int LED_1 = 2;
const int LED_2 = 4;
const int LED_3 = 7;
const int LED_4 = 8;
const int LED_5 = 12;
const int LED_6 = 13;

const int LED_array[6] = {LED_1, LED_2, LED_3, LED_4, LED_5, LED_6};
int LED_state[6] = {LOW, LOW, LOW ,LOW, LOW, LOW}; //states
unsigned long LED_millis[6] = {0,0,0,0,0,0}; //delay
unsigned long LED_interval; //currentMillis - LED_millis[LED_idx];
int LED_idx = 0;
int LED_dir = 1;
int LED_onTime;

// the setup routine runs once when you press reset:
void setup() {
  // initialize serial communication at 9600 bits per second:
  pinMode(LED_1, OUTPUT);
  pinMode(LED_2, OUTPUT);
  pinMode(LED_3, OUTPUT);
  pinMode(LED_4, OUTPUT);
  pinMode(LED_5, OUTPUT);
  pinMode(LED_6, OUTPUT);
  Serial.begin(9600); //remove if not print
}

// the loop routine runs over and over again forever:
void loop() {


  // read the input on analog pin 0:
  int sensorValue = analogRead(A0);
  // print out the value you read:
  Serial.println(sensorValue); //remove if not print

  //check LED_spd, LED_dir
  if (sensorValue < 300){
    LED_dir = 1;
    LED_onTime = 40;
  }
  else if (sensorValue <723){
    LED_onTime = 100;
  }
  else{
    LED_dir = -1;
    LED_onTime = 40;
  }

  //Check LED_idx
  if (LED_dir == 1 && LED_idx > 5){
    LED_idx = 0;
  }
  else if(LED_dir == -1 && LED_idx < 0){
    LED_idx = 5;
  }

  unsigned long currentMillis = millis();

  LED_interval = currentMillis - LED_millis[LED_idx];

  if ( LED_state[LED_idx] == HIGH  && LED_interval >= LED_onTime){
    LED_state[LED_idx] = LOW;
    LED_millis[LED_idx] = currentMillis;
    digitalWrite(LED_array[LED_idx], LOW);
    LED_idx += LED_dir;
  }
  else if ( LED_state[LED_idx] == LOW){
    LED_state[LED_idx] = HIGH;
    LED_millis[LED_idx] = currentMillis;
    digitalWrite(LED_array[LED_idx], HIGH);
  }
}