// Copyright 2017 Parity Technologies (UK) Ltd.
// This file is part of Polkadot.

// Polkadot is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// Polkadot is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.

//! Collation node logic.
//!
//! A collator node lives on a distinct parachain and submits a proposal for
//! a state transition, along with a proof for its validity
//! (what we might call a witness or block data).
//!
//! One of collators' other roles is to route messages between chains.
//! Each parachain produces a list of "egress" posts of messages for each other
//! parachain on each block, for a total of N^2 lists all together.
//!
//! We will refer to the egress list at relay chain block X of parachain A with
//! destination B as egress(X)[A -> B]
//!
//! On every block, each parachain will be intended to route messages from some
//! subset of all the other parachains. (NOTE: in practice this is not done until PoC-3)
//!
//! Since the egress information is unique to every block, when routing from a
//! parachain a collator must gather all egress posts from that parachain
//! up to the last point in history that messages were successfully routed
//! from that parachain, accounting for relay chain blocks where no candidate
//! from the collator's parachain was produced.
//!
//! In the case that all parachains route to each other and a candidate for the
//! collator's parachain was included in the last relay chain block, the collator
//! only has to gather egress posts from other parachains one block back in relay
//! chain history.
//!
//! This crate defines traits which provide context necessary for collation logic
//! to be performed, as the collation logic itself.

use std::collections::HashSet;
use std::fmt;
use std::sync::Arc;
use std::time::Duration;

use futures::{future, Future, Stream, FutureExt, TryFutureExt, StreamExt, task::Spawn};
use log::{warn, error};
use client::BlockchainEvents;
use primitives::{Pair, Blake2Hasher};
use polkadot_primitives::{
	BlockId, Hash, Block,
	parachain::{
		self, BlockData, DutyRoster, HeadData, ConsolidatedIngress, Message, Id as ParaId,
		OutgoingMessages, PoVBlock, Status as ParachainStatus, ValidatorId, CollatorPair,
	}
};
use polkadot_cli::{
	Worker, IntoExit, ProvideRuntimeApi, AbstractService, CustomConfiguration, ParachainHost,
};
use polkadot_network::validation::{LeafWorkParams, ValidationNetwork};
use polkadot_network::{PolkadotNetworkService, PolkadotProtocol};
use polkadot_runtime::RuntimeApi;

pub use polkadot_cli::VersionInfo;
pub use polkadot_network::validation::Incoming;
pub use polkadot_validation::SignedStatement;
pub use polkadot_primitives::parachain::CollatorId;
pub use sc_network::PeerId;

const COLLATION_TIMEOUT: Duration = Duration::from_secs(30);

/// An abstraction over the `Network` with useful functions for a `Collator`.
pub trait Network: Send + Sync {
	/// Convert the given `CollatorId` to a `PeerId`.
	fn collator_id_to_peer_id(&self, collator_id: CollatorId) ->
		Box<dyn Future<Output=Option<PeerId>> + Send>;

	/// Create a `Stream` of checked statements for the given `relay_parent`.
	///
	/// The returned stream will not terminate, so it is required to make sure that the stream is
	/// dropped when it is not required anymore. Otherwise, it will stick around in memory
	/// infinitely.
	fn checked_statements(&self, relay_parent: Hash) -> Box<dyn Stream<Item=SignedStatement>>;
}

impl<P, E, SP> Network for ValidationNetwork<P, E, PolkadotNetworkService, SP> where
	P: 'static + Send + Sync,
	E: 'static + Send + Sync,
	SP: 'static + Spawn + Clone + Send + Sync,
{
	fn collator_id_to_peer_id(&self, collator_id: CollatorId) ->
		Box<dyn Future<Output=Option<PeerId>> + Send>
	{
		Box::new(Self::collator_id_to_peer_id(self, collator_id))
	}

	fn checked_statements(&self, relay_parent: Hash) -> Box<dyn Stream<Item=SignedStatement>> {
		Box::new(Self::checked_statements(self, relay_parent))
	}
}

