Extension Development

Learn how to build your own MDS extensions using the official skeleton plugin and best practices.

Getting Started

Use the Skeleton Plugin

The MDS Skeleton plugin provides a clean starting point for new extensions:

Copy the mds-skeleton folder from the extensions repository
Rename the folder and main PHP file to match your extension name
Update namespaces and text domain throughout
Run composer install to set up autoloading
Activate and test in WordPress

File Structure

A typical MDS extension follows this structure:

my-extension/
├── my-extension.php           # Main plugin file (bootstrap)
├── README.md                  # Documentation
├── readme.txt                 # WordPress.org-style readme
├── composer.json              # Composer dependencies & autoload
├── assets/
│   ├── css/
│   │   ├── admin.css          # Admin styles
│   │   └── frontend.css       # Frontend styles
│   └── js/
│       ├── admin.js           # Admin JavaScript
│       └── frontend.js        # Frontend JavaScript
├── src/
│   └── Plugin.php             # Main plugin class
├── includes/                  # Additional PHP classes (alternative to src/)
├── languages/
│   └── my-extension.pot       # Translation template
└── tests/
    └── ...                    # PHPUnit test suite

Essential Components

Main Plugin File

The main plugin file bootstraps your extension:

<?php
/**
 * Plugin Name: My MDS Extension
 * Plugin URI: https://example.com/my-extension
 * Description: Description of what your extension does.
 * Version: 1.0.0
 * Author: Your Name
 * Author URI: https://example.com
 * Text Domain: my-mds-extension
 * Domain Path: /languages
 * Requires at least: 6.7
 * Requires PHP: 8.1
 * License: GPL-2.0-or-later
 */

// Prevent direct access
if (!defined('ABSPATH')) {
    exit;
}

// Define constants
define('MY_EXT_VERSION', '1.0.0');
define('MY_EXT_DIR', plugin_dir_path(__FILE__));
define('MY_EXT_URL', plugin_dir_url(__FILE__));
define('MY_EXT_BASENAME', plugin_basename(__FILE__));

// Composer autoloader
if (file_exists(MY_EXT_DIR . 'vendor/autoload.php')) {
    require_once MY_EXT_DIR . 'vendor/autoload.php';
}

// Initialize after plugins are loaded (ensures MDS is available)
add_action('plugins_loaded', function () {
    // Check if MDS core is active
    if (!class_exists('MillionDollarScript')) {
        add_action('admin_notices', function () {
            echo '<div class="notice notice-error"><p>';
            echo esc_html__('My MDS Extension requires Million Dollar Script to be installed and activated.', 'my-mds-extension');
            echo '</p></div>';
        });
        return;
    }

    // Initialize the extension
    My_Extension\Plugin::instance();
});

Plugin Class

The main plugin class handles initialization and hooks:

<?php
namespace My_Extension;

class Plugin {
    private static ?Plugin $instance = null;

    public static function instance(): Plugin {
        if (null === self::$instance) {
            self::$instance = new self();
        }
        return self::$instance;
    }

    private function __construct() {
        $this->init_hooks();
    }

    private function init_hooks(): void {
        // Load translations
        add_action('init', [$this, 'load_textdomain']);

        // Admin hooks
        add_action('admin_menu', [$this, 'register_admin_page']);
        add_action('admin_enqueue_scripts', [$this, 'enqueue_admin_assets']);

        // Frontend hooks
        add_action('wp_enqueue_scripts', [$this, 'enqueue_frontend_assets']);

        // MDS integration
        add_action('mds_main_menu_extensions_submenu', [$this, 'add_menu_link']);

