import java.awt.*;
import java.applet.Applet;

public class equation extends Applet
{	
	float[] A,B,C,D;
	FloatTextField[] aField,bField,cField,dField;	
	Color bkground,fground;
	TextField detField, xAnswerField,yAnswerField, zAnswerField;
	Label specialCase;
	
    public void init() 
	{	/* SET UP THE GUI */
		A=new float[3];	B=new float[3];
		C=new float[3];	D=new float[3];
		aField = new FloatTextField[3];
		bField = new FloatTextField[3];
		cField = new FloatTextField[3];
		dField = new FloatTextField[3];
		
		Color light_blue = new Color(140, 140, 255);
		bkground=light_blue;
		fground=Color.black;
		setBackground(bkground);
		setForeground(fground);
		setLayout(new GridLayout(9,1));

		Label titleLabel1=new Label("Three equations", Label.CENTER);
		Label titleLabel2=new Label("three unknowns", Label.CENTER);
		titleLabel1.setFont(new Font("Dialog", Font.BOLD, 14));
		titleLabel2.setFont(new Font("Dialog", Font.BOLD, 14));
		add(titleLabel1);
		add(titleLabel2);
		/* THE INPUT FIELDS */
		Panel[] inputPanel=new Panel[3];
		for(int i=0;i<3;i++)
		{	inputPanel[i]=new Panel();
			inputPanel[i].setLayout(new GridLayout(1,9));
			inputPanel[i].setBackground(bkground);
			inputPanel[i].setForeground(fground);
			aField[i] = new FloatTextField(0, 5);
			bField[i] = new FloatTextField(0, 5);
			cField[i] = new FloatTextField(0, 5);
			dField[i] = new FloatTextField(0, 5);
			inputPanel[i].add(new Label(""));
			inputPanel[i].add(aField[i]);
			inputPanel[i].add(new Label(" X +",Label.LEFT));
			inputPanel[i].add(bField[i]); 
			inputPanel[i].add(new Label(" Y +",Label.LEFT));
			inputPanel[i].add(cField[i]);
			inputPanel[i].add(new Label(" Z =",Label.LEFT));
			inputPanel[i].add(dField[i]);
			inputPanel[i].add(new Label(""));
			add(inputPanel[i]);
		}
		
		Button solveMe=new Button("Solve it!");
		add(solveMe);
		specialCase=new Label("The solution", Label.CENTER);
		specialCase.setFont(new Font("Dialog", Font.BOLD, 14));
		specialCase.setForeground(Color.blue);
		add(specialCase);
		/* THE ANSWER FIELDS */
		Panel answerTop=new Panel();
		answerTop.add(new Label("Determinant",Label.RIGHT));
		detField=new TextField("",5);
		detField.setEditable(false);
		answerTop.add(detField);
		add(answerTop);
		Panel answerBottom=new Panel();
		answerBottom.add(new Label(" X=",Label.RIGHT));
		xAnswerField=new TextField("",5);
		xAnswerField.setEditable(false);
		answerBottom.add(xAnswerField);
		answerBottom.add(new Label(" Y=",Label.RIGHT));
		yAnswerField=new TextField("",5);
		yAnswerField.setEditable(false);
		answerBottom.add(yAnswerField);
		answerBottom.add(new Label(" Z=",Label.RIGHT));
		zAnswerField=new TextField("",5);
		zAnswerField.setEditable(false);
		answerBottom.add(zAnswerField);
		add(answerBottom);								
	 }

	public boolean action(Event evt, Object arg)
	{	if(arg.equals("Solve it!"))
		{	
			xAnswerField.setText("");
			yAnswerField.setText("");
			zAnswerField.setText("");
			detField.setText("");
			/* TEST IF INPUTS ARE VALID NUMBERS */
			boolean validTest=true;
			for(int i=0;i<3;i++)
			{			
			validTest = validTest && aField[i].isValid() && bField[i].isValid() 
						&& cField[i].isValid() && dField[i].isValid();
			}
			if(validTest)
				solve();			
			else
				specialCase.setText("Fix inputs");;
		}
		else return false;
		return true;
	}
		
	public void solve()
	{	/* CALCULATION ROUTINE */
		for(int i=0;i<3; i++)
		{	A[i]=aField[i].getValue();
			B[i]=bField[i].getValue();
			C[i]=cField[i].getValue();
			D[i]=dField[i].getValue();
		}
		/* use Cramer's rule*/
		float aDeter=Determinate(D,B,C);
		float bDeter=Determinate(A,D,C);
		float cDeter=Determinate(A,B,D);
		float dDeter=Determinate(A,B,C);
		detField.setText(new Float(dDeter).toString());

		if(dDeter==0)
		{	if(aDeter==0 && bDeter==0 && cDeter==0)
			{	/*dependent equations*/
				/*an infinite number of solutions exist*/
				specialCase.setText("DEPENDENT");
			}
			else
			{	/*no solution exists*/
				specialCase.setText("NULL");
			}
		}   
		else
		{	specialCase.setText("Solved!");
			xAnswerField.setText(new Float(aDeter/dDeter).toString());
			yAnswerField.setText(new Float(bDeter/dDeter).toString());
			zAnswerField.setText(new Float(cDeter/dDeter).toString());
		}
		repaint();
		return;
	}
	
	public float Determinate(float[] a, float[] b,float[] c)
	{
		float det=0;
		det=a[0]*b[1]*c[2]
			+b[0]*c[1]*a[2]
			+c[0]*a[1]*b[2]
			-a[2]*b[1]*c[0]
			-b[2]*c[1]*a[0]
			-c[2]*a[1]*b[0];
		return det;
	}

	public void start()
	{
		this.show();
    }
}