ts3j/ts3-client/swing/src/main/java/com/ts3client/ui/DropDownToggleButton.java

package com.ts3client.ui;

import javax.swing.BorderFactory;
import javax.swing.Icon;
import javax.swing.JButton;
import javax.swing.JPanel;
import javax.swing.JPopupMenu;
import javax.swing.JToggleButton;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Insets;
import java.awt.RenderingHints;
import java.awt.event.ActionListener;
import java.util.function.Supplier;

/**
 * A toolbar toggle button with a small arrow next to it that opens a menu:
 * clicking the button toggles, clicking the arrow offers the related actions.
 *
 * <p>The menu is built on every click by the supplier, so it can reflect the
 * current state (checked items, the presets that exist right now).
 */
public final class DropDownToggleButton extends JPanel {

    private final JToggleButton button = new JToggleButton();
    private final JButton arrow = new JButton(new ArrowIcon());

    public DropDownToggleButton(Icon icon, String tooltip, Supplier<JPopupMenu> menu) {
        super(new BorderLayout());
        setOpaque(false);
        button.setIcon(icon);
        button.setToolTipText(tooltip);

        arrow.setToolTipText(tooltip);
        arrow.setMargin(new Insets(0, 2, 0, 2));
        arrow.setFocusable(false);
        arrow.addActionListener(e -> {
            JPopupMenu popup = menu.get();
            if (popup != null) popup.show(this, 0, getHeight());
        });

        // Keep the whole control the size of a plain toolbar button: the arrow's
        // width comes out of the toggle half instead of being added to it.
        Dimension plain = button.getPreferredSize();
        button.setPreferredSize(new Dimension(
                Math.max(icon.getIconWidth() + 8, plain.width - arrow.getPreferredSize().width),
                plain.height));

        add(button, BorderLayout.CENTER);
        add(arrow, BorderLayout.EAST);
    }

    /** Listener for the toggle half only; the arrow half opens the menu instead. */
    public void addActionListener(ActionListener l) {
        button.addActionListener(l);
    }

    public boolean isSelected() {
        return button.isSelected();
    }

    public void setSelected(boolean selected) {
        button.setSelected(selected);
    }

    public void setIcon(Icon icon) {
        button.setIcon(icon);
    }

    @Override
    public void setEnabled(boolean enabled) {
        super.setEnabled(enabled);
        button.setEnabled(enabled);
        arrow.setEnabled(enabled);
    }

    /** Disables the toggle half on its own, leaving the menu reachable. */
    public void setToggleEnabled(boolean enabled) {
        button.setEnabled(enabled);
    }

    @Override
    public Dimension getMaximumSize() {
        return getPreferredSize(); // keep the toolbar from stretching us
    }

    /** The downward triangle on the menu half of the button. */
    private static final class ArrowIcon implements Icon {

        @Override
        public void paintIcon(Component c, Graphics g0, int x, int y) {
            Graphics2D g = (Graphics2D) g0.create();
            g.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
            g.setColor(c.isEnabled() ? Color.DARK_GRAY : Color.GRAY);
            int[] xs = {x, x + getIconWidth(), x + getIconWidth() / 2};
            int[] ys = {y, y, y + getIconHeight()};
            g.fillPolygon(xs, ys, 3);
            g.dispose();
        }

        @Override
        public int getIconWidth() {
            return 7;
        }

        @Override
        public int getIconHeight() {
            return 4;
        }
    }
}