use crate::{
    pubsub_client::{PubsubClient, PubsubClientError, PubsubClientSubscription},
    rpc_client::RpcClient,
    rpc_response::SlotUpdate,
};
use bincode::serialize;
use log::*;
use solana_sdk::{clock::Slot, pubkey::Pubkey, transaction::Transaction};
use std::{
    collections::{HashMap, HashSet, VecDeque},
    net::{SocketAddr, UdpSocket},
    str::FromStr,
    sync::{
        atomic::{AtomicBool, Ordering},
        Arc, RwLock,
    },
    thread::JoinHandle,
    time::{Duration, Instant},
};
use thiserror::Error;

#[derive(Error, Debug)]
pub enum TpuSenderError {
    #[error("Pubsub error: {0:?}")]
    PubsubError(#[from] PubsubClientError),
    #[error("RPC error: {0:?}")]
    RpcError(#[from] crate::client_error::ClientError),
    #[error("IO error: {0:?}")]
    IoError(#[from] std::io::Error),
}

type Result<T> = std::result::Result<T, TpuSenderError>;

/// Default number of slots used to build TPU socket fanout set
pub const DEFAULT_FANOUT_SLOTS: u64 = 12;

/// Maximum number of slots used to build TPU socket fanout set
pub const MAX_FANOUT_SLOTS: u64 = 100;

/// Config params for `TpuClient`
#[derive(Clone, Debug)]
pub struct TpuClientConfig {
    /// The range of upcoming slots to include when determining which
    /// leaders to send transactions to (min: 1, max: 100)
    pub fanout_slots: u64,
}

impl Default for TpuClientConfig {
    fn default() -> Self {
        Self {
            fanout_slots: DEFAULT_FANOUT_SLOTS,
        }
    }
}

/// Client which sends transactions directly to the current leader's TPU port over UDP.
/// The client uses RPC to determine the current leader and fetch node contact info
pub struct TpuClient {
    send_socket: UdpSocket,
    fanout_slots: u64,
    leader_tpu_service: LeaderTpuService,
    exit: Arc<AtomicBool>,
}

impl TpuClient {
    /// Serializes and sends a transaction to the current leader's TPU port
    pub fn send_transaction(&self, transaction: &Transaction) -> bool {
        let wire_transaction = serialize(transaction).expect("serialization should succeed");
        self.send_wire_transaction(&wire_transaction)
    }

    /// Sends a transaction to the current leader's TPU port
    pub fn send_wire_transaction(&self, wire_transaction: &[u8]) -> bool {
        let mut sent = false;
        for tpu_address in self
            .leader_tpu_service
            .leader_tpu_sockets(self.fanout_slots)
        {
            if self
                .send_socket
                .send_to(wire_transaction, tpu_address)
                .is_ok()
            {
                sent = true;
            }
        }
        sent
    }

    /// Create a new client that disconnects when dropped
    pub fn new(
        rpc_client: Arc<RpcClient>,
        websocket_url: &str,
        config: TpuClientConfig,
    ) -> Result<Self> {
        let exit = Arc::new(AtomicBool::new(false));
        let leader_tpu_service = LeaderTpuService::new(rpc_client, websocket_url, exit.clone())?;

        Ok(Self {
            send_socket: UdpSocket::bind("0.0.0.0:0").unwrap(),
            fanout_slots: config.fanout_slots.min(MAX_FANOUT_SLOTS).max(1),
            leader_tpu_service,
            exit,
        })
    }
}

impl Drop for TpuClient {
    fn drop(&mut self) {
        self.exit.store(true, Ordering::Relaxed);
        self.leader_tpu_service.join();
    }
}

struct LeaderTpuCache {
    first_slot: Slot,
    leaders: Vec<Pubkey>,
    leader_tpu_map: HashMap<Pubkey, SocketAddr>,
}

impl LeaderTpuCache {
    fn new(rpc_client: &RpcClient, first_slot: Slot) -> Self {
        let leaders = Self::fetch_slot_leaders(rpc_client, first_slot).unwrap_or_default();
        let leader_tpu_map = Self::fetch_cluster_tpu_sockets(&rpc_client).unwrap_or_default();
        Self {
            first_slot,
            leaders,
            leader_tpu_map,
        }
    }

    // Last slot that has a cached leader pubkey
    fn last_slot(&self) -> Slot {
        self.first_slot + self.leaders.len().saturating_sub(1) as u64
    }

