// 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.

extern crate futures;
extern crate substrate_client as client;
extern crate substrate_codec as codec;
extern crate substrate_primitives as primitives;
extern crate ed25519;

extern crate polkadot_api;
extern crate polkadot_cli;
extern crate polkadot_runtime;
extern crate polkadot_primitives;

#[macro_use]
extern crate log;

use std::collections::{BTreeSet, BTreeMap};
use std::sync::Arc;

use futures::{future, stream, Stream, Future, IntoFuture};
use client::BlockchainEvents;
use polkadot_api::PolkadotApi;
use polkadot_primitives::BlockId;
use polkadot_primitives::parachain::{self, BlockData, HeadData, ConsolidatedIngress, Collation, Message, Id as ParaId};
use polkadot_cli::{ServiceComponents, Service};
use polkadot_cli::Worker;

/// 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 {
	/// Produce a candidate, given the latest ingress queue information and the last parachain head.
	fn produce_candidate<I: IntoIterator<Item=(ParaId, Message)>>(
		&self,
		last_head: HeadData,
		ingress: I,
	) -> (BlockData, HeadData);
}

/// 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;

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

	/// Provide a set of all parachains meant to be routed to at a block.
	fn routing_parachains(&self) -> BTreeSet<ParaId>;

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

/// Collate the necessary ingress queue using the given context.
pub fn collate_ingress<'a, R>(relay_context: R)
	-> impl Future<Item=ConsolidatedIngress, Error=R::Error> + 'a
	where
		R: RelayChainContext,
		R::Error: 'a,
		R::FutureEgress: 'a,
{
	let mut egress_fetch = Vec::new();

	for routing_parachain in relay_context.routing_parachains() {
		let fetch = relay_context
			.unrouted_egress(routing_parachain)
			.into_future()
			.map(move |egresses| (routing_parachain, egresses));

		egress_fetch.push(fetch);
	}

	// create a map ordered first by the depth of the egress queue
	// and then by the parachain ID.
	//
	// then transform that into the consolidated egress queue.
	stream::futures_unordered(egress_fetch)
		.fold(BTreeMap::new(), |mut map, (routing_id, egresses)| {
			for (depth, egress) in egresses.into_iter().rev().enumerate() {
				let depth = -(depth as i64);
				map.insert((depth, routing_id), egress);
			}

			Ok(map)
		})
		.map(|ordered| ordered.into_iter().map(|((_, id), egress)| (id, egress)))
		.map(|i| i.collect::<Vec<_>>())
		.map(ConsolidatedIngress)
}

/// Produce a candidate for the parachain, with given contexts, parent head, and signing key.
pub fn collate<'a, R, P>(
	local_id: ParaId,
	last_head: HeadData,
	relay_context: R,
	para_context: P,
	key: Arc<ed25519::Pair>,
)
	-> impl Future<Item=parachain::Collation, Error=R::Error> + 'a
	where
		R: RelayChainContext + 'a,
		R::Error: 'a,
		R::FutureEgress: 'a,
		P: ParachainContext + 'a,
{
	collate_ingress(relay_context).map(move |ingress| {
		let (block_data, head_data) = para_context.produce_candidate(
			last_head,
			ingress.0.iter().flat_map(|&(id, ref msgs)| msgs.iter().cloned().map(move |msg| (id, msg)))
		);

		let block_data_hash = block_data.hash();
		let signature = key.sign(&block_data_hash.0[..]).into();
		let pubkey_bytes: [u8; 32] = key.public().into();

		let receipt = parachain::CandidateReceipt {
			parachain_index: local_id,
			collator: pubkey_bytes.into(),
			signature,
			head_data,
			balance_uploads: Vec::new(),
			egress_queue_roots: Vec::new(),
			fees: 0,
			block_data_hash,
		};

		parachain::Collation {
			receipt,
			block_data,
		}
	})
}

/// Polkadot-api context.
struct ApiContext;

impl RelayChainContext for ApiContext {
	type Error = ();
	type FutureEgress = Result<Vec<Vec<Message>>, Self::Error>;

	fn routing_parachains(&self) -> BTreeSet<ParaId> {
		BTreeSet::new()
	}

	fn unrouted_egress(&self, _id: ParaId) -> Self::FutureEgress {
		Ok(Vec::new())
	}
}

struct CollationNode<P, E> {
	parachain_context: P,
	exit: E,
	para_id: ParaId,
	key: Arc<ed25519::Pair>,
}

