// Copyright 2018-2019 Parity Technologies (UK) Ltd
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//! Logic for a single round of GRANDPA.

mod context;

use context::{Context, VoteNode, Vote};

#[cfg(feature = "derive-codec")]
use parity_scale_codec::{Encode, Decode};

use crate::std::{
	self,
	collections::btree_map::{BTreeMap, Entry},
	fmt,
	vec::Vec,
};
use crate::vote_graph::VoteGraph;
use crate::voter_set::{VoterSet, VoterInfo};
use crate::weights::{VoteWeight, VoterWeight};

use super::{Equivocation, Prevote, Precommit, Chain, BlockNumberOps, HistoricalVotes, Message, SignedMessage};

/// The (voting) phases of a round, each corresponding to the type of
/// votes cast in that phase.
#[derive(PartialEq, Eq, Copy, Clone, Debug)]
pub enum Phase {
	/// The prevote phase in which [`Prevote`]s are cast.
	Prevote,
	/// The precommit phase in which [`Precommit`]s are cast.
	Precommit
}

/// The observed vote from a single voter.
enum VoteMultiplicity<Vote, Signature> {
	/// A single vote has been observed from the voter.
	Single(Vote, Signature),
 	/// At least two votes have been observed from the voter,
	/// i.e. an equivocation.
	Equivocated((Vote, Signature), (Vote, Signature)),
}

impl<Vote: Eq, Signature: Eq> VoteMultiplicity<Vote, Signature> {
	fn contains(&self, vote: &Vote, signature: &Signature) -> bool {
		match self {
			VoteMultiplicity::Single(v, s) =>
				v == vote && s == signature,
			VoteMultiplicity::Equivocated((v1, s1), (v2, s2)) => {
				v1 == vote && s1 == signature ||
					v2 == vote && s2 == signature
			},
		}
	}
}

struct VoteTracker<Id: Ord + Eq, Vote, Signature> {
	votes: BTreeMap<Id, VoteMultiplicity<Vote, Signature>>,
	current_weight: VoteWeight
}

/// Result of adding a vote.
pub(crate) struct AddVoteResult<'a, Vote, Signature> {
	multiplicity: Option<&'a VoteMultiplicity<Vote, Signature>>,
	duplicated: bool,
}

impl<Id: Ord + Eq + Clone, Vote: Clone + Eq, Signature: Clone + Eq> VoteTracker<Id, Vote, Signature> {
	fn new() -> Self {
		VoteTracker {
			votes: BTreeMap::new(),
			current_weight: VoteWeight(0),
		}
	}

	// track a vote, returning a value containing the multiplicity of all votes from this ID
	// and a bool indicating if the vote is duplicated.
	// if the vote is the first equivocation, returns a value indicating
	// it as such (the new vote is always the last in the multiplicity).
	//
	// if the vote is a further equivocation, it is ignored and there is nothing
	// to do.
	//
	// since this struct doesn't track the round-number of votes, that must be set
	// by the caller.
	fn add_vote(&mut self, id: Id, vote: Vote, signature: Signature, weight: VoterWeight)
		-> AddVoteResult<Vote, Signature>
	{
		match self.votes.entry(id) {
			Entry::Vacant(vacant) => {
				self.current_weight = self.current_weight + weight;
				let multiplicity = vacant.insert(VoteMultiplicity::Single(vote, signature));

				AddVoteResult {
					multiplicity: Some(multiplicity),
					duplicated: false,
				}
			}
			Entry::Occupied(mut occupied) => {
				if occupied.get().contains(&vote, &signature) {
					return AddVoteResult { multiplicity: None, duplicated: true };
				}

				// import, but ignore further equivocations.
				let new_val = match *occupied.get_mut() {
					VoteMultiplicity::Single(ref v, ref s) =>
						Some(VoteMultiplicity::Equivocated((v.clone(), s.clone()), (vote, signature))),
					VoteMultiplicity::Equivocated(_, _) => {
						return AddVoteResult { multiplicity: None, duplicated: false }
					}
				};

				if let Some(new_val) = new_val {
					*occupied.get_mut() = new_val;
				}

				AddVoteResult {
					multiplicity: Some(&*occupied.into_mut()),
					duplicated: false
				}
			}
		}
	}

