package main

import (
	"errors"
	"log"
	"os"
	"regexp"
	"strconv"
	"time"

	"github.com/coreos/go-etcd/etcd"
	"github.com/fsouza/go-dockerclient"
)

const (
	timeout time.Duration = 10 * time.Second
	etcdTTL time.Duration = timeout * 2
)

func getopt(name, dfault string) string {
	value := os.Getenv(name)
	if value == "" {
		value = dfault
	}
	return value
}

func main() {
	endpoint := getopt("DOCKER_HOST", "unix:///var/run/docker.sock")
    etcdHost := getopt("ETCD_HOST", "127.0.0.1")

	client, err := docker.NewClient(endpoint)
	if err != nil {
		log.Fatal(err)
	}

	etcdClient := etcd.NewClient([]string{"http://" + etcdHost + ":4001"})

	go listenContainers(client, etcdClient, etcdTTL)

	for {
		go pollContainers(client, etcdClient, etcdTTL)
		time.Sleep(timeout)
	}
}

func listenContainers(client *docker.Client, etcdClient *etcd.Client, ttl time.Duration) {

	listener := make(chan *docker.APIEvents)
	// TODO: figure out why we need to sleep for 10 milliseconds
	// https://github.com/fsouza/go-dockerclient/blob/0236a64c6c4bd563ec277ba00e370cc753e1677c/event_test.go#L43
	defer func() { time.Sleep(10 * time.Millisecond); client.RemoveEventListener(listener) }()
	err := client.AddEventListener(listener)
	if err != nil {
		log.Fatal(err)
	}
	for {
		select {
		case event := <-listener:
			if event.Status == "start" {
				container, err := getContainer(client, event.ID)
				if err != nil {
					log.Fatal(err)
				}
				publishContainer(etcdClient, container, ttl)
			}
		}
	}
}

func getContainer(client *docker.Client, id string) (*docker.APIContainers, error) {
	containers, err := client.ListContainers(docker.ListContainersOptions{})
	if err != nil {
		return nil, err
	}

	for _, container := range containers {
		// send container to channel for processing
		if container.ID == id {
			return &container, nil
		}
	}
	return nil, errors.New("could not find container")
}

func pollContainers(client *docker.Client, etcdClient *etcd.Client, ttl time.Duration) {
	containers, err := client.ListContainers(docker.ListContainersOptions{})
	if err != nil {
		log.Fatal(err)
	}

	for _, container := range containers {
		// send container to channel for processing
		publishContainer(etcdClient, &container, ttl)
	}
}

func publishContainer(client *etcd.Client, container *docker.APIContainers, ttl time.Duration) {

	var publishableContainerName = regexp.MustCompile(`[a-z0-9-]+_v[1-9][0-9]*.(cmd|web).[1-9][0-9]*`)
	var publishableContainerBaseName = regexp.MustCompile(`^[a-z0-9-]+`)

	// this is where we publish to etcd
	for _, name := range container.Names {
		// HACK: remove slash from container name
		// see https://github.com/docker/docker/issues/7519
		containerName := name[1:]
		if !publishableContainerName.MatchString(containerName) {
			continue
		}
		containerBaseName := publishableContainerBaseName.FindString(containerName)
		keyPath := "/deis/services/" + containerBaseName + "/" + containerName
		for _, p := range container.Ports {
			host := os.Getenv("HOST")
			port := strconv.Itoa(int(p.PublicPort))
			setEtcd(client, keyPath, host+":"+port, uint64(ttl.Seconds()))
			// TODO: support multiple exposed ports
			break
		}
	}
}

func setEtcd(client *etcd.Client, key, value string, ttl uint64) {
	_, err := client.Set(key, value, ttl)
	if err != nil {
		log.Println(err)
	}
	log.Println("set", key, "->", value)
}

func unsetEtcd(client *etcd.Client, key string) {
	_, err := client.Delete(key, true)
	if err != nil {
		log.Println(err)
	}
	log.Println("unset", key)
}