#include WiFi.h
                        #include PubSubClient.h
                        #include Adafruit_NeoPixel.h

                        const char* ssid = "YourSSID";
                        const char* password = "YourPassword";
                        const char* mqtt_server = "broker.emqx.io";

                        const char* topic = "week13/wifi"; // same topic to publisher

                        #define NEOPIXEL_PIN D10
                        #define NUM_PIXELS 1

                        WiFiClient espClient;
                        PubSubClient client(espClient);

                        Adafruit_NeoPixel pixels(NUM_PIXELS, NEOPIXEL_PIN, NEO_GRB + NEO_KHZ800);

                        void setup() {
                        Serial.begin(115200);
                        setup_wifi();
                        client.setServer(mqtt_server, 1883);
                        client.setCallback(callback);
                        pixels.begin();
                        }

                        void setup_wifi() {
                        delay(10);
                        Serial.println();
                        Serial.print("Connecting to ");
                        Serial.println(ssid);

                        WiFi.begin(ssid, password);

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

                        Serial.println("");
                        Serial.println("WiFi connected");
                        Serial.println("IP Address: ");
                        Serial.println(WiFi.localIP());
                        }

                        void callback(char* topic, byte* payload, unsigned int length) {
                        String message = "";
                        for (int i = 0; i < length; i++) {
                        message += (char)payload[i];
                        }
                        Serial.print("Message received from topic ");
                        Serial.print(topic);
                        Serial.print(": ");
                        Serial.println(message);

                        if (message == "a") {
                        pixels.setPixelColor(0, pixels.Color(255, 0, 0)); // Red
                        pixels.show();
                        } else {
                        pixels.setPixelColor(0, pixels.Color(0, 255, 0)); // Green
                        pixels.show();
                        }
                        }

                        void reconnect() {
                        while (!client.connected()) {
                        Serial.print("Connecting to MQTT server...");
                        if (client.connect("neopixelClient")) {
                        Serial.println("Connected");
                        client.subscribe(topic);
                        } else {
                        Serial.print("Failed, rc=");
                        Serial.print(client.state());
                        Serial.println(" trying again in 5 seconds");
                        delay(5000);
                        }
                        }
                        }

                        void loop() {
                        if (!client.connected()) {
                        reconnect();
                        }
                        client.loop();
                        }