	// Returns all imported votes.
	fn votes(&self) -> Vec<(Id, Vote, Signature)> {
		let mut votes = Vec::new();

		for (id, vote) in &self.votes {
			match vote {
				VoteMultiplicity::Single(v, s) => {
					votes.push((id.clone(), v.clone(), s.clone()))
				},
				VoteMultiplicity::Equivocated((v1, s1), (v2, s2)) => {
					votes.push((id.clone(), v1.clone(), s1.clone()));
					votes.push((id.clone(), v2.clone(), s2.clone()));
				},
			}
		}

		votes
	}

	// Current vote weight and number of participants.
	fn participation(&self) -> (VoteWeight, usize) {
		(self.current_weight, self.votes.len())
	}
}

/// State of the round.
#[derive(PartialEq, Clone)]
#[cfg_attr(any(feature = "std", test), derive(Debug))]
#[cfg_attr(feature = "derive-codec", derive(Encode, Decode))]
pub struct State<H, N> {
	/// The prevote-GHOST block.
	pub prevote_ghost: Option<(H, N)>,
	/// The finalized block.
	pub finalized: Option<(H, N)>,
	/// The new round-estimate.
	pub estimate: Option<(H, N)>,
	/// Whether the round is completable.
	pub completable: bool,
}

impl<H: Clone, N: Clone> State<H, N> {
	/// Genesis state.
	pub fn genesis(genesis: (H, N)) -> Self {
		State {
			prevote_ghost: Some(genesis.clone()),
			finalized: Some(genesis.clone()),
			estimate: Some(genesis),
			completable: true,
		}
	}
}

/// Parameters for starting a round.
pub struct RoundParams<Id: Ord + Eq, H, N> {
	/// The round number for votes.
	pub round_number: u64,
	/// Actors and weights in the round.
	pub voters: VoterSet<Id>,
	/// The base block to build on.
	pub base: (H, N),
}

/// Stores data for a round.
pub struct Round<Id: Ord + Eq, H: Ord + Eq, N, Signature> {
	round_number: u64,
	context: Context<Id>,
	graph: VoteGraph<H, N, VoteNode>, // DAG of blocks which have been voted on.
	prevote: VoteTracker<Id, Prevote<H, N>, Signature>, // tracks prevotes that have been counted
	precommit: VoteTracker<Id, Precommit<H, N>, Signature>, // tracks precommits
	historical_votes: HistoricalVotes<H, N, Signature, Id>,
	prevote_ghost: Option<(H, N)>, // current memoized prevote-GHOST block
	precommit_ghost: Option<(H, N)>, // current memoized precommit-GHOST block
	finalized: Option<(H, N)>, // best finalized block in this round.
	estimate: Option<(H, N)>, // current memoized round-estimate
	completable: bool, // whether the round is completable
}

/// Result of importing a Prevote or Precommit.
pub(crate) struct ImportResult<Id, P, Signature> {
	/// Indicates if the voter is part of the voter set.
	pub(crate) valid_voter: bool,
	/// Indicates if the vote is duplicated.
	pub(crate) duplicated: bool,
	/// An equivocation proof, if the vote is an equivocation.
	pub(crate) equivocation: Option<Equivocation<Id, P, Signature>>,
}

impl<Id, P, Signature> Default for ImportResult<Id, P, Signature> {
	fn default() -> Self {
		ImportResult {
			valid_voter: false,
			duplicated: false,
			equivocation: None,
		}
	}
}

impl<Id, H, N, Signature> Round<Id, H, N, Signature> where
	Id: Ord + Clone + Eq + fmt::Debug,
	H: Ord + Clone + Eq + Ord + fmt::Debug,
	N: Copy + fmt::Debug + BlockNumberOps,
	Signature: Eq + Clone,
{
	/// Create a new round accumulator for given round number and with given weight.
	pub fn new(round_params: RoundParams<Id, H, N>) -> Self {
		let (base_hash, base_number) = round_params.base;

		Round {
			round_number: round_params.round_number,
			context: Context::new(round_params.voters),
			graph: VoteGraph::new(base_hash, base_number, VoteNode::default()),
			prevote: VoteTracker::new(),
			precommit: VoteTracker::new(),
			historical_votes: HistoricalVotes::new(),
			prevote_ghost: None,
			precommit_ghost: None,
			finalized: None,
			estimate: None,
			completable: false,
		}
	}

