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// 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.

//! Maintains the `VoterSet` of the blockchain.
//!
//! See docs on `VoterSet` for more information.

use crate::std::{self, collections::BTreeMap, vec::Vec};

use super::threshold;

/// A voter set, with accompanying indices.
#[derive(Clone, PartialEq, Eq)]
#[cfg_attr(any(feature = "std", test), derive(Debug))]
pub struct VoterSet<Id: Ord + Eq> {
	weights: BTreeMap<Id, VoterInfo>,
	voters: Vec<(Id, u64)>,
	threshold: u64,
}

impl<Id: Ord + Eq> VoterSet<Id> {
	/// Get the voter info for a voter.
	pub fn info<'a>(&'a self, id: &Id) -> Option<&'a VoterInfo> {
		self.weights.get(id)
	}

	/// Get the length of the set.
	pub fn len(&self) -> usize { self.voters.len() }

	/// Whether the set contains the key.
	pub fn contains_key(&self, id: &Id) -> bool {
		self.weights.contains_key(id)
	}

	// Get voter by index.
	pub fn voter_by_index(&self, idx: usize) -> &(Id, u64) {
		&self.voters[idx]
	}

	/// Get voter info by index.
	pub fn weight_by_index(&self, idx: usize) -> Option<u64> {
		self.voters.get(idx).map(|&(_, weight)| weight)
	}

	/// Get the threshold weight.
	pub fn threshold(&self) -> u64 { self.threshold }

	/// Get the total weight.
	pub fn total_weight(&self) -> u64 {
		self.voters.iter().map(|&(_, weight)| weight).sum()
	}

	/// Get the voters.
	pub fn voters(&self) -> &[(Id, u64)] {
		&self.voters
	}
}

impl<Id: Eq + Clone + Ord> std::iter::FromIterator<(Id, u64)> for VoterSet<Id> {
	fn from_iter<I: IntoIterator<Item = (Id, u64)>>(iterable: I) -> Self {
		let iter = iterable.into_iter();
		let (lower, _) = iter.size_hint();

		let mut voters = Vec::with_capacity(lower);
		let mut weights = BTreeMap::new();

		let mut total_weight = 0;
		for (id, weight) in iter {
			voters.push((id.clone(), weight));
			total_weight += weight;
		}

		voters.sort_unstable();

		for (idx, (id, weight)) in voters.iter().enumerate() {
			weights.insert(id.clone(), VoterInfo { canon_idx: idx, weight: *weight });
		}

		let threshold = threshold(total_weight);
		VoterSet { weights, voters, threshold }
	}
}

#[derive(Clone, PartialEq, Eq)]
#[cfg_attr(any(feature = "std", test), derive(Debug))]
pub struct VoterInfo {
	canon_idx: usize,
	weight: u64,
}

impl VoterInfo {
	/// Get the canonical index of the voter.
	pub fn canon_idx(&self) -> usize { self.canon_idx }

	/// Get the weight of the voter.
	pub fn weight(&self) -> u64 { self.weight }
}


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

	#[test]
	fn voters_are_sorted() {
		let v1: VoterSet<usize> = [
			(1, 5),
			(4, 1),
			(3, 9),
			(5, 7),
			(9, 9),
			(2, 7),
		].iter().cloned().collect();

		let v2: VoterSet<usize> = [
			(1, 5),
			(2, 7),
			(3, 9),
			(4, 1),
			(5, 7),
			(9, 9),
		].iter().cloned().collect();

		assert_eq!(v1, v2);
	}

	#[test]
	fn voter_by_index_works() {
		let v: VoterSet<usize> = [
			(1, 5),
			(4, 1),
			(3, 9),
			(5, 7),
			(9, 9),
			(2, 7),
		].iter().cloned().collect();

		assert_eq!(v.len(), 6);
		assert_eq!(v.total_weight(), 38);

		assert_eq!(v.voter_by_index(0), &(1, 5));
		assert_eq!(v.voter_by_index(1), &(2, 7));
		assert_eq!(v.voter_by_index(2), &(3, 9));
		assert_eq!(v.voter_by_index(3), &(4, 1));
		assert_eq!(v.voter_by_index(4), &(5, 7));
		assert_eq!(v.voter_by_index(5), &(9, 9));
	}
}