consensus/pkg/go/core/dag/horizon.go

package dag

// VertexID represents a vertex identifier in the DAG
type VertexID [32]byte

// Meta interface represents metadata for a DAG vertex
type Meta interface {
	ID() VertexID
	Author() string
	Round() uint64
	Parents() []VertexID
}

// View interface provides access to DAG structure and vertex relationships
type View interface {
	Get(VertexID) (Meta, bool)
	ByRound(round uint64) []Meta
	Supports(from VertexID, author string, round uint64) bool
}

// Params holds DAG consensus parameters
type Params struct{ N, F int }

// VID represents a generic vertex identifier for new protocol interfaces
type VID interface{ comparable }

// BlockView represents a view of a block/vertex in the DAG (generic version)
type BlockView[V VID] interface {
	ID() V
	Parents() []V
	Author() string
	Round() uint64
}

// Store represents DAG storage interface (generic version)
type Store[V VID] interface {
	Head() []V
	Get(V) (BlockView[V], bool)
	Children(V) []V
}

// ComputeSafePrefix computes the safe prefix of vertices that can be committed
// based on DAG order theory using horizon (reachability) and flare (cert/skip) analysis
func ComputeSafePrefix[V VID](store Store[V], frontier []V) []V {
	// TODO: Implement using horizon reachability analysis and flare cert/skip detection
	// This should return vertices that have achieved finality according to DAG consensus rules

	// Placeholder implementation - return empty for now
	return []V{}
}

// ChooseFrontier selects appropriate parents for a new vertex proposal
// This typically involves choosing a subset of frontier vertices to reference
func ChooseFrontier[V VID](frontier []V) []V {
	// TODO: Implement frontier selection logic
	// Common strategies:
	// - Choose all recent vertices (small frontier)
	// - Choose 2f+1 vertices for Byzantine tolerance
	// - Choose based on validator weight or other criteria

	// Placeholder implementation - return first few vertices
	if len(frontier) <= 3 {
		return frontier
	}
	return frontier[:3]
}

// IsReachable checks if vertex 'from' can reach vertex 'to' in the DAG
func IsReachable[V VID](store Store[V], from, to V) bool {
	// TODO: Implement reachability check using DFS/BFS
	return false
}

// LCA finds the lowest common ancestor of two vertices
func LCA[V VID](store Store[V], a, b V) V {
	// TODO: Implement LCA algorithm
	var zero V
	return zero
}

// Antichain computes an antichain (set of mutually unreachable vertices) in the DAG
func Antichain[V VID](store Store[V], vertices []V) []V {
	// TODO: Implement antichain computation
	return []V{}
}

// EventHorizon represents the finality boundary in Quasar P-Chain consensus
// Beyond this horizon, no events can affect the finalized state
type EventHorizon[V VID] struct {
	// Checkpoint represents a finalized state boundary
	Checkpoint V
	// Height at which this horizon was established
	Height uint64
	// Validators that signed this horizon
	Validators []string
	// Post-quantum signature (Corona + BLS)
	Signature []byte
}

// Horizon computes the event horizon for Quasar P-Chain finality
// This determines which vertices are beyond the point of no return
func Horizon[V VID](store Store[V], checkpoints []EventHorizon[V]) EventHorizon[V] {
	// TODO: Implement event horizon computation for P-Chain finality
	// This should:
	// 1. Analyze reachability from latest checkpoints
	// 2. Find vertices that have achieved post-quantum finality
	// 3. Establish new event horizon boundary

	// Placeholder - return latest checkpoint
	if len(checkpoints) > 0 {
		return checkpoints[len(checkpoints)-1]
	}

	var zero EventHorizon[V]
	return zero
}

// BeyondHorizon checks if a vertex is beyond the event horizon (finalized)
func BeyondHorizon[V VID](store Store[V], vertex V, horizon EventHorizon[V]) bool {
	// TODO: Implement horizon reachability check
	// Vertices beyond the event horizon cannot be affected by future consensus
	return IsReachable(store, horizon.Checkpoint, vertex)
}

// ComputeHorizonOrder determines the canonical order of vertices beyond the event horizon
func ComputeHorizonOrder[V VID](store Store[V], horizon EventHorizon[V]) []V {
	// TODO: Implement canonical ordering for finalized vertices
	// This provides deterministic ordering for P-Chain state transitions
	return []V{}
}