// Class definition for LineSegment

import java.awt.*;
import java.util.*;

public class LineSegment {

    LSPoint p1, p2;
    int id;
    LineSegmentCollection collection;
    Vector intersections;
    public LSPoint getP1() { return p1; }
    public LSPoint getP2() { return p2; }

    public LineSegment(int anID, LineSegmentCollection theCollection) {
        id = anID;
        collection = theCollection;
        p1 = new LSPoint();
        p2 = new LSPoint();
        computeIntersections();
    }

    public void paint(Graphics g) {
        g.drawLine(p1.getX(), p1.getY(), p2.getX(), p2.getY());
        plotIntersections(g);
    }

    public void computeIntersections() {
        intersections = new Vector();
        for (Enumeration segments = 
                (collection.otherSegments(this)).elements();
             segments.hasMoreElements();) {
            LineSegment aLineSeg = (LineSegment) segments.nextElement();
	    LSPoint p = segIntersection(aLineSeg);
	    //System.out.println("Intersection of lines is: (" + p.getX()
	    //		       + ", " + p.getY() + ")" );
            if (p != null) intersections.addElement(p);
        }
    }

    private LSPoint segIntersection(LineSegment ls) {
        LSPoint p3 = ls.getP1();
        LSPoint p4 = ls.getP2();
        int x1 = p1.getX();
        int y1 = p1.getY();
        int x2 = p2.getX();
        int y2 = p2.getY();
	int x3 = p3.getX();
        int y3 = p3.getY();
	int x4 = p4.getX();
        int y4 = p4.getY();
        double d1 = (x1 * y2) - (x2 * y1);
        double d2 = (x3 * y4) - (x4 * y3);
        double d3 = ((x1 - x2)  * (y3 - y4)) - ((x3 - x4) * (y1 - y2));
	int x = (int) (((d1 * (x3 - x4)) - (d2 * (x1 - x2))) / d3);
        int y = (int) (((d1 * (y3 - y4)) - (d2 * (y1 - y2))) / d3);

        
        int minx1 = Math.min(x1, x2);
        if (x < minx1) return null;
        int maxx1 = Math.max(x1, x2);
        if (x > maxx1) return null;
        int miny1 = Math.min(y1, y2);
        if (y < miny1) return null;
        int maxy1 = Math.max(y1, y2);
        if (y > maxy1) return null;
        int minx2 = Math.min(x3, x4);
        if (x < minx2) return null;
        int maxx2 = Math.max(x3, x4);
        if (x > maxx2) return null;
        int miny2 = Math.min(y3, y4);
        if (y < miny2) return null;
        int maxy2 = Math.max(y3, y4);
        if (y > maxy2) return null;
        return new LSPoint(x, y);
    }

    private void plotIntersections(Graphics g) {
        for (Enumeration intPoints = 
                intersections.elements();
             intPoints.hasMoreElements();) {
            LSPoint p = (LSPoint) intPoints.nextElement();
            int x = p.getX();
            int y = p.getY();
            int radius = 5;
	    g.fillOval(x - radius, y - radius, 2 * radius, 2 * radius);
	}
    }
}