#define TRIG_PIN 7            
#define ECHO_PIN 6            
#define LED_PIN 11            
#define BUTTON_PIN 4          

const int safeDistance = 30;     
const int maxSpeed = 255;        
const int minSpeed = 50;         

bool accEnabled = false;         

void setup() {
  pinMode(TRIG_PIN, OUTPUT);     
  pinMode(ECHO_PIN, INPUT);      
  pinMode(LED_PIN, OUTPUT);      
  pinMode(BUTTON_PIN, INPUT_PULLUP); 

  Serial.begin(9600);            
}

void loop() {
  if (digitalRead(BUTTON_PIN) == LOW) {
    accEnabled = true;  
  } else {
    accEnabled = false; 
  }

  if (accEnabled) {
    int distance = getDistance(); 

    if (distance < safeDistance) {
      digitalWrite(LED_PIN, HIGH); 
      analogWrite(LED_PIN, 0);     
      Serial.print("Distance: ");
      Serial.print(distance);
      Serial.print(" cm, Throttle: 0\n");
    } else {
      digitalWrite(LED_PIN, LOW);  
      int throttleSpeed = map(distance, safeDistance, 200, minSpeed, maxSpeed); 
      throttleSpeed = max(minSpeed, throttleSpeed); 
      analogWrite(LED_PIN, throttleSpeed); 
      Serial.print("Distance: ");
      Serial.print(distance);
      Serial.print(" cm, Throttle: ");
      Serial.println(throttleSpeed);  
    }

    delay(500);  
  } else {
    digitalWrite(LED_PIN, LOW); 
    analogWrite(LED_PIN, 0); 
  }
}

int getDistance() {
  long duration, distance;
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);
  
  duration = pulseIn(ECHO_PIN, HIGH);
  distance = (duration * 0.034) / 2;
  
  return distance;
}