int LED = 13;
int OFF = 0;
int ON = 1;
int AUTO = 2;

const int THRESHOLD = 50;

const float GAMMA = 0.7;
const float RL10 = 50;

unsigned long previousMillis = 0;

void setup() {
  pinMode(LED, OUTPUT);
  pinMode(OFF, INPUT_PULLUP);
  pinMode(ON, INPUT_PULLUP);
  pinMode(AUTO, INPUT_PULLUP);
}

void loop() {
  if (digitalRead(OFF)) {
    digitalWrite(LED, LOW);
    return;
  }
  
  if (digitalRead(ON)) {
    digitalWrite(LED, HIGH);
    return;
  }

  unsigned long currentMillis = millis();

  if (currentMillis - previousMillis > 300) {
    previousMillis = currentMillis;

    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));

    if (lux < THRESHOLD) {
      digitalWrite(LED, HIGH);
    }
    else {
      digitalWrite(LED, LOW);
    }
  }

}