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// Copyright (c) The Diem Core Contributors
// SPDX-License-Identifier: Apache-2.0

// Copyright 2021 Conflux Foundation. All rights reserved.
// Conflux is free software and distributed under GNU General Public License.
// See http://www.gnu.org/licenses/

use crate::pos::consensus::liveness::proposer_election::ProposerElection;
use consensus_types::common::{Author, Round};

/// The rotating proposer maps a round to an author according to a round-robin
/// rotation. A fixed proposer strategy loses liveness when the fixed proposer
/// is down. Rotating proposers won't gather quorum certificates to machine
/// loss/byzantine behavior on f/n rounds.
pub struct RotatingProposer {
    // Ordering of proposers to rotate through (all honest replicas must agree
    // on this)
    proposers: Vec<Author>,
    // Number of contiguous rounds (i.e. round numbers increase by 1) a
    // proposer is active in a row
    contiguous_rounds: u32,
}

/// Choose a proposer that is going to be the single leader (relevant for a mock
/// fixed proposer election only).
pub fn choose_leader(peers: Vec<Author>) -> Author {
    // As it is just a tmp hack function, pick the min PeerId to be a proposer.
    peers.into_iter().min().expect("No trusted peers found!")
}

impl RotatingProposer {
    /// With only one proposer in the vector, it behaves the same as a fixed
    /// proposer strategy.
    pub fn new(proposers: Vec<Author>, contiguous_rounds: u32) -> Self {
        Self {
            proposers,
            contiguous_rounds,
        }
    }
}

impl ProposerElection for RotatingProposer {
    fn get_valid_proposer(&self, round: Round) -> Author {
        self.proposers[((round / u64::from(self.contiguous_rounds))
            % self.proposers.len() as u64) as usize]
    }
}