/*
Package stream provides a publish/subscribe system for events produced by changes
to the state store.
*/
package stream

import "fmt"

// Topic is an identifier that partitions events. A subscription will only receive
// events which match the Topic.
type Topic fmt.Stringer

// Event is a structure with identifiers and a payload. Events are Published to
// EventPublisher and returned to Subscribers.
type Event struct {
	Topic   Topic
	Key     string
	Index   uint64
	Payload interface{}
}

// IsEndOfSnapshot returns true if this is a framing event that indicates the
// snapshot has completed. Future events from Subscription.Next will be
// change events.
func (e Event) IsEndOfSnapshot() bool {
	return e.Payload == endOfSnapshot{}
}

// IsEndOfEmptySnapshot returns true if this is a framing event that indicates
// there is no snapshot. Future events from Subscription.Next will be
// change events.
func (e Event) IsEndOfEmptySnapshot() bool {
	return e.Payload == endOfEmptySnapshot{}
}

type endOfSnapshot struct{}

type endOfEmptySnapshot struct{}

type closeSubscriptionPayload struct {
	tokensSecretIDs []string
}

// NewCloseSubscriptionEvent returns a special Event that is handled by the
// stream package, and is never sent to subscribers. EventProcessor handles
// these events, and closes any subscriptions which were created using a token
// which matches any of the tokenSecretIDs.
//
// tokenSecretIDs may contain duplicate IDs.
func NewCloseSubscriptionEvent(tokenSecretIDs []string) Event {
	return Event{Payload: closeSubscriptionPayload{tokensSecretIDs: tokenSecretIDs}}
}