	/// Return the round number.
	pub fn number(&self) -> u64 {
		self.round_number
	}

	/// Import a prevote. Returns an equivocation proof, if the vote is an equivocation,
	/// and a bool indicating if the vote is duplicated (see `ImportResult`).
	///
	/// Ignores duplicate prevotes (not equivocations).
	#[cfg_attr(not(feature = "std"), allow(unused))]
	pub(crate) fn import_prevote<C: Chain<H, N>>(
		&mut self,
		chain: &C,
		prevote: Prevote<H, N>,
		signer: Id,
		signature: Signature,
	) -> Result<ImportResult<Id, Prevote<H, N>, Signature>, crate::Error> {
		let mut import_result = ImportResult::default();

		let info = match self.context.voters().get(&signer) {
			Some(info) => info.clone(),
			None => return Ok(import_result),
		};

		import_result.valid_voter = true;
		let weight = info.weight();

		let equivocation = {
			let multiplicity = match self.prevote.add_vote(signer.clone(), prevote.clone(), signature.clone(), weight) {
				AddVoteResult { multiplicity: Some(m), .. } => m,
				AddVoteResult { duplicated, .. } => {
					import_result.duplicated = duplicated;
					return Ok(import_result)
				},
			};
			let round_number = self.round_number;

			match multiplicity {
				VoteMultiplicity::Single(single_vote, _) => {
					let vote = Vote::new(&info, Phase::Prevote);

					self.graph.insert(
						single_vote.target_hash.clone(),
						single_vote.target_number,
						vote,
						chain,
					)?;

					// Push the vote into HistoricalVotes.
					let message = Message::Prevote(prevote);
					let signed_message = SignedMessage { id: signer, signature, message };
					self.historical_votes.push_vote(signed_message);

					None
				}
				VoteMultiplicity::Equivocated(ref first, ref second) => {
					// mark the equivocator as such. no need to "undo" the first vote.
					self.context.equivocated(&info, Phase::Prevote);

					// Push the vote into HistoricalVotes.
					let message = Message::Prevote(prevote);
					let signed_message = SignedMessage { id: signer.clone(), signature, message };
					self.historical_votes.push_vote(signed_message);

					Some(Equivocation {
						round_number,
						identity: signer,
						first: first.clone(),
						second: second.clone(),
					})
				}
			}
		};

		// update prevote-GHOST
		let threshold = self.threshold();
		if self.prevote.current_weight >= threshold {
			self.prevote_ghost = self.graph.find_ghost(
				self.prevote_ghost.take(),
				|v| self.context.weight(v, Phase::Prevote) >= threshold,
			);
		}

		self.update();
		import_result.equivocation = equivocation;
		Ok(import_result)
	}

	/// Import a precommit. Returns an equivocation proof, if the vote is an
	/// equivocation, and a bool indicating if the vote is duplicated (see `ImportResult`).
	///
	/// Ignores duplicate precommits (not equivocations).
	pub(crate) fn import_precommit<C: Chain<H, N>>(
		&mut self,
		chain: &C,
		precommit: Precommit<H, N>,
		signer: Id,
		signature: Signature,
	) -> Result<ImportResult<Id, Precommit<H, N>, Signature>, crate::Error> {
		let mut import_result = ImportResult::default();

		let info = match self.context.voters().get(&signer) {
			Some(info) => info.clone(),
			None => return Ok(import_result),
		};
		import_result.valid_voter = true;
		let weight = info.weight();

		let equivocation = {
			let multiplicity = match self.precommit.add_vote(signer.clone(), precommit.clone(), signature.clone(), weight) {
				AddVoteResult { multiplicity: Some(m), .. } => m,
				AddVoteResult { duplicated, .. } => {
					import_result.duplicated = duplicated;
					return Ok(import_result)
				},
			};

			let round_number = self.round_number;

			match multiplicity {
				VoteMultiplicity::Single(single_vote, _) => {
					let vote = Vote::new(&info, Phase::Precommit);

					self.graph.insert(
						single_vote.target_hash.clone(),
						single_vote.target_number,
						vote,
						chain,
					)?;

					let message = Message::Precommit(precommit);
					let signed_message = SignedMessage { id: signer, signature, message };
					self.historical_votes.push_vote(signed_message);

