use crate::validator_store::ValidatorStore;
use environment::RuntimeContext;
use exit_future::Signal;
use futures::{Future, IntoFuture, Stream};
use parking_lot::RwLock;
use remote_beacon_node::{RemoteBeaconNode, ValidatorDuty};
use slog::{crit, error, info, trace, warn};
use slot_clock::SlotClock;
use std::collections::HashMap;
use std::ops::Deref;
use std::sync::Arc;
use std::time::{Duration, Instant};
use tokio::timer::Interval;
use types::{ChainSpec, Epoch, EthSpec, PublicKey, Slot};

/// Delay this period of time after the slot starts. This allows the node to process the new slot.
const TIME_DELAY_FROM_SLOT: Duration = Duration::from_millis(100);

/// Remove any duties where the `duties_epoch < current_epoch - PRUNE_DEPTH`.
const PRUNE_DEPTH: u64 = 4;

type BaseHashMap = HashMap<PublicKey, HashMap<Epoch, ValidatorDuty>>;

enum InsertOutcome {
    /// The duties were previously unknown and have been stored.
    New,
    /// The duties were identical to some already in the store.
    Identical,
    /// There were duties for this validator and epoch in the store that were different to the ones
    /// provided. The existing duties were replaced.
    Replaced,
    /// The given duties were invalid.
    Invalid,
}

#[derive(Default)]
pub struct DutiesStore {
    store: RwLock<BaseHashMap>,
}

impl DutiesStore {
    fn block_producers(&self, slot: Slot, slots_per_epoch: u64) -> Vec<PublicKey> {
        self.store
            .read()
            .iter()
            // As long as a `HashMap` iterator does not return duplicate keys, neither will this
            // function.
            .filter_map(|(_validator_pubkey, validator_map)| {
                let epoch = slot.epoch(slots_per_epoch);

                validator_map.get(&epoch).and_then(|duties| {
                    if duties.block_proposal_slot == Some(slot) {
                        Some(duties.validator_pubkey.clone())
                    } else {
                        None
                    }
                })
            })
            .collect()
    }

    fn attesters(&self, slot: Slot, slots_per_epoch: u64) -> Vec<ValidatorDuty> {
        self.store
            .read()
            .iter()
            // As long as a `HashMap` iterator does not return duplicate keys, neither will this
            // function.
            .filter_map(|(_validator_pubkey, validator_map)| {
                let epoch = slot.epoch(slots_per_epoch);

                validator_map.get(&epoch).and_then(|duties| {
                    if duties.attestation_slot == Some(slot) {
                        Some(duties)
                    } else {
                        None
                    }
                })
            })
            .cloned()
            .collect()
    }

    fn insert(&self, epoch: Epoch, duties: ValidatorDuty, slots_per_epoch: u64) -> InsertOutcome {
        let mut store = self.store.write();

        if !duties_match_epoch(&duties, epoch, slots_per_epoch) {
            return InsertOutcome::Invalid;
        }

        if store.contains_key(&duties.validator_pubkey) {
            let validator_map = store.get_mut(&duties.validator_pubkey).expect(
                "Store is exclusively locked and this path is guarded to ensure the key exists.",
            );

            // TODO: validate that the slots in the duties are all in the given epoch.

            if validator_map.contains_key(&epoch) {
                let known_duties = validator_map.get_mut(&epoch).expect(
                    "Validator map is exclusively mutable and this path is guarded to ensure the key exists.",
                );

                if *known_duties == duties {
                    InsertOutcome::Identical
                } else {
                    *known_duties = duties;
                    InsertOutcome::Replaced
                }
            } else {
                validator_map.insert(epoch, duties);

                InsertOutcome::New
            }
        } else {
            let validator_pubkey = duties.validator_pubkey.clone();

            let mut validator_map = HashMap::new();
            validator_map.insert(epoch, duties);

            store.insert(validator_pubkey, validator_map);

