import java.awt.*;
import java.net.*;
import java.applet.Applet;
//import jahuwaldt.gui.*;

/**
 *	Applet to calculate the equation of a line from two input points.  This
 *	is the 1st Applet I've ever written.
 *
 *	<p>	Modified by:	Joseph A. Huwaldt		</p>
 *
 *	@author	Joseph A. Huwaldt	Date:	November 22, 1997
 *	@version	November 26, 2003
 **/
public class LineEquation extends Applet {
	static final short	fWidth = 290;	//	Application frame width & height.
	static final short	fHeight = 200;
	
//	Define class variables here.
	Label		yeqlabel, xeqlabel;		//	Y equation and X equation output labels.
	ParamInput	x1pi, y1pi, x2pi, y2pi;	//	Input panels for this program.
	

	//-----------------------------------------------------------------------------------
	/**
	*	This is the "main" routine that is called when an application first
	*   starts up.  This routine instantiates the applet when using this
	*   object as an application.  If you are using this object as an applet
	*   then this routine is never called.		</p>
	*
	*	@param	args:	The arguments passed to the main routine from the command line.
	**/
	public static void main (String args[]) {
		Frame frame = new Frame("Linear Equation Calculator");
		
		frame.setSize(fWidth, fHeight);
		frame.setLocation(20,15);

		LineEquation applet1 = new LineEquation();
		
		frame.add("Center", applet1);
		
		applet1.init();
		applet1.start();
		
		frame.show();
		
	}	//	end main()
	
	
	/**
	*	Reads the inputs from the TextFields and calculates the
	*   new line equations.  These equations are then output in
	*   the x & y equation labels.
	**/
	void CalcLineEq() {
		float	x1,y1, x2,y2;
		float	m,b;			//	Line equation parameters
		String	aString;
		
		
		//	First read in the input values.
		try {
			x1 = x1pi.getInput();
			y1 = y1pi.getInput();
			x2 = x2pi.getInput();
			y2 = y2pi.getInput();
			
			//	Check to see if any inputs are "blank".
			if (Float.isNaN(x1) || Float.isNaN(y1) || Float.isNaN(x2) || Float.isNaN(y2) )
				throw new NumberFormatException();
				
		} catch (NumberFormatException e) {
			yeqlabel.setText("Error: All inputs must be floating point numbers!");
			xeqlabel.setText("");
			return;
		}
		
		//	Check for degenerative case.
		if (x2 - x1 == 0f) {
			yeqlabel.setText("A vertical line!");
			aString = new String("    x = " + x1);
			xeqlabel.setText(aString);
		} else {
		
			//	Calculate slope
			m = (y2 - y1)/(x2 - x1);
			
			//	Calculate axis intercept.
			b = y1 - m*x1;
			
			//	Output the results.
			if (m == 0f) {
				aString = new String("    y = " + y1);
				yeqlabel.setText(aString);
				xeqlabel.setText("    A horizontal line!");
			} else {
				aString = new String("    y = (" + m + ")x ");
				if (b > 0f)
					aString += "+ " + b;
				else
					aString += " " + b;
				yeqlabel.setText(aString);
				
				b *= -1;
				aString = new String("    x = (" + 1f/m + ")y ");
				if (b/m > 0f)
					aString += "+ " + b/m;
				else
					aString += " " + b/m;
				xeqlabel.setText( aString );
			}
		}
		
	}	//	end CalcLineEq()


	/**
	*	Fills in the GridBagConstraints record for a given component with input items.
	*
	*	@param	gx,gy	Grid (cell) indicies for this compenent in the x and y dir
	*						(1,3 == 2nd column, 4th row).
	*	@param	gw,gy	The number of cells this component spans.
	*	@param	wx,wy	Proportional width/height of this grid cell compared to others.
	**/
	void buildConstraints(GridBagConstraints gbc, int gx, int gy, int gw, int gh, int wx, int wy) {

		gbc.gridx = gx;
		gbc.gridy = gy;
		
		gbc.gridwidth = gw;
		gbc.gridheight = gh;
		
		gbc.weightx = wx;
		gbc.weighty = wy;
		