					None
				},
				VoteMultiplicity::Equivocated(ref first, ref second) => {
					// mark the equivocator as such. no need to "undo" the first vote.
					self.context.equivocated(&info, Phase::Precommit);

					// Push the vote into HistoricalVotes.
					let message = Message::Precommit(precommit);
					let signed_message = SignedMessage { id: signer.clone(), signature, message };
					self.historical_votes.push_vote(signed_message);

					Some(Equivocation {
						round_number,
						identity: signer,
						first: first.clone(),
						second: second.clone(),
					})
				},
			}
		};

		self.update();
		import_result.equivocation = equivocation;
		Ok(import_result)
	}

	/// Return the current state.
	pub fn state(&self) -> State<H, N> {
		State {
			prevote_ghost: self.prevote_ghost.clone(),
			finalized: self.finalized.clone(),
			estimate: self.estimate.clone(),
			completable: self.completable,
		}
	}

	/// Compute and cache the precommit-GHOST.
	pub fn precommit_ghost(&mut self) -> Option<(H, N)> {
		// update precommit-GHOST
		let threshold = self.threshold();
		if self.precommit.current_weight >= threshold {
			self.precommit_ghost = self.graph.find_ghost(
				self.precommit_ghost.take(),
				|v| self.context.weight(v, Phase::Precommit) >= threshold,
			);
		}

		self.precommit_ghost.clone()
	}

	/// Returns an iterator of all precommits targeting the finalized hash.
	///
	/// Only returns `None` if no block has been finalized in this round.
	pub fn finalizing_precommits<'a, C: 'a + Chain<H, N>>(&'a mut self, chain: &'a C)
		-> Option<impl Iterator<Item=crate::SignedPrecommit<H, N, Signature, Id>> + 'a>
	{
		struct YieldVotes<'b, V: 'b, S: 'b> {
			yielded: usize,
			multiplicity: &'b VoteMultiplicity<V, S>,
		}

		impl<'b, V: 'b + Clone, S: 'b + Clone> Iterator for YieldVotes<'b, V, S> {
			type Item = (V, S);

			fn next(&mut self) -> Option<(V, S)> {
				match self.multiplicity {
					VoteMultiplicity::Single(ref v, ref s) => {
						if self.yielded == 0 {
							self.yielded += 1;
							Some((v.clone(), s.clone()))
						} else {
							None
						}
					}
					VoteMultiplicity::Equivocated(ref a, ref b) => {
						let res = match self.yielded {
							0 => Some(a.clone()),
							1 => Some(b.clone()),
							_ => None,
						};

						self.yielded += 1;
						res
					}
				}
			}
		}

		let (f_hash, _f_num) = self.finalized.clone()?;
		let find_valid_precommits = self.precommit.votes.iter()
			.filter(move |&(_id, multiplicity)| {
				if let VoteMultiplicity::Single(ref v, _) = *multiplicity {
					// if there is a single vote from this voter, we only include it
					// if it branches off of the target.
					chain.is_equal_or_descendent_of(f_hash.clone(), v.target_hash.clone())
				} else {
					// equivocations count for everything, so we always include them.
					true
				}
			})
			.flat_map(|(id, multiplicity)| {
				let yield_votes = YieldVotes { yielded: 0, multiplicity };

				yield_votes.map(move |(v, s)| crate::SignedPrecommit {
					precommit: v,
					signature: s,
					id: id.clone(),
				})
			});

		Some(find_valid_precommits)
	}

	// update the round-estimate and whether the round is completable.
	fn update(&mut self) {
		let threshold = self.threshold();

		if self.prevote.current_weight < threshold {
			return
		}

		let (g_hash, g_num) = match self.prevote_ghost.clone() {
			None => return,
			Some(x) => x,
		};

		let ctx = &self.context;

		// anything new finalized? finalized blocks are those which have both
		// 2/3+ prevote and precommit weight.
		let current_precommits = self.precommit.current_weight;
		if current_precommits >= self.threshold() {
			self.finalized = self.graph.find_ancestor(
				g_hash.clone(),
				g_num,
				|v| ctx.weight(v, Phase::Precommit) >= threshold,
			);
		};

