package de.intevation.flys.geom;

import java.awt.geom.Point2D;

public final class VectorUtils
{
    public static final double EPSILON = 1e-4;

    private VectorUtils() {
    }

    private static final double X(Point2D p) {
        return p.getX();
    }

    private static final double Y(Point2D p) {
        return p.getY();
    }

    public static final Point2D sub(Point2D a, Point2D b) {
        return new Point2D.Double(X(a)-X(b), Y(a)-Y(b));
    }

    public static final double dot(Point2D a, Point2D b) {
        return X(a)*X(b) + Y(a)*Y(b);
    }

    public static final Point2D add(Point2D a, Point2D b) {
        return new Point2D.Double(X(a)+X(b), Y(a)+Y(b));
    }

    public static final Point2D negate(Point2D a) {
        return new Point2D.Double(-X(a), -Y(a));
    }

    public static final Point2D ortho(Point2D a) {
        return new Point2D.Double(-Y(a), X(a));
    }

    public static final Point2D scale(Point2D a, double s) {
        return new Point2D.Double(s*X(a), s*Y(a));
    }

    public static final double lengthSq(Point2D a) {
        double x = X(a);
        double y = Y(a);
        return x*x + y*y;
    }

    public static final double length(Point2D a) {
        return Math.sqrt(lengthSq(a));
    }

    public static final Point2D normalize(Point2D a) {
        double length = length(a);
        return length != 0d
            ? scale(a, 1d/length) 
            : new Point2D.Double(X(a), Y(a));
    }

    public static final double L1(Point2D a, Point2D b) {
        return Math.abs(X(a)-X(b)) + Math.abs(Y(a)-Y(b));
    }

    public static final boolean collinear(Point2D a, Point2D b, Point2D c) {
        double x1 = X(a);
        double y1 = Y(a);
        double x2 = X(b);
        double y2 = Y(b);
        double x3 = X(c);
        double y3 = Y(c);

        return Math.abs((x2-x1)*(y3-y1)-(y2-y1)*(x3-x1)) < EPSILON;
    }

    public static boolean epsilonEquals(Point2D a, Point2D b) {
        return Math.abs(X(a)-X(b)) < EPSILON 
            && Math.abs(Y(a)-Y(b)) < EPSILON;
    }

}
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