package bus

import (
	"context"
	"fmt"
	"runtime"
	"sync"
)

type InProcBus struct {
	ctx              context.Context
	once             sync.Once
	eventChan        chan *Event
	subscriberLocker sync.RWMutex
	subscribers      map[string]Subscriber
}

func (bus *InProcBus) Subscribers() []Subscriber {
	bus.subscriberLocker.RLock()
	defer bus.subscriberLocker.RUnlock()
	vs := make([]Subscriber, len(bus.subscribers))
	i := 0
	for _, v := range bus.subscribers {
		vs[i] = v
		i++
	}
	return vs
}

func (bus *InProcBus) worker() {
	for {
		select {
		case e, ok := <-bus.eventChan:
			if ok {
				_ = bus.Dispatch(e)
			}
		case <-bus.ctx.Done():
			return
		}
	}
}

// Publish 发布一个事件
func (bus *InProcBus) Publish(e *Event) {
	bus.once.Do(func() {
		for i := 0; i < runtime.NumCPU(); i++ {
			go bus.worker()
		}
	})
	select {
	case bus.eventChan <- e:
	default:
	}
	return
}

// Dispatch 分配事件，关心返回值
func (bus *InProcBus) Dispatch(e *Event) (err error) {
	return bus.DispatchCtx(context.Background(), e)
}

func (bus *InProcBus) DispatchCtx(ctx context.Context, e *Event) (err error) {
	bus.subscriberLocker.RLock()
	defer bus.subscriberLocker.RUnlock()
	for _, sub := range bus.subscribers {
		if sub.HasTopic(e.Name) {
			err = sub.Process(ctx, e)
		}
	}
	releaseEvent(e)
	return
}

func (bus *InProcBus) Subscribe(sub Subscriber) (err error) {
	bus.subscriberLocker.Lock()
	defer bus.subscriberLocker.Unlock()
	if _, ok := bus.subscribers[sub.ID()]; ok {
		err = fmt.Errorf("subscriber %s already exists", sub.ID())
		return
	}
	if err = sub.OnAttach(); err != nil {
		return
	}
	bus.subscribers[sub.ID()] = sub
	return
}

func (bus *InProcBus) UnSubscribe(sub Subscriber) (err error) {
	bus.subscriberLocker.Lock()
	defer bus.subscriberLocker.Unlock()
	if instance, ok := bus.subscribers[sub.ID()]; !ok {
		err = fmt.Errorf("subscriber %s not exists", sub.ID())
		return
	} else {
		delete(bus.subscribers, sub.ID())
		err = instance.OnDetach()
	}
	return
}

func NewInPrcBus(ctx context.Context) *InProcBus {
	return &InProcBus{
		ctx:         ctx,
		eventChan:   make(chan *Event, 100),
		subscribers: make(map[string]Subscriber),
	}
}