package traverse

// EventStage indicates whether a TraversalEvent is fired at the start or
// completion of processing a Referral.
type EventStage int

// Event stage constants.
const (
	EventStart    EventStage = iota // fired when a Referral is about to be queried
	EventComplete                   // fired after the Response has been produced
)

// TraversalEvent carries context for a single traversal event delivered to
// the OnEvent hook.
type TraversalEvent struct {
	// Stage is EventStart or EventComplete.
	Stage EventStage
	// Result carries the Referral and (for EventComplete) the Response.
	Result TraversalResult
	// IsResolve is true when the event relates to a nameserver address
	// resolution sub-traversal rather than the main traversal.
	IsResolve bool
}

// EventHandler is the function signature for traversal event callbacks.
type EventHandler func(TraversalEvent)

// TraverserHooks holds the optional event callback for a Traverser.
// Assigning OnEvent enables progress and result notifications.
type TraverserHooks struct {
	OnEvent EventHandler
}

func (h *TraverserHooks) emit(stage EventStage, result TraversalResult, isResolve bool) {
	if h == nil || h.OnEvent == nil {
		return
	}
	h.OnEvent(TraversalEvent{
		Stage:     stage,
		Result:    result,
		IsResolve: isResolve,
	})
}