Mastering WordPress Architecture: Real-World Projects for Themes & Plugins

Complete Plugin Example

<?php
/**
 * Plugin Name: My Custom Plugin
 * Description: Demonstrates WordPress Hook System
 * Version: 1.0.0
 */

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

class My_Custom_Plugin {
    
    private static $instance = null;
    
    public static function get_instance() {
        if ( null === self::$instance ) {
            self::$instance = new self();
        }
        return self::$instance;
    }
    
    private function __construct() {
        // Activation/Deactivation hooks
        register_activation_hook( __FILE__, array( $this, 'activate' ) );
        register_deactivation_hook( __FILE__, array( $this, 'deactivate' ) );
        
        // Action hooks
        add_action( 'init', array( $this, 'init' ) );
        add_action( 'wp_enqueue_scripts', array( $this, 'enqueue_assets' ) );
        add_action( 'admin_menu', array( $this, 'add_admin_menu' ) );
        add_action( 'wp_footer', array( $this, 'footer_content' ) );
        
        // Filter hooks
        add_filter( 'the_content', array( $this, 'modify_content' ) );
        add_filter( 'the_title', array( $this, 'modify_title' ), 10, 2 );
        
        // Custom hooks
        add_action( 'my_plugin_loaded', array( $this, 'plugin_loaded' ) );
    }
    
    public function activate() {
        // Create database tables, set options, etc.
        add_option( 'my_plugin_version', '1.0.0' );
        flush_rewrite_rules();
    }
    
    public function deactivate() {
        // Cleanup tasks
        flush_rewrite_rules();
    }
    
    public function init() {
        // Register custom post type
        register_post_type( 'my_custom_post', array(
            'labels' => array(
                'name' => 'Custom Posts',
                'singular_name' => 'Custom Post',
            ),
            'public' => true,
            'has_archive' => true,
        ));
        
        // Fire custom action
        do_action( 'my_plugin_loaded' );
    }
    
    public function enqueue_assets() {
        wp_enqueue_style( 
            'my-plugin-style', 
            plugin_dir_url( __FILE__ ) . 'css/style.css',
            array(),
            '1.0.0'
        );
        
        wp_enqueue_script(
            'my-plugin-script',
            plugin_dir_url( __FILE__ ) . 'js/script.js',
            array( 'jquery' ),
            '1.0.0',
            true
        );
    }
    
    public function add_admin_menu() {
        add_menu_page(
            'My Plugin',
            'My Plugin',
            'manage_options',
            'my-plugin',
            array( $this, 'admin_page' ),
            'dashicons-admin-plugins',
            100
        );
    }
    
    public function admin_page() {
        echo '<div class="wrap">';
        echo '<h1>My Plugin Settings</h1>';
        
        // Allow others to add content
        do_action( 'my_plugin_admin_page' );
        
        echo '</div>';
    }
    
    public function modify_content( $content ) {
        if ( is_single() ) {
            $additional = apply_filters( 'my_plugin_additional_content', '' );
            $content .= $additional;
        }
        return $content;
    }
    
    public function modify_title( $title, $post_id ) {
        if ( get_post_type( $post_id ) === 'my_custom_post' ) {
            $title = '⭐ ' . $title;
        }
        return $title;
    }
    
    public function footer_content() {
        echo '<!-- My Plugin Active -->';
    }
    
    public function plugin_loaded() {
        // Plugin is fully loaded
        error_log( 'My Plugin Loaded!' );
    }
}

// Initialize plugin
My_Custom_Plugin::get_instance();

---

Complete Theme Example (functions.php)

<?php
/**
 * Theme Functions - Demonstrating Hook System
 */

// Theme Setup
add_action( 'after_setup_theme', 'my_theme_setup' );

function my_theme_setup() {
    // Add theme support
    add_theme_support( 'title-tag' );
    add_theme_support( 'post-thumbnails' );
    add_theme_support( 'html5', array(
        'search-form',
        'comment-form',
        'comment-list',
        'gallery',
        'caption',
    ));
    
    // Register navigation menus
    register_nav_menus( array(
        'primary' => 'Primary Menu',
        'footer'  => 'Footer Menu',
    ));
}

// Enqueue styles and scripts
add_action( 'wp_enqueue_scripts', 'my_theme_assets' );

function my_theme_assets() {
    // Styles
    wp_enqueue_style( 
        'my-theme-style', 
        get_stylesheet_uri(),
        array(),
        wp_get_theme()->get( 'Version' )
    );
    
