/* I am a point in two space.  I am represented in cartesian coordinates, but I can answer my polar coordinates.  I am immutable. */

public class TwoDPoint
{

	/* Create a point in cartesian (x,y) or polar (r,theta) coordinates, depending on the specified type.  Angles are specified in radians. */

	public TwoDPoint (double arg1, double arg2, int type)
	{
		if (type == CARTESIAN)
		{
			x = arg1;
			y = arg2;
		}
		else if (type == POLAR)
		{
			x = arg1 * Math.cos (arg2);
			y = arg1 * Math.sin (arg2);
		}
		else
			throw new Error ("unknown point type");
	}

	/* Cartesian accessors. */
	public double getX () {return x;}
	public double getY () {return y;}

	/* Polar radius accessor. */

	public double getR ()
	{
		return Math.sqrt (x * x + y * y);
	}

	/* Polar angle accessor.  Answer the angle the receiver makes with origin in radians.  Result will be between 0 and 2*pi radians.  Right is 0.  Up or down, depending on your coordinate system, is pi/2 (90 degrees).  When using the standard trig coordinate system, angles increase counter-clockwise from right.  When using the standard computer coordinate system, angles increase clockwise from right. */

	public double getTheta ()
	{
		if (x == 0)
		{
			if (y >= 0)
				return Math.PI * 0.5;
			else
				return Math.PI * 1.5;
		}
		double result = Math.atan (y / x);
		if (x < 0)
			result += Math.PI;
		else
		{
			if (result < 0)
				result += Math.PI * 2;
		}
		return result;
	}

	/* Euclidean distance metric. */

	public double distanceTo (TwoDPoint p)
	{
		double dx = getX () - p.getX ();
		double dy = getY () - p.getY ();
		return Math.sqrt (dx * dx + dy * dy);
	}

	/* Vector angle between two points. */

	public double angleTo (TwoDPoint p)
	{
		double dx = getX () - p.getX ();
		double dy = getY () - p.getY ();
		TwoDPoint delta = new TwoDPoint (dx, dy, CARTESIAN);
		return delta.getTheta ();
	}

	private double x;
	private double y;

	public final static int CARTESIAN = 0;
	public final static int POLAR = 1;
}