use std::collections::VecDeque;
use std::sync::{Arc, Mutex, Condvar};
use std::sync::atomic::Ordering;
use std::collections::HashMap;

use crate::protocol::ComponentCreationError;
use crate::protocol::eval::ValueGroup;

use super::{ConnectorKey, ConnectorId, RuntimeInner};
use super::branch::{BranchId, FakeTree, QueueKind, SpeculativeState};
use super::scheduler::{SchedulerCtx, ComponentCtx};
use super::port::{Port, PortIdLocal, Channel, PortKind};
use super::consensus::{Consensus, Consistency, find_ports_in_value_group};
use super::connector::{ConnectorScheduling, ConnectorPDL};
use super::inbox::{Message, DataContent, DataMessage, SyncMessage, ControlContent, ControlMessage};

/// Generic connector interface from the scheduler's point of view.
pub(crate) trait Connector {
    /// Should run the connector's behaviour up until the next blocking point.
    /// One should generally request and handle new messages from the component
    /// context. Then perform any logic the component has to do, and in the
    /// process perhaps queue up some state changes using the same context.
    fn run(&mut self, sched_ctx: SchedulerCtx, comp_ctx: &mut ComponentCtx) -> ConnectorScheduling;
}

pub(crate) struct FinishedSync {
    // In the order of the `get` calls
    inbox: Vec<ValueGroup>,
}

type SyncDone = Arc<(Mutex<Option<FinishedSync>>, Condvar)>;
type JobQueue = Arc<Mutex<VecDeque<ApplicationJob>>>;

enum ApplicationJob {
    NewChannel((Port, Port)),
    NewConnector(ConnectorPDL, Vec<PortIdLocal>),
    SyncRound(Vec<ApplicationSyncAction>),
    Shutdown,
}

// -----------------------------------------------------------------------------
// ConnectorApplication
// -----------------------------------------------------------------------------

/// The connector which an application can directly interface with. Once may set
/// up the next synchronous round, and retrieve the data afterwards.
// TODO: Strong candidate for logic reduction in handling put/get. A lot of code
//  is an approximate copy-pasta from the regular component logic. I'm going to
//  wait until I'm implementing more native components to see which logic is
//  truly common.
pub struct ConnectorApplication {
    // Communicating about new jobs and setting up sync rounds
    sync_done: SyncDone,
    job_queue: JobQueue,
    is_in_sync: bool,
    // Handling current sync round
    sync_desc: Vec<ApplicationSyncAction>,
    tree: FakeTree,
    consensus: Consensus,
    last_finished_handled: Option<BranchId>,
    branch_extra: Vec<usize>, // instruction counter per branch
}

impl Connector for ConnectorApplication {
    fn run(&mut self, sched_ctx: SchedulerCtx, comp_ctx: &mut ComponentCtx) -> ConnectorScheduling {
        if self.is_in_sync {
            let scheduling = self.run_in_sync_mode(sched_ctx, comp_ctx);
            let mut iter_id = self.last_finished_handled.or(self.tree.get_queue_first(QueueKind::FinishedSync));
            while let Some(branch_id) = iter_id {
                iter_id = self.tree.get_queue_next(branch_id);
                self.last_finished_handled = Some(branch_id);

                if let Some(solution_branch) = self.consensus.handle_new_finished_sync_branch(branch_id, comp_ctx) {
                    // Can finish sync round immediately
                    self.collapse_sync_to_solution_branch(solution_branch, comp_ctx);
                    return ConnectorScheduling::Immediate;
                }
            }

            return scheduling;
        } else {
            return self.run_in_deterministic_mode(sched_ctx, comp_ctx);
        }
    }
}

impl ConnectorApplication {
    pub(crate) fn new(runtime: Arc<RuntimeInner>) -> (Self, ApplicationInterface) {
        let sync_done = Arc::new(( Mutex::new(None), Condvar::new() ));
        let job_queue = Arc::new(Mutex::new(VecDeque::with_capacity(32)));

