Create temperature monitoring SDK for Wireless Temp Sensor

Hey, I have been looking for SDK platform which helps me to develop the application for wireless temperature sensor which sends the value to gateway receiver which is connected with ESP32 to communicate with firebase real-time database.
I need advice which helps me to develop the cross-platform application which displays the sensor data in a smartphone as well as sends the data to the Firebase-realtime database.

Leads on this will be much appreciated

I took a look at the IOT Arduino tutorial
I think you can implement the same setup with the esp32.
You’d need the xbee module that communicates serially or through I2C protocol, Then use the Stream or I2C Library on the ESP32 to handle the incoming information from the sensor.

As for the firebase-realtime database, You can use the Zerynth MQTT library.
You can also use Ubidots library what makes it way easier to have IOT database.

For the smartphone application you can develop it for android/IOS or you can useZerynth app and develop your software with Javascript and Bootstrap.
Zerynth app is crossplatform too.

Hope this helps!