package freegraph;


import java.awt.*;
import java.awt.event.*;
import java.applet.*;

/**
 * ExpressionParsingApplet displays the RPN expression stack
 * generated from an infix expression entered by the user.
 */

public class ExpressionParsingApplet extends Applet implements ActionListener
{

    TextField txtFunction;
    Button btnConvert;
    Panel pnlTop;
    List lstStack;
    /***
     * Initialize the applet by setting up the GUI.  This method calls the
     * internalInit() method to do the actual initialization.  If any errors
     * occur, the stack trace is printed to System.err.
     */
    public void init()
    {
        try
        {
            internalInit();
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }
    }


    /***
     * internally used method to setup the Applet's GUI.
     */
    private void internalInit() throws Exception
    {
        setBackground(new Color(getParameterAsInt("bgcolor", 0xFFFFFF, 16)));
        txtFunction = new TextField();
        btnConvert = new Button("Convert");
        pnlTop = new Panel();
        lstStack = new List();

        pnlTop.setLayout(new BorderLayout());
        pnlTop.add(txtFunction, BorderLayout.CENTER);
        pnlTop.add(btnConvert, BorderLayout.EAST);

        this.setLayout(new BorderLayout());
        this.add(pnlTop, BorderLayout.NORTH);
        this.add(lstStack, BorderLayout.CENTER);
        btnConvert.addActionListener(this);
        txtFunction.addActionListener(this);
        txtFunction.requestFocus();
    }


    public String getAppletInfo()
    {
        return "Expression Parsing Applet Information";
    }

    /**
     * responds to action events from convert button of text field by parsing
     * the expression and displaying the RPN stack
     */
    public void actionPerformed(ActionEvent e)
    {
        if (e.getSource() == btnConvert || e.getSource() == txtFunction)
        {
            lstStack.removeAll();
            try
            {
                ExpressionStack expr = new ExpressionStack(txtFunction.getText());
                while (expr.size() > 0)
                {
                    lstStack.add(expr.pop().toString());
                }
            }
            catch (Exception e2)
            {
                lstStack.add(e2.getMessage());
            }
        }
    }


    /***
     * returns the value of a parameter as a String.  If the parameter
     * is not defined, def is returned.
     */
    public String getParameter(String key, String def)
    {
        return (getParameter(key) != null ? getParameter(key) : def);
    }


    /***
     * returns the value of a parameter as an int.  If the parameter
     * is not defined, def is returned.  The parameter is parsed to integer
     * using the default radix of 10
     */
    public int getParameterAsInt(String key, int def)
    {
        return getParameterAsInt(key, def, 10);
    }

    /***
     * returns the value of a parameter as an int.  If the parameter
     * is not defined, def is returned.  The parameter is parsed to integer
     * using the provided radix
     */
    public int getParameterAsInt(String key, int def, int radix)
    {
        try
        {
            return (getParameter(key) != null ?
                Integer.parseInt(getParameter(key), radix)
                : def);
        }
        catch (Exception e)
        {
            return def;
        }
    }

}