int ledPin = D2;
int switchPin = D4;
int switchState; //store the reading from the button 
int switchState_prev = LOW;

int photoresPin = A4;
int photoresRead = 0;

void setup() {
    
    //Set the LED as Output
    pinMode(ledPin, OUTPUT);
    
    //Set the switch as input
    pinMode (switchPin, INPUT_PULLUP); 
    
    Particle.variable("photoResValue", photoresRead);
    
}

void loop() {
    
    switchState = digitalRead( switchPin );
    
    
    if(switchState == HIGH){
        
        
        // added the below code to make sure publish happens only when..
        // switch state changes from previous state
        if (switchState != switchState_prev){
            Particle.publish( "Switch ON" );
        }
        switchState_prev = switchState;
        
        //0-4095
         photoresRead = analogRead(photoresPin);
    
        //using map function to convert the range
        int brightness = map(photoresRead, 0 , 4095, 0, 255 );
    
        analogWrite( ledPin, brightness );
    
        delay(200);
    
    }else{
        
        if (switchState != switchState_prev){
             Particle.publish( "Switch OFF" );
        }
        switchState_prev = switchState;
        
        
        int brightness = 0;
        analogWrite( ledPin, brightness );
        
    }

}