exclude light sensor calls on unsupported devices

add mqtt default host define

src/lib/defaults.hpp

@@ -57,6 +57,7 @@
 #define DEFAULT_BITAXE_HOSTNAME "bitaxe1"
 
 #define DEFAULT_MQTT_ENABLED false
+#define DEFAULT_MQTT_HOST ""
 #define DEFAULT_MQTT_ROOTTOPIC "home/"
 
 #define DEFAULT_ZAP_NOTIFY_ENABLED false

src/lib/mqtt.cpp

@@ -6,8 +6,10 @@ WiFiClient wifiClient;
 PubSubClient client(wifiClient);
 
 // avoid circular deps, just forward declare externs used here.
+#ifdef HAS_FRONTLIGHT
 bool hasLightLevel();
 float getLightLevel();
+#endif
 String getMyHostname();
 
 void onMqttCallback(char* topic, byte* payload, unsigned int length)
@@ -43,7 +45,7 @@ boolean connectMqtt()
 
 void setupMqtt()
 {
-    const String host = preferences.getString("mqttHost", "");
+    const String host = preferences.getString("mqttHost", DEFAULT_MQTT_HOST);
     if (host == "")
     {
         Serial.println("[MQTT] host not set");
@@ -80,11 +82,13 @@ void mqttTask(void *pvParameters)
                     continue;
             }
 
+#ifdef HAS_FRONTLIGHT
             if (hasLightLevel())
             {
                 std::string lux_s = std::to_string(static_cast<int>(std::round(getLightLevel())));
                 publish("sensors/lux", lux_s.c_str());
             }
+#endif
             if (WiFi.isConnected())
             {
                 int8_t rssi = WiFi.RSSI();