struct Listener {
  public:
    HardwareSerial& port;
    char message[8 + 1];
    byte currentIndex;

    Listener(HardwareSerial& p) : port(p), currentIndex(0) {}

    void begin() {
      port.begin(115200);
    }

    const char * listen() {
      int r = port.read();
      if (r == -1) return nullptr;
      message[currentIndex++] = (char) r;
      if (currentIndex >= 8) {
        message[8] = '\0';
        currentIndex = 0;
        return message;
      }
      if (currentIndex >= 8) currentIndex--;
      return nullptr;
    }
};

Listener ports[] = {{Serial}, {Serial1}, {Serial2}, {Serial3}};

void setup() {
  for (auto&p : ports) p.begin();
  Serial.println("Ready");
}

void loop() {
  static uint32_t t0;
  static uint32_t count = 0;
  const char * m;
  for (auto&p : ports) {
    m = p.listen();
    if (m != nullptr) Serial.println(m);
  }
  count++;
  if (millis() - t0 >= 1000) {
    Serial.println(count);
    count = 0;
    t0 = millis();
  }
}