        let connector = ConnectorApplication {
            sync_done: sync_done.clone(),
            job_queue: job_queue.clone(),
            is_in_sync: false,
            sync_desc: Vec::new(),
            tree: FakeTree::new(),
            consensus: Consensus::new(),
            last_finished_handled: None,
            branch_extra: vec![0],
        };
        let interface = ApplicationInterface::new(sync_done, job_queue, runtime);

        return (connector, interface);
    }

    fn handle_new_messages(&mut self, comp_ctx: &mut ComponentCtx) {
        while let Some(message) = comp_ctx.read_next_message() {
            match message {
                Message::Data(message) => self.handle_new_data_message(message, comp_ctx),
                Message::Sync(message) => self.handle_new_sync_message(message, comp_ctx),
                Message::Control(_) => unreachable!("control message in native API component"),
            }
        }
    }

    pub(crate) fn handle_new_data_message(&mut self, message: DataMessage, ctx: &mut ComponentCtx) {
        // Go through all branches that are awaiting new messages and see if
        // there is one that can receive this message.
        if !self.consensus.handle_new_data_message(&message, ctx) {
            // Old message, so drop it
            return;
        }

        let mut iter_id = self.tree.get_queue_first(QueueKind::AwaitingMessage);
        while let Some(branch_id) = iter_id {
            iter_id = self.tree.get_queue_next(branch_id);

            let branch = &self.tree[branch_id];
            if branch.awaiting_port != message.data_header.target_port { continue; }
            if !self.consensus.branch_can_receive(branch_id, &message) { continue; }

            // This branch can receive, so fork and given it the message
            let receiving_branch_id = self.tree.fork_branch(branch_id);
            debug_assert!(receiving_branch_id.index as usize == self.branch_extra.len());
            self.branch_extra.push(self.branch_extra[branch_id.index as usize]); // copy instruction index
            self.consensus.notify_of_new_branch(branch_id, receiving_branch_id);
            let receiving_branch = &mut self.tree[receiving_branch_id];

            receiving_branch.insert_message(message.data_header.target_port, message.content.as_message().unwrap().clone());
            self.consensus.notify_of_received_message(receiving_branch_id, &message);

            // And prepare the branch for running
            self.tree.push_into_queue(QueueKind::Runnable, receiving_branch_id);
        }
    }

    pub(crate) fn handle_new_sync_message(&mut self, message: SyncMessage, ctx: &mut ComponentCtx) {
        if let Some(solution_branch_id) = self.consensus.handle_new_sync_message(message, ctx) {
            self.collapse_sync_to_solution_branch(solution_branch_id, ctx);
        }
    }

    fn run_in_sync_mode(&mut self, _sched_ctx: SchedulerCtx, comp_ctx: &mut ComponentCtx) -> ConnectorScheduling {
        debug_assert!(self.is_in_sync);

        self.handle_new_messages(comp_ctx);

        let branch_id = self.tree.pop_from_queue(QueueKind::Runnable);
        if branch_id.is_none() {
            return ConnectorScheduling::NotNow;
        }

        let branch_id = branch_id.unwrap();
        let branch = &mut self.tree[branch_id];
        let mut instruction_idx = self.branch_extra[branch_id.index as usize];

        if instruction_idx >= self.sync_desc.len() {
            // Performed last instruction, so this branch is officially at the
            // end of the synchronous interaction.
            let consistency = self.consensus.notify_of_finished_branch(branch_id);
            if consistency == Consistency::Valid {
                branch.sync_state = SpeculativeState::ReachedSyncEnd;
                self.tree.push_into_queue(QueueKind::FinishedSync, branch_id);
            } else {
                branch.sync_state = SpeculativeState::Inconsistent;
            }
        } else {
            // We still have instructions to perform
            let cur_instruction = &self.sync_desc[instruction_idx];
            self.branch_extra[branch_id.index as usize] += 1;

            match &cur_instruction {
                ApplicationSyncAction::Put(port_id, content) => {
                    let port_id = *port_id;

                    let (sync_header, data_header) = self.consensus.handle_message_to_send(branch_id, port_id, &content, comp_ctx);
                    let message = Message::Data(DataMessage {
                        sync_header,
                        data_header,
                        content: DataContent::Message(content.clone()),
                    });
                    comp_ctx.submit_message(message);
                    self.tree.push_into_queue(QueueKind::Runnable, branch_id);
                    return ConnectorScheduling::Immediate;
                },
                ApplicationSyncAction::Get(port_id) => {
                    let port_id = *port_id;

