#include <SPI.h>
#include <RF24.h>
#define RADIO_CE_PIN 4
#define RADIO_CS_PIN 21
#define TRIG_PIN 5
#define ECHO_PIN 13
#define TX_LED_PIN 2
RF24 radio(RADIO_CE_PIN, RADIO_CS_PIN);
const byte address[6] = "00001";
void setup() {
  Serial.begin(115200);
  pinMode(TX_LED_PIN, OUTPUT);
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
  radio.begin();
  radio.setChannel(115);
  radio.setPALevel(RF24_PA_HIGH);
  radio.setAutoAck(true);
  radio.openWritingPipe(address);
  radio.openReadingPipe(1, address);
  radio.startListening(); // start in receive mode
  Serial.println("Ping-pong Ultrasonic <-> LED setup started");
}
long getDistance() {
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);
  long duration = pulseIn(ECHO_PIN, HIGH);
  return duration * 0.034 / 2;
}
void loop() {
  checkUltrasonic();
  receiveData();  // Check for data after sending
  delay(400);
}
void checkUltrasonic() {
  long distance = getDistance();
  int data = (distance <= 30) ? 1 : 0;
  Serial.print("Measured distance: ");
  Serial.print(distance);
  Serial.println(" cm");
  // --- PING: Send ---
  radio.stopListening();
  bool ok = radio.write(&data, sizeof(data));
  Serial.println(ok ? "TX success" : "TX failed");
  delay(10);
  // --- Immediately go to PONG mode ---
  radio.startListening();
}
void receiveData() {
  if (radio.available()) {
    int receivedData;
    radio.read(&receivedData, sizeof(receivedData));
    Serial.print("Received: ");
    Serial.println(receivedData);
    digitalWrite(TX_LED_PIN, receivedData == 1 ? HIGH : LOW);
  } else {
    Serial.println("No data received (listening)...");
  }
}