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

LiquidCrystal_I2C lcd(0x27, 20, 4);

const bool SENSOR_INVERTED = true;

const int lightPin = 2;    
const int buttonPin = 3;   
const int led1 = 4;        
const int buzzer1 = 6;
const int buzzer2 = 7;
const int buzzer3 = 8;

const int freq1 = 1000;  
const int freq2 = 1500;  
const int freq3 = 2000;  

bool systemActive = true;
bool lastButtonState = HIGH;

unsigned long previousMillis = 0;
const long buzzerInterval = 500; 
int buzzerStep = 0;

// BACKLIGHT CONTROL
unsigned long lastLightDetectedTime = 0;
const unsigned long backlightTimeout = 3000; 

void setup() {
  pinMode(lightPin, INPUT_PULLUP);
  pinMode(buttonPin, INPUT_PULLUP);
  pinMode(led1, OUTPUT);
  pinMode(buzzer1, OUTPUT);
  pinMode(buzzer2, OUTPUT);
  pinMode(buzzer3, OUTPUT);

  lcd.init();
  lcd.backlight();
  lcd.clear();
  lcd.setCursor(0,0);
  lcd.print(" Security System ");
  delay(1500);
  lcd.clear();

  digitalWrite(led1, HIGH); // system armed by default
}

void turnBuzzersOff() {
  noTone(buzzer1);
  noTone(buzzer2);
  noTone(buzzer3);
}

void cycleBuzzers() {
  unsigned long currentMillis = millis();
  if(currentMillis - previousMillis >= buzzerInterval){
    previousMillis = currentMillis;
    buzzerStep = (buzzerStep + 1) % 3;

    turnBuzzersOff();

    if(buzzerStep == 0) tone(buzzer1, freq1);
    else if(buzzerStep == 1) tone(buzzer2, freq2);
    else tone(buzzer3, freq3);
  }
}

void loop() {
  unsigned long currentMillis = millis();

  // -------- BUTTON TOGGLE --------
  bool buttonState = digitalRead(buttonPin);
  if(buttonState == LOW && lastButtonState == HIGH){
    systemActive = !systemActive; 
    lcd.backlight(); // turn backlight on when button pressed
    lcd.clear();
    lastLightDetectedTime = currentMillis; // reset backlight timer
    delay(200); // simple debounce
  }
  lastButtonState = buttonState;

  digitalWrite(led1, systemActive ? HIGH : LOW);

  // -------- READ LIGHT SENSOR --------
  int rawLight = digitalRead(lightPin);
  bool lightDetected = SENSOR_INVERTED ? (rawLight == LOW) : (rawLight == HIGH);

  // reset backlight timer if light detected
  if(lightDetected) {
    lcd.backlight();
    lastLightDetectedTime = currentMillis;
  }

  // -------- BACKLIGHT TIMEOUT --------
  if(currentMillis - lastLightDetectedTime >= backlightTimeout){
    lcd.noBacklight();
  }

  // -------- SYSTEM DISARMED --------
  if(!systemActive){
    turnBuzzersOff();
    lcd.setCursor(0,0);
    lcd.print(" SYSTEM DISARMED    ");
    lcd.setCursor(0,1);
    lcd.print(" no alarm ");
    lcd.setCursor(0,2);
    lcd.print(" Press button to ARM ");
    return;
  }

  // -------- NO LIGHT DETECTED --------
  if(!lightDetected){
    turnBuzzersOff();
    lcd.setCursor(0,0);
    lcd.print("      SECURED       ");
    lcd.setCursor(0,1);
    lcd.print("   No Activity      ");
    lcd.setCursor(0,2);
    lcd.print("   DOOR CLOSED      ");
    lcd.setCursor(0,3);
    lcd.print("System: ARMED       ");
  }
  // -------- LIGHT DETECTED (ALARM) --------
  else{
    lcd.setCursor(0,0);
    lcd.print("    DOOR OPENED     ");
    lcd.setCursor(0,1);
    lcd.print(" UNAUTHORIZED USE   ");

    cycleBuzzers();
    lcd.setCursor(0,2);
    if(buzzerStep == 0) lcd.print("Buzzer 1 ACTIVE      ");
    else if(buzzerStep == 1) lcd.print("Buzzer 2 ACTIVE      ");
    else lcd.print("Buzzer 3 ACTIVE      ");

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