                    branch.sync_state = SpeculativeState::HaltedAtBranchPoint;
                    branch.awaiting_port = port_id;
                    self.tree.push_into_queue(QueueKind::AwaitingMessage, branch_id);

                    let mut any_message_received = false;
                    for message in comp_ctx.get_read_data_messages(port_id) {
                        if self.consensus.branch_can_receive(branch_id, &message) {
                            // This branch can receive the message, so we do the
                            // fork-and-receive dance
                            let receiving_branch_id = self.tree.fork_branch(branch_id);
                            let branch = &mut self.tree[receiving_branch_id];
                            debug_assert!(receiving_branch_id.index as usize == self.branch_extra.len());
                            self.branch_extra.push(instruction_idx + 1);

                            branch.insert_message(port_id, message.content.as_message().unwrap().clone());

                            self.consensus.notify_of_new_branch(branch_id, receiving_branch_id);
                            self.consensus.notify_of_received_message(receiving_branch_id, &message);
                            self.tree.push_into_queue(QueueKind::Runnable, receiving_branch_id);

                            any_message_received = true;
                        }
                    }

                    if any_message_received {
                        return ConnectorScheduling::Immediate;
                    }
                }
            }
        }

        if self.tree.queue_is_empty(QueueKind::Runnable) {
            return ConnectorScheduling::NotNow;
        } else {
            return ConnectorScheduling::Later;
        }
    }

    fn run_in_deterministic_mode(&mut self, _sched_ctx: SchedulerCtx, comp_ctx: &mut ComponentCtx) -> ConnectorScheduling {
        debug_assert!(!self.is_in_sync);

        // In non-sync mode the application component doesn't really do anything
        // except performing jobs submitted from the API. This is the only
        // case where we expect to be woken up.
        // Note that we have to communicate to the scheduler when we've received
        // ports or created components (hence: given away ports) *before* we
        // enter a sync round.
        let mut queue = self.job_queue.lock().unwrap();
        while let Some(job) = queue.pop_front() {
            match job {
                ApplicationJob::NewChannel((endpoint_a, endpoint_b)) => {
                    comp_ctx.push_port(endpoint_a);
                    comp_ctx.push_port(endpoint_b);

                    return ConnectorScheduling::Immediate;
                }
                ApplicationJob::NewConnector(connector, initial_ports) => {
                    comp_ctx.push_component(connector, initial_ports);

                    return ConnectorScheduling::Later;
                },
                ApplicationJob::SyncRound(mut description) => {
                    // Entering sync mode
                    comp_ctx.notify_sync_start();
                    self.sync_desc = description;
                    self.is_in_sync = true;
                    debug_assert!(self.last_finished_handled.is_none());
                    debug_assert!(self.branch_extra.len() == 1);

                    let first_branch_id = self.tree.start_sync();
                    self.tree.push_into_queue(QueueKind::Runnable, first_branch_id);
                    debug_assert!(first_branch_id.index == 1);
                    self.consensus.start_sync(comp_ctx);
                    self.consensus.notify_of_new_branch(BranchId::new_invalid(), first_branch_id);
                    self.branch_extra.push(0); // set first branch to first instruction

                    return ConnectorScheduling::Immediate;
                },
                ApplicationJob::Shutdown => {
                    debug_assert!(queue.is_empty());

                    return ConnectorScheduling::Exit;
                }
            }
        }

        // Queue was empty
        return ConnectorScheduling::NotNow;
    }

    fn collapse_sync_to_solution_branch(&mut self, branch_id: BranchId, comp_ctx: &mut ComponentCtx) {
        debug_assert!(self.branch_extra[branch_id.index as usize] >= self.sync_desc.len()); // finished program
        // Notifying tree, consensus algorithm and context of ending sync
        let mut fake_vec = Vec::new();
        let mut solution_branch = self.tree.end_sync(branch_id);
        self.consensus.end_sync(branch_id, &mut fake_vec);

        for port in fake_vec {
            debug_assert!(comp_ctx.get_port_by_id(port).is_some());
        }

        comp_ctx.notify_sync_end(&[]);

