Consensus mechanism

pub struct Block {
    // Consensus epoch
    epoch: Epoch,
    // Round number
    round: Round,
    // Validator proposing the block
    author: AuthorityIndex,
    // Block creation timestamp
    timestamp_ms: BlockTimestampMs,
    // References to blocks from previous round
    ancestors: Vec<BlockRef>,
    // Transactions included in this block
    transactions: Vec<Transaction>,
    // Votes for committing previous leaders
    commit_votes: Vec<CommitVote>,
}

pub struct BlockRef {
    // Round number
    round: Round,
    // Author validator index
    author: AuthorityIndex,
    // Cryptographic hash of block
    digest: BlockDigest,
}

// Rounds are simple integers
pub type Round = u32;

// Genesis round is round 0
const GENESIS_ROUND: Round = 0;

// Validators build on top of each other's blocks
let current_round = last_included_round + 1;

pub struct LeaderSchedule {
    // Determines leader for each round
    leader_swap_table: Arc<RwLock<LeaderSwapTable>>,
    // Number of leaders to elect per round
    num_leaders: usize,
}

// Get leader for a specific round
fn leader_at_round(&self, round: Round) -> AuthorityIndex {
    // Uses reputation scores and rotation to select leader
}

// Each wave has a minimum length
const MINIMUM_WAVE_LENGTH: Round = 3;

// Typical wave structure:
// Round N:   Leader proposes
// Round N+1: Validators vote on leader
// Round N+2: Decision round

pub struct UniversalCommitter {
    // Consensus context
    context: Arc<Context>,
    // Leader selection
    leader_schedule: Arc<LeaderSchedule>,
    // DAG state
    dag_state: Arc<RwLock<DagState>>,
    // Number of leaders per round
    number_of_leaders: usize,
    // Whether to use pipelining
    pipelined: bool,
}

pub struct CommittedSubDag {
    // The leader block being committed
    leader: VerifiedBlock,
    // All blocks that causally precede the leader
    blocks: Vec<VerifiedBlock>,
    // Timestamp of the commit
    timestamp_ms: BlockTimestampMs,
    // Commit index
    commit_index: CommitIndex,
}

pub struct StakeAggregator<T> {
    // Stake by authority
    stake_by_authority: Vec<Stake>,
    // Total stake in committee
    total_stake: Stake,
    // Collected stakes
    collected: HashMap<AuthorityIndex, T>,
}

// Check if we have a quorum (2f+1)
pub fn has_quorum(&self, threshold: QuorumThreshold) -> bool {
    match threshold {
        QuorumThreshold::Quorum => {
            // 2f+1 stake (can tolerate f Byzantine failures)
            self.collected_stake >= self.quorum_threshold()
        }
        QuorumThreshold::All => {
            // All validators must participate
            self.collected_stake == self.total_stake
        }
    }
}

pub trait BlockVerifier {
    fn verify(&self, block: &SignedBlock) -> ConsensusResult<()>;
}

// Verification checks:
// - Valid signature from claimed author
// - Correct epoch and protocol version
// - Round number is sequential
// - Ancestors are from previous round
// - Timestamp is not too far in past/future
// - Transactions are valid
// - Block size is within limits

pub struct CommitObserver {
    // Channel to send committed output
    sender: Sender<CommittedSubDag>,
    // Last processed commit index
    last_processed: CommitIndex,
}

// Process a committed sub-DAG
pub fn handle_commit(&mut self, committed: CommittedSubDag) {
    // Extract transactions in commit order
    let transactions = self.order_transactions(&committed);
    
    // Send to execution layer
    self.sender.send(committed)?;
    
    // Update last processed index
    self.last_processed = committed.commit_index;
}

// Order blocks in a committed sub-DAG
fn order_blocks(subdag: &CommittedSubDag) -> Vec<VerifiedBlock> {
    // Topological sort by round and authority
    subdag.blocks
        .iter()
        .sorted_by_key(|b| (b.round(), b.author()))
        .collect()
}

pub struct Commit {
    // Sequential commit index
    index: CommitIndex,
    // Hash of previous commit (forming a chain)
    previous_digest: CommitDigest,
    // Commit timestamp
    timestamp_ms: BlockTimestampMs,
    // The committed leader block
    leader: BlockRef,
    // All blocks in the committed sub-DAG
    blocks: Vec<BlockRef>,
}

pub struct CheckpointSummary {
    // Epoch of this checkpoint
    epoch: EpochId,
    // Sequence number within epoch
    sequence_number: CheckpointSequenceNumber,
    // Hash of previous checkpoint
    previous_digest: CheckpointDigest,
    // Transactions in this checkpoint
    transactions: Vec<TransactionDigest>,
    // Checkpoint timestamp
    timestamp_ms: CheckpointTimestamp,
}

pub struct Synchronizer {
    // Fetch missing blocks from peers
    pub fn fetch_blocks(&self, refs: Vec<BlockRef>) -> Vec<VerifiedBlock> {
        // Request missing blocks from other validators
    }
}

let committer = UniversalCommitterBuilder::new(context, leader_schedule, dag_state)
    .with_pipeline(true) // Enable pipelining
    .build();

pub struct Epoch {
    // Epoch identifier
    epoch_id: EpochId,
    // Committee for this epoch
    committee: Committee,
    // Protocol version
    protocol_version: ProtocolVersion,
    // Epoch start time
    epoch_start_timestamp: u64,
}