#include <Arduino.h>
#include <WiFi.h>
#include <PubSubClient.h>
 
#ifndef WIFI_SSID
#define WIFI_SSID     "UPB-Guest"
#endif
#ifndef WIFI_PASSWORD
#define WIFI_PASSWORD ""
#endif
#ifndef MQTT_HOST
#define MQTT_HOST     "test.mosquitto.org"
#endif
#ifndef MQTT_PORT
#define MQTT_PORT     1883
#endif
#ifndef BASE_TOPIC
#define BASE_TOPIC    "devices/esp32"
#endif
 
WiFiClient      net;
PubSubClient    mqtt(net);         // PubSubClient uses a separate setServer(...)
unsigned long   lastPub = 0;
 
// ---------- Wi-Fi ----------
void connectWiFi() {
  if (WiFi.status() == WL_CONNECTED) return;
  WiFi.mode(WIFI_STA);
  WiFi.begin(WIFI_SSID, WIFI_PASSWORD);
  Serial.print("WiFi connecting");
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }
  Serial.printf("\nWiFi OK, IP: %s\n", WiFi.localIP().toString().c_str());
}
 
// ---------- MQTT callback (PubSubClient signature) ----------
void mqttCallback(char* topic, byte* payload, unsigned int length) {
  // payload is NOT null-terminated; build a String safely
  String msg;
  msg.reserve(length);
  for (unsigned int i = 0; i < length; i++) msg += (char)payload[i];
 
  Serial.printf("Message on %s: %s\n", topic, msg.c_str());
}
 
// ---------- MQTT connect & subscribe ----------
void connectMQTT() {
  // Build clientId like before
  String clientId = "esp32-client-" + String((uint32_t)ESP.getEfuseMac(), HEX);
 
  // Last Will
  String willTopic = String(BASE_TOPIC) + "/status";
  const char* willMsg = "offline";
  const bool  willRetain = true;
  const uint8_t willQos = 0;   // PubSubClient is QoS 0 only
 
  Serial.println("MQTT connecting...");
  while (!mqtt.connect(clientId.c_str(),
                       willTopic.c_str(), willQos, willRetain, willMsg)) {
    Serial.print(".");
    delay(1000);
  }
  Serial.println("\nMQTT connected!");
 
  // Optional subscription
  String subTopic = String(BASE_TOPIC) + "/#";
  mqtt.subscribe(subTopic.c_str());    // QoS 0
  Serial.printf("Subscribed to %s\n", subTopic.c_str());
 
  // Publish "online" once connected (retain)
  mqtt.publish(willTopic.c_str(), "online", true);
}
 
void setup() {
  Serial.begin(115200);
  delay(500);
 
  connectWiFi();
 
  mqtt.setServer(MQTT_HOST, MQTT_PORT);
  mqtt.setCallback(mqttCallback);
 
  // Match your 1KB buffer from 256dpi/client
  mqtt.setBufferSize(1024);
 
  connectMQTT();
}
 
void loop() {
  connectWiFi();                  // ensure WiFi
 
  if (!mqtt.connected()) {
    connectMQTT();
  }
  mqtt.loop();                    // must be called often; non-blocking
  delay(10);
 
  // Publish every 5 seconds
  if (millis() - lastPub > 5000) {
    lastPub = millis();
    String topic = String(BASE_TOPIC) + "/heartbeat";
    String payload = String("{\"uptime_ms\":") + millis() + "}";
    bool ok = mqtt.publish(topic.c_str(), payload.c_str());  // QoS 0
    Serial.printf("Publish %s => %s (%s)\n",
                  topic.c_str(), payload.c_str(), ok ? "OK" : "FAIL");
  }
}