int trig = 3;
int echo = 4;
int led = 7;
int leftSensor = 5;
int rightSensor = 6;
int light_init = 0;

void forward() {
  digitalWrite(8,LOW);
  digitalWrite(11,HIGH);
  digitalWrite(10,HIGH);
  digitalWrite(12,LOW);
}

void backward() {
  digitalWrite(8,HIGH);
  digitalWrite(11,LOW);
  digitalWrite(10,LOW);
  digitalWrite(12,HIGH);
}

void rightTurn() {
  digitalWrite(8,LOW);
  digitalWrite(11,HIGH);
  digitalWrite(10,LOW);
  digitalWrite(12,LOW);
  delay(300);
  stop();
}

void leftTurn() {
  digitalWrite(8,LOW);
  digitalWrite(11,LOW);
  digitalWrite(10,HIGH);
  digitalWrite(12,LOW);
  delay(300);
  stop();
}

void forwardLeft() {
  digitalWrite(8,LOW);
  digitalWrite(11,HIGH);
}

void backwardLeft() {
  digitalWrite(8,HIGH);
  digitalWrite(11,LOW);
}

void backwardRight() {
  digitalWrite(10,LOW);
  digitalWrite(12,HIGH);
}

void forwardRight() {
  digitalWrite(10,HIGH);
  digitalWrite(12,LOW);
}

void stop() {
  digitalWrite(8,LOW);
  digitalWrite(11,LOW);
  digitalWrite(10,LOW);
  digitalWrite(12,LOW);
}

void setup() {
  pinMode(trig, OUTPUT);
  pinMode(echo, INPUT);
  pinMode(led, OUTPUT);
  
  pinMode(leftSensor, INPUT);
  pinMode(rightSensor, INPUT);
  
  pinMode(8, OUTPUT);
  pinMode(11, OUTPUT);
  pinMode(10, OUTPUT);
  pinMode(12, OUTPUT);
  
  pinMode(2, INPUT);

  pinMode(A0, INPUT_PULLUP);
  pinMode(A1, INPUT_PULLUP);

  Serial.begin(9600);

  //- get initial light intensity of room
  light_init = analogRead(A0);
}

void loop() {

    //- wait for button press before doing anything
    while (digitalRead(2) == HIGH) {
      //- do nothing
    }
    delay(500);

    //- loop here forever after the button is pressed
    while (true) {
      // Code for light following
      
      //- Darkest: Analog Value = 255;
      //- Brightest: Analog Value = 0;
            
      int left_light = analogRead(A0);
      int right_light = analogRead(A1);
      
      Serial.print("Left Light Value:" );
      Serial.println(left_light);
      Serial.print("Right Light Value:" );
      Serial.println(right_light);

      //- turn right if light is more intense on the right
      if (right_light < light_init - 10 && left_light < right_light - 10) {
        backwardLeft();
        forwardRight();
      }
      //- turn left if light is more intense on the left
      else if (left_light < light_init - 10 && right_light < left_light - 10) {
        backwardRight();
        forwardLeft();
      }
      //- go forward if light is evenly intense on both sides
      else if (left_light < light_init - 10 && right_light < light_init - 10) {
        forward();
      }
      //- don't move if light is not intense at all
      else {
        stop();
      }
    }
}