import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class CalculatorGui {

    // just returns the name which should be used for a button
    public static String buttonName(ButtonType b) {
        switch (b) {
            // all the numbered ones just return the number part
            case N0:
            case N1:
            case N2:
            case N3:
            case N4:
            case N5:
            case N6:
            case N7:
            case N8:
            case N9:
                // return the name's substring starting at 1
                return b.name().substring(1);

                // the rest
            case DOT:
                return ".";
            case PLUS:
                return "+";
            case MINUS:
                return "-";
            case TIMES:
                return "×";
            case DIVIDE:
                return "÷";
            case SQRT:
                return "√";
            case EQUALS:
                return "=";
            case CLEAR:
                return "C";
        }

        throw new IllegalArgumentException("Invlaid button type " + b.name());
    }

    public static void main(String args[]) {
        // create the calculator object which handles calculations
        Calculator calc = new Calculator();

        // create and set up the window.
        JFrame frame = new JFrame("Calculator");

        // make the program close when the window closes
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        // we need a "panel" for the grid buttons
        JPanel grid = new JPanel();

        // create a grid layout for the 16 buttons other than clear and equals
        GridLayout layout = new GridLayout(4, 4);
        grid.setLayout(layout);

        // add those first 16 buttons to it
        for (int i = 0; i < 16; i++) {
            // find this button type
            ButtonType b = ButtonType.values()[i];

            // create a GUI button for it with the right name
            String name = buttonName(b);
            JButton button = new JButton(name);

            // create a listener for it
            ButtonListener listener = new ButtonListener(b, calc);
            button.addActionListener(listener);

            // add it to the grid
            grid.add(button);
        }

        // now we create a vertical box layout for the textbox, grid of buttons
        // and the row of buttons at the bottom
        BoxLayout mainLayout = new BoxLayout(frame.getContentPane(), BoxLayout.Y_AXIS);
        frame.getContentPane().setLayout(mainLayout);

        // add the calculator display line to the layout
        frame.getContentPane().add(calc);

        // add the grid
        frame.getContentPane().add(grid);

        // now create another panel and layout for displaying the two buttons at bottom
        JPanel bottom = new JPanel();
        BoxLayout bottomLayout = new BoxLayout(bottom, BoxLayout.X_AXIS);

        // create the bottom two buttons and listeners for them
        JButton clear = new JButton(buttonName(ButtonType.CLEAR));
        ButtonListener clearListener = new ButtonListener(ButtonType.CLEAR, calc);
        clear.addActionListener(clearListener);
        JButton equals = new JButton(buttonName(ButtonType.EQUALS));
        ButtonListener equalsListener = new ButtonListener(ButtonType.EQUALS, calc);
        equals.addActionListener(equalsListener);

        // add them to the bottom panel
        bottom.add(clear);
        bottom.add(equals);

        // add the bottom row to the window
        frame.getContentPane().add(bottom);

        // display the window.
        frame.pack();
        frame.setVisible(true);
    }
}