Bustin' up cache's in WordPress. Doing it H5BP style, and without a build script.

filename-based-cache-busting.php

<?php
/**
 * Plugin Name: Filename Based Cache Busting
 * Plugin URI:  https://gist.github.com/gMagicScott/5400268
 * Description: Bustin' up cache's in WordPress. Doing it H5BP style, and without a build script.
 * Author:      Scott Lesovic, forked from Ben Sampo
 * Author URI:  
 * Version:     0.2-dev
 */

class FilenameBasedCacheBusting {
	/**
	 * Hold and protect options
	 *
	 * @var array
	 */
	private $data;

	/** Singleton *************************************************************/

	/**
	 * @var FilenameBasedCacheBusting The one true FilenameBasedCacheBusting
	 */
	private static $instance;

	/**
	 * Main FilenameBasedCacheBusting Instance
	 *
	 * Ensures that only one instance exists in memory at any one
	 * time. Also prevents needing to define globals all over the place.
	 */
	public static function instance() {
		if ( ! isset( self::$instance ) ) {
			self::$instance = new FilenameBasedCacheBusting;
			self::$instance->setup_globals();
			self::$instance->setup_actions();
		}
		return self::$instance;
	}

	/**
	 * A dummy constructor to prevent class from being loaded more than once.
	 */
	private function __construct() {
		/* Do nothing here */
	}


	/** Private Methods *******************************************************/

	/**
	 * Set some smart defaults to class variables. Allow some of them to be
	 * filtered to allow for early overriding.
	 */
	private function setup_globals() {

		/** Version ***********************************************************/

		$this->version        = '0.2-dev'; // plugin version

		/** Paths *************************************************************/

		// Setup some base path and URL information
		$this->file           = __FILE__;
		$this->basename       = apply_filters( 'FilenameBasedCacheBusting_plugin_basenname', plugin_basename( $this->file ) );

		// Grab Options from DB
		$this->data           = get_option( $this->basename . '-options', array() );

	}


	/**
	 * Setup the default hooks and actions
	 */
	private function setup_actions() {
		add_action( 'generate_rewrite_rules', array( $this, 'action_generate_rewrite_rules' ) );
		add_action( 'admin_init', array( $this, 'action_admin_init' ) );

		add_filter( 'script_loader_src', array( $this, 'filter_script_style_loader_src'), 10, 1 );
		add_filter( 'style_loader_src', array( $this, 'filter_script_style_loader_src'), 10, 1 );

		do_action_ref_array( 'FilenameBasedCacheBusting_after_setup_actions', array( &$this ) );
	}

	/**
	 * Install / Upgrade routine
	 *
	 * Avoiding standard WordPress Activation/Deactivation method to make plugin
	 * work as 'must-use' dropin.
	 */
	public function action_admin_init() {
		$saved_version = $this->get( 'version' );

		if ( $this->version !== $saved_version ) {
			$this->flush_rewrite();
			$this->set( 'version', $this->version );
		}
	}

	public function filter_script_style_loader_src( $src ) {
  
		// Don't touch admin scripts.
		if ( is_admin() ) {
			return $src;
		}
	 
		// Only for scripts on current domain
		$domain = get_site_url();
		if ( strpos( $src, $domain) === false ) {
			return $src;
		}

		// Remove version string from the source.
		if ( strpos( $src, 'ver=' ) ) {
			$src = remove_query_arg( 'ver', $src );
		}
		
		// Get the sources local file path
		$src_local_path = str_replace( get_site_url(), ABSPATH, $src );
	 
		// Get the files last updated timestamp
		$timestamp = filemtime( $src_local_path );
	 
		// Get the extension of the file, can be '.js' or '.css'.
		$ext = '.' . pathinfo( $src, PATHINFO_EXTENSION );
	 
		// Build the new source.
		$src = str_replace( $ext, '.' . $timestamp . '.fbcb' . $ext, $src );
	 
		// Return the new source.
		return $src;

	}

	private function flush_rewrite () {
		global $wp_rewrite;
		$wp_rewrite->flush_rules( true );
	}

	public function action_generate_rewrite_rules () {
		global $wp_rewrite;
		$new_non_wp_rules = array(
			'^(.+)\.(.+)\.fbcb\.(js|css)$' => '$1.$3',
			);
		$wp_rewrite->non_wp_rules = $new_non_wp_rules + $wp_rewrite->non_wp_rules;
	}

	private function get( $key ) {
		return isset( $this->data[$key] ) ? $this->data[$key] : null;
	}

	private function set( $key, $value ) {
		$this->data[$key] = $value;
		update_option( $this->basename . '-options', $this->data );
	}

	public static function uninstall()	{
		$plug = new FilenameBasedCacheBusting;
		$plug->setup_globals();

		delete_option( plugin_basename( __FILE__ ) . '-options');

		global $wp_rewrite;
		$wp_rewrite->flush_rules( true );
	}
}

/**
 * The main function responsible for returning the one true theme instance
 * to functions everywhere.
 */
function FilenameBasedCacheBusting() {
	return FilenameBasedCacheBusting::instance();
}

add_action( 'plugins_loaded', 'FilenameBasedCacheBusting' );

/**
 * Uninstall the plugin
 *
 * 1. Comment out the line above
 * 2. Un-comment the line below.
 * 3. Refresh the admin screen.
 */
// add_action( 'admin_init', 'FilenameBasedCacheBusting::uninstall' );