package ac.essex.ooechs.imaging.commons.util; 
 
/** 
 * Finds the equation of a line. Once two line equations are found, the 
 * intersection between them can be discovered. 
 */ 
public class LineEquation implements Comparable { 
 
    protected double m, c; 
 
    public static void main(String[] args) { 
 
        LineEquation l1 = new LineEquation(-3, -3, 4, 4); 
 
        LineEquation l2 = new LineEquation(-4, 4, 3, 0); 
 
        l1.getIntersectionWith(l2); 
 
    }         
 
    public LineEquation(double m, double c) { 
        this.m = m; 
        this.c = c; 
    } 
 
    public LineEquation(double x1, double y1, double x2, double y2) { 
 
        if (x1 == x2) { 
            throw new RuntimeException("Cannot calculate line equation - x1 and x2 values must be different"); 
        } 
 
        double dx = x2 - x1; 
        double dy = y2 - y1; 
 
        m = dy / dx; 
        c = y1 - (m * x1); 
 
    } 
 
    /** 
     * Returns the intersection between two line equations. 
     * @param other Another line equation. 
     * @return 
     */ 
    public double[] getIntersectionWith(LineEquation other) { 
 
        double x = (other.c - c) / (m - other.m); 
 
        double y1 = getY(x); 
 
        return new double[]{x, y1}; 
 
    } 
 
    public void setM(double m) { 
        this.m = m; 
    } 
 
    public void setC(double c) { 
        this.c = c; 
    } 
 
    public double getM() { 
        return m; 
    } 
 
    public double getC() { 
        return c; 
    } 
 
    public double getY(double x) { 
        return (m * x) + c; 
    } 
 
    public double getX(double y) { 
        return (y - c)  / m; 
    } 
 
    /** 
     * Returns a metric of how similar the two line equations are. 
     * @param other 
     * @return 
     */ 
    public double getSimilarity(LineEquation other) { 
        double dm = Math.abs(other.m - m) / Math.max(Math.abs(other.m), Math.abs(m)); 
        double dc = Math.abs(other.c - c) / Math.max(Math.abs(other.c), Math.abs(c)); 
        return dm + dc; 
    } 
 
    public LineEquation getPerpendicular() { 
        return new LineEquation(-1/m, c); 
    } 
 
    public int compareTo(Object o) { 
        LineEquation other = (LineEquation) o; 
        if (other.c > c) return +1; 
        if (other.c < c) return -1; 
        return 0; 
    } 
}