/// Error to return when the head data was invalid.
#[derive(Clone, Copy, Debug)]
pub struct InvalidHead;

/// Collation errors.
#[derive(Debug)]
pub enum Error<R> {
	/// Error on the relay-chain side of things.
	Polkadot(R),
	/// Error on the collator side of things.
	Collator(InvalidHead),
}

impl<R: fmt::Display> fmt::Display for Error<R> {
	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
		match *self {
			Error::Polkadot(ref err) => write!(f, "Polkadot node error: {}", err),
			Error::Collator(_) => write!(f, "Collator node error: Invalid head data"),
		}
	}
}

/// The Polkadot client type.
pub type PolkadotClient<B, E> = client::Client<B, E, Block, RuntimeApi>;

/// Something that can build a `ParachainContext`.
pub trait BuildParachainContext {
	/// The parachain context produced by the `build` function.
	type ParachainContext: self::ParachainContext;

	/// Build the `ParachainContext`.
	fn build<B, E, SP>(
		self,
		client: Arc<PolkadotClient<B, E>>,
		spawner: SP,
		network: Arc<dyn Network>,
	) -> Result<Self::ParachainContext, ()>
		where
			B: client_api::backend::Backend<Block, Blake2Hasher> + 'static,
			E: client::CallExecutor<Block, Blake2Hasher> + Clone + Send + Sync + 'static,
			SP: Spawn + Clone + Send + Sync + 'static;
}

/// Parachain context needed for collation.
///
/// This can be implemented through an externally attached service or a stub.
/// This is expected to be a lightweight, shared type like an Arc.
pub trait ParachainContext: Clone {
	type ProduceCandidate: Future<Output = Result<(BlockData, HeadData, OutgoingMessages), InvalidHead>>;

	/// Produce a candidate, given the relay parent hash, the latest ingress queue information
	/// and the last parachain head.
	fn produce_candidate<I: IntoIterator<Item=(ParaId, Message)>>(
		&mut self,
		relay_parent: Hash,
		status: ParachainStatus,
		ingress: I,
	) -> Self::ProduceCandidate;
}

/// Relay chain context needed to collate.
/// This encapsulates a network and local database which may store
/// some of the input.
pub trait RelayChainContext {
	type Error: std::fmt::Debug;

	/// Future that resolves to the un-routed egress queues of a parachain.
	/// The first item is the oldest.
	type FutureEgress: Future<Output = Result<ConsolidatedIngress, Self::Error>>;

	/// Get un-routed egress queues from a parachain to the local parachain.
	fn unrouted_egress(&self, _id: ParaId) -> Self::FutureEgress;
}

/// Produce a candidate for the parachain, with given contexts, parent head, and signing key.
pub async fn collate<R, P>(
	relay_parent: Hash,
	local_id: ParaId,
	parachain_status: ParachainStatus,
	relay_context: R,
	mut para_context: P,
	key: Arc<CollatorPair>,
)
	-> Result<(parachain::Collation, OutgoingMessages), Error<R::Error>>
	where
		R: RelayChainContext,
		P: ParachainContext,
		P::ProduceCandidate: Send,
{
	let ingress = relay_context.unrouted_egress(local_id).await.map_err(Error::Polkadot)?;

	let (block_data, head_data, mut outgoing) = para_context.produce_candidate(
		relay_parent,
		parachain_status,
		ingress.0.iter().flat_map(|&(id, ref msgs)| msgs.iter().cloned().map(move |msg| (id, msg)))
	).map_err(Error::Collator).await?;

	let block_data_hash = block_data.hash();
	let signature = key.sign(block_data_hash.as_ref());
	let egress_queue_roots =
		polkadot_validation::egress_roots(&mut outgoing.outgoing_messages);

	let info = parachain::CollationInfo {
		parachain_index: local_id,
		collator: key.public(),
		signature,
		egress_queue_roots,
		head_data,
		block_data_hash,
		upward_messages: Vec::new(),
	};

	let collation = parachain::Collation {
		info,
		pov: PoVBlock {
			block_data,
			ingress,
		},
	};