	}
	
	
	/**
	*	We are adding an inset to our Applet panel.  This is called by the
	*   container to determine our insets.
	*
	*	@return	An Inset object is returned
	**/
	public Insets getInsets() {
		return new Insets(10,5, 0,25);
	}


	/**
	*	Initialization that occures when applet is first loaded.
	**/
	public void init() {
		GridBagConstraints constraints = new GridBagConstraints();
		GridBagLayout gridbag = new GridBagLayout();
		setLayout(gridbag);
		

		try {
		//	X1 parameter
		buildConstraints(constraints, 0,0, 1,1, 50,15);
		constraints.fill = GridBagConstraints.BOTH;		//	How the component should fill cell.
		constraints.anchor = GridBagConstraints.CENTER;	//	Justification in cell
		x1pi = new ParamInput( new Param("x1") );
		gridbag.setConstraints(x1pi, constraints);
		add(x1pi);
		
		//	Y1 parameter
		buildConstraints(constraints, 1,0, 1,1, 50,15);
		constraints.fill = GridBagConstraints.BOTH;		//	How the component should fill cell.
		constraints.anchor = GridBagConstraints.CENTER;	//	Justification in cell
		y1pi = new ParamInput( new Param("y1") );
		gridbag.setConstraints(y1pi, constraints);
		add(y1pi);
		
		//	X2 parameter
		buildConstraints(constraints, 0,1, 1,1, 50,15);
		constraints.fill = GridBagConstraints.BOTH;		//	How the component should fill cell.
		constraints.anchor = GridBagConstraints.CENTER;	//	Justification in cell
		x2pi = new ParamInput( new Param("x2") );
		gridbag.setConstraints(x2pi, constraints);
		add(x2pi);
		
		//	Y2 parameter
		buildConstraints(constraints, 1,1, 1,1, 50,15);
		constraints.fill = GridBagConstraints.BOTH;		//	How the component should fill cell.
		constraints.anchor = GridBagConstraints.CENTER;	//	Justification in cell
		y2pi = new ParamInput( new Param("y2") );
		gridbag.setConstraints(y2pi, constraints);
		add(y2pi);
		
		
		//	Calculate Button
		buildConstraints(constraints, 0,2, 2,1, 90,30);
		constraints.fill = GridBagConstraints.NONE;
		constraints.anchor = GridBagConstraints.CENTER;
		Button calcb = new Button("Calculate");
		gridbag.setConstraints(calcb, constraints);
		add(calcb);
		
		
		//	Y Equation output label.
		buildConstraints(constraints, 0,3, 2,1, 100,20);
		constraints.fill = GridBagConstraints.NONE;
		constraints.anchor = GridBagConstraints.WEST;
		yeqlabel = new Label(" Enter two points, the equation for the line                 ");
		gridbag.setConstraints(yeqlabel, constraints);
		add(yeqlabel);
		
		//	X Equation output label.
		buildConstraints(constraints, 0,4, 2,1, 100,20);
		constraints.fill = GridBagConstraints.NONE;
		constraints.anchor = GridBagConstraints.WEST;
		xeqlabel = new Label(" will be calculated.                                         ");
		gridbag.setConstraints(xeqlabel, constraints);
		add(xeqlabel);
		
		}	catch (Exception e) {
			System.out.println("An Error occured: " + e.getMessage() );
			e.printStackTrace();
		}
		
	}	//	end init()
	

	/**
	*	Action events to our applet are handled here.
	*
	*	@param	evt		Object containing the action event that occured.
	*	@param	arg		Object containing any arguments.
	**/
	public boolean action(Event evt, Object arg) {
		
		if (evt.target instanceof Button) {
			CalcLineEq();						//	Handle calc button action events.
			return true;
		}
		
		return(false);
	}
	


}	//	end class LineEquation