        // Turning hashmapped inbox into vector of values
        let mut inbox = Vec::with_capacity(solution_branch.inbox.len());
        for action in &self.sync_desc {
            match action {
                ApplicationSyncAction::Put(_, _) => {},
                ApplicationSyncAction::Get(port_id) => {
                    debug_assert!(solution_branch.inbox.contains_key(port_id));
                    inbox.push(solution_branch.inbox.remove(port_id).unwrap());
                },
            }
        }

        // Notifying interface of ending sync
        self.is_in_sync = false;
        self.sync_desc.clear();
        self.branch_extra.truncate(1);
        self.last_finished_handled = None;

        let (results, notification) = &*self.sync_done;
        let mut results = results.lock().unwrap();
        *results = Some(FinishedSync{ inbox });
        notification.notify_one();
    }
}

// -----------------------------------------------------------------------------
// ApplicationInterface
// -----------------------------------------------------------------------------

#[derive(Debug)]
pub enum ChannelCreationError {
    InSync,
}

#[derive(Debug)]
pub enum ApplicationStartSyncError {
    AlreadyInSync,
    NoSyncActions,
    IncorrectPortKind,
    UnownedPort,
}

#[derive(Debug)]
pub enum ApplicationEndSyncError {
    NotInSync,
}

pub enum ApplicationSyncAction {
    Put(PortIdLocal, ValueGroup),
    Get(PortIdLocal),
}

/// The interface to a `ApplicationConnector`. This allows setting up the
/// interactions the `ApplicationConnector` performs within a synchronous round.
pub struct ApplicationInterface {
    sync_done: SyncDone,
    job_queue: JobQueue,
    runtime: Arc<RuntimeInner>,
    is_in_sync: bool,
    connector_id: ConnectorId,
    owned_ports: Vec<(PortKind, PortIdLocal)>,
}

impl ApplicationInterface {
    fn new(sync_done: SyncDone, job_queue: JobQueue, runtime: Arc<RuntimeInner>) -> Self {
        return Self{
            sync_done, job_queue, runtime,
            is_in_sync: false,
            connector_id: ConnectorId::new_invalid(),
            owned_ports: Vec::new(),
        }
    }

    /// Creates a new channel. Can only fail if the application interface is
    /// currently in sync mode.
    pub fn create_channel(&mut self) -> Result<Channel, ChannelCreationError> {
        if self.is_in_sync {
            return Err(ChannelCreationError::InSync);
        }

        let (getter_port, putter_port) = self.runtime.create_channel(self.connector_id);
        debug_assert_eq!(getter_port.kind, PortKind::Getter);
        let getter_id = getter_port.self_id;
        let putter_id = putter_port.self_id;

        {
            let mut lock = self.job_queue.lock().unwrap();
            lock.push_back(ApplicationJob::NewChannel((getter_port, putter_port)));
        }

        // Add to owned ports for error checking while creating a connector
        self.owned_ports.reserve(2);
        self.owned_ports.push((PortKind::Putter, putter_id));
        self.owned_ports.push((PortKind::Getter, getter_id));

        return Ok(Channel{ putter_id, getter_id });
    }

    /// Creates a new connector. Note that it is not scheduled immediately, but
    /// depends on the `ApplicationConnector` to run, followed by the created
    /// connector being scheduled.
    pub fn create_connector(&mut self, module: &str, routine: &str, arguments: ValueGroup) -> Result<(), ComponentCreationError> {
        if self.is_in_sync {
            return Err(ComponentCreationError::InSync);
        }

        // Retrieve ports and make sure that we own the ones that are currently
        // specified. This is also checked by the scheduler, but that is done
        // asynchronously.
        let mut initial_ports = Vec::new();
        find_ports_in_value_group(&arguments, &mut initial_ports);
        for initial_port in &initial_ports {
            if !self.owned_ports.iter().any(|(_, v)| v == initial_port) {
                return Err(ComponentCreationError::UnownedPort);
            }
        }

