/*********************Wifi Client init **************************************/
bool resolveHosts(bool rtcValid) {
  if (rtcValid && rtcData.mqttServer.isV4()) {
    mqttBroker = rtcData.mqttServer;
  }
  else {
    //DNS lookup
    if(WiFi.hostByName(MQTT_SERVER, mqttBroker)) {
      rtcData.mqttServer = mqttBroker;
    }
    else {
      return false;
    }
  }
  return true;
}
bool wifi_connect() {
  bool rtcValid = false;
  // Try to read WiFi settings from RTC memory
  if( ESP.rtcUserMemoryRead( WiFi_RTC, (uint32_t*)&rtcData, sizeof( rtcData ) ) ) {
    // Calculate the CRC of what we just read from RTC memory, but skip the first 4 bytes as that's the checksum itself.
    uint32_t crc = calculateCRC32( ((uint8_t*)&rtcData) + 4, sizeof( rtcData ) - 4 );
    if( crc == rtcData.crc32 ) {
      rtcValid = true;
    }
    #ifdef SERIAL_DEBUG 
    Serial.println("\trtcData.channel: \t\t" + String(rtcData.channel));
    Serial.println("\trtcData.txPow: \t\t" + String(rtcData.txPow)); 
    Serial.println("\trtcData.mqttServer:\t" + String(((IPAddress)rtcData.mqttServer).toString()));  
    #endif
  }
#ifdef OLED_OUTPUT
  display.clear();
  display.drawStringMaxWidth(0, 0, 128, "WiFi  init" );
  display.display();
  display.drawStringMaxWidth(0, 16, 128, "WiFi: " + String(WLAN_SSID));
  display.display();
#endif

#ifdef SERIAL_DEBUG
  Serial.println();
  Serial.print("Connecting to ");
  Serial.println(WLAN_SSID);
#endif
  WiFi.forceSleepWake();
  delay(10);
  WiFi.mode(WIFI_STA);
  yield();
  // Disable the WiFi persistence.  The ESP8266 will not load and save WiFi settings in the flash memory.
  // http://arduino-esp8266.readthedocs.io/en/latest/esp8266wifi/generic-class.html#persistent
  WiFi.persistent (false);
  WiFi.hostname(name); //ToDo Change to correct value
  WiFi.config(ip, gateway, subnet, dns);
  // Connect to WiFi access point.
  if( rtcValid ) {
    // The RTC data was good, make a quick connection
    if (rtcData.txPow > 0 ) {
      rtcData.txPow=rtcData.txPow-1;
      WiFi.setOutputPower(rtcData.txPow);
      yield();
    }
    WiFi.begin( WLAN_SSID, WLAN_PASS, rtcData.channel, rtcData.bssid, true );
    #ifdef SERIAL_DEBUG
      Serial.println("RTC WiFi used");
      Serial.println("\tCurrent Powerlevel: \t" + String(rtcData.txPow*4) + "dB");
    #endif
  }
  else {
    //raise outputPower to max
    WiFi.setOutputPower(10);
    rtcData.txPow = 10;
    // The RTC data was not valid, so make a regular connection
    WiFi.begin( WLAN_SSID, WLAN_PASS );
    yield();
    delay(10);
  }
#ifdef SERIAL_DEBUG
  Serial.print("WiFi started");
  //WiFi.printDiag(Serial);
#endif
  int i = 0;
  uint64_t sTime = millis();
  while (WiFi.status() != WL_CONNECTED) {
    delay(200);
    i++;
    yield();
    #ifdef SERIAL_DEBUG
    Serial.print(".");
    #endif
    if ((millis() - sTime) > WIFI_CONNECT_TIMEOUT * 1000)  // wifi connection lasts too ling, retry
    {
      #ifdef SERIAL_DEBUG
      Serial.println("WiFi connect timeout!");
      #endif
      //raise transmit power for next retry
      rtcData.txPow=rtcData.txPow+1;
      //make the crc invalid
      ESP.rtcUserMemoryWrite (WiFi_RTC, (uint32_t*)&rtcData , sizeof( rtcData ) );
      return false;
    }
    //every two second raise the TX power 
    if (i%4 == 0)
    {
      rtcData.txPow = rtcData.txPow+1;
      WiFi.setOutputPower(rtcData.txPow);
      yield();
      #ifdef SERIAL_DEBUG
      Serial.println("\tWiFi TX Power raised: \t" + String(rtcData.txPow) + "counter");
      #endif
    }
    yield();
  }
  //ToDo stupid TX power correlation --needs improvement
  long rssi = WiFi.RSSI();
  //rtcData.txPow = int((72+rssi)/4)+rtcData.txPow;
  if (rssi > -60 ) 
  {
    rtcData.txPow = 0;
  }
#ifdef SERIAL_DEBUG
    Serial.println("\n\r\tWiFi Connect Time: \t" + String(float((millis() - sTime)/1000)) + " s");
    Serial.println("\tWiFi RSSI: \t\t" + String(rssi) + " dB");
    Serial.println("\tWiFi next TX Power: \t" + String(rtcData.txPow) + " counter");
#endif
  // Write current connection info back to RTC
  resolveHosts( rtcValid );
  rtcData.channel = WiFi.channel();
  memcpy( rtcData.bssid, WiFi.BSSID(), 6 ); // Copy 6 bytes of BSSID (AP's MAC address)
  rtcData.crc32 = calculateCRC32( ((uint8_t*)&rtcData) + 4, sizeof( rtcData ) - 4 );
  ESP.rtcUserMemoryWrite (WiFi_RTC, (uint32_t*)&rtcData , sizeof( rtcData ) );

#ifdef SERIAL_DEBUG
  Serial.println("\tIP address: \t\t" + WiFi.localIP().toString() );
#endif

#ifdef OLED_OUTPUT
  display.drawStringMaxWidth(0, 32, 128, "IP:   " + WiFi.localIP().toString());
  display.display();
#endif
  return true;
}

bool wifi_disconnect() {
  //exit gracefully from WiFi AP - delete credentials
  WiFi.disconnect(true);
  yield();
#ifdef SERIAL_DEBUG
  Serial.println("WiFi disconnected");
#endif
  //shutdown WiFi modul
  WiFi.mode(WIFI_OFF);
  // set WiFi to sleep
  WiFi.forceSleepBegin();
  yield();
  return true;
}