package bus

import (
	"sync"
)

type (
	Event struct {
		EvType string
		Data   interface{}
	}

	listeners []chan<- Event

	bus struct {
		sync.RWMutex
		subs map[string]listeners
	}

	Bus interface {
		Sub(topic string, ch chan<- Event)
		Unsub(topic string, ch chan<- Event)
		Pub(topic string, data interface{})
		ShutdownBus()
	}
)

func New() Bus {
	bus := &bus{
		subs: make(map[string]listeners),
	}

	return bus
}

func (b *bus) Sub(topic string, ch chan<- Event) {
	b.Lock()
	defer b.Unlock()

	if prev, ok := b.subs[topic]; ok {
		b.subs[topic] = append(prev, ch)
	} else {
		b.subs[topic] = append(listeners{}, ch)
	}
}

func (b *bus) Unsub(topic string, ch chan<- Event) {
	b.Lock()
	defer b.Unlock()

	for i, v := range b.subs[topic] {
		if v == ch {
			// we don't care about order, replace and reslice
			b.subs[topic][i] = b.subs[topic][len(b.subs[topic])-1]
			b.subs[topic] = b.subs[topic][:len(b.subs[topic])-1]
		}
	}
}

func (b *bus) Pub(topic string, data interface{}) {
	b.RLock()
	defer b.RUnlock()

	tc, ok := b.subs[topic]
	if !ok {
		return
	}

	for _, ch := range tc {
		ch <- Event{EvType: topic, Data: data}
	}
}

func (b *bus) ShutdownBus() {
	for _, v := range b.subs {
		for _, c := range v {
			close(c)
		}
	}
}