#define PCELL1_PIN A1
#define LED_PIN 9
#define POT_PIN A0
#define DELAY 525

double lightValue, photocellValue;
bool currState = false, prevState = false, changed = false;

bool dark(){
  return photocellValue < lightValue;
}

void setup() {
  Serial.begin(9600);
  analogWrite(LED_PIN, 0);
}

void loop() {
  photocellValue = analogRead(PCELL1_PIN);
  lightValue = analogRead(POT_PIN);
  Serial.print("Photocell:     "); Serial.println(photocellValue);
  Serial.print("Potentiomater: "); Serial.println(lightValue);

  fadeTrigger();
  checkPhotoCell();
}

void fade(int value){
  if (value == 1){
    for (int i = 0; i < 255; i++) {
      analogWrite(LED_PIN, i+1);
      delay(DELAY/255);

    }
  } else {
    for (int i = 255; i >= 0; i--) {
      analogWrite(LED_PIN, i);
      delay(DELAY/255);

    }
  }
}

void checkPhotoCell(){
  if (dark()) currState = true;
  if (!dark()) currState = false;
  if (currState != prevState) changed = true;
}

void fadeTrigger(){
  if (changed){
    changed = false;
    if (currState){
      fade(1);//fade in
    } else {
      fade(0);//fade out
    }
    prevState = currState;
  }

}