    // Scripts
    wp_enqueue_script(
        'my-theme-script',
        get_template_directory_uri() . '/js/main.js',
        array( 'jquery' ),
        '1.0.0',
        true
    );
    
    // Localize script
    wp_localize_script( 'my-theme-script', 'myTheme', array(
        'ajaxUrl' => admin_url( 'admin-ajax.php' ),
        'nonce'   => wp_create_nonce( 'my_theme_nonce' ),
    ));
}

// Register widget areas
add_action( 'widgets_init', 'my_theme_widgets' );

function my_theme_widgets() {
    register_sidebar( array(
        'name'          => 'Main Sidebar',
        'id'            => 'sidebar-main',
        'before_widget' => '<div class="widget %2$s">',
        'after_widget'  => '</div>',
        'before_title'  => '<h3 class="widget-title">',
        'after_title'   => '</h3>',
    ));
}

// Custom excerpt length
add_filter( 'excerpt_length', 'my_theme_excerpt_length' );

function my_theme_excerpt_length( $length ) {
    return 25; // 25 words
}

// Custom excerpt more text
add_filter( 'excerpt_more', 'my_theme_excerpt_more' );

function my_theme_excerpt_more( $more ) {
    return '... <a href="' . get_permalink() . '">Read More</a>';
}

// Add custom body classes
add_filter( 'body_class', 'my_theme_body_classes' );

function my_theme_body_classes( $classes ) {
    // Add class for logged-in users
    if ( is_user_logged_in() ) {
        $classes[] = 'user-logged-in';
    }
    
    // Add class for specific page templates
    if ( is_page_template( 'template-fullwidth.php' ) ) {
        $classes[] = 'full-width-layout';
    }
    
    return $classes;
}

// Modify main query
add_action( 'pre_get_posts', 'my_theme_modify_query' );

function my_theme_modify_query( $query ) {
    // Only modify main query on frontend
    if ( ! is_admin() && $query->is_main_query() ) {
        // Custom posts per page for archive
        if ( is_archive() ) {
            $query->set( 'posts_per_page', 12 );
        }
        
        // Exclude category from homepage
        if ( is_home() ) {
            $query->set( 'cat', '-5' ); // Exclude category ID 5
        }
    }
}

// Add custom meta boxes
add_action( 'add_meta_boxes', 'my_theme_meta_boxes' );

function my_theme_meta_boxes() {
    add_meta_box(
        'my_theme_options',
        'Page Options',
        'my_theme_meta_box_callback',
        'page',
        'side',
        'default'
    );
}

function my_theme_meta_box_callback( $post ) {
    wp_nonce_field( 'my_theme_meta_box', 'my_theme_meta_box_nonce' );
    
    $value = get_post_meta( $post->ID, '_hide_title', true );
    
    echo '<label>';
    echo '<input type="checkbox" name="hide_title" value="1" ' . checked( $value, '1', false ) . '>';
    echo ' Hide page title';
    echo '</label>';
}

// Save meta box data
add_action( 'save_post', 'my_theme_save_meta_box' );

function my_theme_save_meta_box( $post_id ) {
    // Verify nonce
    if ( ! isset( $_POST['my_theme_meta_box_nonce'] ) ) {
        return;
    }
    
    if ( ! wp_verify_nonce( $_POST['my_theme_meta_box_nonce'], 'my_theme_meta_box' ) ) {
        return;
    }
    
    // Check autosave
    if ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) {
        return;
    }
    
    // Check permissions
    if ( ! current_user_can( 'edit_post', $post_id ) ) {
        return;
    }
    
    // Save data
    $hide_title = isset( $_POST['hide_title'] ) ? '1' : '0';
    update_post_meta( $post_id, '_hide_title', $hide_title );
}

// AJAX handler
add_action( 'wp_ajax_my_theme_action', 'my_theme_ajax_handler' );
add_action( 'wp_ajax_nopriv_my_theme_action', 'my_theme_ajax_handler' );

function my_theme_ajax_handler() {
    check_ajax_referer( 'my_theme_nonce', 'nonce' );
    
    $data = sanitize_text_field( $_POST['data'] );
    
    // Process data
    $response = array(
        'success' => true,
        'message' => 'Data processed: ' . $data,
    );
    
    wp_send_json( $response );
}

// Custom login logo
add_action( 'login_head', 'my_theme_login_logo' );

function my_theme_login_logo() {
    echo '<style>
        .login h1 a {
            background-image: url(' . get_template_directory_uri() . '/images/logo.png);
            background-size: contain;
            width: 200px;
        }
    </style>';
}

---