const int PINS[]={12,11,10};
unsigned long StartTime,CurrentTime,Duration=1500;
bool BuzzerOn=false,LED_On=false;

void setup() {
  for (int j=0; j<3; j++){
    pinMode(PINS[j], OUTPUT);
  }
  analogWrite(PINS[2], 236);
  StartTime=millis();
  Serial.begin(9600);
  Serial.println("Choose an option from below:\n1. Toggle Buzzer ON/OFF\n2. Increase speed of Purple LED\n3. Decrease speed of Purple LED\n4. Toggle brightness of blue LED HIGH/LOW\n");
}

void loop() {
  //Ensure LED 2 is always blinking
  CurrentTime=millis();
  if ((CurrentTime-StartTime) >= Duration){
    digitalWrite(PINS[1],!digitalRead(PINS[1])); //reverse the state of the second LED
    StartTime=CurrentTime;
  }
  //checking user input
  if (Serial.available()){
    switch(Serial.read()){
      //Option 1
      case '1':
        if (BuzzerOn==false){
          tone(PINS[0],1000);
          BuzzerOn=true;
        }
        else{
          noTone(PINS[0]);
          BuzzerOn=false;
        }
        break;
      //Option 2
      case '2':
        if (Duration>=200){
          Duration=Duration-100;
        }
        break;
      //Option 3
      case '3':
         Duration=Duration+100;
         break;
      //Option 4
      case '4':
        if (LED_On==false){
          LED_On=true;
          analogWrite(PINS[2],236);
        }
        else{
          LED_On=false;
          analogWrite(PINS[2],5);
        }
    }
  }
}