		// figuring out whether a block can still be committed for is
		// not straightforward because we have to account for all possible future
		// equivocations and thus cannot discount weight from validators who
		// have already voted.
		let possible_to_precommit = {
			// find how many more equivocations we could still get.
			//
			// it is only important to consider the voters whose votes
			// we have already seen, because we are assuming any votes we
			// haven't seen will target this block.
			let tolerated_equivocations = ctx.voters().total_weight() - threshold;
			let current_equivocations = ctx.equivocation_weight(Phase::Precommit);
			let additional_equiv = tolerated_equivocations - current_equivocations;
			let remaining_commit_votes = ctx.voters().total_weight() - self.precommit.current_weight;

			move |node: &VoteNode| {
				// total precommits for this block, including equivocations.
				let precommitted_for = ctx.weight(node, Phase::Precommit);

				// equivocations we could still get are out of those who
				// have already voted, but not on this block.
				let possible_equivocations = std::cmp::min(
					current_precommits - precommitted_for,
					additional_equiv,
				);

				// all the votes already applied on this block,
				// assuming all remaining actors commit to this block,
				// and that we get further equivocations
				let full_possible_weight = precommitted_for
					+ remaining_commit_votes
					+ possible_equivocations;

				full_possible_weight >= threshold
			}
		};

		// until we have threshold precommits, any new block could get supermajority
		// precommits because there are at least f + 1 precommits remaining and then
		// f equivocations.
		//
		// once it's at least that level, we only need to consider blocks
		// already referenced in the graph, because no new leaf nodes
		// could ever have enough precommits.
		//
		// the round-estimate is the highest block in the chain with head
		// `prevote_ghost` that could have supermajority-commits.
		if self.precommit.current_weight >= threshold {
			self.estimate = self.graph.find_ancestor(
				g_hash.clone(),
				g_num,
				possible_to_precommit,
			);
		} else {
			self.estimate = Some((g_hash, g_num));
			return;
		}

		self.completable = self.estimate.clone().map_or(false, |(b_hash, b_num)| {
			b_hash != g_hash || {
				// round-estimate is the same as the prevote-ghost.
				// this round is still completable if no further blocks
				// could have commit-supermajority.
				self.graph.find_ghost(Some((b_hash, b_num)), possible_to_precommit)
					.map_or(true, |x| x == (g_hash, g_num))
			}
		})
	}

	/// Fetch the "round-estimate": the best block which might have been finalized
	/// in this round.
	///
	/// Returns `None` when new new blocks could have been finalized in this round,
	/// according to our estimate.
	pub fn estimate(&self) -> Option<&(H, N)> {
		self.estimate.as_ref()
	}

	/// Fetch the most recently finalized block.
	pub fn finalized(&self) -> Option<&(H, N)> {
		self.finalized.as_ref()
	}

	/// Returns `true` when the round is completable.
	///
	/// This is the case when the round-estimate is an ancestor of the prevote-ghost head,
	/// or when they are the same block _and_ none of its children could possibly have
	/// enough precommits.
	pub fn completable(&self) -> bool {
		self.completable
	}

	/// Threshold weight for supermajority.
	pub fn threshold(&self) -> VoterWeight {
		self.context.voters().threshold()
	}

	/// Return the round base.
	pub fn base(&self) -> (H, N) {
		self.graph.base()
	}

	/// Return the round voters and weights.
	pub fn voters(&self) -> &VoterSet<Id> {
		self.context.voters()
	}

	/// Return the primary voter of the round.
	pub fn primary_voter(&self) -> (&Id, &VoterInfo) {
		self.context.voters().nth_mod(self.round_number as usize)
	}

	/// Get the current weight and number of voters who have participated in prevoting.
	pub fn prevote_participation(&self) -> (VoteWeight, usize) {
		self.prevote.participation()
	}

	/// Get the current weight and number of voters who have participated in precommitting.
	pub fn precommit_participation(&self) -> (VoteWeight, usize) {
		self.precommit.participation()
	}