    // Get the TPU sockets for the current leader and upcoming leaders according to fanout size
    fn get_leader_sockets(&self, current_slot: Slot, fanout_slots: u64) -> Vec<SocketAddr> {
        let mut leader_set = HashSet::new();
        let mut leader_sockets = Vec::new();
        for leader_slot in current_slot..current_slot + fanout_slots {
            if let Some(leader) = self.get_slot_leader(leader_slot) {
                if let Some(tpu_socket) = self.leader_tpu_map.get(leader) {
                    if leader_set.insert(*leader) {
                        leader_sockets.push(*tpu_socket);
                    }
                }
            }
        }
        leader_sockets
    }

    fn get_slot_leader(&self, slot: Slot) -> Option<&Pubkey> {
        if slot >= self.first_slot {
            let index = slot - self.first_slot;
            self.leaders.get(index as usize)
        } else {
            None
        }
    }

    fn fetch_cluster_tpu_sockets(rpc_client: &RpcClient) -> Result<HashMap<Pubkey, SocketAddr>> {
        let cluster_contact_info = rpc_client.get_cluster_nodes()?;
        Ok(cluster_contact_info
            .into_iter()
            .filter_map(|contact_info| {
                Some((
                    Pubkey::from_str(&contact_info.pubkey).ok()?,
                    contact_info.tpu?,
                ))
            })
            .collect())
    }

    fn fetch_slot_leaders(rpc_client: &RpcClient, start_slot: Slot) -> Result<Vec<Pubkey>> {
        Ok(rpc_client.get_slot_leaders(start_slot, 2 * MAX_FANOUT_SLOTS)?)
    }
}

// 48 chosen because it's unlikely that 12 leaders in a row will miss their slots
const MAX_SLOT_SKIP_DISTANCE: u64 = 48;

#[derive(Clone, Debug)]
struct RecentLeaderSlots(Arc<RwLock<VecDeque<Slot>>>);
impl RecentLeaderSlots {
    fn new(current_slot: Slot) -> Self {
        let mut recent_slots = VecDeque::new();
        recent_slots.push_back(current_slot);
        Self(Arc::new(RwLock::new(recent_slots)))
    }

    fn record_slot(&self, current_slot: Slot) {
        let mut recent_slots = self.0.write().unwrap();
        recent_slots.push_back(current_slot);
        // 12 recent slots should be large enough to avoid a misbehaving
        // validator from affecting the median recent slot
        while recent_slots.len() > 12 {
            recent_slots.pop_front();
        }
    }

    // Estimate the current slot from recent slot notifications.
    fn estimated_current_slot(&self) -> Slot {
        let mut recent_slots: Vec<Slot> = self.0.read().unwrap().iter().cloned().collect();
        assert!(!recent_slots.is_empty());
        recent_slots.sort_unstable();

        // Validators can broadcast invalid blocks that are far in the future
        // so check if the current slot is in line with the recent progression.
        let max_index = recent_slots.len() - 1;
        let median_index = max_index / 2;
        let median_recent_slot = recent_slots[median_index];
        let expected_current_slot = median_recent_slot + (max_index - median_index) as u64;
        let max_reasonable_current_slot = expected_current_slot + MAX_SLOT_SKIP_DISTANCE;

        // Return the highest slot that doesn't exceed what we believe is a
        // reasonable slot.
        recent_slots
            .into_iter()
            .rev()
            .find(|slot| *slot <= max_reasonable_current_slot)
            .unwrap()
    }
}

#[cfg(test)]
impl From<Vec<Slot>> for RecentLeaderSlots {
    fn from(recent_slots: Vec<Slot>) -> Self {
        assert!(!recent_slots.is_empty());
        Self(Arc::new(RwLock::new(recent_slots.into_iter().collect())))
    }
}

/// Service that tracks upcoming leaders and maintains an up-to-date mapping
/// of leader id to TPU socket address.
struct LeaderTpuService {
    recent_slots: RecentLeaderSlots,
    leader_tpu_cache: Arc<RwLock<LeaderTpuCache>>,
    subscription: Option<PubsubClientSubscription<SlotUpdate>>,
    t_leader_tpu_service: Option<JoinHandle<()>>,
}

impl LeaderTpuService {
    fn new(rpc_client: Arc<RpcClient>, websocket_url: &str, exit: Arc<AtomicBool>) -> Result<Self> {
        let start_slot = rpc_client.get_max_shred_insert_slot()?;

        let recent_slots = RecentLeaderSlots::new(start_slot);
        let leader_tpu_cache = Arc::new(RwLock::new(LeaderTpuCache::new(&rpc_client, start_slot)));

        let subscription = if !websocket_url.is_empty() {
            let recent_slots = recent_slots.clone();
            Some(PubsubClient::slot_updates_subscribe(
                websocket_url,
                move |update| {
                    let current_slot = match update {
                        // This update indicates that a full slot was received by the connected
                        // node so we can stop sending transactions to the leader for that slot
                        SlotUpdate::Completed { slot, .. } => slot.saturating_add(1),
                        // This update indicates that we have just received the first shred from
                        // the leader for this slot and they are probably still accepting transactions.
                        SlotUpdate::FirstShredReceived { slot, .. } => slot,
                        _ => return,
                    };

