// ESP32 LED + Buzzer + Ultrasonic Sensor Distance Alert System
// LED: GPIO 12, Buzzer: GPIO 13, Ultrasonic Trig: GPIO 14, Echo: GPIO 15

#define LED_PIN 12
#define BUZZER_PIN 13
#define TRIG_PIN 14
#define ECHO_PIN 15

// Distance thresholds in cm
#define FAR_THRESHOLD 30
#define MEDIUM_THRESHOLD 20
#define CLOSE_THRESHOLD 10

// Timing variables
unsigned long previousMillis = 0;
unsigned long buzzerPreviousMillis = 0;
bool ledState = false;
bool buzzerState = false;

void setup() {
  // Initialize pins
  pinMode(LED_PIN, OUTPUT);
  pinMode(BUZZER_PIN, OUTPUT);
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
  
  // Initialize serial communication
  Serial.begin(115200);
  Serial.println("ESP32 Distance Alert System Started");
  
  // Ensure devices start in OFF state
  digitalWrite(LED_PIN, LOW);
  digitalWrite(BUZZER_PIN, LOW);
}

void loop() {
  float distance = getDistance();
  
  // Print distance for debugging
  Serial.print("Distance: ");
  Serial.print(distance);
  Serial.println(" cm");
  
  // Control LED and buzzer based on distance
  if (distance > FAR_THRESHOLD) {
    // No activity for distances > 30cm
    digitalWrite(LED_PIN, LOW);
    digitalWrite(BUZZER_PIN, LOW);
    Serial.println("Status: Safe distance - No alerts");
    
  } else if (distance > MEDIUM_THRESHOLD && distance <= FAR_THRESHOLD) {
    // 20-30cm: Slow LED blinking, no buzzer
    slowLedBlink();
    digitalWrite(BUZZER_PIN, LOW);
    Serial.println("Status: Medium distance - Slow LED blink");
    
  } else if (distance > CLOSE_THRESHOLD && distance <= MEDIUM_THRESHOLD) {
    // 10-20cm: Fast LED blinking + slow buzzer beeps
    fastLedBlink();
    slowBuzzerBeep();
    Serial.println("Status: Close distance - Fast LED + Slow buzzer");
    
  } else if (distance <= CLOSE_THRESHOLD) {
    // < 10cm: Constant buzzer + very fast LED blinking
    veryFastLedBlink();
    digitalWrite(BUZZER_PIN, HIGH);
    Serial.println("Status: Very close - Constant buzzer + Very fast LED");
  }
  
  delay(50); // Small delay for stability
}

float getDistance() {
  // Send ultrasonic pulse
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);
  
  // Read echo pulse duration
  long duration = pulseIn(ECHO_PIN, HIGH);
  
  // Calculate distance in cm (speed of sound = 343 m/s)
  float distance = (duration * 0.034) / 2;
  
  // Return 400 if no echo received (out of range)
  if (distance == 0) {
    return 400;
  }
  
  return distance;
}

void slowLedBlink() {
  unsigned long currentMillis = millis();
  if (currentMillis - previousMillis >= 1000) { // 1 second interval
    previousMillis = currentMillis;
    ledState = !ledState;
    digitalWrite(LED_PIN, ledState);
  }
}

void fastLedBlink() {
  unsigned long currentMillis = millis();
  if (currentMillis - previousMillis >= 300) { // 300ms interval
    previousMillis = currentMillis;
    ledState = !ledState;
    digitalWrite(LED_PIN, ledState);
  }
}

void veryFastLedBlink() {
  unsigned long currentMillis = millis();
  if (currentMillis - previousMillis >= 100) { // 100ms interval
    previousMillis = currentMillis;
    ledState = !ledState;
    digitalWrite(LED_PIN, ledState);
  }
}

void slowBuzzerBeep() {
  unsigned long currentMillis = millis();
  if (currentMillis - buzzerPreviousMillis >= 800) { // 800ms interval
    buzzerPreviousMillis = currentMillis;
    buzzerState = !buzzerState;
    digitalWrite(BUZZER_PIN, buzzerState);
  }
}