functions.php

<?php
/**
 * Theme Functions and Definitions
 *
 * @package YourThemeName
 * @since 1.0.0
 */

// Exit if accessed directly
if ( ! defined( 'ABSPATH' ) ) {
    exit;
}

/**
 * Define Constants
 */
define( 'THEME_VERSION', '1.0.0' );
define( 'THEME_DIR', get_template_directory() );
define( 'THEME_URI', get_template_directory_uri() );

/**
 * Set up theme defaults and register support for various WordPress features
 */
if ( ! function_exists( 'mytheme_setup' ) ) {
    function mytheme_setup() {
        // Make theme available for translation
        load_theme_textdomain( 'mytheme', THEME_DIR . '/languages' );
        
        // Add default posts and comments RSS feed links
        add_theme_support( 'automatic-feed-links' );
        
        // Let WordPress manage the document title
        add_theme_support( 'title-tag' );
        
        // Enable support for Post Thumbnails
        add_theme_support( 'post-thumbnails' );
        
        // TODO: Add more theme support features here
    }
}
add_action( 'after_setup_theme', 'mytheme_setup' );

/**
 * Set the content width in pixels
 */
if ( ! isset( $content_width ) ) {
    $content_width = 1200;
}

/**
 * Include required files
 */
$mytheme_includes = array(
    '/inc/setup.php',           // Theme setup
    '/inc/assets.php',          // Scripts and styles
    '/inc/navigation.php',      // Navigation functions
    '/inc/widgets.php',         // Widget areas
    '/inc/helpers.php',         // Helper functions
    '/inc/ajax-handlers.php',   // AJAX handlers
    '/inc/shortcodes.php',      // Custom shortcodes
);

foreach ( $mytheme_includes as $file ) {
    $filepath = THEME_DIR . $file;
    if ( file_exists( $filepath ) ) {
        require_once $filepath;
    } else {
        trigger_error( sprintf( 'Error locating %s for inclusion', $file ), E_USER_ERROR );
    }
}