package main

import (
	"fmt"
	"log"
	"time"

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

const (
	QOS                        = byte(1)
	RETAINED                   = true
	MQTT_CONNECT_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
}

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

	opts := mqtt.NewClientOptions()
	opts.AddBroker(config.Broker)
	opts.SetClientID(config.ClientID)
	opts.SetCleanSession(true)
	opts.SetOnConnectHandler(MQTTOnConnectHandler)
	opts.SetConnectionLostHandler(MQTTConnectionLostHandler)
	opts.SetAutoReconnect(true)
	opts.SetConnectRetry(true)
	opts.SetConnectTimeout(MQTT_CONNECT_TIMEOUT)
	opts.SetKeepAlive(MQTT_KEEPALIVE_PERIOD)
	opts.SetWill(mqttServerHealthTopic, `bad`, QOS, 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, QOS, RETAINED, message.Payload)
	}
}

func MQTTOnConnectHandler(c mqtt.Client) {
	log.Printf("Connected to MQTT broker.")
	c.Publish(mqttServerHealthTopic, QOS, true, []byte(`good`))
}

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