[WordPress] Rapid Prototyping: Prototype To Code, Part 1

00-class-meta-box.php

<?php
/**
 * Registers the Meta Box with WordPress.
 *
 * @author Tom McFarlin
 * @since  0.2.0
 */

/**
 * Registers the Meta Box with WordPress. Defines the ID, title, display function,
 * and the post type on which it will live.
 *
 * @author Tom McFarlin
 * @since  0.2.0
 */
class Meta_Box {

	/**
	 * A reference to the class that will display the contents in the meta box.
	 *
	 * @access private
	 * @var    Meta_Box_Display
	 */
	private $meta_box_display;

	/**
	 * Instantiates the class by setting its property equal to a reference to its display.
	 */
	public function __construct() {
		$this->meta_box_display = new Meta_Box_Display();
	}

	/**
	 * The function responsible for hooking into the WordPress API.
	 */
	public function init() {

		add_meta_box(
			'three-recent-posts',
			'Three Recent Posts',
			array( $this->meta_box_display, 'display' ),
			'post',
			'side'
		);
	}
}

01-class-meta-box-display.php

<?php
/**
 * Defines the display for the meta box.
 *
 * @author Tom McFarlin
 * @since  0.2.0
 */

/**
 * Defines the display for the meta box that will render the content in the
 * context of its meta box.
 *
 * @author Tom McFarlin
 * @since  0.2.0
 */
class Meta_Box_Display {

	/**
	 * A reference to the class that will display the contents in the meta box.
	 *
	 * @access private
	 * @var    Post_Messenger
	 */
	private $messenger;

	/**
	 * Instantiates the object by setting a property equal to that of the class
	 * responsible for rendering the messages from the post query.
	 */
	public function __construct() {
		$this->messenger = new Post_Messenger( $this );
	}

	/**
	 * If there are posts to display, renders them in the metabox. Otherwise, displays
	 * a note that there are no posts to display.
	 */
	public function display( $message ) {
		$this->messenger->get_message();
	}
}

02-class-post-messenger.php

<?php
/**
 * Display content for the meta box when requested.
 *
 * @author Tom McFarlin
 * @since  0.2.0
 */

/**
 * Retrieves information from the class responsible for querying the database and
 * renders it in the context of our meta box when called via the Meta Box Display.
 *
 * @author Tom McFarlin
 * @since  0.2.0
 */
class Post_Messenger {

	/**
	 * A reference to the query resonsible for retrieving post information from
	 * the database.
	 *
	 * @access private
	 * @var    WP_Query
	 */
	private $query;

	/**
	 * A reference to the message that's displayed in the view of the
	 * meta box.
	 *
	 * @access private
	 */
	private $message;

	/**
	 * Instantiates the class by setting a reference to the query.
	 */
	public function __construct() {
		$this->query = new Post_Query();
	}

	/**
	 * Retrieves the content to be displayed in the meta box.
	 */
	public function get_message() {

		$this->get_description();

		if ( $this->query->has_posts() ) {
			$this->get_post_message();
		} else {
			$this->get_no_posts_message();
		}
	}

	/**
	 * Displays the description of the content of the meta box.
	 *
	 * @access private
	 */
	private function get_post_message() {
		include_once 'post-list.php';
	}

	/**
	 * Displays the description of the content of the meta box.
	 *
	 * @access private
	 */
	private function get_description() {
		include_once 'message-description.php';
	}

	/**
	 * Displays a message of there are no recent posts.
	 *
	 * @access private
	 */
	private function get_no_posts_message() {
		include_once 'no-post-list.php';
	}
}

03-post-query.php

<?php
/**
 * Queries the database for three most recent posts.
 *
 * @author Tom McFarlin
 * @since  0.2.0
 */

/**
 * Queries the database for three most recent posts. Returns the query to the
 * caller so that it can be interrogates for posts or not.
 *
 * @author Tom McFarlin
 * @since  0.2.0
 */
class Post_Query {

	/**
	 * A reference to the WP_Query this class wraps.
	 *
	 * @access private
	 * @var    WP_Query
	 */
	private $query;

	/**
	 * Instantiates the class by preparing instance data and executing the
	 * query so the display can render the contents.
	 */
	public function __construct() {

		$this->query = null;
		$this->get_posts();
	}

	/**
	 * Executes the query for returning the post recent posts ordered by date.
	 *
	 * @access private
	 */
	private function get_posts() {

		$args = array(
			'post_type'   => 'post',
			'post_status' => 'publish',
			'orderby'     => 'date',
			'order'       => 'desc',
		);
		$this->query = new WP_Query( $args );

		return $this->query;
	}

	/**
	 * A helper function to determine if the query has any posts.
	 */
	public function has_posts() {
		return ! $this->query->have_posts();
	}

	/**
	 * A helper function for retrieving the next post in the list of
	 * posts
	 */
	public function the_post() {
		return $this->query->the_post();
	}
}

04-post-list.php

<ol>
	<?php while ( $this->query->has_posts() ) {  ?>
		<?php $this->query->the_post(); ?>
		<li>
			<a href="<?php get_the_permalink(); ?>" target="_blank">
				<?php echo get_the_title(); ?>
			</a>
		</li>
	<?php } ?>
</ol>

06-message-description.php

<p>
	<span class="description">
		Displays up to the three most recent posts.
	</span><!-- .description -->
</p>

07-no-post-list.php

<p>There are no recent posts.</p>

08-three-recent-posts.php

<?php
/**
 * Three Recent Posts
 *
 * @package     TRP
 * @author      Tom McFarlin
 * @copyright   2017 Tom McFarlin
 * @license     MIT
 *
 * @wordpress-plugin
 * Plugin Name: Three Recent Posts
 * Plugin URI:  https://tommcfarlin.com/three-recent-posts/
 * Description: Displays the three mot recent posts in your post editor screen.
 * Version:     0.2.0
 * Author:      Tom McFarlin
 * Author URI:  https://tommcfarlin.com
 * Text Domain: three-recent-posts
 * License:     GPL
 * License URI: http://www.gnu.org/licenses/gpl-3.0.txt
 */

include 'class-meta-box.php';
include 'class-meta-box-display.php';
include 'class-post-messenger.php';
include 'class-post-query.php';

add_action( 'add_meta_boxes', 'trp_start' );
/**
 * Starts the plugin.
 */
function trp_start() {

	$meta_box = new Meta_Box();
	$meta_box->init();
}