	/// Return all imported prevotes.
	pub fn prevotes(&self) -> Vec<(Id, Prevote<H, N>, Signature)> {
		self.prevote.votes()
	}

	/// Return all imported precommits.
	pub fn precommits(&self) -> Vec<(Id, Precommit<H, N>, Signature)> {
		self.precommit.votes()
	}

	/// Return all votes for the round (prevotes and precommits), sorted by
	/// imported order and indicating the indices where we voted. At most two
	/// prevotes and two precommits per voter are present, further equivocations
	/// are not stored (as they are redundant).
	pub fn historical_votes(&self) -> &HistoricalVotes<H, N, Signature, Id> {
		&self.historical_votes
	}

	/// Set the number of prevotes and precommits received at the moment of prevoting.
	/// It should be called inmediatly after prevoting.
	pub fn set_prevoted_index(&mut self) {
		self.historical_votes.set_prevoted_idx()
	}

	/// Set the number of prevotes and precommits received at the moment of precommiting.
	/// It should be called inmediatly after precommiting.
	pub fn set_precommitted_index(&mut self) {
		self.historical_votes.set_precommitted_idx()
	}

	/// Get the number of prevotes and precommits received at the moment of prevoting.
	/// Returns None if the prevote wasn't realized.
	pub fn prevoted_index(&self) -> Option<u64> {
		self.historical_votes.prevote_idx
	}

	/// Get the number of prevotes and precommits received at the moment of precommiting.
	/// Returns None if the precommit wasn't realized.
	pub fn precommitted_index(&self) -> Option<u64> {
		self.historical_votes.precommit_idx
	}
}

#[cfg(test)]
mod tests {
	use super::*;
	use crate::testing::chain::{GENESIS_HASH, DummyChain};

	fn voters() -> VoterSet<&'static str> {
		VoterSet::new([
			("Alice", 4),
			("Bob", 7),
			("Eve", 3),
		].iter().cloned()).expect("nonempty")
	}

	#[derive(PartialEq, Eq, Clone, Debug)]
	struct Signature(&'static str);

	#[test]
	fn estimate_is_valid() {
		let mut chain = DummyChain::new();
		chain.push_blocks(GENESIS_HASH, &["A", "B", "C", "D", "E", "F"]);
		chain.push_blocks("E", &["EA", "EB", "EC", "ED"]);
		chain.push_blocks("F", &["FA", "FB", "FC"]);

		let mut round = Round::new(RoundParams {
			round_number: 1,
			voters: voters(),
			base: ("C", 4),
		});

		round.import_prevote(
			&chain,
			Prevote::new("FC", 10),
			"Alice",
			Signature("Alice"),
		).unwrap();

		round.import_prevote(
			&chain,
			Prevote::new("ED", 10),
			"Bob",
			Signature("Bob"),
		).unwrap();

		assert_eq!(round.prevote_ghost, Some(("E", 6)));
		assert_eq!(round.estimate(), Some(&("E", 6)));
		assert!(!round.completable());

		round.import_prevote(
			&chain,
			Prevote::new("F", 7),
			"Eve",
			Signature("Eve"),
		).unwrap();

		assert_eq!(round.prevote_ghost, Some(("E", 6)));
		assert_eq!(round.estimate(), Some(&("E", 6)));
	}

	#[test]
	fn finalization() {
		let mut chain = DummyChain::new();
		chain.push_blocks(GENESIS_HASH, &["A", "B", "C", "D", "E", "F"]);
		chain.push_blocks("E", &["EA", "EB", "EC", "ED"]);
		chain.push_blocks("F", &["FA", "FB", "FC"]);

		let mut round = Round::new(RoundParams {
			round_number: 1,
			voters: voters(),
			base: ("C", 4),
		});

		round.import_precommit(
			&chain,
			Precommit::new("FC", 10),
			"Alice",
			Signature("Alice"),
		).unwrap();

		round.import_precommit(
			&chain,
			Precommit::new("ED", 10),
			"Bob",
			Signature("Bob"),
		).unwrap();

		assert_eq!(round.finalized, None);