impl<P, E> Worker for CollationNode<P, E> where
	P: ParachainContext + 'static,
	E: Future<Item=(),Error=()> + Send + 'static
{
	type Work = Box<Future<Item=(),Error=()>>;
	type Exit = E;

	fn exit_only(self) -> Self::Exit {
		self.exit
	}

	fn work<C: ServiceComponents>(self, service: &Service<C>) -> Self::Work {
		let CollationNode { parachain_context, exit, para_id, key } = self;
		let client = service.client();
		let api = service.api();

		let work = client.import_notification_stream()
			.and_then(move |notification| {
				let id = BlockId::hash(notification.hash);

				match api.parachain_head(&id, para_id) {
					Ok(Some(last_head)) => {
						let collation_work = collate(
							para_id,
							HeadData(last_head),
							ApiContext,
							parachain_context.clone(),
							key.clone(),
						).map(Some);

						future::Either::A(collation_work)
					}
					Ok(None) => {
						info!("Parachain {:?} appears to be inactive. Cannot collate.", id);
						future::Either::B(future::ok(None))
					}
					Err(e) => {
						warn!("Could not collate for parachain {:?}: {:?}", id, e);
						future::Either::B(future::ok(None)) // returning error would shut down the collation node
					}
				}
			})
			.for_each(|_collation: Option<Collation>| {
				// TODO: import into network.
				Ok(())
			});

		let work_and_exit = work.select(exit).then(|_| Ok(()));
		Box::new(work_and_exit) as Box<_>
	}
}

/// Run a collator node with the given `RelayChainContext` and `ParachainContext` 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>(
	parachain_context: P,
	para_id: ParaId,
	exit: E,
	key: Arc<ed25519::Pair>,
	args: Vec<::std::ffi::OsString>
) -> polkadot_cli::error::Result<()> where
	P: ParachainContext + 'static,
	E: IntoFuture<Item=(),Error=()>,
	E::Future: Send + 'static,
{
	let node_logic = CollationNode { parachain_context, exit: exit.into_future(), para_id, key };
	polkadot_cli::run(args, node_logic)
}

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

	use std::collections::{HashMap, BTreeSet};

	use futures::Future;
	use polkadot_primitives::parachain::{Message, Id as ParaId};

	pub struct DummyRelayChainCtx {
		egresses: HashMap<ParaId, Vec<Vec<Message>>>,
		currently_routing: BTreeSet<ParaId>,
	}

	impl RelayChainContext for DummyRelayChainCtx {
		type Error = ();
		type FutureEgress = Result<Vec<Vec<Message>>, ()>;

		fn routing_parachains(&self) -> BTreeSet<ParaId> {
			self.currently_routing.clone()
		}

		fn unrouted_egress(&self, id: ParaId) -> Result<Vec<Vec<Message>>, ()> {
			Ok(self.egresses.get(&id).cloned().unwrap_or_default())
		}
	}

	#[test]
	fn collates_ingress() {
		let route_from = |x: &[ParaId]| {
			 let mut set = BTreeSet::new();
			 set.extend(x.iter().cloned());
			 set
		};

		let message = |x: Vec<u8>| vec![Message(x)];

		let dummy_ctx = DummyRelayChainCtx {
			currently_routing: route_from(&[2.into(), 3.into()]),
			egresses: vec![
				// egresses for `2`: last routed successfully 5 blocks ago.
				(2.into(), vec![
					message(vec![1, 2, 3]),
					message(vec![4, 5, 6]),
					message(vec![7, 8]),
					message(vec![10]),
					message(vec![12]),
				]),

				// egresses for `3`: last routed successfully 3 blocks ago.
				(3.into(), vec![
					message(vec![9]),
					message(vec![11]),
					message(vec![13]),
				]),
			].into_iter().collect(),
		};

		assert_eq!(
			collate_ingress(dummy_ctx).wait().unwrap(),
			ConsolidatedIngress(vec![
				(2.into(), message(vec![1, 2, 3])),
				(2.into(), message(vec![4, 5, 6])),
				(2.into(), message(vec![7, 8])),
				(3.into(), message(vec![9])),
				(2.into(), message(vec![10])),
				(3.into(), message(vec![11])),
				(2.into(), message(vec![12])),
				(3.into(), message(vec![13])),
			]
		))
	}
}