package aether

import (
	"sync"
	"sync/atomic"
)

// BroadcasterMetrics provides observability metrics for EventBroadcaster implementations.
// All methods are safe for concurrent use.
type BroadcasterMetrics interface {
	// EventsPublished returns the total number of events published per namespace.
	EventsPublished(namespaceID string) int64

	// EventsReceived returns the total number of events received per namespace.
	// For EventBus this equals events delivered to subscribers.
	// For NATSEventBus this includes events received from NATS.
	EventsReceived(namespaceID string) int64

	// ActiveSubscriptions returns the current number of active subscriptions per namespace.
	ActiveSubscriptions(namespaceID string) int64

	// TotalActiveSubscriptions returns the total number of active subscriptions across all namespaces.
	TotalActiveSubscriptions() int64

	// PublishErrors returns the total number of publish errors per namespace.
	PublishErrors(namespaceID string) int64

	// SubscribeErrors returns the total number of subscribe errors per namespace.
	SubscribeErrors(namespaceID string) int64

	// DroppedEvents returns the total number of events dropped (e.g., full channel) per namespace.
	DroppedEvents(namespaceID string) int64

	// Namespaces returns a list of all namespaces that have metrics.
	Namespaces() []string

	// Reset resets all metrics. Useful for testing.
	Reset()
}

// MetricsCollector provides methods for collecting metrics.
// This interface is implemented internally and used by EventBus implementations.
type MetricsCollector interface {
	BroadcasterMetrics

	// RecordPublish records a successful publish event.
	RecordPublish(namespaceID string)

	// RecordReceive records a received event.
	RecordReceive(namespaceID string)

	// RecordSubscribe records a new subscription.
	RecordSubscribe(namespaceID string)

	// RecordUnsubscribe records a removed subscription.
	RecordUnsubscribe(namespaceID string)

	// RecordPublishError records a publish error.
	RecordPublishError(namespaceID string)

	// RecordSubscribeError records a subscribe error.
	RecordSubscribeError(namespaceID string)

	// RecordDroppedEvent records a dropped event (e.g., channel full).
	RecordDroppedEvent(namespaceID string)
}

// namespaceMetrics holds counters for a single namespace.
type namespaceMetrics struct {
	eventsPublished     int64
	eventsReceived      int64
	activeSubscriptions int64
	publishErrors       int64
	subscribeErrors     int64
	droppedEvents       int64
}

// DefaultMetricsCollector is the default implementation of MetricsCollector.
// It uses atomic operations for thread-safe counter updates.
type DefaultMetricsCollector struct {
	mu         sync.RWMutex
	namespaces map[string]*namespaceMetrics
}

// NewMetricsCollector creates a new DefaultMetricsCollector.
func NewMetricsCollector() *DefaultMetricsCollector {
	return &DefaultMetricsCollector{
		namespaces: make(map[string]*namespaceMetrics),
	}
}

// getOrCreateNamespace returns metrics for a namespace, creating if needed.
func (m *DefaultMetricsCollector) getOrCreateNamespace(namespaceID string) *namespaceMetrics {
	m.mu.RLock()
	ns, exists := m.namespaces[namespaceID]
	m.mu.RUnlock()

	if exists {
		return ns
	}

	m.mu.Lock()
	defer m.mu.Unlock()

	// Double-check after acquiring write lock
	if ns, exists = m.namespaces[namespaceID]; exists {
		return ns
	}

	ns = &namespaceMetrics{}
	m.namespaces[namespaceID] = ns
	return ns
}

// EventsPublished returns the total number of events published for a namespace.
func (m *DefaultMetricsCollector) EventsPublished(namespaceID string) int64 {
	m.mu.RLock()
	ns, exists := m.namespaces[namespaceID]
	m.mu.RUnlock()

	if !exists {
		return 0
	}
	return atomic.LoadInt64(&ns.eventsPublished)
}

// EventsReceived returns the total number of events received for a namespace.
func (m *DefaultMetricsCollector) EventsReceived(namespaceID string) int64 {
	m.mu.RLock()
	ns, exists := m.namespaces[namespaceID]
	m.mu.RUnlock()

