package pubsub

import "context"

// Event represents a real-time event to be published.
type Event struct {
	Type      string                 `json:"type"`       // message_created, conversation_updated, etc
	AccountID uint                   `json:"account_id"`
	Payload   map[string]interface{} `json:"payload"`
}

// PubSub defines the interface for publishing and subscribing to real-time events.
// Implementations can use Redis pub/sub, NATS, or in-process channels.
type PubSub interface {
	// Publish sends an event to all subscribers of the given topic.
	Publish(ctx context.Context, topic string, event Event) error

	// Subscribe registers a handler for events on the given topic.
	Subscribe(ctx context.Context, topic string, handler EventHandler) error

	// Unsubscribe removes a handler from the given topic.
	Unsubscribe(ctx context.Context, topic string) error
}

// EventHandler is a callback function that processes received events.
type EventHandler func(event Event)

// InMemoryPubSub is a simple in-process pub/sub for development/testing.
type InMemoryPubSub struct {
	subscribers map[string][]EventHandler
}

// NewInMemoryPubSub creates a new in-memory pub/sub instance.
func NewInMemoryPubSub() *InMemoryPubSub {
	return &InMemoryPubSub{
		subscribers: make(map[string][]EventHandler),
	}
}

func (ps *InMemoryPubSub) Publish(ctx context.Context, topic string, event Event) error {
	handlers, ok := ps.subscribers[topic]
	if !ok {
		return nil
	}
	for _, handler := range handlers {
		handler(event)
	}
	return nil
}

func (ps *InMemoryPubSub) Subscribe(ctx context.Context, topic string, handler EventHandler) error {
	ps.subscribers[topic] = append(ps.subscribers[topic], handler)
	return nil
}

func (ps *InMemoryPubSub) Unsubscribe(ctx context.Context, topic string) error {
	delete(ps.subscribers, topic)
	return nil
}