use std::{sync::Arc, time::Duration};

use async_trait::async_trait;
use color_eyre::{
    eyre::{bail, ensure, Context},
    Result,
};
use ethers::{core::types::H256, signers::Signer, types::Address};
use futures_util::future::select_all;
use rocksdb::DB;
use tokio::{
    sync::{
        mpsc::{self, Receiver, Sender},
        Mutex,
    },
    task::JoinHandle,
    time::sleep,
};
use tracing::{error, info, instrument::Instrumented, Instrument};

use optics_base::{
    agent::{AgentCore, OpticsAgent},
    db::UsingPersistence,
    home::Homes,
};
use optics_core::{
    traits::{Common, Home},
    SignedUpdate, Signers, Update,
};

use crate::settings::UpdaterSettings as Settings;

#[derive(Debug)]
struct UpdateHandler {
    home: Arc<Homes>,

    rx: Receiver<Update>,
    update_pause: u64,
    signer: Arc<Signers>,
    db: Arc<DB>,
    mutex: Arc<Mutex<()>>,
}

impl UsingPersistence<H256, SignedUpdate> for UpdateHandler {
    const KEY_PREFIX: &'static [u8] = "update_".as_bytes();

    fn key_to_bytes(key: H256) -> Vec<u8> {
        key.as_bytes().to_owned()
    }
}

impl UpdateHandler {
    fn new(
        home: Arc<Homes>,
        rx: Receiver<Update>,
        update_pause: u64,
        signer: Arc<Signers>,
        db: Arc<DB>,
        mutex: Arc<Mutex<()>>,
    ) -> Self {
        Self {
            home,
            rx,
            update_pause,
            signer,
            db,
            mutex,
        }
    }

    fn check_conflict(&self, update: &Update) -> Option<SignedUpdate> {
        Self::db_get(&self.db, update.previous_root).unwrap()
    }

    #[tracing::instrument(err)]
    async fn acceptable(&self, update: &Update) -> Result<bool> {
        // Poll chain API to see if queue still contains new root
        // and old root still equals home's current root
        let (in_queue, current_root) = tokio::join!(
            self.home.queue_contains(update.new_root),
            self.home.current_root()
        );

        if in_queue.is_err() {
            info!("Update no longer in queue");
        }
        if current_root.is_err() {
            error!("Connection gone");
        }

        let in_queue = in_queue?;
        let current_root = current_root?;

        let old_root = update.previous_root;
        Ok(in_queue && current_root == old_root)
    }

    #[tracing::instrument(err)]
    async fn handle_update(&self, update: Update) -> Result<()> {
        info!("Have an update, awaiting the tick");
        // Wait `update_pause` seconds
        sleep(Duration::from_secs(self.update_pause)).await;

        if !self.acceptable(&update).await? {
            info!("Declined to submit update. No longer current");
            return Ok(());
        }

        // acquire guard. If the guard can't be acquired, that
        // means a tx is in flight and we should try again later.
        let _guard = self
            .mutex
            .try_lock()
            .wrap_err("Declined to submit update.")?;

        // If update still valid and doesn't conflict with local
        // history of signed updates, sign and submit update. Note
        // that because we acquire a guard, only one task
        // can check and enter the below `if` block at a time,
        // protecting from races between threads.

        if self.check_conflict(&update).is_some() {
            bail!("Found conflicting update in DB");
        }

        // If we have a conflict, we grab that one instead
        let signed = update.sign_with(self.signer.as_ref()).await.unwrap();

        // If successfully submitted update, record in db
        info!(
            "Dispatching signed update to contract. Current root is {:?}, new root is {:?}",
            &signed.update.previous_root, &signed.update.new_root
        );

        self.home.update(&signed).await?;

        info!("Storing signed update in db");
        Self::db_put(&self.db, update.previous_root, signed).expect("!db_put");
        Ok(())
        // guard dropped here
    }

    fn spawn(mut self) -> Instrumented<JoinHandle<Result<()>>> {
        tokio::spawn(async move {
            while let Some(update) = self.rx.recv().await {
                self.handle_update(update).await?;
            }
            Ok(())
        })
        .in_current_span()
    }
}

struct UpdatePoller {
    home: Arc<Homes>,
    tx: Sender<Update>,
    interval_seconds: u64,
}

impl UpdatePoller {
    fn new(home: Arc<Homes>, tx: Sender<Update>, interval_seconds: u64) -> Self {
        Self {
            home,
            tx,
            interval_seconds,
        }
    }

    fn spawn(self) -> Instrumented<JoinHandle<Result<()>>> {
        tokio::spawn(async move {
            loop {
                match self.home.produce_update().await? {
                    Some(update) => self.tx.send(update).await?,
                    None => info!("No update available"),
                }
                sleep(Duration::from_secs(self.interval_seconds)).await;
            }
        })
        .in_current_span()
    }
}

/// An updater agent
#[derive(Debug)]
pub struct Updater {
    signer: Arc<Signers>,
    interval_seconds: u64,
    update_pause: u64,
    core: AgentCore,
}

impl AsRef<AgentCore> for Updater {
    fn as_ref(&self) -> &AgentCore {
        &self.core
    }
}

impl Updater {
    /// Instantiate a new updater
    pub fn new(signer: Signers, interval_seconds: u64, update_pause: u64, core: AgentCore) -> Self {
        Self {
            signer: Arc::new(signer),
            interval_seconds,
            update_pause,
            core,
        }
    }
}

#[async_trait]
// This is a bit of a kludge to make from_settings work.
// Ideally this hould be generic across all signers.
// Right now we only have one
impl OpticsAgent for Updater {
    type Settings = Settings;

    async fn from_settings(settings: Self::Settings) -> Result<Self>
    where
        Self: Sized,
    {
        let signer = settings.updater.try_into_signer().await?;
        let interval_seconds = settings.polling_interval.parse().expect("invalid uint");
        let update_pause = settings.update_pause.parse().expect("invalid uint");
        let core = settings.as_ref().try_into_core().await?;
        Ok(Self::new(signer, interval_seconds, update_pause, core))
    }

    fn run(&self, _replica: &str) -> Instrumented<JoinHandle<Result<()>>> {
        // First we check that we have the correct key to sign with.
        let home = self.home();
        let address = self.signer.address();

        let (tx, rx) = mpsc::channel(32);
        let poller = UpdatePoller::new(self.home(), tx, self.interval_seconds);
        let handler = UpdateHandler::new(
            self.home(),
            rx,
            self.update_pause,
            self.signer.clone(),
            self.db(),
            Default::default(),
        );

        tokio::spawn(async move {
            let expected: Address = home.updater().await?.into();
            ensure!(
                expected == address,
                "Contract updater does not match keys. On-chain: {}. Local: {}",
                expected,
                address
            );
            let poller_task = poller.spawn();
            let handler_task = handler.spawn();

            let (res, _, rem) = select_all(vec![poller_task, handler_task]).await;

            for task in rem.into_iter() {
                task.into_inner().abort();
            }
            res?
        })
        .in_current_span()
    }
}

#[cfg(test)]
mod test {}