package main

import (
	"fmt"
	"log"
	"time"
	"strings"

	mqtt "github.com/eclipse/paho.mqtt.golang"
)

const (
	QoS0                       = byte(0)
	QoS1                       = byte(1)
	QoS2                       = byte(2)
	RETAINED                   = true
	MQTT_CONNECT_TIMEOUT       = 1 * time.Second
	MQTT_SUBSCRIBE_TIMEOUT     = 1 * time.Second
	MQTT_DISCONNECT_TIMEOUT_US = 500
	MQTT_KEEPALIVE_PERIOD      = 2 * time.Second
)

var (
	mqttServerHealthTopic string
)

type MQTTMessage struct {
	Topic   string
	Payload []byte
	Retain  bool
}

type Route struct {
	Topic       string
	QoS         byte
	Destination chan MQTTMessage
}

func NewRoute(topic string, qos byte) Route {
	return Route{topic, qos, make(chan MQTTMessage)}
}

func (m MQTTMessage) String() string {
	return fmt.Sprintf("topic='%s' message='%s'", m.Topic, string(m.Payload))
}

func MQTTRun(config MQTTConfig, tx chan MQTTMessage, routes ...Route) {
	mqttServerHealthTopic = fmt.Sprintf("%s/server/health", config.TopicPrefix)
	mqttServerVersionTopic := fmt.Sprintf("%s/server/version", config.TopicPrefix)

	opts := mqtt.NewClientOptions()
	opts.AddBroker(config.Broker)
	opts.SetClientID(config.ClientID)
	opts.SetCleanSession(true)
	opts.SetOnConnectHandler(func(c mqtt.Client) {
		log.Printf("Connected to MQTT broker.")
		c.Publish(mqttServerHealthTopic, QoS1, true, []byte(`good`))
		c.Publish(mqttServerVersionTopic, QoS1, true, []byte(Version()))

		for _, route := range routes {
			topic := config.TopicPrefix + "/" + route.Topic
			token := c.Subscribe(topic, route.QoS, func(c mqtt.Client, msg mqtt.Message) {
				message := MQTTMessage{
					Topic: strings.TrimPrefix(msg.Topic(), config.TopicPrefix + "/"),
					Payload: msg.Payload(),
					Retain: msg.Retained(),
				}
				route.Destination <- message
			})
			success := token.WaitTimeout(MQTT_SUBSCRIBE_TIMEOUT)
			if !success {
				log.Fatalf("Topic subscription failed for topic '%s'", topic)
			}
		}
	})
	opts.SetConnectionLostHandler(MQTTConnectionLostHandler)
	opts.SetAutoReconnect(true)
	opts.SetConnectRetry(true)
	opts.SetConnectTimeout(MQTT_CONNECT_TIMEOUT)
	opts.SetKeepAlive(MQTT_KEEPALIVE_PERIOD)
	opts.SetWill(mqttServerHealthTopic, `bad`, QoS1, true)

	client := mqtt.NewClient(opts)

	token := client.Connect()

	success := token.WaitTimeout(MQTT_CONNECT_TIMEOUT)
	if !success {
		log.Fatal("Initial connection to MQTT broker failed.")
	}
	defer client.Disconnect(MQTT_DISCONNECT_TIMEOUT_US)

	for message := range tx {
		topic := fmt.Sprintf("%s/%s", config.TopicPrefix, message.Topic)
		client.Publish(topic, QoS1, message.Retain, message.Payload)
	}
}

func MQTTConnectionLostHandler(c mqtt.Client, err error) {
	log.Printf("Connection to MQTT broker lost: %v", err)
}