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

LiquidCrystal_I2C lcd(0x27, 20, 4);

const int trigPin = 9;
const int echoPin = 10;
const int greenLED = 6;
const int redLED = 7;
const int buzzer = 8;
const int ldrPin = A0;

long duration;
int distance;
int lightValue;

unsigned long startTime;
unsigned long lastBreakTime = 0;
const unsigned long breakInterval = 120000; // 2 minutes

// --- Helper Function to Draw Labels ---
void printLabels() {
  lcd.setCursor(0, 0);
  lcd.print("Distance: ");

  lcd.setCursor(0, 1);
  lcd.print("Posture: ");

  lcd.setCursor(0, 2);
  lcd.print("Screen Time: ");

  lcd.setCursor(0, 3);
  lcd.print("Light: ");
}

void setup()
{
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  pinMode(greenLED, OUTPUT);
  pinMode(redLED, OUTPUT);
  pinMode(buzzer, OUTPUT);

  lcd.init();
  lcd.backlight();

  startTime = millis();

  lcd.setCursor(0, 0);
  lcd.print("Eye Strain &");
  lcd.setCursor(0, 1);
  lcd.print("Posture Detector");
  delay(2000);
  lcd.clear();

  // Print the static labels ONCE here
  printLabels();
}

void loop()
{
  // -------- Measure Distance --------
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);

  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);

  digitalWrite(trigPin, LOW);

  duration = pulseIn(echoPin, HIGH);
  distance = duration * 0.034 / 2;

  // -------- Read Light --------
  lightValue = analogRead(ldrPin);

  // -------- Screen Time --------
  unsigned long currentTime = millis();
  unsigned long totalSeconds = (currentTime - startTime) / 1000;

  int minutes = totalSeconds / 60;
  int seconds = totalSeconds % 60;

  // -------- Default OFF --------
  digitalWrite(greenLED, LOW);
  digitalWrite(redLED, LOW);
  noTone(buzzer);

  String posture = "GOOD";
  String lightStatus = "SAFE";

  // -------- Posture Check --------
  if (distance <= 45)
  {
    posture = "BAD "; // Added space to ensure it overwrites "GOOD" cleanly
    digitalWrite(redLED, HIGH);
    tone(buzzer, 1000);
  }

  // -------- Light Check --------
  if (lightValue < 200)
  {
    lightStatus = "LOW "; // Added space for clean overwrite

    digitalWrite(redLED, HIGH);
    delay(50);
    digitalWrite(redLED, LOW);
    delay(50);
  
  }
  else if (lightValue > 700)
  {
    lightStatus = "HIGH";

    digitalWrite(redLED, HIGH);
    delay(50);
    digitalWrite(redLED, LOW);
    delay(50);
  
  }
  else
  {
    lightStatus = "SAFE";
  }

  // -------- Ideal Condition --------
  if (distance > 45 && lightValue >= 200 && lightValue <= 700)
  {
    digitalWrite(greenLED, HIGH);
  }

  // -------- Water Break Reminder --------
  if (currentTime - lastBreakTime >= breakInterval)
  {
    lcd.clear();
    lcd.setCursor(0, 0);
    lcd.print("*** WATER BREAK ***");
    lcd.setCursor(0, 1);
    lcd.print("Drink Water");
    lcd.setCursor(0, 2);
    lcd.print("Relax Eyes");

    for (int i = 0; i < 6; i++)
    {
      digitalWrite(greenLED, HIGH);
      digitalWrite(redLED, HIGH);
      tone(buzzer, 1000);
      delay(650);

      digitalWrite(greenLED, LOW);
      digitalWrite(redLED, LOW);
      noTone(buzzer);
      delay(650);
    }

    lastBreakTime = currentTime;
    lcd.clear();

    // Restore the static labels after clearing the screen
    printLabels();
  }

  // -------- Display ONLY Changing Values --------

  // Update Distance (Cursor placed right after "Distance: ")
  lcd.setCursor(10, 0);
  lcd.print(distance);
  lcd.print(" cm  "); // Spaces clear out any leftover digits if distance goes from 100 to 99

  // Update Posture (Cursor placed right after "Posture: ")
  lcd.setCursor(9, 1);
  lcd.print(posture);
  lcd.print("    ");

  // Update Screen Time (Cursor placed right after "Screen Time: ")
  lcd.setCursor(13, 2);
  if (minutes < 10) lcd.print("0");
  lcd.print(minutes);
  lcd.print(":");
  if (seconds < 10) lcd.print("0");
  lcd.print(seconds);
  lcd.print("  ");

  // Update Light Status (Cursor placed right after "Light: ")
  lcd.setCursor(7, 3);
  lcd.print(lightStatus);
  lcd.print("    ");

  delay(200);
}