Plugin Product Editor Column

product-editor-column.php

<?php # -*- coding: utf-8 -*-
/**
 * Plugin Name: Product Editor Column
 * Description: Adds a column to the products table backend with the name of the last editor. Requires at least PHP 5.4.
 * Author:      Fuxia
 * Version:     2014.08.09
 * Licence:     MIT
 * Plugin URI:  http://wordpress.stackexchange.com/a/157258/73
 */
namespace WPSE;

interface Column_Data
{
	/**
	 * @param array $columns
	 * @return array
	 */
	public function add_column( Array $columns );

	/**
	 * @param  int    $post_id
	 * @return string
	 */
	public function get_column_content( $post_id );

	/**
	 * @return string
	 */
	public function get_post_type();

	/**
	 * @param $column_name
	 * @return bool
	 */
	public function is_valid_column( $column_name );
}

class Last_Mod_Author_Column_Data implements Column_Data
{
	/**
	 * @var string
	 */
	private $post_type;

	/**
	 * @var string
	 */
	private $column_name = 'modified_author';

	/**
	 * @param string $post_type
	 */
	public function __construct( $post_type )
	{
		$this->post_type = $post_type;
	}

	/**
	 * @param array $columns
	 * @return array
	 */
	public function add_column( Array $columns )
	{
		$columns[ $this->column_name ] = 'Last modified by';

		return $columns;
	}

	/**
	 * @param  int    $post_id
	 * @return string
	 */
	public function get_column_content( $post_id )
	{
		$last_id = get_post_meta( $post_id, '_edit_last', TRUE );

		if ( ! $last_id ) {
			return '';
		}

		$last_user = get_userdata( $last_id );

		return $last_user->display_name;
	}

	/**
	 * @return string
	 */
	public function get_post_type()
	{
		return $this->post_type;
	}

	/**
	 * @param $column_name
	 * @return bool
	 */
	public function is_valid_column( $column_name )
	{
		return $this->column_name === $column_name;
	}
}

interface Column_View
{
	/**
	 * @param  string $column_name
	 * @param  int    $post_id
	 * @return void
	 */
	public function render_column( $column_name, $post_id );
}

class Last_Mod_Author_Column_Output implements Column_View
{
	/**
	 * @var Column_Data
	 */
	private $data;

	/**
	 * @param Column_Data $data
	 */
	public function __construct( Column_Data $data )
	{
		$this->data = $data;
	}

	/**
	 * @param  string $column_name
	 * @param  int    $post_id
	 * @return void
	 */
	public function render_column( $column_name, $post_id )
	{
		if ( ! $this->data->is_valid_column( $column_name ) )
			return;

		$content = $this->data->get_column_content( $post_id );

		if ( '' === $content )
			print '<i>Unknown</i>';
		else
			print esc_html( $content );
	}
}

class Controller
{
	/**
	 * @var Column_Data
	 */
	private $data;

	/**
	 * @var Column_View
	 */
	private $view;

	/**
	 * @param Column_Data $data
	 * @param Column_View $view
	 */
	public function __construct( Column_Data $data, Column_View $view ) {

		$this->data = $data;
		$this->view = $view;
	}

	/**
	 * @return void
	 */
	public function setup()
	{
		$screen    = get_current_screen();
		$post_type = $this->data->get_post_type();

		if ( ! isset ( $screen->id ) )
			return;

		if ( "edit-$post_type" !== $screen->id )
			return;

		add_filter(
			"manage_{$post_type}_posts_columns",
			[ $this->data, 'add_column' ]
		);

		add_action(
			"manage_{$post_type}_posts_custom_column",
			[ $this->view, 'render_column' ],
			10, 2
		);
	}
}

add_action( 'load-edit.php', function() {

	$model      = new Last_Mod_Author_Column_Data( 'product' );
	$view       = new Last_Mod_Author_Column_Output( $model );
	$controller = new Controller( $model, $view );

	$controller->setup();
});