        // We own all ports, so remove them on this side
        for initial_port in &initial_ports {
            let position = self.owned_ports.iter().position(|(_, v)| v == initial_port).unwrap();
            self.owned_ports.remove(position);
        }

        let prompt = self.runtime.protocol_description.new_component_v2(module.as_bytes(), routine.as_bytes(), arguments)?;
        let connector = ConnectorPDL::new(prompt);

        // Put on job queue
        {
            let mut queue = self.job_queue.lock().unwrap();
            queue.push_back(ApplicationJob::NewConnector(connector, initial_ports));
        }

        self.wake_up_connector_with_ping();

        return Ok(());
    }

    /// Queues up a description of a synchronous round to run. Will not actually
    /// run the synchronous behaviour in blocking fashion. The results *must* be
    /// retrieved using `try_wait` or `wait` for the interface to be considered
    /// in non-sync mode.
    // TODO: Maybe change API in the future. For now it does the job
    pub fn perform_sync_round(&mut self, actions: Vec<ApplicationSyncAction>) -> Result<(), ApplicationStartSyncError> {
        if self.is_in_sync {
            return Err(ApplicationStartSyncError::AlreadyInSync);
        }

        // Check the action ports for consistency
        for action in &actions {
            let (port_id, expected_kind) = match action {
                ApplicationSyncAction::Put(port_id, _) => (*port_id, PortKind::Putter),
                ApplicationSyncAction::Get(port_id) => (*port_id, PortKind::Getter),
            };

            match self.find_port_by_id(port_id) {
                Some(port_kind) => {
                    if port_kind != expected_kind {
                        return Err(ApplicationStartSyncError::IncorrectPortKind)
                    }
                },
                None => {
                    return Err(ApplicationStartSyncError::UnownedPort);
                }
            }
        }

        // Everything is consistent, go into sync mode and send the actions off
        // to the component that will actually perform the sync round
        self.is_in_sync = true;
        {
            let (is_done, _) = &*self.sync_done;
            let mut lock = is_done.lock().unwrap();
            *lock = None;
        }

        {
            let mut lock = self.job_queue.lock().unwrap();
            lock.push_back(ApplicationJob::SyncRound(actions));
        }

        self.wake_up_connector_with_ping();
        return Ok(())
    }

    /// Wait until the next sync-round is finished, returning the received
    /// messages in order of `get` calls.
    pub fn wait(&mut self) -> Result<Vec<ValueGroup>, ApplicationEndSyncError> {
        if !self.is_in_sync {
            return Err(ApplicationEndSyncError::NotInSync);
        }

        let (is_done, condition) = &*self.sync_done;
        let mut lock = is_done.lock().unwrap();
        lock = condition.wait_while(lock, |v| v.is_none()).unwrap(); // wait while not done

        self.is_in_sync = false;
        return Ok(lock.take().unwrap().inbox);
    }

    /// Called by runtime to set associated connector's ID.
    pub(crate) fn set_connector_id(&mut self, id: ConnectorId) {
        self.connector_id = id;
    }

    fn wake_up_connector_with_ping(&self) {
        let connector = self.runtime.get_component_public(self.connector_id);
        connector.inbox.insert_message(Message::Control(ControlMessage {
            id: 0,
            sending_component_id: self.connector_id,
            content: ControlContent::Ping,
        }));

        let should_wake_up = connector.sleeping
            .compare_exchange(true, false, Ordering::SeqCst, Ordering::Acquire)
            .is_ok();

        if should_wake_up {
            let key = unsafe{ ConnectorKey::from_id(self.connector_id) };
            self.runtime.push_work(key);
        }
    }

    fn find_port_by_id(&self, port_id: PortIdLocal) -> Option<PortKind> {
        return self.owned_ports.iter()
            .find(|(_, owned_id)| *owned_id == port_id)
            .map(|(port_kind, _)| *port_kind);
    }
}

impl Drop for ApplicationInterface {
    fn drop(&mut self) {
        {
            let mut lock = self.job_queue.lock().unwrap();
            lock.push_back(ApplicationJob::Shutdown);
        }

        self.wake_up_connector_with_ping();
        self.runtime.decrement_active_interfaces();
    }
}