#include <WiFi.h> //Key parts to understand:
#include <PubSubClient.h>

// Wi-Fi Credentials
const char* ssid = "Wokwi-GUEST";
const char* password = "";

// MQTT Broker Settings
const char* mqtt_server = "mqtt.eclipseprojects.io"; // Example public broker
const char* mqtt_topic = "esp32/test/topic"; // Topic to subscribe to
WiFiClient espClient;
PubSubClient client(espClient);

// Function to connect to Wi-Fi
void connectWiFi() {
 WiFi.begin(ssid, password);
 while (WiFi.status() != WL_CONNECTED) {
 delay(1000);
 Serial.println("Connecting to WiFi...");
 }
 Serial.println("WiFi Connected");
}

// Function to connect to the MQTT broker
void connectMQTT() {
 while (!client.connected()) {
 Serial.print("Attempting MQTT connection...");
 // Create a unique client ID
 String clientId = "ESP32Client-" + String(random(0xffff), HEX);
 if (client.connect(clientId.c_str())) {
 Serial.println("Connected to MQTT broker");
 } else {
 Serial.print("Failed to connect, state ");
 Serial.println(client.state());
 delay(5000);
 }
 }
}
void setup() {
 Serial.begin(115200); // Initialize Serial Monitor
 connectWiFi(); // Connect to Wi-Fi
 client.setServer(mqtt_server, 1883); // Set MQTT broker address and port
 connectMQTT();
}
void loop() {
 if (!client.connected()) {
 connectMQTT(); // Reconnect if the connection is lost
 }
 client.loop(); // Keep the connection alive
 // Publish a test message every 5 seconds
 String payload = "Hello from ESP32";
 client.publish(mqtt_topic, payload.c_str());
 Serial.println("Published: " + payload);
 delay(5000); // Delay for 5 seconds before sending the next message
}