package example;

import javax.swing.*;
import java.awt.event.*;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.GridLayout;

public class Calculator extends JFrame
{
	private JPanel panel;
	private JTextField display;
	private JButton[] buttons;
	private String[] labels = {
			"Backspace", "", "", "CE", "C",
			"7", "8", "9", "/", "sqrt",
			"4", "5", "6", "x", "%",
			"1", "2", "3", "-", "1/x",
			"0", "-/+", ".", "+", "=", };
	private double result = 0;
	private String operator = "=";
	private boolean startOfNumber = true;

	public Calculator() {
		display = new JTextField(35);
		panel = new JPanel();
		display.setText("0.0");
		//display.setEnabled(true);


		panel.setLayout(new GridLayout(0, 5, 3, 3));
		buttons = new JButton[25];
		int index = 0;
		for (int rows = 0; rows < 5; rows++)
		{
			for (int cols = 0; cols < 5; cols++)
			{
				buttons[index] = new JButton(labels[index]);
				if (cols >= 3)
					buttons[index].setForeground(Color.red);
				else
					buttons[index].setForeground(Color.blue);
				buttons[index].setBackground(Color.yellow);
				panel.add(buttons[index]);

				buttons[index].addActionListener((e)->
				{
					String command = e.getActionCommand();
					if (command.charAt(0) == 'C')
					{
						startOfNumber = true;
						result = 0;
						operator = "=";
						display.setText("0.0");
					}
					else if (command.charAt(0) >= '0' && command.charAt(0) <= '9'|| command.equals("."))
					{
						if (startOfNumber == true)
							display.setText(command);
						else
							display.setText(display.getText() + command);
						startOfNumber = false;
					}
					else
					{
						if (startOfNumber)
						{
							if (command.equals("-"))
							{
								display.setText(command);
								startOfNumber = false;
							}
							else
								operator = command;
						}
						else
						{
							double x = Double.parseDouble(display.getText());
							calculate(x);
							operator = command;
							startOfNumber = true;
						}
					}
				});
				index++;
			}
		}
		add(display, BorderLayout.NORTH);
		add(panel, BorderLayout.CENTER);
		setVisible(true);
		pack();
	}

	private void calculate(double n)
	{
		if (operator.equals("+"))
			result += n;
		else if (operator.equals("-"))
			result -= n;
		else if (operator.equals("*"))
			result *= n;
		else if (operator.equals("/"))
			result /= n;
		else if (operator.equals("="))
			result = n;
		display.setText("" + result);
	}

	public static void main(String args[])
	{
		Calculator s = new Calculator();
	}
}