public class Simulation {

    // Number of particles (N), the xy location of each, and color.
    static int N = 10;
    static double[] x;
    static double[] y;
    static boolean[] isRed;

    // The bounds of the region.
    static double size = 10;

    static int numSteps = 100;

    // How close do you have to be to get infected?
    static double infectionDistance = 0.5;


    public static void main (String[] argv)
    {
	DrawTool.display ();
	DrawTool.setXYRange (0, size, 0, size);
	DrawTool.startAnimationMode ();

	initialize ();

	for (int step=1; step<=numSteps; step++) {

	    // Spread.
	    infectionSpread ();

	    // Move each particle and draw
	    for (int i=0; i<N; i++) {
		move (i);
		draw (i);
	    }

	    DrawTool.animationPause (100);
	}

	DrawTool.endAnimationMode ();
    }

    public static int simulateNumSteps (
        int numParticles,               // Desired # particles
        double infDist,                 // Infection distance
        int targetCount)                // Simulate until so many infected.
    {
	// INSERT YOUR CODE HERE

	// Temporarily (so it compiles):
	return -1;
    }

    public static int simulateNumInfected (
        int numParticles,               // Desired # particles
        double infDist,                 // Infection distance
        int desiredNumSteps)            // Simulate for this many steps
    {
	// INSERT YOUR CODE HERE

	// Temporarily (so it compiles):
	return -1;
    }

    static int countInfected ()
    {
	int count = 0;
	for (int i=0; i<N; i++) {
	    if (isRed[i]) {
		count ++;
	    }
	}
	return count;
    }

    static void initialize ()
    {
	// Random initial locations.
	x = makeRandomArray ();
	y = makeRandomArray ();
	
	// Default: all false;
	isRed = new boolean [N];

	// The first particle is infected:
	isRed[0] = true;
    }

    static double[] makeRandomArray ()
    {
	double[] z = new double [N];
	for (int i=0; i<N; i++) {
	    z[i] = 10 * Math.random ();
	}
	return z;
    }

    static void move (int i)
    {
	double xDiff = randomDouble (-1, 1);
	double yDiff = randomDouble (-1, 1);
	if ( withinBounds(x[i]+xDiff, y[i]) ) {
	    x[i] += xDiff;
	}
	if ( withinBounds(x[i], y[i]+yDiff) ) {
	    y[i] += yDiff;
	}
    }

    static void draw (int i)
    {
	if (isRed[i]) {
	    DrawTool.setOvalColor ("red");
	}
	else {
	    DrawTool.setOvalColor ("blue");
	}
	DrawTool.drawCircle (x[i], y[i], 0.1);
    }

    static void infectionSpread ()
    {
	for (int n=0; n<N; n++) {
	    if (! isRed[n]) {
		// See if this blue is near some other red
		for (int m=0; m<N; m++) {
		    if (isRed[m]) {
			// Check distance.
			double d = distance (x[n],y[n], x[m], y[m]);
			if (d < infectionDistance) {
			    isRed[n] = true;
			}
		    }
		}
	    }
	}
    }

    static boolean withinBounds (double x1, double y1)
    {
	if ( (x1 < 0) || (x1 > size) ) {
	    return false;
	}

	if ( (y1 < 0) || (y1 > size) ) {
	    return false;
	}
	
	return true;
    }

    static double distance (double x1, double y1, double x2, double y2)
    {
	return Math.sqrt ((x1-x2)*(x1-x2) + (y1-y2)*(y1-y2));
    }

    static double randomDouble (double low, double high)
    {
	double u = Math.random ();
	double v = low + u * (high-low);
	return v;
    }

    static int randomInt (int low, int high)
    {
	double u = randomDouble (low, high+1);
	int k = (int) Math.floor (u);
	return k;
    }

}