consensus/pkg/go/protocol/quasar/quasar.go

package quasar

import (
	"context"
	"time"

	"github.com/luxfi/consensus/config"
	"github.com/luxfi/consensus/core/dag"
)

// CertBundle contains both classical and quantum certificates
type CertBundle struct {
	BLSAgg []byte // BLS aggregate signature
	PQCert []byte // Post-quantum certificate
}

// Bundle represents a finalized epoch bundle
type Bundle struct {
	Epoch   uint64
	Root    []byte
	BLSAgg  []byte
	PQBatch []byte
	Binding []byte
}

// Verify checks both BLS and PQ certificates
func (c *CertBundle) Verify(_ []string) bool {
	// Placeholder verification
	// In production: verify BLS signature and PQ certificate
	return c.BLSAgg != nil && c.PQCert != nil && len(c.BLSAgg) > 0 && len(c.PQCert) > 0
}

// QBlock represents a quantum-finalized block
type QBlock struct {
	Height    uint64
	Hash      string
	Timestamp time.Time
	Cert      *CertBundle
}

// Client interface for Quasar operations
type Client interface {
	SubmitCheckpoint(epoch uint64, root []byte, attest []byte) error
	FetchBundle(epoch uint64) (Bundle, error)
	Verify(Bundle) bool
}

// VertexID represents a P-Chain vertex identifier
type VertexID [32]byte

// Quasar implements P-Chain post-quantum consensus with event horizon finality
type Quasar struct {
	// Configuration
	K     int
	Alpha float64
	Beta  uint32

	// Keys
	blsKey []byte
	pqKey  []byte

	// P-Chain state
	horizons []dag.EventHorizon[VertexID]
	store    dag.Store[VertexID]

	// Callback
	finalizedCb func(QBlock)
}

// New creates a new Quasar P-Chain instance
func New(cfg config.Parameters, store dag.Store[VertexID]) *Quasar {
	return &Quasar{
		K:        cfg.K,
		Alpha:    cfg.Alpha,
		Beta:     cfg.Beta,
		horizons: make([]dag.EventHorizon[VertexID], 0),
		store:    store,
	}
}

// Initialize sets up keys for Quasar
func (q *Quasar) Initialize(_ context.Context, blsKey, pqKey []byte) error {
	q.blsKey = blsKey
	q.pqKey = pqKey
	return nil
}

// SetFinalizedCallback sets the callback for finalized blocks
func (q *Quasar) SetFinalizedCallback(cb func(QBlock)) {
	q.finalizedCb = cb
}

// phaseI proposes a block from the DAG frontier
func (q *Quasar) phaseI(frontier []string) string {
	// Select highest confidence block
	// Placeholder: return first block
	if len(frontier) > 0 {
		return frontier[0]
	}
	return ""
}

// phaseII creates certificates if threshold is met
func (q *Quasar) phaseII(votes map[string]int, proposal string) *CertBundle {
	total := 0
	support := 0

	for block, count := range votes {
		total += count
		if block == proposal {
			support = count
		}
	}

	if total == 0 {
		return nil
	}

	// Check if support meets alpha threshold
	if float64(support)/float64(total) >= q.Alpha {
		// Create certificates (placeholder)
		return &CertBundle{
			BLSAgg: []byte("mock-bls-aggregate"),
			PQCert: []byte("mock-pq-certificate"),
		}
	}

	return nil
}

// EstablishHorizon creates a new event horizon for P-Chain finality
func (q *Quasar) EstablishHorizon(ctx context.Context, checkpoint VertexID, validators []string) (*dag.EventHorizon[VertexID], error) {
	// Compute new event horizon using Corona + BLS signatures
	horizon := dag.EventHorizon[VertexID]{
		Checkpoint: checkpoint,
		Height:     uint64(len(q.horizons)) + 1,
		Validators: validators,
		Signature:  q.createHorizonSignature(checkpoint, validators),
	}

	q.horizons = append(q.horizons, horizon)
	return &horizon, nil
}

// IsBeyondHorizon checks if a vertex is beyond the event horizon (finalized)
func (q *Quasar) IsBeyondHorizon(vertex VertexID) bool {
	if len(q.horizons) == 0 {
		return false
	}

	latestHorizon := q.horizons[len(q.horizons)-1]
	return dag.BeyondHorizon(q.store, vertex, latestHorizon)
}

// ComputeCanonicalOrder returns the canonical order of finalized vertices
func (q *Quasar) ComputeCanonicalOrder() []VertexID {
	if len(q.horizons) == 0 {
		return []VertexID{}
	}

	latestHorizon := q.horizons[len(q.horizons)-1]
	return dag.ComputeHorizonOrder(q.store, latestHorizon)
}

// GetLatestHorizon returns the most recent event horizon
func (q *Quasar) GetLatestHorizon() *dag.EventHorizon[VertexID] {
	if len(q.horizons) == 0 {
		return nil
	}
	return &q.horizons[len(q.horizons)-1]
}

// createHorizonSignature creates a Corona + BLS signature for the event horizon
func (q *Quasar) createHorizonSignature(checkpoint VertexID, validators []string) []byte {
	// TODO: Implement Corona + BLS fusion signature
	// This should combine:
	// 1. BLS aggregate signature for efficiency
	// 2. Corona post-quantum threshold signature for security

	// Placeholder implementation
	signature := append(q.blsKey, q.pqKey...)
	signature = append(signature, checkpoint[:]...)
	return signature
}