aether/eventbus.go

package aether

import (
	"context"
	"strings"
	"sync"
)

// SubscriptionFilter defines criteria for filtering events in a subscription.
// Multiple filters are combined with AND logic - an event must match all
// non-empty filter criteria to be delivered.
//
// # Event Type Filtering
//
// EventTypes specifies which event types to receive. If empty, all event types
// are delivered. Otherwise, only events with a matching EventType are delivered.
//
//	filter := SubscriptionFilter{
//	    EventTypes: []string{"OrderPlaced", "OrderShipped"},
//	}
//
// # Actor Pattern Filtering
//
// ActorPattern specifies a pattern to match against actor IDs. Patterns support
// two matching modes:
//
// Prefix matching with "*" suffix:
//
//	"order-*"   // matches "order-123", "order-456", etc.
//	"user-*"    // matches "user-abc", "user-xyz", etc.
//
// Exact matching (no wildcard):
//
//	"order-123" // matches only "order-123"
//
// An empty ActorPattern matches all actor IDs.
//
// # Combining Filters
//
// When both EventTypes and ActorPattern are specified, an event must match
// both criteria (AND logic):
//
//	filter := SubscriptionFilter{
//	    EventTypes:   []string{"OrderPlaced"},
//	    ActorPattern: "order-*",
//	}
//	// Only delivers OrderPlaced events from actors starting with "order-"
type SubscriptionFilter struct {
	// EventTypes limits delivery to events with matching EventType.
	// Empty slice means all event types are accepted.
	EventTypes []string

	// ActorPattern matches against event ActorID.
	// Supports prefix matching with "*" suffix (e.g., "order-*").
	// Empty string matches all actor IDs.
	ActorPattern string
}

// Matches returns true if the event passes all filter criteria.
// An empty filter (no event types, no actor pattern) matches all events.
func (f SubscriptionFilter) Matches(event *Event) bool {
	if event == nil {
		return false
	}

	// Check event type filter
	if len(f.EventTypes) > 0 {
		found := false
		for _, et := range f.EventTypes {
			if event.EventType == et {
				found = true
				break
			}
		}
		if !found {
			return false
		}
	}

	// Check actor pattern filter
	if f.ActorPattern != "" {
		if strings.HasSuffix(f.ActorPattern, "*") {
			// Prefix matching
			prefix := strings.TrimSuffix(f.ActorPattern, "*")
			if !strings.HasPrefix(event.ActorID, prefix) {
				return false
			}
		} else {
			// Exact matching
			if event.ActorID != f.ActorPattern {
				return false
			}
		}
	}

	return true
}

// EventBroadcaster defines the interface for publishing and subscribing to events
type EventBroadcaster interface {
	Subscribe(namespaceID string) <-chan *Event
	SubscribeWithFilter(namespaceID string, filter SubscriptionFilter) <-chan *Event
	Unsubscribe(namespaceID string, ch <-chan *Event)
	Publish(namespaceID string, event *Event)
	Stop()
	SubscriberCount(namespaceID string) int
}

// filteredSubscriber holds a subscriber channel and its filter
type filteredSubscriber struct {
	ch     chan *Event
	filter SubscriptionFilter
}

// EventBus broadcasts events to multiple subscribers within a namespace
type EventBus struct {
	subscribers map[string][]filteredSubscriber // namespaceID -> filtered subscribers
	mutex       sync.RWMutex
	ctx         context.Context
	cancel      context.CancelFunc
}

// NewEventBus creates a new event bus
func NewEventBus() *EventBus {
	ctx, cancel := context.WithCancel(context.Background())
	return &EventBus{
		subscribers: make(map[string][]filteredSubscriber),
		ctx:         ctx,
		cancel:      cancel,
	}
}

// Subscribe creates a new subscription channel for a namespace.
// All events published to the namespace will be delivered.
func (eb *EventBus) Subscribe(namespaceID string) <-chan *Event {
	return eb.SubscribeWithFilter(namespaceID, SubscriptionFilter{})
}

// SubscribeWithFilter creates a new subscription channel for a namespace with filtering.
// Only events matching the filter criteria will be delivered.
func (eb *EventBus) SubscribeWithFilter(namespaceID string, filter SubscriptionFilter) <-chan *Event {
	eb.mutex.Lock()
	defer eb.mutex.Unlock()

	// Create buffered channel to prevent blocking publishers
	ch := make(chan *Event, 100)
	sub := filteredSubscriber{
		ch:     ch,
		filter: filter,
	}
	eb.subscribers[namespaceID] = append(eb.subscribers[namespaceID], sub)

	return ch
}

// Unsubscribe removes a subscription channel
func (eb *EventBus) Unsubscribe(namespaceID string, ch <-chan *Event) {
	eb.mutex.Lock()
	defer eb.mutex.Unlock()

	subs := eb.subscribers[namespaceID]
	for i, subscriber := range subs {
		if subscriber.ch == ch {
			// Remove subscriber from slice
			eb.subscribers[namespaceID] = append(subs[:i], subs[i+1:]...)
			close(subscriber.ch)
			break
		}
	}

	// Clean up empty namespace entries
	if len(eb.subscribers[namespaceID]) == 0 {
		delete(eb.subscribers, namespaceID)
	}
}

// Publish sends an event to all subscribers of a namespace whose filters match
func (eb *EventBus) Publish(namespaceID string, event *Event) {
	eb.mutex.RLock()
	defer eb.mutex.RUnlock()

	subscribers := eb.subscribers[namespaceID]
	for _, sub := range subscribers {
		// Apply filter before delivering
		if !sub.filter.Matches(event) {
			continue
		}

		select {
		case sub.ch <- event:
			// Event delivered
		default:
			// Channel full, skip this subscriber (non-blocking)
		}
	}
}

// Stop closes the event bus
func (eb *EventBus) Stop() {
	eb.mutex.Lock()
	defer eb.mutex.Unlock()

	eb.cancel()

	// Close all subscriber channels
	for _, subs := range eb.subscribers {
		for _, sub := range subs {
			close(sub.ch)
		}
	}

	eb.subscribers = make(map[string][]filteredSubscriber)
}

// SubscriberCount returns the number of subscribers for a namespace
func (eb *EventBus) SubscriberCount(namespaceID string) int {
	eb.mutex.RLock()
	defer eb.mutex.RUnlock()
	return len(eb.subscribers[namespaceID])
}