Enqueue Shortcode

class-enqueue-shortcode.php

<?php
// Based heavily on http://wordpress.stackexchange.com/a/77946

/**
 * This class allows child classes to easily enqueue styles and scripts.
 *
 * Children of this class should be instantiate as 
 * 	new Child_Enqueue_Shortcode( 'shortcode-name' )
 * and should have methods enqueue() and output_shortcode(). The method enqueue()
 * should simply have wp_enqueue_style() and wp_enqueue_script() (as well as
 * wp_register_*()) calls. The output_shortcode() method should contain the HTML
 * for display of the shortcode.
 */
abstract class Enqueue_Shortcode {
	/**
	 * Properties
	 */

	public $shortcode_name;
	public $post_meta_key;

	/**
	 * Methods
	 */

	abstract protected function output_shortcode( $attributes, $content );
	abstract protected function enqueue();

	public function __construct( $shortcode_name ) {
		$this->shortcode_name = $shortcode_name;
		$this->post_meta_key = md5( $shortcode_name );

		add_shortcode( $this->shortcode_name, array( $this, 'do_shortcode' ) );

		add_action( 'save_post', array( $this, 'save_post' ) );
		add_action( 'wp_print_styles', array( $this, 'wp_print_styles' ) );
	}

	public function do_shortcode( $attributes, $content ) {
		$this->output_shortcode( $attributes, $content );
	}

	public function save_post( $post_id ) {
		$post = get_post( $post_id );
		if ( has_shortcode( $post->post_content, $this->shortcode_name ) ) {
			$this->found_shortcode( $post_id );
		} else {
			$this->found_no_shortcode( $post_id );
		}
	}

	public function wp_print_styles( $args ) {
		global $post;

		if ( 'yes' == get_post_meta( $post->ID, $this->post_meta_key, true ) ) {
			$this->enqueue();
		}
	}

	protected function found_shortcode( $post_id ) {
		update_post_meta( $post_id, $this->post_meta_key, 'yes' );
	}

	protected function found_no_shortcode( $post_id ) {
		update_post_meta( $post_id, $this->post_meta_key, 'no' );
	}
}