocked_get(&mut self, port: PortId) {
        self.mode = CompMode::BlockedGet;
        self.mode_port = port;
        debug_assert!(self.mode_value.values.is_empty());
    }

    pub(crate) fn is_blocked_on_get(&self, port: PortId) -> bool {
        return
            self.mode == CompMode::BlockedGet &&
            self.mode_port == port;
    }

    pub(crate) fn set_as_blocked_put(&mut self, port: PortId, value: ValueGroup) {
        self.mode = CompMode::BlockedPut;
        self.mode_port = port;
        self.mode_value = value;
    }

    pub(crate) fn is_blocked_on_put(&self, port: PortId) -> bool {
        return
            self.mode == CompMode::BlockedPut &&
            self.mode_port == port;
    }
}

// TODO: Replace when implementing port sending. Should probably be incorporated
//  into CompCtx (and rename CompCtx into CompComms)
pub(crate) type InboxMain = Vec<Option<DataMessage>>;
pub(crate) type InboxMainRef = [Option<DataMessage>];
pub(crate) type InboxBackup = Vec<DataMessage>;

/// Creates a new component based on its definition. Meaning that if it is a
/// user-defined component then we set up the PDL code state. Otherwise we
/// construct a custom component. This does NOT take care of port and message
/// management.
pub(crate) fn create_component(
    protocol: &ProtocolDescription,
    definition_id: ProcedureDefinitionId, type_id: TypeId,
    arguments: ValueGroup, num_ports: usize
) -> Box<dyn Component> {
    let definition = &protocol.heap[definition_id];
    debug_assert!(definition.kind == ProcedureKind::Primitive || definition.kind == ProcedureKind::Composite);

    if definition.source.is_builtin() {
        // Builtin component
        let component: Box<dyn Component> = match definition.source {
            ProcedureSource::CompRandomU32 => Box::new(ComponentRandomU32::new(arguments)),
            ProcedureSource::CompTcpClient => Box::new(ComponentTcpClient::new(arguments)),
            _ => unreachable!(),
        };

        return component;
    } else {
        // User-defined component
        let prompt = Prompt::new(
            &protocol.types, &protocol.heap,
            definition_id, type_id, arguments
        );
        let component = CompPDL::new(prompt, num_ports);
        return Box::new(component);
    }
}

// -----------------------------------------------------------------------------
// Generic component messaging utilities (for sending and receiving)
// -----------------------------------------------------------------------------

/// Default handling of sending a data message. In case the port is blocked then
/// the `ExecState` will become blocked as well. Note that
/// `default_handle_control_message` will ensure that the port becomes
/// unblocked if so instructed by the receiving component. The returned
/// scheduling value must be used.
#[must_use]
pub(crate) fn default_send_data_message(
    exec_state: &mut CompExecState, transmitting_port_id: PortId,
    port_instruction: PortInstruction, value: ValueGroup,
    sched_ctx: &SchedulerCtx, consensus: &mut Consensus, comp_ctx: &mut CompCtx
) -> Result<CompScheduling, (PortInstruction, String)> {
    debug_assert_eq!(exec_state.mode, CompMode::Sync);

    let port_handle = comp_ctx.get_port_handle(transmitting_port_id);
    let port_info = comp_ctx.get_port_mut(port_handle);
    port_info.last_instruction = port_instruction;

    let port_info = comp_ctx.get_port(port_handle);
    debug_assert_eq!(port_info.kind, PortKind::Putter);

    if port_info.state.is_closed() {
        // Note: normally peer is eventually consistent, but if it has shut down
        // then we can be sure it is consistent (I think?)
        return Err((
            port_info.last_instruction,
            format!("Cannot send on this port, as the peer (id:{}) has shut down", port_info.peer_comp_id.0)
        ))
    } else if port_info.state.is_blocked() {
        // Port is blocked, so we cannot send
        exec_state.set_as_blocked_put(transmitting_port_id, value);