        // Register shortcode
        add_shortcode('my_extension', [$this, 'shortcode_callback']);
    }

    public function load_textdomain(): void {
        load_plugin_textdomain(
            'my-mds-extension',
            false,
            dirname(MY_EXT_BASENAME) . '/languages'
        );
    }

    public function register_admin_page(): void {
        add_submenu_page(
            'milliondollarscript',          // Parent slug
            __('My Extension', 'my-mds-extension'),  // Page title
            __('My Extension', 'my-mds-extension'),  // Menu title
            'manage_options',               // Capability
            'my-extension',                 // Menu slug
            [$this, 'render_admin_page']    // Callback
        );
    }

    public function add_menu_link(): void {
        if (!current_user_can('manage_options')) {
            return;
        }
        echo '<li><a href="' . esc_url(admin_url('admin.php?page=my-extension')) . '">'
            . esc_html__('My Extension', 'my-mds-extension')
            . '</a></li>';
    }

    public function render_admin_page(): void {
        // Check permissions
        if (!current_user_can('manage_options')) {
            wp_die(__('You do not have permission to access this page.', 'my-mds-extension'));
        }
        ?>
        <div class="wrap">
            <h1><?php echo esc_html(get_admin_page_title()); ?></h1>
            <!-- Your admin content here -->
        </div>
        <?php
    }

    public function enqueue_admin_assets(string $hook): void {
        // Only load on our admin page
        if ('million-dollar-script_page_my-extension' !== $hook) {
            return;
        }

        wp_enqueue_style(
            'my-extension-admin',
            MY_EXT_URL . 'assets/css/admin.css',
            [],
            MY_EXT_VERSION
        );

        wp_enqueue_script(
            'my-extension-admin',
            MY_EXT_URL . 'assets/js/admin.js',
            ['jquery'],
            MY_EXT_VERSION,
            true
        );
    }

    public function enqueue_frontend_assets(): void {
        wp_enqueue_style(
            'my-extension-frontend',
            MY_EXT_URL . 'assets/css/frontend.css',
            [],
            MY_EXT_VERSION
        );
    }

    public function shortcode_callback(array $atts): string {
        $atts = shortcode_atts([
            'title'   => __('Default Title', 'my-mds-extension'),
            'option'  => 'value',
        ], $atts, 'my_extension');

        ob_start();
        ?>
        <div class="my-extension-wrapper">
            <h3><?php echo esc_html($atts['title']); ?></h3>
            <!-- Shortcode output here -->
        </div>
        <?php
        return ob_get_clean();
    }
}

Adding to MDS Menu

The recommended way to add admin links is via the Extensions dropdown:

add_action('mds_main_menu_extensions_submenu', function () {
    if (!current_user_can('manage_options')) {
        return;
    }
    echo '<li><a href="' . esc_url(admin_url('admin.php?page=my-extension')) . '">'
        . esc_html__('My Extension', 'my-mds-extension')
        . '</a></li>';
});

This keeps extensions organized and doesn't clutter the WordPress sidebar.

Using Carbon Fields

MDS uses Carbon Fields for options. You can add your own options:

use Carbon_Fields\Container;
use Carbon_Fields\Field;

add_action('carbon_fields_register_fields', function () {
    Container::make('theme_options', __('My Extension Settings', 'my-mds-extension'))
        ->set_page_parent('milliondollarscript')
        ->add_fields([
            Field::make('text', 'my_ext_api_key', __('API Key', 'my-mds-extension'))
                ->set_help_text(__('Enter your API key here.', 'my-mds-extension')),

            Field::make('checkbox', 'my_ext_enabled', __('Enable Feature', 'my-mds-extension'))
                ->set_option_value('yes'),

            Field::make('select', 'my_ext_mode', __('Mode', 'my-mds-extension'))
                ->add_options([
                    'basic'    => __('Basic', 'my-mds-extension'),
                    'advanced' => __('Advanced', 'my-mds-extension'),
                ]),
        ]);
});

// Retrieve option values
$api_key = carbon_get_theme_option('my_ext_api_key');
$enabled = carbon_get_theme_option('my_ext_enabled');

Creating Shortcodes

public function __construct() {
    add_shortcode('my_extension', [$this, 'shortcode_callback']);
}

public function shortcode_callback($atts): string {
    $atts = shortcode_atts([
        'title'       => __('Default Title', 'my-mds-extension'),
        'show_option' => 'true',
        'class'       => '',
    ], $atts, 'my_extension');