	if !exists {
		return 0
	}
	return atomic.LoadInt64(&ns.eventsReceived)
}

// ActiveSubscriptions returns the current number of active subscriptions for a namespace.
func (m *DefaultMetricsCollector) ActiveSubscriptions(namespaceID string) int64 {
	m.mu.RLock()
	ns, exists := m.namespaces[namespaceID]
	m.mu.RUnlock()

	if !exists {
		return 0
	}
	return atomic.LoadInt64(&ns.activeSubscriptions)
}

// TotalActiveSubscriptions returns the total number of active subscriptions across all namespaces.
func (m *DefaultMetricsCollector) TotalActiveSubscriptions() int64 {
	m.mu.RLock()
	defer m.mu.RUnlock()

	var total int64
	for _, ns := range m.namespaces {
		total += atomic.LoadInt64(&ns.activeSubscriptions)
	}
	return total
}

// PublishErrors returns the total number of publish errors for a namespace.
func (m *DefaultMetricsCollector) PublishErrors(namespaceID string) int64 {
	m.mu.RLock()
	ns, exists := m.namespaces[namespaceID]
	m.mu.RUnlock()

	if !exists {
		return 0
	}
	return atomic.LoadInt64(&ns.publishErrors)
}

// SubscribeErrors returns the total number of subscribe errors for a namespace.
func (m *DefaultMetricsCollector) SubscribeErrors(namespaceID string) int64 {
	m.mu.RLock()
	ns, exists := m.namespaces[namespaceID]
	m.mu.RUnlock()

	if !exists {
		return 0
	}
	return atomic.LoadInt64(&ns.subscribeErrors)
}

// DroppedEvents returns the total number of dropped events for a namespace.
func (m *DefaultMetricsCollector) DroppedEvents(namespaceID string) int64 {
	m.mu.RLock()
	ns, exists := m.namespaces[namespaceID]
	m.mu.RUnlock()

	if !exists {
		return 0
	}
	return atomic.LoadInt64(&ns.droppedEvents)
}

// Namespaces returns a list of all namespaces that have metrics.
func (m *DefaultMetricsCollector) Namespaces() []string {
	m.mu.RLock()
	defer m.mu.RUnlock()

	namespaces := make([]string, 0, len(m.namespaces))
	for ns := range m.namespaces {
		namespaces = append(namespaces, ns)
	}
	return namespaces
}

// Reset resets all metrics.
func (m *DefaultMetricsCollector) Reset() {
	m.mu.Lock()
	defer m.mu.Unlock()
	m.namespaces = make(map[string]*namespaceMetrics)
}

// RecordPublish records a successful publish event.
func (m *DefaultMetricsCollector) RecordPublish(namespaceID string) {
	ns := m.getOrCreateNamespace(namespaceID)
	atomic.AddInt64(&ns.eventsPublished, 1)
}

// RecordReceive records a received event.
func (m *DefaultMetricsCollector) RecordReceive(namespaceID string) {
	ns := m.getOrCreateNamespace(namespaceID)
	atomic.AddInt64(&ns.eventsReceived, 1)
}

// RecordSubscribe records a new subscription.
func (m *DefaultMetricsCollector) RecordSubscribe(namespaceID string) {
	ns := m.getOrCreateNamespace(namespaceID)
	atomic.AddInt64(&ns.activeSubscriptions, 1)
}

// RecordUnsubscribe records a removed subscription.
func (m *DefaultMetricsCollector) RecordUnsubscribe(namespaceID string) {
	ns := m.getOrCreateNamespace(namespaceID)
	atomic.AddInt64(&ns.activeSubscriptions, -1)
}

// RecordPublishError records a publish error.
func (m *DefaultMetricsCollector) RecordPublishError(namespaceID string) {
	ns := m.getOrCreateNamespace(namespaceID)
	atomic.AddInt64(&ns.publishErrors, 1)
}

// RecordSubscribeError records a subscribe error.
func (m *DefaultMetricsCollector) RecordSubscribeError(namespaceID string) {
	ns := m.getOrCreateNamespace(namespaceID)
	atomic.AddInt64(&ns.subscribeErrors, 1)
}

// RecordDroppedEvent records a dropped event.
func (m *DefaultMetricsCollector) RecordDroppedEvent(namespaceID string) {
	ns := m.getOrCreateNamespace(namespaceID)
	atomic.AddInt64(&ns.droppedEvents, 1)
}