package pubsub

import (
	"sync"
	"time"
)

type (
	subscriber chan interface{}         //订阅者，类型为管道
	topicFunc  func(v interface{}) bool //主题，是一个过滤器函数
)

// 发布者对象
type publisher struct {
	m           sync.RWMutex             //读写锁
	buffer      int                      //订阅队列缓存大小
	timeout     time.Duration            //发布超时时间
	subscribers map[subscriber]topicFunc //订阅者信息
}

// 构建一个新的发布者对象
func NewPublisher(buffer int, publishTimeout time.Duration) *publisher {
	return &publisher{
		m:           sync.RWMutex{},
		buffer:      buffer,
		timeout:     publishTimeout,
		subscribers: make(map[subscriber]topicFunc),
	}
}

// 添加一个新的订阅者，订阅过滤器筛选后的主题
func (p *publisher) SubscriberTopic(topic topicFunc) chan interface{} {
	ch := make(chan interface{}, p.buffer)
	p.m.Lock()
	defer p.m.Unlock()
	p.subscribers[ch] = topic
	return ch
}

// 添加一个订阅者，订阅所有主题
func (p *publisher) SubscriberAllTopic() chan interface{} {
	return p.SubscriberTopic(nil)
}

// 退出订阅
func (p *publisher) Exict(sub chan interface{}) {
	p.m.Lock()
	defer p.m.Unlock()
	delete(p.subscribers, sub)
	close(sub)
}

// 关闭发布者对象，同时关闭所有订阅者管道
func (p *publisher) Close() {
	p.m.Lock()
	defer p.m.Unlock()

	for sub := range p.subscribers {
		close(sub)
		delete(p.subscribers, sub)
	}
}

// 发布一个主题
func (p *publisher) Publish(v interface{}) {
	p.m.RLock()
	defer p.m.RUnlock()
	wg := sync.WaitGroup{}
	for sub, topic := range p.subscribers { //向所有的订阅者管道发送主题
		wg.Add(1)
		go p.SendTopic(sub, topic, v, &wg)
	}
}

// 向订阅者发送主题
func (p *publisher) SendTopic(sub subscriber, topic topicFunc, v interface{}, wg *sync.WaitGroup) {
	defer wg.Done()
	if topic != nil && !topic(v) { //订阅者未订阅这个主题，不发送
		return
	}
	select {
	case sub <- v:
	case <-time.After(p.timeout): //超时后就不再发送
	}
}