	Ok((collation, outgoing))
}

/// Polkadot-api context.
struct ApiContext<P, E, SP> {
	network: Arc<ValidationNetwork<P, E, PolkadotNetworkService, SP>>,
	parent_hash: Hash,
	validators: Vec<ValidatorId>,
}

impl<P: 'static, E: 'static, SP: 'static> RelayChainContext for ApiContext<P, E, SP> where
	P: ProvideRuntimeApi + Send + Sync,
	P::Api: ParachainHost<Block>,
	E: futures::Future<Output=()> + Clone + Send + Sync + 'static,
	SP: Spawn + Clone + Send + Sync
{
	type Error = String;
	type FutureEgress = Box<dyn Future<Output=Result<ConsolidatedIngress, String>> + Unpin + Send>;

	fn unrouted_egress(&self, _id: ParaId) -> Self::FutureEgress {
		// TODO: https://github.com/paritytech/polkadot/issues/253
		//
		// Fetch ingress and accumulate all unrounted egress
		let _session = self.network.instantiate_leaf_work(LeafWorkParams {
			local_session_key: None,
			parent_hash: self.parent_hash,
			authorities: self.validators.clone(),
		})
			.map_err(|e| format!("unable to instantiate validation session: {:?}", e));

		Box::new(future::ok(ConsolidatedIngress(Vec::new())))
	}
}

struct CollationNode<P, E> {
	build_parachain_context: P,
	exit: E,
	para_id: ParaId,
	key: Arc<CollatorPair>,
}

impl<P, E> IntoExit for CollationNode<P, E> where
	E: futures::Future<Output=()> + Unpin + Send + 'static
{
	type Exit = E;
	fn into_exit(self) -> Self::Exit {
		self.exit
	}
}

impl<P, E> Worker for CollationNode<P, E> where
	P: BuildParachainContext + Send + 'static,
	P::ParachainContext: Send + 'static,
	<P::ParachainContext as ParachainContext>::ProduceCandidate: Send + 'static,
	E: futures::Future<Output=()> + Clone + Unpin + Send + Sync + 'static,
{
	type Work = Box<dyn Future<Output=()> + Unpin + Send>;

	fn configuration(&self) -> CustomConfiguration {
		let mut config = CustomConfiguration::default();
		config.collating_for = Some((
			self.key.public(),
			self.para_id,
		));
		config
	}

	fn work<S, SC, B, CE, SP>(self, service: &S, spawner: SP) -> Self::Work
	where
		S: AbstractService<
			Block = Block,
			RuntimeApi = RuntimeApi,
			Backend = B,
			SelectChain = SC,
			NetworkSpecialization = PolkadotProtocol,
			CallExecutor = CE,
		>,
		SC: polkadot_service::SelectChain<Block> + 'static,
		B: client_api::backend::Backend<Block, Blake2Hasher> + 'static,
		CE: client::CallExecutor<Block, Blake2Hasher> + Clone + Send + Sync + 'static,
		SP: Spawn + Clone + Send + Sync + 'static,
	{
		let CollationNode { build_parachain_context, exit, para_id, key } = self;
		let client = service.client();
		let network = service.network();
		let known_oracle = client.clone();
		let select_chain = if let Some(select_chain) = service.select_chain() {
			select_chain
		} else {
			error!("The node cannot work because it can't select chain.");
			return Box::new(future::ready(()));
		};

		let is_known = move |block_hash: &Hash| {
			use consensus_common::BlockStatus;
			use polkadot_network::gossip::Known;

