import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.function.BiFunction;

public class Operate {
    private JFrame frame;
    private JTextField displayField;
    private double firstNumber = 0;
    private double secondNumber = 0;
    private String operator = "";
    private boolean newNumber = true;

    public static void main(String[] args) {
        EventQueue.invokeLater(() -> {
            try {
                Operate window = new Operate();
                window.frame.setVisible(true);
            } catch (Exception e) {
                e.printStackTrace();
            }
        });
    }

    public Operate() {
        initialize();
    }

    private void initialize() {
        frame = new JFrame("Improved Calculator");
        frame.setBounds(100, 100, 300, 400);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().setLayout(new BorderLayout());
        frame.setLocationRelativeTo(null);

        // 显示区域
        displayField = new JTextField();
        displayField.setEditable(false);
        displayField.setFont(new Font("Arial", Font.BOLD, 20));
        displayField.setHorizontalAlignment(JTextField.RIGHT);
        frame.getContentPane().add(displayField, BorderLayout.NORTH);

        // 按钮面板
        JPanel buttonPanel = new JPanel();
        buttonPanel.setLayout(new GridLayout(5, 4));
        frame.getContentPane().add(buttonPanel, BorderLayout.CENTER);

        // 数字按钮
        for (int i = 1; i <= 9; i++) {
            JButton button = new JButton(Integer.toString(i));
            button.addActionListener(new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    if (newNumber) {
                        displayField.setText(e.getActionCommand());
                        newNumber = false;
                    } else {
                        displayField.setText(displayField.getText() + e.getActionCommand());
                    }
                }
            });
            buttonPanel.add(button);
            if (i % 3 == 0) buttonPanel.add(new JButton()); // 空位
        }

        // 添加0按钮
        JButton buttonZero = new JButton("0");
        buttonZero.addActionListener(e -> {
            if (!displayField.getText().equals("0")) {
                displayField.setText(displayField.getText() + "0");
            }
        });
        buttonPanel.add(buttonZero);

        // 小数点按钮
        JButton buttonDecimal = new JButton(".");
        buttonDecimal.addActionListener(e -> {
            if (!displayField.getText().contains(".")) {
                displayField.setText(displayField.getText() + ".");
            }
        });
        buttonPanel.add(buttonDecimal);

        // 运算符按钮
        addOperatorButton(buttonPanel, "+", (a, b) -> a + b);
        addOperatorButton(buttonPanel, "-", (a, b) -> a - b);
        addOperatorButton(buttonPanel, "*", (a, b) -> a * b);
        addOperatorButton(buttonPanel, "/", (a, b) -> {
            if (b == 0) {
                JOptionPane.showMessageDialog(frame, "除数不能为0！", "错误", JOptionPane.ERROR_MESSAGE);
                return Double.NaN;
            }
            return a / b;
        });

        // 清除按钮
        JButton clearButton = new JButton("C");
        clearButton.addActionListener(e -> {
            displayField.setText("");
            firstNumber = 0;
            secondNumber = 0;
            operator = "";
            newNumber = true;
        });
        buttonPanel.add(clearButton);

        // 等于号按钮
        JButton equalsButton = new JButton("=");
        equalsButton.addActionListener(e -> calculate());
        buttonPanel.add(equalsButton);

        // 设置按钮样式
        setButtonStyle(buttonPanel);
    }

    private void addOperatorButton(JPanel panel, String op, BiFunction<Double, Double, Double> operation) {
        JButton button = new JButton(op);
        button.addActionListener(e -> {
            firstNumber = Double.parseDouble(displayField.getText());
            operator = op;
            // 重置 displayField 的内容
            displayField.setText("");
            newNumber = true;
        });
        panel.add(button);
    }

    private void calculate() {
        secondNumber = Double.parseDouble(displayField.getText());
        switch (operator) {
            case "+":
                displayField.setText(String.valueOf(firstNumber + secondNumber));
                break;
            case "-":
                displayField.setText(String.valueOf(firstNumber - secondNumber));
                break;
            case "*":
                displayField.setText(String.valueOf(firstNumber * secondNumber));
                break;
            case "/":
                if (secondNumber == 0) {
                    JOptionPane.showMessageDialog(frame, "除数不能为0！", "错误", JOptionPane.ERROR_MESSAGE);
                    return;
                }
                displayField.setText(String.valueOf(firstNumber / secondNumber));
                break;
        }
        newNumber = true;
    }

    private void setButtonStyle(JPanel panel) {
        for (Component c : panel.getComponents()) {
            if (c instanceof JButton) {
                JButton button = (JButton) c;
                button.setFont(new Font("Arial", Font.BOLD, 16));
                button.setBackground(Color.LIGHT_GRAY);
                button.setForeground(Color.BLACK);
                button.setBorder(BorderFactory.createLineBorder(Color.DARK_GRAY));
            }
        }
    }
}