int photoCellPin = A0;

// Create a variable to hold the light reading
int photoCellReading = 0;

// Define a pin we'll place an LED on
int ledPin = D2;

// Create a variable to store the LED brightness.
int ledBrightness = 0;

void setup() {
    pinMode(ledPin, OUTPUT);
    
    // Create a cloud variable of type integer
    // called 'light' mapped to photoCellReading
    Particle.variable("light", &photoCellReading, INT);
}

void loop() {
    // Use analogRead to read the photo cell reading
    // This gives us a value from 0 to 4095
    photoCellReading = analogRead(photoCellPin);
    
    // Map this value into the PWM range (0-255)
    // and store as the led brightness
    ledBrightness = map(photoCellReading, 0, 4095, 255, 0);
    
    // fade the LED to the desired brightness
    analogWrite(ledPin, ledBrightness);
    
    // wait 1/10th of a second and then loop
    delay(100);
}