        return Ok(CompScheduling::Sleep);
    } else {
        // Check if there are any ports that are being transmitted
        let mut ports = Vec::new();
        find_ports_in_value_group(&value, &mut ports);
        if !ports.is_empty() {


            for (value_location, port_id) in ports {
                let transmitted_port_handle = comp_ctx.get_port_handle(port_id);
                let transmitted_port = comp_ctx.get_port(transmitted_port_handle);

                if transmitted_port.state.is_set(PortStateFlag::Transmitted) {
                    // Note: We could also attach where the port has been
                    //  transferred
                    return Err((
                        port_info.last_instruction,
                        String::from("Cannot send this message, as it contains a previously transmitted port")
                    ));
                }

                // Prepare ack for PPC
                // Prepare PPC message
            }
        }

        // Port is not blocked, so send to the peer
        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 = consensus.annotate_data_message(comp_ctx, port_info, value);
        peer_info.handle.send_message_logged(sched_ctx, Message::Data(annotated_message), true);

        return Ok(CompScheduling::Immediate);
    }
}

pub(crate) enum IncomingData {
    PlacedInSlot,
    SlotFull(DataMessage),
}

/// Default handling of receiving a data message. In case there is no room for
/// the message it is returned from this function. Note that this function is
/// different from PDL code performing a `get` on a port; this is the case where
/// the message first arrives at the component.
// NOTE: This is supposed to be a somewhat temporary implementation. It would be
//  nicest if the sending component can figure out it cannot send any more data.
#[must_use]
pub(crate) fn default_handle_incoming_data_message(
    exec_state: &mut CompExecState, inbox_main: &mut InboxMain,
    comp_ctx: &mut CompCtx, incoming_message: DataMessage,
    sched_ctx: &SchedulerCtx, control: &mut ControlLayer
) -> IncomingData {
    let port_handle = comp_ctx.get_port_handle(incoming_message.data_header.target_port);
    let port_index = comp_ctx.get_port_index(port_handle);
    comp_ctx.get_port_mut(port_handle).received_message_for_sync = true;
    let port_value_slot = &mut inbox_main[port_index];
    let target_port_id = incoming_message.data_header.target_port;

    if port_value_slot.is_none() {
        // We can put the value in the slot
        *port_value_slot = Some(incoming_message);

        // Check if we're blocked on receiving this message.
        dbg_code!({
            // Our port cannot have been blocked itself, because we're able to
            // directly insert the message into its slot.
            assert!(!comp_ctx.get_port(port_handle).state.is_blocked());
        });

        if exec_state.is_blocked_on_get(target_port_id) {
            // Return to normal operation
            exec_state.mode = CompMode::Sync;
            exec_state.mode_port = PortId::new_invalid();
            debug_assert!(exec_state.mode_value.values.is_empty());
        }

        return IncomingData::PlacedInSlot
    } else {
        // Slot is already full, so if the port was previously opened, it will
        // now become closed
        let port_info = comp_ctx.get_port_mut(port_handle);
        if port_info.state.is_open() {
            port_info.state.set(PortStateFlag::BlockedDueToFullBuffers);

            let (peer_handle, message) =
                control.initiate_port_blocking(comp_ctx, port_handle);
            let peer = comp_ctx.get_peer(peer_handle);
            peer.handle.send_message_logged(sched_ctx, Message::Control(message), true);
        }

        return IncomingData::SlotFull(incoming_message)
    }
}

pub(crate) enum GetResult {
    Received(DataMessage),
    NoMessage,
    Error((PortInstruction, String)),
}