    // Sanitize attributes
    $show_option = filter_var($atts['show_option'], FILTER_VALIDATE_BOOLEAN);
    $class = sanitize_html_class($atts['class']);

    ob_start();
    ?>
    <div class="my-extension <?php echo esc_attr($class); ?>">
        <h3><?php echo esc_html($atts['title']); ?></h3>
        <?php if ($show_option) : ?>
            <p><?php esc_html_e('Option is enabled', 'my-mds-extension'); ?></p>
        <?php endif; ?>
    </div>
    <?php
    return ob_get_clean();
}

AJAX Handlers

// Register AJAX actions
add_action('wp_ajax_my_extension_action', [$this, 'handle_ajax']);
add_action('wp_ajax_nopriv_my_extension_action', [$this, 'handle_ajax']); // For non-logged-in users

public function handle_ajax(): void {
    // Verify nonce
    if (!check_ajax_referer('my_extension_nonce', 'nonce', false)) {
        wp_send_json_error(['message' => __('Security check failed.', 'my-mds-extension')]);
    }

    // Check permissions if needed
    if (!current_user_can('manage_options')) {
        wp_send_json_error(['message' => __('Permission denied.', 'my-mds-extension')]);
    }

    // Process the request
    $data = isset($_POST['data']) ? sanitize_text_field($_POST['data']) : '';

    // Return response
    wp_send_json_success([
        'message' => __('Success!', 'my-mds-extension'),
        'data'    => $data,
    ]);
}

Testing

The skeleton includes PHPUnit setup with Brain Monkey for WordPress mocks:

# Install dependencies
composer install

# Run tests
composer test
# or
./vendor/bin/phpunit

Example test:

<?php
namespace My_Extension\Tests;

use PHPUnit\Framework\TestCase;
use Brain\Monkey;
use Brain\Monkey\Functions;

class PluginTest extends TestCase {
    protected function setUp(): void {
        parent::setUp();
        Monkey\setUp();
    }

    protected function tearDown(): void {
        Monkey\tearDown();
        parent::tearDown();
    }

    public function test_shortcode_returns_html(): void {
        Functions\when('shortcode_atts')->returnArg(1);
        Functions\when('esc_html')->returnArg(1);
        Functions\when('__')->returnArg(1);

        $plugin = new \My_Extension\Plugin();
        $output = $plugin->shortcode_callback(['title' => 'Test']);

        $this->assertStringContainsString('Test', $output);
    }
}

Activation and Deactivation

Handle plugin lifecycle events:

// In main plugin file
register_activation_hook(__FILE__, [My_Extension\Plugin::class, 'activate']);
register_deactivation_hook(__FILE__, [My_Extension\Plugin::class, 'deactivate']);

// In Plugin class
public static function activate(): void {
    // Create database tables
    // Set default options
    // Flush rewrite rules if registering custom post types
    flush_rewrite_rules();
}

public static function deactivate(): void {
    // Clean up scheduled events
    wp_clear_scheduled_hook('my_extension_cron');
    // Flush rewrite rules
    flush_rewrite_rules();
}

Uninstall Cleanup

Create uninstall.php in your plugin root:

<?php
// Exit if not called by WordPress
if (!defined('WP_UNINSTALL_PLUGIN')) {
    exit;
}

// Delete options
delete_option('my_extension_settings');

// Delete custom tables (if any)
global $wpdb;
$wpdb->query("DROP TABLE IF EXISTS {$wpdb->prefix}my_extension_data");

// Delete user meta (if any)
delete_metadata('user', 0, 'my_extension_preference', '', true);

Release Checklist

Before releasing your extension:

Unique text domain that won't conflict with other plugins
All strings wrapped in translation functions
Proper capability checks on all admin functions
Nonce verification on all form submissions
Input sanitization on all user data
Output escaping on all rendered content
Activation/deactivation hooks handle setup/cleanup
Uninstall.php removes all plugin data
README.md with installation and usage instructions
Changelog documenting all versions
Tests passing
Code follows WordPress Coding Standards
Tested with latest WordPress and PHP versions
Tested with latest MDS version

Resources

Hooks Reference - Available MDS hooks
List Page Customization - Extending the advertiser list
WordPress Plugin Handbook
Carbon Fields Documentation