// linebot2.nqc
//    automatic thresholds

// sensor and motors
#define EYE     SENSOR_2
#define LEFT    OUT_A
#define RIGHT   OUT_C


// use variables for thresholds
int tooDark;
int tooBright;


void setup()
{
 int delta;
    // remember bright value
    tooBright = EYE;
    PlaySound(SOUND_UP);
    
    // wait 3 seconds
    Wait(300);
    
    // get dark value
    tooDark = EYE;
    
    // move values in
    delta = (tooBright - tooDark) / 3;
    tooDark = tooDark + delta;
    tooBright = tooBright - delta;
}


task main()
{
    SetSensor(EYE, SENSOR_LIGHT);
    
    setup();

    On(LEFT+RIGHT);

    while(true)
    {
        if (EYE <= tooDark)
        {
            Off(LEFT);
            On(RIGHT);
        }
        else if (EYE >= tooBright)
        {
            Off(RIGHT);
            On(LEFT);
        }
        else
        {
            On(LEFT+RIGHT);
        }
    }
}