#include <LiquidCrystal_I2C.h>

#define LDR_PIN A0

// LDR Characteristics
const float GAMMA = 0.7;
const float RL10 = 50;

LiquidCrystal_I2C lcd(0x27, 20, 4);

void setup() {
  pinMode(LDR_PIN, INPUT);

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

int getLightState(float lux) {
  if (lux <= 50 ) {
    return 0;
  } else if (lux <= 200) {
    return 1;
  } else if (lux <= 400) {
    return 2;
  } else {
    return 3;
  }
}

void loop() {
  int analogValue = analogRead(A0);
  float voltage = analogValue / 1024. * 5;
  float resistance = 2000 * voltage / (1 - voltage / 5);
  float lux = pow(RL10 * 1e3 * pow(10, GAMMA) / resistance, (1 / GAMMA));

  int currentState = getLightState(lux);

  lcd.setCursor(0, 0);
  lcd.print("Room: ");

  if (currentState == 0) {
    lcd.print("Dark  ");
  }
  else if (currentState == 1) {
    lcd.print("Low  ");
  }
  else if (currentState == 2) {
    lcd.print("Dim  ");
  }
  else if (currentState == 3) {
    lcd.print("Bright ");
  }

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

  delay(10);
}