            InsertOutcome::New
        }
    }

    fn prune(&self, prior_to: Epoch) {
        self.store
            .write()
            .retain(|_validator_pubkey, validator_map| {
                validator_map.retain(|epoch, _duties| *epoch >= prior_to);
                !validator_map.is_empty()
            });
    }
}

pub struct DutiesServiceBuilder<T, E: EthSpec> {
    validator_store: Option<ValidatorStore<T, E>>,
    slot_clock: Option<T>,
    beacon_node: Option<RemoteBeaconNode<E>>,
    context: Option<RuntimeContext<E>>,
}

impl<T: SlotClock + 'static, E: EthSpec> DutiesServiceBuilder<T, E> {
    pub fn new() -> Self {
        Self {
            validator_store: None,
            slot_clock: None,
            beacon_node: None,
            context: None,
        }
    }

    pub fn validator_store(mut self, store: ValidatorStore<T, E>) -> Self {
        self.validator_store = Some(store);
        self
    }

    pub fn slot_clock(mut self, slot_clock: T) -> Self {
        self.slot_clock = Some(slot_clock);
        self
    }

    pub fn beacon_node(mut self, beacon_node: RemoteBeaconNode<E>) -> Self {
        self.beacon_node = Some(beacon_node);
        self
    }

    pub fn runtime_context(mut self, context: RuntimeContext<E>) -> Self {
        self.context = Some(context);
        self
    }

    pub fn build(self) -> Result<DutiesService<T, E>, String> {
        Ok(DutiesService {
            inner: Arc::new(Inner {
                store: Arc::new(DutiesStore::default()),
                validator_store: self
                    .validator_store
                    .ok_or_else(|| "Cannot build DutiesService without validator_store")?,
                slot_clock: self
                    .slot_clock
                    .ok_or_else(|| "Cannot build DutiesService without slot_clock")?,
                beacon_node: self
                    .beacon_node
                    .ok_or_else(|| "Cannot build DutiesService without beacon_node")?,
                context: self
                    .context
                    .ok_or_else(|| "Cannot build DutiesService without runtime_context")?,
            }),
        })
    }
}

pub struct Inner<T, E: EthSpec> {
    store: Arc<DutiesStore>,
    validator_store: ValidatorStore<T, E>,
    slot_clock: T,
    beacon_node: RemoteBeaconNode<E>,
    context: RuntimeContext<E>,
}

pub struct DutiesService<T, E: EthSpec> {
    inner: Arc<Inner<T, E>>,
}

impl<T, E: EthSpec> Clone for DutiesService<T, E> {
    fn clone(&self) -> Self {
        Self {
            inner: self.inner.clone(),
        }
    }
}

impl<T, E: EthSpec> Deref for DutiesService<T, E> {
    type Target = Inner<T, E>;

    fn deref(&self) -> &Self::Target {
        self.inner.deref()
    }
}

impl<T: SlotClock + 'static, E: EthSpec> DutiesService<T, E> {
    /// Returns the pubkeys of the validators which are assigned to propose in the given slot.
    ///
    /// In normal cases, there should be 0 or 1 validators returned. In extreme cases (i.e., deep forking)
    ///
    /// It is possible that multiple validators have an identical proposal slot, however that is
    /// likely the result of heavy forking (lol) or inconsistent beacon node connections.
    pub fn block_producers(&self, slot: Slot) -> Vec<PublicKey> {
        self.store.block_producers(slot, E::slots_per_epoch())
    }

    /// Returns all `ValidatorDuty` for the given `slot`.
    pub fn attesters(&self, slot: Slot) -> Vec<ValidatorDuty> {
        self.store.attesters(slot, E::slots_per_epoch())
    }

    pub fn start_update_service(&self, spec: &ChainSpec) -> Result<Signal, String> {
        let log = self.context.log.clone();

        let duration_to_next_slot = self
            .slot_clock
            .duration_to_next_slot()
            .ok_or_else(|| "Unable to determine duration to next slot".to_string())?;

        let interval = {
            let slot_duration = Duration::from_millis(spec.milliseconds_per_slot);
            Interval::new(
                Instant::now() + duration_to_next_slot + TIME_DELAY_FROM_SLOT,
                slot_duration,
            )
        };

        let (exit_signal, exit_fut) = exit_future::signal();
        let service = self.clone();
        let log_1 = log.clone();
        let log_2 = log.clone();