                    recent_slots.record_slot(current_slot);
                },
            )?)
        } else {
            None
        };

        let t_leader_tpu_service = Some({
            let recent_slots = recent_slots.clone();
            let leader_tpu_cache = leader_tpu_cache.clone();
            std::thread::Builder::new()
                .name("ldr-tpu-srv".to_string())
                .spawn(move || Self::run(rpc_client, recent_slots, leader_tpu_cache, exit))
                .unwrap()
        });

        Ok(LeaderTpuService {
            recent_slots,
            leader_tpu_cache,
            subscription,
            t_leader_tpu_service,
        })
    }

    fn join(&mut self) {
        if let Some(mut subscription) = self.subscription.take() {
            let _ = subscription.send_unsubscribe();
            let _ = subscription.shutdown();
        }
        if let Some(t_handle) = self.t_leader_tpu_service.take() {
            t_handle.join().unwrap();
        }
    }

    fn leader_tpu_sockets(&self, fanout_slots: u64) -> Vec<SocketAddr> {
        let current_slot = self.recent_slots.estimated_current_slot();
        self.leader_tpu_cache
            .read()
            .unwrap()
            .get_leader_sockets(current_slot, fanout_slots)
    }

    fn run(
        rpc_client: Arc<RpcClient>,
        recent_slots: RecentLeaderSlots,
        leader_tpu_cache: Arc<RwLock<LeaderTpuCache>>,
        exit: Arc<AtomicBool>,
    ) {
        let mut last_cluster_refresh = Instant::now();
        let mut sleep_ms = 1000;
        loop {
            if exit.load(Ordering::Relaxed) {
                break;
            }

            // Refresh cluster TPU ports every 5min in case validators restart with new port configuration
            // or new validators come online
            if last_cluster_refresh.elapsed() > Duration::from_secs(5 * 60) {
                if let Ok(leader_tpu_map) = LeaderTpuCache::fetch_cluster_tpu_sockets(&rpc_client) {
                    leader_tpu_cache.write().unwrap().leader_tpu_map = leader_tpu_map;
                    last_cluster_refresh = Instant::now();
                } else {
                    sleep_ms = 100;
                    continue;
                }
            }

            // Sleep a few slots before checking if leader cache needs to be refreshed again
            std::thread::sleep(Duration::from_millis(sleep_ms));

            let current_slot = recent_slots.estimated_current_slot();
            if current_slot
                >= leader_tpu_cache
                    .read()
                    .unwrap()
                    .last_slot()
                    .saturating_sub(MAX_FANOUT_SLOTS)
            {
                if let Ok(slot_leaders) =
                    LeaderTpuCache::fetch_slot_leaders(&rpc_client, current_slot)
                {
                    let mut leader_tpu_cache = leader_tpu_cache.write().unwrap();
                    leader_tpu_cache.first_slot = current_slot;
                    leader_tpu_cache.leaders = slot_leaders;
                } else {
                    sleep_ms = 100;
                    continue;
                }
            }

            sleep_ms = 1000;
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    fn assert_slot(recent_slots: RecentLeaderSlots, expected_slot: Slot) {
        assert_eq!(recent_slots.estimated_current_slot(), expected_slot);
    }

    #[test]
    fn test_recent_leader_slots() {
        assert_slot(RecentLeaderSlots::new(0), 0);

        let mut recent_slots: Vec<Slot> = (1..=12).collect();
        assert_slot(RecentLeaderSlots::from(recent_slots.clone()), 12);

        recent_slots.reverse();
        assert_slot(RecentLeaderSlots::from(recent_slots), 12);

        assert_slot(
            RecentLeaderSlots::from(vec![0, 1 + MAX_SLOT_SKIP_DISTANCE]),
            1 + MAX_SLOT_SKIP_DISTANCE,
        );
        assert_slot(
            RecentLeaderSlots::from(vec![0, 2 + MAX_SLOT_SKIP_DISTANCE]),
            0,
        );

        assert_slot(RecentLeaderSlots::from(vec![1]), 1);
        assert_slot(RecentLeaderSlots::from(vec![1, 100]), 1);
        assert_slot(RecentLeaderSlots::from(vec![1, 2, 100]), 2);
        assert_slot(RecentLeaderSlots::from(vec![1, 2, 3, 100]), 3);
        assert_slot(RecentLeaderSlots::from(vec![1, 2, 3, 99, 100]), 3);
    }
}