/// Default attempt at trying to receive from a port (i.e. through a `get`, or
/// the equivalent operation for a builtin component). `target_port` is the port
/// we're trying to receive from, and the `target_port_instruction` is the
/// instruction we're attempting on this port.
pub(crate) fn default_attempt_get(
    exec_state: &mut CompExecState, target_port: PortId, target_port_instruction: PortInstruction,
    inbox_main: &mut InboxMainRef, inbox_backup: &mut InboxBackup, sched_ctx: &SchedulerCtx,
    comp_ctx: &mut CompCtx, control: &mut ControlLayer, consensus: &mut Consensus
) -> GetResult {
    let port_handle = comp_ctx.get_port_handle(target_port);
    let port_index = comp_ctx.get_port_index(port_handle);

    let port_info = comp_ctx.get_port_mut(port_handle);
    port_info.last_instruction = target_port_instruction;
    if port_info.state.is_closed() {
        let peer_id = port_info.peer_comp_id;
        return GetResult::Error((
            target_port_instruction,
            format!("Cannot get from this port, as the peer component (id:{}) closed the port", peer_id.0)
        ));
    }

    if let Some(message) = &inbox_main[port_index] {
        if consensus.try_receive_data_message(sched_ctx, comp_ctx, message) {
            // We're allowed to receive this message
            let message = inbox_main[port_index].take().unwrap();
            debug_assert_eq!(target_port, message.data_header.target_port);

            // Note: we can still run into an unrecoverable error when actually
            // receiving this message
            match default_handle_received_data_message(
                target_port, target_port_instruction, inbox_main, inbox_backup,
                comp_ctx, sched_ctx, control,
            ) {
                Ok(()) => return GetResult::Received(message),
                Err(location_and_message) => return GetResult::Error(location_and_message)
            }
        } else {
            // We're not allowed to receive this message. This means that the
            // receiver is attempting to receive something out of order with
            // respect to the sender.
            return GetResult::Error((target_port_instruction, String::from(
                "Cannot get from this port, as this causes a deadlock. This happens if you `get` in a different order as another component `put`s"
            )));
        }
    } else {
        // We don't have a message waiting for us and the port is not blocked.
        // So enter the BlockedGet state
        exec_state.set_as_blocked_get(target_port);
        return GetResult::NoMessage;
    }
}

/// Default handling that has been received through a `get`. Will check if any
/// more messages are waiting, and if the corresponding port was blocked because
/// of full buffers (hence, will use the control layer to make sure the peer
/// will become unblocked).
pub(crate) fn default_handle_received_data_message(
    targeted_port: PortId, port_instruction: PortInstruction,
    inbox_main: &mut InboxMainRef, inbox_backup: &mut InboxBackup,
    comp_ctx: &mut CompCtx, sched_ctx: &SchedulerCtx, control: &mut ControlLayer
) -> Result<(), (PortInstruction, String)> {
    let port_handle = comp_ctx.get_port_handle(targeted_port);
    let port_index = comp_ctx.get_port_index(port_handle);
    let slot = &mut inbox_main[port_index];
    debug_assert!(slot.is_none()); // because we've just received from it

    // Modify last-known location where port instruction was retrieved
    let port_info = comp_ctx.get_port(port_handle);
    debug_assert_ne!(port_info.last_instruction, PortInstruction::None); // set by caller
    debug_assert!(port_info.state.is_open()); // checked by caller

    // Check if there are any more messages in the backup buffer
    for message_index in 0..inbox_backup.len() {
        let message = &inbox_backup[message_index];
        if message.data_header.target_port == targeted_port {
            // One more message, place it in the slot
            let message = inbox_backup.remove(message_index);
            debug_assert!(comp_ctx.get_port(port_handle).state.is_blocked()); // since we're removing another message from the backup
            *slot = Some(message);

            return Ok(());
        }
    }

    // Did not have any more messages, so if we were blocked, then we need to
    // unblock the port now (and inform the peer of this unblocking)
    if port_info.state.is_set(PortStateFlag::BlockedDueToFullBuffers) {
        let port_info = comp_ctx.get_port_mut(port_handle);
        port_info.state.clear(PortStateFlag::BlockedDueToFullBuffers);