		// import some prevotes.
		{
			round.import_prevote(
				&chain,
				Prevote::new("FC", 10),
				"Alice",
				Signature("Alice"),
			).unwrap();

			round.import_prevote(
				&chain,
				Prevote::new("ED", 10),
				"Bob",
				Signature("Bob"),
			).unwrap();

			round.import_prevote(
				&chain,
				Prevote::new("EA", 7),
				"Eve",
				Signature("Eve"),
			).unwrap();

			assert_eq!(round.finalized, Some(("E", 6)));
		}

		round.import_precommit(
			&chain,
			Precommit::new("EA", 7),
			"Eve",
			Signature("Eve"),
		).unwrap();

		assert_eq!(round.finalized, Some(("EA", 7)));
	}

	#[test]
	fn equivocate_does_not_double_count() {
		let mut chain = DummyChain::new();
		chain.push_blocks(GENESIS_HASH, &["A", "B", "C", "D", "E", "F"]);
		chain.push_blocks("E", &["EA", "EB", "EC", "ED"]);
		chain.push_blocks("F", &["FA", "FB", "FC"]);

		let mut round = Round::new(RoundParams {
			round_number: 1,
			voters: voters(),
			base: ("C", 4),
		});

		// first prevote by eve
		assert!(round.import_prevote(
			&chain,
			Prevote::new("FC", 10),
			"Eve", // 3 on F, E
			Signature("Eve-1"),
		).unwrap().equivocation.is_none());


		assert!(round.prevote_ghost.is_none());

		// second prevote by eve: comes with equivocation proof
		assert!(round.import_prevote(
			&chain,
			Prevote::new("ED", 10),
			"Eve", // still 3 on E
			Signature("Eve-2"),
		).unwrap().equivocation.is_some());

		// third prevote: returns nothing.
		assert!(round.import_prevote(
			&chain,
			Prevote::new("F", 7),
			"Eve", // still 3 on F and E
			Signature("Eve-2"),
		).unwrap().equivocation.is_none());

		// three eves together would be enough.

		assert!(round.prevote_ghost.is_none());

		assert!(round.import_prevote(
			&chain,
			Prevote::new("FA", 8),
			"Bob", // add 7 to FA and you get FA.
			Signature("Bob-1"),
		).unwrap().equivocation.is_none());

		assert_eq!(round.prevote_ghost, Some(("FA", 8)));
	}

	#[test]
	fn historical_votes_works() {
		let mut chain = DummyChain::new();
		chain.push_blocks(GENESIS_HASH, &["A", "B", "C", "D", "E", "F"]);
		chain.push_blocks("E", &["EA", "EB", "EC", "ED"]);
		chain.push_blocks("F", &["FA", "FB", "FC"]);

		let mut round = Round::new(RoundParams {
			round_number: 1,
			voters: voters(),
			base: ("C", 4),
		});

		round.import_prevote(
			&chain,
			Prevote::new("FC", 10),
			"Alice",
			Signature("Alice"),
		).unwrap();

		round.set_prevoted_index();

		round.import_prevote(
			&chain,
			Prevote::new("EA", 7),
			"Eve",
			Signature("Eve"),
		).unwrap();

		round.import_precommit(
			&chain,
			Precommit::new("EA", 7),
			"Eve",
			Signature("Eve"),
		).unwrap();

		round.import_prevote(
			&chain,
			Prevote::new("EC", 10),
			"Alice",
			Signature("Alice"),
		).unwrap();

		round.set_precommitted_index();

		assert_eq!(round.historical_votes(), &HistoricalVotes::new_with(
			vec![
				SignedMessage {
					message: Message::Prevote(
						Prevote { target_hash: "FC", target_number: 10 }
					),
					signature: Signature("Alice"),
					id: "Alice"
				},
				SignedMessage {
					message: Message::Prevote(
						Prevote { target_hash: "EA", target_number: 7 }
					),
					signature: Signature("Eve"),
					id: "Eve"
				},
				SignedMessage {
					message: Message::Precommit(
						Precommit { target_hash: "EA", target_number: 7 }
					),
					signature: Signature("Eve"),
					id: "Eve"
				},
				SignedMessage {
					message: Message::Prevote(
						Prevote { target_hash: "EC", target_number: 10 }
					),
					signature: Signature("Alice"),
					id: "Alice"
				},
			],
			Some(1),
			Some(4),
		));
	}
}