			match known_oracle.block_status(&BlockId::hash(*block_hash)) {
				Err(_) | Ok(BlockStatus::Unknown) | Ok(BlockStatus::Queued) => None,
				Ok(BlockStatus::KnownBad) => Some(Known::Bad),
				Ok(BlockStatus::InChainWithState) | Ok(BlockStatus::InChainPruned) =>
					match select_chain.leaves() {
						Err(_) => None,
						Ok(leaves) => if leaves.contains(block_hash) {
							Some(Known::Leaf)
						} else {
							Some(Known::Old)
						},
					}
			}
		};

		let message_validator = polkadot_network::gossip::register_validator(
			network.clone(),
			(is_known, client.clone()),
		);

		let validation_network = Arc::new(ValidationNetwork::new(
			network.clone(),
			exit.clone(),
			message_validator,
			client.clone(),
			spawner.clone(),
		));

		let parachain_context = match build_parachain_context.build(
			client.clone(),
			spawner,
			validation_network.clone(),
		) {
			Ok(ctx) => ctx,
			Err(()) => {
				error!("Could not build the parachain context!");
				return Box::new(future::ready(()))
			}
		};

		let inner_exit = exit.clone();
		let work = client.import_notification_stream()
			.for_each(move |notification| {
				macro_rules! try_fr {
					($e:expr) => {
						match $e {
							Ok(x) => x,
							Err(e) => return future::Either::Left(future::err(Error::Polkadot(
								format!("{:?}", e)
							))),
						}
					}
				}

				let relay_parent = notification.hash;
				let id = BlockId::hash(relay_parent);

				let network = network.clone();
				let client = client.clone();
				let key = key.clone();
				let parachain_context = parachain_context.clone();
				let validation_network = validation_network.clone();
				let inner_exit_2 = inner_exit.clone();

				let work = future::lazy(move |_| {
					let api = client.runtime_api();
					let status = match try_fr!(api.parachain_status(&id, para_id)) {
						Some(status) => status,
						None => return future::Either::Left(future::ok(())),
					};

					let validators = try_fr!(api.validators(&id));

					let targets = compute_targets(
						para_id,
						validators.as_slice(),
						try_fr!(api.duty_roster(&id)),
					);

					let context = ApiContext {
						network: validation_network,
						parent_hash: relay_parent,
						validators,
					};

					let collation_work = collate(
						relay_parent,
						para_id,
						status,
						context,
						parachain_context,
						key,
					).map_ok(move |(collation, outgoing)| {
						network.with_spec(move |spec, ctx| {
							let res = spec.add_local_collation(
								ctx,
								relay_parent,
								targets,
								collation,
								outgoing,
							);

							let exit = inner_exit_2.clone();
							tokio::spawn(future::select(res, exit).map(drop));
						})
					});

					future::Either::Right(collation_work)
				});

				let deadlined = future::select(
					work,
					futures_timer::Delay::new(COLLATION_TIMEOUT)
				);

				let silenced = deadlined
					.map(|either| {
						if let future::Either::Right(_) = either {
							warn!("Collation failure: timeout");
						}
					});

				let future = future::select(
					silenced,
					inner_exit.clone()
				).map(drop);

				tokio::spawn(future);
				future::ready(())
			});

		let work_and_exit = future::select(work, exit)
			.map(|_| ());

		Box::new(work_and_exit)
	}
}

fn compute_targets(para_id: ParaId, session_keys: &[ValidatorId], roster: DutyRoster) -> HashSet<ValidatorId> {
	use polkadot_primitives::parachain::Chain;

	roster.validator_duty.iter().enumerate()
		.filter(|&(_, c)| c == &Chain::Parachain(para_id))
		.filter_map(|(i, _)| session_keys.get(i))
		.cloned()
		.collect()
}