        let (peer_handle, message) = control.cancel_port_blocking(comp_ctx, port_handle);
        let peer_info = comp_ctx.get_peer(peer_handle);
        peer_info.handle.send_message_logged(sched_ctx, Message::Control(message), true);
    }

    return Ok(());
}

/// Handles control messages in the default way. Note that this function may
/// take a lot of actions in the name of the caller: pending messages may be
/// sent, ports may become blocked/unblocked, etc. So the execution
/// (`CompExecState`), control (`ControlLayer`) and consensus (`Consensus`)
/// state may all change.
pub(crate) fn default_handle_control_message(
    exec_state: &mut CompExecState, control: &mut ControlLayer, consensus: &mut Consensus,
    message: ControlMessage, sched_ctx: &SchedulerCtx, comp_ctx: &mut CompCtx
) -> Result<(), (PortInstruction, String)> {
    match message.content {
        ControlMessageContent::Ack => {
            default_handle_ack(control, message.id, sched_ctx, comp_ctx);
        },
        ControlMessageContent::BlockPort => {
            // One of our messages was accepted, but the port should be
            // blocked.
            let port_to_block = message.target_port_id.unwrap();
            let port_handle = comp_ctx.get_port_handle(port_to_block);
            let port_info = comp_ctx.get_port_mut(port_handle);
            debug_assert_eq!(port_info.kind, PortKind::Putter);
            port_info.state.set(PortStateFlag::BlockedDueToFullBuffers);
        },
        ControlMessageContent::ClosePort(content) => {
            // Request to close the port. We immediately comply and remove
            // the component handle as well
            let port_to_close = message.target_port_id.unwrap();
            let port_handle = comp_ctx.get_port_handle(port_to_close);

            // We're closing the port, so we will always update the peer of the
            // port (in case of error messages)
            let port_info = comp_ctx.get_port_mut(port_handle);
            port_info.peer_comp_id = message.sender_comp_id;
            port_info.close_at_sync_end = true; // might be redundant (we might set it closed now)

            let peer_comp_id = port_info.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) = control.has_close_port_entry(port_handle, comp_ctx) {
                // The two components (sender and this component) are closing
                // the channel at the same time. So we don't care about the
                // content of the `ClosePort` message.
                default_handle_ack(control, control_id, sched_ctx, comp_ctx);
            } else {
                // Respond to the message
                let port_info = comp_ctx.get_port(port_handle);
                let last_instruction = port_info.last_instruction;
                let port_has_had_message = port_info.received_message_for_sync;
                default_send_ack(message.id, peer_handle, sched_ctx, comp_ctx);
                comp_ctx.change_port_peer(sched_ctx, port_handle, None);

                // Handle any possible error conditions (which boil down to: the
                // port has been used, but the peer has died). If not in sync
                // mode then we close the port immediately.

                // Note that `port_was_used` does not mean that any messages
                // were actually received. It might also mean that e.g. the
                // component attempted a `get`, but there were no messages, so
                // now it is in the `BlockedGet` state.
                let port_was_used = last_instruction != PortInstruction::None;

                if exec_state.mode.is_in_sync_block() {
                    let closed_during_sync_round = content.closed_in_sync_round && port_was_used;
                    let closed_before_sync_round = !content.closed_in_sync_round && !port_has_had_message;

                    if closed_during_sync_round || closed_before_sync_round {
                        return Err((
                            last_instruction,
                            format!("Peer component (id:{}) shut down, so communication cannot (have) succeed(ed)", peer_comp_id.0)
                        ));
                    }
                } else {
                    let port_info = comp_ctx.get_port_mut(port_handle);
                    port_info.state.set(PortStateFlag::Closed);
                }
            }
        },
        ControlMessageContent::UnblockPort => {
            // We were previously blocked (or already closed)
            let port_to_unblock = message.target_port_id.unwrap();
            let port_handle = comp_ctx.get_port_handle(port_to_unblock);
            let port_info = comp_ctx.get_port_mut(port_handle);

