#define SOFT_TX_PIN PA2
#define SOFT_RX_PIN PA3
#define BUTTON_PIN PA0
#define LED_PIN PC13

HardwareSerial DemoUart(SOFT_RX_PIN, SOFT_TX_PIN); // RX, TX on PA3/PA2 (USART2 pins)

bool ledOn = false;
bool lastButton = HIGH;
char rxBuf[32];
uint8_t rxLen = 0;

void setLed(bool on) {
  ledOn = on;
  digitalWrite(LED_PIN, on ? LOW : HIGH); // PC13 is active-low.
}

void handleRxByte(uint8_t value) {
  if (value == '\r' || value == '\n') {
    rxBuf[rxLen] = '\0';
    if (rxLen > 0 && strcmp(rxBuf, "hello") == 0) {
      setLed(!ledOn);
      DemoUart.print("PC13 toggled\r\n");
    }
    rxLen = 0;
    return;
  }

  if (rxLen < sizeof(rxBuf) - 1) {
    rxBuf[rxLen++] = (char)value;
  } else {
    rxLen = 0;
  }
}

void setup() {
  pinMode(BUTTON_PIN, INPUT_PULLUP);
  pinMode(LED_PIN, OUTPUT);
  setLed(false);

  DemoUart.begin(115200);
  DemoUart.print("ready: PA2 TX, PA3 RX, PA0 button, PC13 LED\r\n");
}

void loop() {
  bool button = digitalRead(BUTTON_PIN);
  if (lastButton == HIGH && button == LOW) {
    DemoUart.print("hello\r\n");
  }
  lastButton = button;

  while (DemoUart.available()) {
    handleRxByte((uint8_t)DemoUart.read());
  }
}