/// Run a collator node with the given `RelayChainContext` and `ParachainContext`
/// build by the given `BuildParachainContext` and arguments to the underlying polkadot node.
///
/// Provide a future which resolves when the node should exit.
/// This function blocks until done.
pub fn run_collator<P, E>(
	build_parachain_context: P,
	para_id: ParaId,
	exit: E,
	key: Arc<CollatorPair>,
	version: VersionInfo,
) -> polkadot_cli::error::Result<()> where
	P: BuildParachainContext + Send + 'static,
	P::ParachainContext: Send + 'static,
	<P::ParachainContext as ParachainContext>::ProduceCandidate: Send + 'static,
	E: futures::Future<Output = ()> + Unpin + Send + Clone + Sync + 'static,
{
	let node_logic = CollationNode { build_parachain_context, exit, para_id, key };
	polkadot_cli::run(node_logic, version)
}

#[cfg(test)]
mod tests {
	use std::collections::HashMap;
	use polkadot_primitives::parachain::{TargetedMessage, FeeSchedule};
	use keyring::Sr25519Keyring;
	use super::*;

	#[derive(Default, Clone)]
	struct DummyRelayChainContext {
		ingress: HashMap<ParaId, ConsolidatedIngress>
	}

	impl RelayChainContext for DummyRelayChainContext {
		type Error = ();
		type FutureEgress = Box<dyn Future<Output=Result<ConsolidatedIngress,()>> + Unpin>;

		fn unrouted_egress(&self, para_id: ParaId) -> Self::FutureEgress {
			match self.ingress.get(&para_id) {
				Some(ingress) => Box::new(future::ok(ingress.clone())),
				None => Box::new(future::pending()),
			}
		}
	}

	#[derive(Clone)]
	struct DummyParachainContext;

	impl ParachainContext for DummyParachainContext {
		type ProduceCandidate = future::Ready<Result<(BlockData, HeadData, OutgoingMessages), InvalidHead>>;

		fn produce_candidate<I: IntoIterator<Item=(ParaId, Message)>>(
			&mut self,
			_relay_parent: Hash,
			_status: ParachainStatus,
			ingress: I,
		) -> Self::ProduceCandidate {
			// send messages right back.
			future::ok((
				BlockData(vec![1, 2, 3, 4, 5,]),
				HeadData(vec![9, 9, 9]),
				OutgoingMessages {
					outgoing_messages: ingress.into_iter().map(|(id, msg)| TargetedMessage {
						target: id,
						data: msg.0,
					}).collect(),
				}
			))
		}
	}

	#[test]
	fn collates_correct_queue_roots() {
		let mut context = DummyRelayChainContext::default();

		let id = ParaId::from(100);

		let a = ParaId::from(123);
		let b = ParaId::from(456);

		let messages_from_a = vec![
			Message(vec![1, 1, 1]),
			Message(b"helloworld".to_vec()),
		];
		let messages_from_b = vec![
			Message(b"dogglesworth".to_vec()),
			Message(b"buy_1_chili_con_carne_here_is_my_cash".to_vec()),
		];

		let root_a = ::polkadot_validation::message_queue_root(
			messages_from_a.iter().map(|msg| &msg.0)
		);

		let root_b = ::polkadot_validation::message_queue_root(
			messages_from_b.iter().map(|msg| &msg.0)
		);

		context.ingress.insert(id, ConsolidatedIngress(vec![
			(b, messages_from_b),
			(a, messages_from_a),
		]));

		let future = collate(
			Default::default(),
			id,
			ParachainStatus {
				head_data: HeadData(vec![5]),
				balance: 10,
				fee_schedule: FeeSchedule {
					base: 0,
					per_byte: 1,
				},
			},
			context.clone(),
			DummyParachainContext,
			Arc::new(Sr25519Keyring::Alice.pair().into()),
		);

		let collation = futures::executor::block_on(future).unwrap().0;

		// ascending order by root.
		assert_eq!(collation.info.egress_queue_roots, vec![(a, root_a), (b, root_b)]);
	}
}