package main

import "log"
import "fmt"
import "os"
import "os/signal"
import "strings"
// import "time"
import MQTT "github.com/eclipse/paho.mqtt.golang"
import "github.com/google/uuid"
import "crypto/tls"


type Message struct {
  topic string
  payload []byte
}

var messageInputChannel chan Message = make(chan Message, 100)
var messageOutputChannel chan Message = make(chan Message, 100)


func onMessageReceived(client MQTT.Client, message MQTT.Message) {
  // log.Printf("Message received, topic: %s, payload: %s\n", message.Topic(), message.Payload())
  m := Message { 
    topic: message.Topic(), 
    payload: message.Payload(),
  }
  select {
  case messageInputChannel <- m:
    {}
    //log.Println("Message sent to channel")
  default:
    log.Println("Channel full, message lost")
  }
}

func onConnectionLost(client MQTT.Client, error error) {
  log.Printf("Connection lost, error %s", error)
}

func onReconnecting(client MQTT.Client, clientOpts *MQTT.ClientOptions) {
  log.Println("Oops, connection lost, already reconnecting ...")
}


func onConnect(client MQTT.Client) {
  topicsStr := os.Getenv("MQTT_SUBSCRIBE_TOPICS")
  if topicsStr == "" {
    log.Fatal("No topics given, set env var MQTT_SUBSCRIBE_TOPICS")
  }
  topics := strings.Split(topicsStr, ",")
  for _, topic := range topics {
    if token := client.Subscribe(topic, 0, onMessageReceived); token.Wait() && token.Error() != nil {
      log.Fatalf("Unable to subscribe to topic %s, error %s", topic, token.Error())
    }
    log.Printf("Successfully subscribed to topic %s", topic)
  }
}

func inputDispatcher() {
  for {
    select {
    case message := <- messageInputChannel:
      log.Printf("Message arrived in inputDispatcher, topic: %s, payload: %s\n", message.topic, message.payload)
    }
  }
}

func outputDispatcher(client MQTT.Client) {
  for {
    select {
    case message := <- messageOutputChannel:
      log.Printf("Message arrived in outputDispatcher, topic: %s, payload: %s\n", message.topic, message.payload)
      if token := client.Publish(message.topic, 0, false, message.payload); token.Wait() && token.Error() != nil {
        log.Printf("Unable to publish, error %s", token.Error())
      }
      log.Println("Successfully published")
    }
  }
}

func startMqttClient() MQTT.Client {
  broker := os.Getenv("MQTT_BROKER")
  if broker == "" {
    log.Fatal("No broker given, set env var MQTT_BROKER")
  }

  prefix := "UDI"
  uuid := uuid.New()
  clientId := fmt.Sprintf("%s-%s", prefix, uuid)

  opts := MQTT.NewClientOptions().
    AddBroker(broker).
    SetClientID(clientId).
    SetConnectionLostHandler(onConnectionLost).
    SetOnConnectHandler(onConnect).
    SetReconnectingHandler(onReconnecting).
    SetConnectRetry(true)

  username := os.Getenv("MQTT_USERNAME")
  if username != "" {
    opts.SetUsername(username)
  }

  password := os.Getenv("MQTT_PASSWORD")
  if password != "" {
    opts.SetPassword(password)
  }

  enableTls := os.Getenv("MQTT_ENABLE_TLS")
  if enableTls == "true" {
    log.Println("Enableing TLS connection")
    tlsConfig := &tls.Config { 
      InsecureSkipVerify: true, 
    }
    opts.SetTLSConfig(tlsConfig)
	}

  log.Println("Trying to connect to broker")
  client := MQTT.NewClient(opts)
  if token := client.Connect(); token.Wait() && token.Error() != nil {
    log.Fatalf("Unable to connect to broker %s, error %s", broker, token.Error())
  }
  log.Printf("Successfully connected to broker %s", broker)

  return client
}

func stopMqttClient(client MQTT.Client) {
  log.Println("Disconnecting from broker")
  client.Disconnect(250)
}

func main() {
  log.SetPrefix("UDI: ")
  log.SetFlags(log.Ldate | log.Ltime | log.Lshortfile)

  log.Println("UDI starting")

  go inputDispatcher()

  mqttClient := startMqttClient()
  defer stopMqttClient(mqttClient)

  go outputDispatcher(mqttClient)

  log.Println("UDI running")

  c := make(chan os.Signal, 1)
	signal.Notify(c, os.Interrupt, os.Kill)
	<-c

  log.Println("Terminating UDI")
}