Portable Touchscreen Messenger

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

// Provision these values through the final on-screen Settings page before field use.
// The broker must be a private TLS-capable MQTT service; do not use a public topic for private messages.
static const char *WIFI_SSID = "";
static const char *WIFI_PASSWORD = "";
static const char *MQTT_HOST = "";
static const uint16_t MQTT_PORT = 1883;
static const char *MQTT_USER = "";
static const char *MQTT_PASSWORD = "";
static const char *DEVICE_ID = "message-device-a";
static const char *PEER_ID = "message-device-b";

WiFiClient transport;
PubSubClient mqtt(transport);
Preferences history;
unsigned long lastReconnectAttempt = 0;

String inboxTopic() {
  return String("private-messenger/") + DEVICE_ID + "/in";
}

String outboxTopic() {
  return String("private-messenger/") + PEER_ID + "/in";
}

void appendHistory(const char *direction, const char *text) {
  String previous = history.getString("history", "");
  String line = String(direction) + ": " + text + "\n";
  previous += line;
  if (previous.length() > 3500) {
    previous.remove(0, previous.length() - 3500);
  }
  history.putString("history", previous);
}

void onMqttMessage(char *topic, byte *payload, unsigned int length) {
  String message;
  message.reserve(length);
  for (unsigned int i = 0; i < length; ++i) {
    message += static_cast<char>(payload[i]);
  }
  appendHistory("BE", message.c_str());
  Serial.printf("Uj uzenet [%s]: %s\n", topic, message.c_str());
  // The production display task reads the same stored history and redraws only its message-list region.
}

bool connectMqtt() {
  if (strlen(MQTT_HOST) == 0 || strlen(MQTT_USER) == 0) {
    Serial.println("MQTT nincs beallitva; a vegleges kezelofeluletben add meg a privat broker adatait.");
    return false;
  }
  mqtt.setServer(MQTT_HOST, MQTT_PORT);
  mqtt.setCallback(onMqttMessage);
  if (!mqtt.connect(DEVICE_ID, MQTT_USER, MQTT_PASSWORD)) {
    Serial.printf("MQTT kapcsolat sikertelen, hibakod: %d\n", mqtt.state());
    return false;
  }
  mqtt.subscribe(inboxTopic().c_str(), 1);
  Serial.println("MQTT kapcsolat letrejott.");
  return true;
}

bool sendMessage(const String &text) {
  if (!mqtt.connected() && !connectMqtt()) {
    return false;
  }
  bool sent = mqtt.publish(outboxTopic().c_str(), text.c_str(), false);
  if (sent) {
    appendHistory("EN", text.c_str());
  }
  return sent;
}

void connectWifi() {
  if (strlen(WIFI_SSID) == 0) {
    Serial.println("Wi-Fi nincs beallitva.");
    return;
  }
  WiFi.mode(WIFI_STA);
  WiFi.begin(WIFI_SSID, WIFI_PASSWORD);
  const unsigned long started = millis();
  while (WiFi.status() != WL_CONNECTED && millis() - started < 15000) {
    delay(100);
  }
  if (WiFi.status() == WL_CONNECTED) {
    Serial.print("Wi-Fi kapcsolodva, IP: ");
    Serial.println(WiFi.localIP());
  } else {
    Serial.println("Wi-Fi kapcsolat sikertelen.");
  }
}

void setup() {
  Serial.begin(115200);
  history.begin("messages", false);
  Serial.println("ESP32-S3 uzenetkuldo kommunikacios mag indul.");
  connectWifi();
  if (WiFi.status() == WL_CONNECTED) {
    connectMqtt();
  }
}

void loop() {
  if (WiFi.status() != WL_CONNECTED && strlen(WIFI_SSID) > 0) {
    WiFi.reconnect();
  }
  if (WiFi.status() == WL_CONNECTED) {
    if (!mqtt.connected() && millis() - lastReconnectAttempt > 5000) {
      lastReconnectAttempt = millis();
      connectMqtt();
    }
    mqtt.loop();
  }
  delay(20);
}