            debug_assert_eq!(port_info.kind, PortKind::Putter);
            debug_assert!(port_info.state.is_set(PortStateFlag::BlockedDueToFullBuffers));

            port_info.state.clear(PortStateFlag::BlockedDueToFullBuffers);
            default_handle_recently_unblocked_port(exec_state, consensus, port_handle, sched_ctx, comp_ctx);
        },
        ControlMessageContent::PortPeerChangedBlock => {
            // 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.
            let port_to_change = message.target_port_id.unwrap();
            let port_handle = comp_ctx.get_port_handle(port_to_change);

            let port_info = comp_ctx.get_port_mut(port_handle);
            let peer_comp_id = port_info.peer_comp_id;
            port_info.state.set(PortStateFlag::BlockedDueToPeerChange);
            let peer_handle = comp_ctx.get_peer_handle(peer_comp_id);

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

            let port_info = comp_ctx.get_port_mut(port_handle);
            port_info.peer_port_id = new_port_id;

            port_info.state.clear(PortStateFlag::BlockedDueToPeerChange);
            comp_ctx.change_port_peer(sched_ctx, port_handle, Some(new_comp_id));
            default_handle_recently_unblocked_port(exec_state, consensus, port_handle, sched_ctx, comp_ctx);
        }
    }

    return Ok(());
}

/// Handles a component entering the synchronous block. Will ensure that the
/// `Consensus` and the `ComponentCtx` are initialized properly.
pub(crate) fn default_handle_sync_start(
    exec_state: &mut CompExecState, inbox_main: &mut InboxMainRef,
    sched_ctx: &SchedulerCtx, comp_ctx: &mut CompCtx, consensus: &mut Consensus
) {
    sched_ctx.info("Component starting sync mode");

    // If any messages are present for this sync round, set the appropriate flag
    // and notify the consensus handler of the present messages
    consensus.notify_sync_start(comp_ctx);
    for (port_index, message) in inbox_main.iter().enumerate() {
        if let Some(message) = message {
            consensus.handle_incoming_data_message(comp_ctx, message);
            let port_info = comp_ctx.get_port_by_index_mut(port_index);
            port_info.received_message_for_sync = true;
        }
    }

    // Modify execution state
    debug_assert_eq!(exec_state.mode, CompMode::NonSync);
    exec_state.mode = CompMode::Sync;
}

/// Handles a component that has reached the end of the sync block. This does
/// not necessarily mean that the component will go into the `NonSync` mode, as
/// it might have to wait for the leader to finish the round for everyone (see
/// `default_handle_sync_decision`)
pub(crate) fn default_handle_sync_end(
    exec_state: &mut CompExecState, sched_ctx: &SchedulerCtx, comp_ctx: &mut CompCtx,
    consensus: &mut Consensus
) {
    sched_ctx.info("Component ending sync mode (but possibly waiting for a solution)");
    debug_assert_eq!(exec_state.mode, CompMode::Sync);
    let decision = consensus.notify_sync_end_success(sched_ctx, comp_ctx);
    exec_state.mode = CompMode::SyncEnd;
    default_handle_sync_decision(sched_ctx, exec_state, comp_ctx, decision, consensus);
}

/// Handles a component initiating the exiting procedure, and closing all of its
/// ports. Should only be called once per component (which is ensured by
/// checking and modifying the mode in the execution state).
#[must_use]
pub(crate) fn default_handle_start_exit(
    exec_state: &mut CompExecState, control: &mut ControlLayer,
    sched_ctx: &SchedulerCtx, comp_ctx: &mut CompCtx, consensus: &mut Consensus
) -> CompScheduling {
    debug_assert_eq!(exec_state.mode, CompMode::StartExit);
    sched_ctx.info(&format!("Component starting exit (reason: {:?})", exec_state.exit_reason));
    exec_state.mode = CompMode::BusyExit;
    let exit_inside_sync = exec_state.exit_reason.is_in_sync();

