📨 MQTT Protocol: Panduan Lengkap

#include <WiFi.h>
#include <PubSubClient.h>
#include <DHT.h>

// WiFi credentials
const char* ssid = "WiFi-Rumah";
const char* password = "password123";

// MQTT Broker
const char* mqtt_server = "192.168.1.100";
const int mqtt_port = 1883;
const char* mqtt_user = "sensor_001";
const char* mqtt_pass = "secure_pass";

// Topics
const char* topic_suhu = "gedung1/lantai1/ruang1/suhu";
const char* topic_lembab = "gedung1/lantai1/ruang1/lembab";
const char* topic_status = "gedung1/lantai1/ruang1/status";
const char* topic_cmd_lampu = "gedung1/lantai1/ruang1/cmd/lampu";
const char* topic_cmd_ac = "gedung1/lantai1/ruang1/cmd/ac";

// DHT Sensor
#define DHTPIN 4
#define DHTTYPE DHT22
DHT dht(DHTPIN, DHTTYPE);

// LED dan Relay
#define LED_LAMPU 2
#define RELAY_AC 5

WiFiClient espClient;
PubSubClient client(espClient);
unsigned long lastPublish = 0;
const long publishInterval = 5000; // Publish setiap 5 detik

void setup_wifi() {
    delay(10);
    Serial.println("Menghubungkan ke WiFi...");
    WiFi.begin(ssid, password);

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

    Serial.println("");
    Serial.println("WiFi terhubung!");
    Serial.print("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.printf("Pesan diterima [%s]: %s\n", topic, message.c_str());

    // Handle perintah lampu
    if (String(topic) == topic_cmd_lampu) {
        if (message == "ON") {
            digitalWrite(LED_LAMPU, HIGH);
            client.publish("gedung1/lantai1/ruang1/lampu/status",
                          "ON", true); // retain
            Serial.println("Lampu: ON");
        } else if (message == "OFF") {
            digitalWrite(LED_LAMPU, LOW);
            client.publish("gedung1/lantai1/ruang1/lampu/status",
                          "OFF", true); // retain
            Serial.println("Lampu: OFF");
        }
    }

    // Handle perintah AC
    if (String(topic) == topic_cmd_ac) {
        int targetTemp = message.toInt();
        float currentTemp = dht.readTemperature();
        if (!isnan(currentTemp)) {
            if (currentTemp > targetTemp) {
                digitalWrite(RELAY_AC, HIGH); // AC ON
                client.publish("gedung1/lantai1/ruang1/ac/status",
                              "ON", true);
            } else {
                digitalWrite(RELAY_AC, LOW);  // AC OFF
                client.publish("gedung1/lantai1/ruang1/ac/status",
                              "OFF", true);
            }
        }
    }
}

void reconnect() {
    while (!client.connected()) {
        Serial.print("Menghubungkan ke MQTT Broker...");

        // Client ID unik + Last Will + Clean Session
        if (client.connect(
            "sensor_gedung1_lantai1_ruang1",  // client_id
            mqtt_user,                         // username
            mqtt_pass,                         // password
            topic_status,                      // will topic
            1,                                 // will QoS
            true,                              // will retain
            "offline"                          // will message
        )) {
            Serial.println(" TERHUBUNG!");

            // Publish status online (retained)
            client.publish(topic_status, "online", true);

            // Subscribe ke perintah kontrol (QoS 1)
            client.subscribe(topic_cmd_lampu, 1);
            client.subscribe(topic_cmd_ac, 1);

            Serial.println("Subscribe ke topik kontrol...");
        } else {
            Serial.printf(" GAGAL (rc=%d). Coba lagi 5 detik...\n",
                         client.state());
            delay(5000);
        }
    }
}

void setup() {
    Serial.begin(115200);
    pinMode(LED_LAMPU, OUTPUT);
    pinMode(RELAY_AC, OUTPUT);
    dht.begin();

    setup_wifi();
    client.setServer(mqtt_server, mqtt_port);
    client.setCallback(callback);
}

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

    unsigned long now = millis();
    if (now - lastPublish > publishInterval) {
        lastPublish = now;

        float suhu = dht.readTemperature();
        float lembab = dht.readHumidity();

        if (!isnan(suhu) && !isnan(lembab)) {
            // Publish data sensor (QoS 0, retained)
            char suhuStr[8], lembabStr[8];
            dtostrf(suhu, 1, 2, suhuStr);
            dtostrf(lembab, 1, 2, lembabStr);

            client.publish(topic_suhu, suhuStr, true);   // retained
            client.publish(topic_lembab, lembabStr, true); // retained

            Serial.printf("Published: Suhu=%s°C, Lembab=%s%%\n",
                         suhuStr, lembabStr);

            // Alert jika suhu tinggi (QoS 1)
            if (suhu > 35.0) {
                client.publish("alarm/suhu_tinggi",
                    "{\"device\":\"gedung1_lantai1_ruang1\","
                    "\"temp\":35.5,\"threshold\":35}",
                    1);  // QoS 1
            }
        }
    }
}