        // Run an immediate update before starting the updater service.
        self.context.executor.spawn(service.clone().do_update());

        self.context.executor.spawn(
            exit_fut
                .until(
                    interval
                        .map_err(move |e| {
                            crit! {
                                log_1,
                                "Timer thread failed";
                                "error" => format!("{}", e)
                            }
                        })
                        .for_each(move |_| service.clone().do_update())
                        // Prevent any errors from escaping and stopping the interval.
                        .then(|_| Ok(())),
                )
                .map(move |_| info!(log_2, "Shutdown complete")),
        );

        Ok(exit_signal)
    }

    fn do_update(&self) -> impl Future<Item = (), Error = ()> {
        let service_1 = self.clone();
        let service_2 = self.clone();
        let service_3 = self.clone();
        let log_1 = self.context.log.clone();
        let log_2 = self.context.log.clone();

        self.slot_clock
            .now()
            .ok_or_else(move || {
                error!(log_1, "Duties manager failed to read slot clock");
            })
            .into_future()
            .map(move |slot| {
                let epoch = slot.epoch(E::slots_per_epoch());

                if slot % E::slots_per_epoch() == 0 {
                    let prune_below = epoch - PRUNE_DEPTH;

                    trace!(
                        log_2,
                        "Pruning duties cache";
                        "pruning_below" => prune_below.as_u64(),
                        "current_epoch" => epoch.as_u64(),
                    );

                    service_1.store.prune(prune_below);
                }

                epoch
            })
            .and_then(move |epoch| {
                let log = service_2.context.log.clone();
                service_2.update_epoch(epoch).then(move |result| {
                    if let Err(e) = result {
                        error!(
                            log,
                            "Failed to get current epoch duties";
                            "http_error" => format!("{:?}", e)
                        );
                    }

                    let log = service_3.context.log.clone();
                    service_3.update_epoch(epoch + 1).map_err(move |e| {
                        error!(
                            log,
                            "Failed to get next epoch duties";
                            "http_error" => format!("{:?}", e)
                        );
                    })
                })
            })
            .map(|_| ())
    }

    fn update_epoch(self, epoch: Epoch) -> impl Future<Item = (), Error = String> {
        let service_1 = self.clone();
        let service_2 = self.clone();

        let pubkeys = service_1.validator_store.voting_pubkeys();
        service_1
            .beacon_node
            .http
            .validator()
            .get_duties_bulk(epoch, pubkeys.as_slice())
            .map(move |all_duties| (epoch, all_duties))
            .map_err(move |e| format!("Failed to get duties for epoch {}: {:?}", epoch, e))
            .map(move |(epoch, all_duties)| {
                let mut new = 0;
                let mut identical = 0;
                let mut replaced = 0;
                let mut invalid = 0;

                all_duties.into_iter().for_each(|duties| {
                    match service_2.store.insert(epoch, duties, E::slots_per_epoch()) {
                        InsertOutcome::New => new += 1,
                        InsertOutcome::Identical => identical += 1,
                        InsertOutcome::Replaced => replaced += 1,
                        InsertOutcome::Invalid => invalid += 1,
                    };
                });

                if invalid > 0 {
                    error!(
                        service_2.context.log,
                        "Received invalid duties from beacon node";
                        "bad_duty_count" => invalid,
                        "info" => "Duties are from wrong epoch."
                    )
                }

                trace!(
                    service_2.context.log,
                    "Performed duties update";
                    "replaced_duties" => replaced,
                    "identical_duties" => identical,
                    "new_duties" => new,
                    "epoch" => format!("{}", epoch)
                );

                if replaced > 0 {
                    warn!(
                        service_2.context.log,
                        "Duties changed during routine update";
                        "info" => "Chain re-org likely occurred."
                    )
                }
            })
    }
}

/// Returns `true` if the slots in the `duties` are from the given `epoch`
fn duties_match_epoch(duties: &ValidatorDuty, epoch: Epoch, slots_per_epoch: u64) -> bool {
    if let Some(attestation_slot) = duties.attestation_slot {
        if attestation_slot.epoch(slots_per_epoch) != epoch {
            return false;
        }
    }

    if let Some(block_proposal_slot) = duties.block_proposal_slot {
        if block_proposal_slot.epoch(slots_per_epoch) != epoch {
            return false;
        }
    }

    true
}