    // If exiting while inside sync mode, report to the leader of the current
    // round that we've failed.
    if exit_inside_sync {
        let decision = consensus.notify_sync_end_failure(sched_ctx, comp_ctx);
        default_handle_sync_decision(sched_ctx, exec_state, comp_ctx, decision, consensus);
    }

    // Iterating over ports by index to work around 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.is_closed() || port.close_at_sync_end {
            // Already closed, or in the process of being closed
            continue;
        }

        // Mark as closed
        let port_id = port.self_id;
        port.state.set(PortStateFlag::Closed);

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

    return CompScheduling::Immediate; // to check if we can shut down immediately
}

/// Handles a component waiting until all peers are notified that it is quitting
/// (i.e. after calling `default_handle_start_exit`).
#[must_use]
pub(crate) fn default_handle_busy_exit(
    exec_state: &mut CompExecState, control: &ControlLayer,
    sched_ctx: &SchedulerCtx
) -> CompScheduling {
    debug_assert_eq!(exec_state.mode, CompMode::BusyExit);
    if control.has_acks_remaining() {
        sched_ctx.info("Component busy exiting, still has `Ack`s remaining");
        return CompScheduling::Sleep;
    } else {
        sched_ctx.info("Component busy exiting, now shutting down");
        exec_state.mode = CompMode::Exit;
        return CompScheduling::Exit;
    }
}

/// Handles a potential synchronous round decision. If there was a decision then
/// the `Some(success)` value indicates whether the round succeeded or not.
/// Might also end up changing the `ExecState`.
///
/// Might be called in two cases:
/// 1. The component is in regular execution mode, at the end of a sync round,
///     and is waiting for a solution to the round.
/// 2. The component has encountered an error during a sync round and is
///     exiting, hence is waiting for a "Failure" message from the leader.
pub(crate) fn default_handle_sync_decision(
    sched_ctx: &SchedulerCtx, exec_state: &mut CompExecState, comp_ctx: &mut CompCtx,
    decision: SyncRoundDecision, consensus: &mut Consensus
) -> Option<bool> {
    let success = match decision {
        SyncRoundDecision::None => return None,
        SyncRoundDecision::Solution => true,
        SyncRoundDecision::Failure => false,
    };

    debug_assert!(
        exec_state.mode == CompMode::SyncEnd || (
            exec_state.mode.is_busy_exiting() && exec_state.exit_reason.is_error()
        ) || (
            exec_state.mode.is_in_sync_block() && decision == SyncRoundDecision::Failure
        )
    );

    sched_ctx.info(&format!("Handling decision {:?} (in mode: {:?})", decision, exec_state.mode));
    consensus.notify_sync_decision(decision);
    if success {
        // We cannot get a success message if the component has encountered an
        // error.
        for port_index in 0..comp_ctx.num_ports() {
            let port_info = comp_ctx.get_port_by_index_mut(port_index);
            if port_info.close_at_sync_end {
                port_info.state.set(PortStateFlag::Closed);
            }
        }
        debug_assert_eq!(exec_state.mode, CompMode::SyncEnd);
        exec_state.mode = CompMode::NonSync;
        return Some(true);
    } else {
        // We may get failure both in all possible cases. But we should only
        // modify the execution state if we're not already in exit mode
        if !exec_state.mode.is_busy_exiting() {
            sched_ctx.error("failed synchronous round, initiating exit");
            exec_state.set_as_start_exit(ExitReason::ErrorNonSync);
        }
        return Some(false);
    }
}

