/*  Programming Mobile Robots
	 Example program for line following and bumper sensing
	 Raul Trejo, 
	 Spring 1999  */

/* global variables to identify sensor conections */

int LEFT_BUMP=7, RIGHT_BUMP=8;
int LEFT_LINE=1, RIGHT_LINE=0;
int LINE_TRESHOLD = 208; /*treshold for photo sensors*/

int LEFT_MOTOR =0, RIGHT_MOTOR=1;
int FORWARD_SPEED=60;
int BACK_SPEED= -60;
float TURN_DELAY= 2.0;

/* functions to get impact readings from the bumpers*/

/*return true if left bumper hits something*/
int left_bump()
 {return digital(LEFT_BUMP); 
 }

/*same for right bumper*/
int right_bump()
  {return digital(RIGHT_BUMP); 
  }

/* return true if we have hit a wall */
int bump_on_a_wall()
  {
   return left_bump() || right_bump();
  }
 
/* functions for reading photosensors on the floor */

/* return true if left sensor is over a black line */
int left_on_line()
 {
  return analog(LEFT_LINE) > LINE_TRESHOLD;
 }

 /*same for right sensor*/
int right_on_line()
 {
  return analog(RIGHT_LINE) > LINE_TRESHOLD;
 }

/* behaviour of the robot 
   follow the line, stop if the robot hits an obstacle*/
void main()
 {
  printf("press start to begin \n");
  start_press();
  motor(LEFT_MOTOR, FORWARD_SPEED);
  motor(RIGHT_MOTOR, FORWARD_SPEED);
  while(!bump_on_a_wall())
    {
     if(left_on_line())
       {motor(LEFT_MOTOR, BACK_SPEED);
        sleep(TURN_DELAY);
        motor(LEFT_MOTOR, FORWARD_SPEED);
       }
     if(right_on_line())
       {motor(RIGHT_MOTOR, BACK_SPEED);
        sleep(TURN_DELAY);
        motor(RIGHT_MOTOR, FORWARD_SPEED);
       }
    }
  ao();
  beep();
  printf("It's over!");
 }