#include <WiFi.h>
#include <Firebase_ESP_Client.h>
#include <Wire.h>
#include <Adafruit_Sensor.h>

// Provide the token generation process info.
#include "addons/TokenHelper.h"
// Provide the RTDB payload printing info and other helper functions.
#include "addons/RTDBHelper.h"

// WiFi credentials
#define WIFI_SSID "Wokwi-GUEST"
#define WIFI_PASSWORD ""

// Firebase project API Key
#define API_KEY "AIzaSyAuoeMsdQCP9j9EpjGZ45afQnKJjWBXbAA"

// Firebase Realtime Database URL
#define DATABASE_URL "mq2-iot-93af4-default-rtdb.firebaseio.com/:"

// Define Firebase objects
FirebaseData fbdo;
FirebaseAuth auth;
FirebaseConfig config;

// MQ2 sensor pin
#define MQ2PIN 34  // Analog pin for MQ2 sensor

// Variables
float gasValue = 0.0;
unsigned long sendDataPrevMillis = 0;
bool signupOK = false;

void setup() {
  // Initialize serial communication
  Serial.begin(115200);
  
  // Connect to WiFi
  WiFi.begin(WIFI_SSID, WIFI_PASSWORD);
  Serial.print("Connecting to WiFi");
  while (WiFi.status() != WL_CONNECTED) {
    Serial.print(".");
    delay(300);
  }
  Serial.println();
  Serial.print("Connected with IP: ");
  Serial.println(WiFi.localIP());
  
  // Initialize Firebase
  config.api_key = API_KEY;
  config.database_url = DATABASE_URL;
  
  // Sign up
  if (Firebase.signUp(&config, &auth, "", "")) {
    Serial.println("Firebase signup OK");
    signupOK = true;
  } else {
    Serial.printf("Firebase signup failed: %s\n", config.signer.signupError.message.c_str());
  }
  
  // Assign the callback function for the long running token generation task
  config.token_status_callback = tokenStatusCallback;
  
  Firebase.begin(&config, &auth);
  Firebase.reconnectWiFi(true);
}

void loop() {
  // Send data to Firebase every 15 seconds
  if (Firebase.ready() && signupOK && (millis() - sendDataPrevMillis > 15000 || sendDataPrevMillis == 0)) {
    sendDataPrevMillis = millis();
    
    // Read MQ2 sensor value
    gasValue = analogRead(MQ2PIN);
    gasValue = map(gasValue, 0, 4095, 0, 100); // Convert to percentage (adjust as needed)
    
    Serial.printf("Gas Value: %.2f%%\n", gasValue);
    
    // Send to Firebase
    if (Firebase.RTDB.setFloat(&fbdo, "/MQ2/GasValue", gasValue)) {
      Serial.println("Data sent to Firebase successfully");
    } else {
      Serial.println("Failed to send data");
      Serial.println("REASON: " + fbdo.errorReason());
    }
  }
}


//Activity

package com.example.gassensor;

import android.os.Bundle;
import android.widget.TextView;

import androidx.activity.EdgeToEdge;
import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.graphics.Insets;
import androidx.core.view.ViewCompat;
import androidx.core.view.WindowInsetsCompat;

import com.google.firebase.FirebaseApp;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.ValueEventListener;

public class MainActivity extends AppCompatActivity {

    private DatabaseReference databaseReference;

    private TextView gas;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        //FireBase
        FirebaseApp.initializeApp(this);

        gas = (TextView) findViewById(R.id.gasVal);


        databaseReference = FirebaseDatabase.getInstance().getReference("MQ2");

        databaseReference.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot snapshot) {
                if (snapshot.exists()){
                    String gasVal = snapshot.child("GasValue").getValue(String.class);

                    gas.setText(gasVal);

                }
            }

            @Override
            public void onCancelled(@NonNull DatabaseError error) {

            }
        });

    }
}


//xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:padding="24dp"
    android:background="#F5F5F5"
    tools:context=".MainActivity">

    <TextView
        android:id="@+id/titleId"
        android:text="MQ2 Gas Sensor Data"
        android:layout_gravity="center"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textColor="#212121"
        android:textSize="28sp"
        android:textStyle="bold"
        android:layout_marginBottom="32dp" />

    <TextView
        android:id="@+id/gasVal"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:padding="12dp"
        android:background="@android:drawable/editbox_background"
        android:layout_marginBottom="16dp" />
</LinearLayout>