/// Performs the default action of printing the provided error, and then putting
/// the component in the state where it will shut down. Only to be used for
/// builtin components: their error message construction is simpler (and more
/// common) as they don't have any source code.
pub(crate) fn default_handle_error_for_builtin(
    exec_state: &mut CompExecState, sched_ctx: &SchedulerCtx,
    location_and_message: (PortInstruction, String)
) {
    let (_location, message) = location_and_message;
    sched_ctx.error(&message);

    let exit_reason = if exec_state.mode.is_in_sync_block() {
        ExitReason::ErrorInSync
    } else {
        ExitReason::ErrorNonSync
    };

    exec_state.set_as_start_exit(exit_reason);
}

#[inline]
pub(crate) fn default_handle_exit(_exec_state: &CompExecState) -> CompScheduling {
    debug_assert_eq!(_exec_state.mode, CompMode::Exit);
    return CompScheduling::Exit;
}

// -----------------------------------------------------------------------------
// Internal messaging/state utilities
// -----------------------------------------------------------------------------

/// Handles an `Ack` for the control layer.
fn default_handle_ack(
    control: &mut ControlLayer, control_id: ControlId,
    sched_ctx: &SchedulerCtx, comp_ctx: &mut CompCtx
) {
    // Since an `Ack` may cause another one, handle them in a loop
    let mut to_ack = control_id;
    loop {
        let (action, new_to_ack) = 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_logged(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,
        }
    }
}

/// Little helper for sending the most common kind of `Ack`
fn default_send_ack(
    causer_of_ack_id: ControlId, peer_handle: LocalPeerHandle,
    sched_ctx: &SchedulerCtx, comp_ctx: &CompCtx
) {
    let peer_info = comp_ctx.get_peer(peer_handle);
    peer_info.handle.send_message_logged(sched_ctx, Message::Control(ControlMessage{
        id: causer_of_ack_id,
        sender_comp_id: comp_ctx.id,
        target_port_id: None,
        content: ControlMessageContent::Ack
    }), true);
}

/// Handles the unblocking of a putter port. In case there is a pending message
/// on that port then it will be sent.
fn default_handle_recently_unblocked_port(
    exec_state: &mut CompExecState, consensus: &mut Consensus,
    port_handle: LocalPortHandle, sched_ctx: &SchedulerCtx, comp_ctx: &mut CompCtx,
) {
    let port_info = comp_ctx.get_port_mut(port_handle);
    let port_id = port_info.self_id;
    debug_assert!(!port_info.state.is_blocked()); // should have been done by the caller

    if exec_state.is_blocked_on_put(port_id) {
        // Return to the regular execution mode
        exec_state.mode = CompMode::Sync;
        exec_state.mode_port = PortId::new_invalid();

        // Annotate the message that we're going to send
        let port_info = comp_ctx.get_port(port_handle); // for immutable access
        debug_assert_eq!(port_info.kind, PortKind::Putter);
        let to_send = exec_state.mode_value.take();
        let to_send = consensus.annotate_data_message(comp_ctx, port_info, to_send);

        // Retrieve peer to send the message
        let peer_handle = comp_ctx.get_peer_handle(port_info.peer_comp_id);
        let peer_info = comp_ctx.get_peer(peer_handle);
        peer_info.handle.send_message_logged(sched_ctx, Message::Data(to_send), true);

        exec_state.mode = CompMode::Sync; // because we're blocked on a `put`, we must've started in the sync state.
        exec_state.mode_port = PortId::new_invalid();
    }
}

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

#[inline]
pub(crate) 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<(ValueId, PortId)>) {
    // Helper to check a value for a port and recurse if needed.
    fn find_port_in_value(group: &ValueGroup, value: &Value, value_location: ValueId, ports: &mut Vec<(ValueId, 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.1 {
                        // Already added
                        return;
                    }
                }

                ports.push((value_location, 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 (value_index, embedded_value) in heap_region.iter().enumerate() {
                    let value_location = ValueId::Heap(*heap_pos, value_index as u32);
                    find_port_in_value(group, embedded_value, value_location, ports);
                }
            },
            _ => {}, // values we don't care about
        }
    }

    // Clear the ports, then scan all the available values
    ports.clear();
    for (value_index, value) in &value_group.values.iter().enumerate() {
        find_port_in_value(value_group, value, ValueId::Stack(value_index as u32), ports);
    }
}