#include <Wire.h>
#include <LiquidCrystal_I2C.h>
#include <Servo.h>

// Pin Definitions
#define TRIG_PIN 9
#define ECHO_PIN 8
#define BUZZER_PIN 10
#define GREEN_LED 5
#define RED_LED 6

// Variables
long duration; // Variable to store the duration of the pulse
float distance; // Distance in "m" (assume cm from sensor equals m for display)

Servo gateServo; // Servo for the gate
LiquidCrystal_I2C lcd(0x27, 16, 2);

void setup() {
  // Pin configuration
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
  pinMode(BUZZER_PIN, OUTPUT);
  pinMode(GREEN_LED, OUTPUT);
  pinMode(RED_LED, OUTPUT);

  // Servo initialization
  gateServo.attach(11); // Attach servo to Pin 11
  gateServo.write(0);   // Gate starts open (0°)

  // LCD initialization
  lcd.init();
  lcd.backlight();
  lcd.setCursor(0, 0);
  lcd.print("Runway Safety");
  lcd.setCursor(0, 1);
  lcd.print("System Ready!");
  delay(2000);
  lcd.clear();
}

void loop() {
  distance = measureDistance();

  if (distance <= 100) { 
    alertMode(); // If an obstacle is detected
  } else { 
    clearMode(); // If the runway is clear
  }

  delay(100);
}

float measureDistance() {
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);

  duration = pulseIn(ECHO_PIN, HIGH); // Measure the time for echo
  float cm = duration * 0.034 / 2;    // Convert to cm
  return cm; // Return distance in cm, treated as m for display
}

void alertMode() {
  // Buzzer beeps repeatedly
  for (int i = 0; i < 3; i++) { // 3 beeps
    digitalWrite(BUZZER_PIN, HIGH);
    delay(200); // Sound for 200ms
    digitalWrite(BUZZER_PIN, LOW);
    delay(200); // Pause for 200ms
  }

  digitalWrite(RED_LED, HIGH);   // Red LED turns on
  digitalWrite(GREEN_LED, LOW);  // Green LED turns off
  gateServo.write(90);           // Close the gate (90°)

  lcd.setCursor(0, 0);
  lcd.print("ObstacleDetected");
  lcd.setCursor(0, 1);
  lcd.print("Distance: ");
  lcd.print((int)distance); // Treat cm as m and display as an integer
  lcd.print("m");
}

void clearMode() {
  digitalWrite(BUZZER_PIN, LOW); // Buzzer stops sounding
  digitalWrite(RED_LED, LOW);   // Red LED turns off
  digitalWrite(GREEN_LED, HIGH); // Green LED turns on
  gateServo.write(0);           // Open the gate (0°)

  lcd.setCursor(0, 0);
  lcd.print("Runway Clear    ");
  lcd.setCursor(0, 1);
  lcd.print("Distance: ");
  lcd.print((int)distance); // Treat cm as m and display as an integer
  lcd.print("m");
}