package ui

import (
	"fmt"
	"sync"

	"github.com/nmoniz/gubgub"
)

var eventBusGetter = sync.OnceValue(func() *eventBus {
	return NewSyncEventBus()
})

func EventBus() *eventBus {
	return eventBusGetter()
}

type Event interface {
	Name() string
	Data() any
}

type eventBus struct {
	topics map[string]gubgub.Topic[Event]
}

func NewSyncEventBus() *eventBus {
	return &eventBus{
		topics: make(map[string]gubgub.Topic[Event]),
	}
}

func (eb *eventBus) Emit(e Event) error {
	topic, ok := eb.topics[e.Name()]
	if !ok {
		return nil
	}
	err := topic.Publish(e)
	if err != nil {
		return fmt.Errorf("emit event: %w", err)
	}
	return nil
}

func (eb *eventBus) Listen(name string, handler func(Event)) error {
	topic, ok := eb.topics[name]
	if !ok {
		topic = gubgub.NewSyncTopic[Event]()
		eb.topics[name] = topic
	}

	err := topic.Subscribe(gubgub.Forever(handler))
	if err != nil {
		return fmt.Errorf("listen for event: %w", err)
	}

	return nil
}