iot_code_cpp.txt

#include <Arduino.h>
#include <WiFi.h>
#include <WiFiClientSecure.h>
#include <PubSubClient.h>

// ====== USER CONFIG ======
const char* WIFI_SSID = "___";
const char* WIFI_PASSWORD = "____";

// HiveMQ Cloud broker (TLS)
const char* MQTT_BROKER = "broker url";
const uint16_t MQTT_PORT = 8883;
const char* MQTT_CLIENT_ID = "_____";
const char* MQTT_USER = "____";
const char* MQTT_PASS = "_____";

// Topic used by your MCP server/tool to control bulb
const char* TOPIC_CONTROL = "home/bulb/control"; // payload: ON | OFF | 1 | 0
const char* TOPIC_STATUS = "home/bulb/status";   // publishes current state

// GPIO connected to relay/transistor that drives bulb
const int BULB_PIN = 2;
// =========================

WiFiClientSecure espClient;
PubSubClient mqttClient(espClient);

bool bulbState = false;
unsigned long lastReconnectAttempt = 0;

void setBulb(bool on) {
  bulbState = on;
  digitalWrite(BULB_PIN, on ? HIGH : LOW);
  mqttClient.publish(TOPIC_STATUS, on ? "ON" : "OFF", true);
  Serial.printf("Bulb: %s\n", on ? "ON" : "OFF");
}

void mqttCallback(char* topic, byte* payload, unsigned int length) {
  String msg;
  msg.reserve(length);

  for (unsigned int i = 0; i < length; i++) {
    msg += static_cast<char>(payload[i]);
  }
  msg.trim();
  msg.toUpperCase();

  Serial.printf("MQTT [%s]: %s\n", topic, msg.c_str());

  if (String(topic) == TOPIC_CONTROL) {
    if (msg == "ON" || msg == "1" || msg == "TRUE") {
      setBulb(true);
    } else if (msg == "OFF" || msg == "0" || msg == "FALSE") {
      setBulb(false);
    }
  }
}

void connectWiFi() {
  if (WiFi.status() == WL_CONNECTED) {
    return;
  }

  Serial.printf("Connecting Wi-Fi: %s\n", WIFI_SSID);
  WiFi.mode(WIFI_STA);
  WiFi.begin(WIFI_SSID, WIFI_PASSWORD);

  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }

  Serial.println();
  Serial.print("Wi-Fi connected. IP: ");
  Serial.println(WiFi.localIP());
}

bool connectMQTT() {
  if (mqttClient.connected()) {
    return true;
  }

  Serial.printf("Connecting MQTT: %s:%u\n", MQTT_BROKER, MQTT_PORT);

  if (mqttClient.connect(MQTT_CLIENT_ID, MQTT_USER, MQTT_PASS)) {
    Serial.println("MQTT connected");
    mqttClient.subscribe(TOPIC_CONTROL, 1);
    mqttClient.publish(TOPIC_STATUS, bulbState ? "ON" : "OFF", true);
    return true;
  }

  Serial.printf("MQTT connect failed, state=%d\n", mqttClient.state());
  return false;
}

void setup() {
  Serial.begin(115200);

  pinMode(BULB_PIN, OUTPUT);
  digitalWrite(BULB_PIN, LOW);

  connectWiFi();

  // Quick-start TLS mode for HiveMQ Cloud.
  // For production, use certificate validation with setCACert(...).
  espClient.setInsecure();

  mqttClient.setServer(MQTT_BROKER, MQTT_PORT);
  mqttClient.setCallback(mqttCallback);
}

void loop() {
  if (WiFi.status() != WL_CONNECTED) {
    connectWiFi();
  }

  if (!mqttClient.connected()) {
    unsigned long now = millis();
    if (now - lastReconnectAttempt > 3000) {
      lastReconnectAttempt = now;
      connectMQTT();
    }
  } else {
    mqttClient.loop();
  }
}