// GetTopic performs a thread safe operation
// to return a pointer to a Topic object (potentially new)
func (n *NSQd) GetTopic(topicName string) *Topic {
	n.Lock()
	t, ok := n.topicMap[topicName]
	if ok {
		n.Unlock()
		return t
	} else {
		t = NewTopic(topicName, n.options, n)
		n.topicMap[topicName] = t
		log.Printf("TOPIC(%s): created", t.name)

		// release our global nsqd lock, and switch to a more granular topic lock while we init our
		// channels from lookupd. This blocks concurrent PutMessages to this topic.
		t.Lock()
		defer t.Unlock()
		n.Unlock()
		// if using lookupd, make a blocking call to get the topics, and immediately create them.
		// this makes sure that any message received is buffered to the right channels
		if len(n.lookupPeers) > 0 {
			channelNames, _ := lookupd.GetLookupdTopicChannels(t.name, n.lookupHttpAddrs())
			for _, channelName := range channelNames {
				t.getOrCreateChannel(channelName)
			}
		}
	}
	return t
}

// GetTopic performs a thread safe operation
// to return a pointer to a Topic object (potentially new)
func (n *NSQD) GetTopic(topicName string) *Topic {
	n.Lock()
	t, ok := n.topicMap[topicName]
	if ok {
		n.Unlock()
		return t
	} else {
		deleteCallback := func(t *Topic) {
			n.DeleteExistingTopic(t.name)
		}
		t = NewTopic(topicName, &context{n}, deleteCallback)
		n.topicMap[topicName] = t

		n.logf("TOPIC(%s): created", t.name)

		// release our global nsqd lock, and switch to a more granular topic lock while we init our
		// channels from lookupd. This blocks concurrent PutMessages to this topic.
		t.Lock()
		n.Unlock()
		// if using lookupd, make a blocking call to get the topics, and immediately create them.
		// this makes sure that any message received is buffered to the right channels
		if len(n.lookupPeers) > 0 {
			channelNames, _ := lookupd.GetLookupdTopicChannels(t.name, n.lookupHttpAddrs())
			for _, channelName := range channelNames {
				t.getOrCreateChannel(channelName)
			}
		}
		t.Unlock()

		// NOTE: I would prefer for this to only happen in topic.GetChannel() but we're special
		// casing the code above so that we can control the locks such that it is impossible
		// for a message to be written to a (new) topic while we're looking up channels
		// from lookupd...
		//
		// update messagePump state
		select {
		case t.channelUpdateChan <- 1:
		case <-t.exitChan:
		}
	}
	return t
}

func (s *httpServer) lookupHandler(w http.ResponseWriter, req *http.Request) {
	reqParams, err := util.NewReqParams(req)
	if err != nil {
		log.Printf("ERROR: failed to parse request params - %s", err.Error())
		http.Error(w, "INVALID_REQUEST", 500)
		return
	}

	channels := make(map[string][]string)
	allTopics, _ := lookupd.GetLookupdTopics(s.context.nsqadmin.options.NSQLookupdHTTPAddresses)
	for _, topicName := range allTopics {
		var producers []string
		producers, _ = lookupd.GetLookupdTopicProducers(topicName, s.context.nsqadmin.options.NSQLookupdHTTPAddresses)
		if len(producers) == 0 {
			topicChannels, _ := lookupd.GetLookupdTopicChannels(topicName, s.context.nsqadmin.options.NSQLookupdHTTPAddresses)
			channels[topicName] = topicChannels
		}
	}

	p := struct {
		Title        string
		GraphOptions *GraphOptions
		TopicMap     map[string][]string
		Lookupd      []string
		Version      string
	}{
		Title:        "NSQ Lookup",
		GraphOptions: NewGraphOptions(w, req, reqParams, s.context),
		TopicMap:     channels,
		Lookupd:      s.context.nsqadmin.options.NSQLookupdHTTPAddresses,
		Version:      util.BINARY_VERSION,
	}
	err = templates.T.ExecuteTemplate(w, "lookup.html", p)
	if err != nil {
		log.Printf("Template Error %s", err.Error())
		http.Error(w, "Template Error", 500)
	}
}