Register Revisions for Meta and Taxonomies

hmpmr.php

<?php
/*
Plugin Name: HM Post Meta Revisions
Description: Register Revisions for meta keys.
Version:     1.0
Author:      Matthew Haines-Young (building on code from John Blackbourn)
*/

class HM_Post_Meta_Revisions {

	protected static $instance;

	private $fields     = array();
	private $taxonomies = array();

	function __construct() {

		add_action( 'save_post',                array( $this, 'save_revision_meta' ), 10 );
		add_action( 'save_post',                array( $this, 'save_revision_taxonomies' ), 10 );
		add_action( 'wp_restore_post_revision', array( $this, 'restore_revision_meta' ), 10, 2 );
		add_action( 'wp_restore_post_revision', array( $this, 'restore_revision_taxonomies' ), 10, 2 );

		// Filter the post revision fields.
		add_filter( '_wp_post_revision_fields', array( $this, 'post_revision_fields' ) );

		// Always do a revision on save.
		// @todo This could be a bit cleverer and check for changes in meta/taxonomies.
		add_action( 'wp_save_post_revision_check_for_changes', '__return_false' );

	}

	/**
	 * Creates or returns an instance of this class.
	 *
	 * @return HM_Post_Meta_Revisions A single instance of this class.
	 */
	public static function get_instance() {
		if ( null == self::$instance ) {
			self::$instance = new self;
		}
		return self::$instance;
	}

	/**
	 * Register revisions for meta key.
	 * Enable post revisions for a given key.
	 *
	 * @param  string         $id              meta key
	 * @param  string         $label           label. Used in revisions UI.
	 * @param  string|closure $format_callback UI Format callback. Format raw meta value to be used in revisions UI.
	 * @return null
	 */
	function register_revisions_for_meta_key( $meta_key, $label, $format_callback = null ) {

		$this->fields[ $meta_key ] = $label;

		if ( $format_callback ) {
			add_filter( "_wp_post_revision_field_$meta_key", $format_callback, 10, 3 );
		}

	}

	/**
	 * Register revisions for taxonomy.
	 *
	 * @param  string         $id              meta key
	 * @param  string         $label           label. Used in revisions UI.
	 * @param  string|closure $format_callback UI Format callback. Format raw meta value to be used in revisions UI.
	 * @return null
	 */
	function register_revisions_for_taxonomy( $taxonomy, $format_callback = null ) {

		$taxonomy_object = get_taxonomy( $taxonomy );
		$this->taxonomies[ $taxonomy_object->name ] = $taxonomy_object->label;

		if ( $format_callback ) {
			add_filter( "_wp_post_revision_field_$taxonomy", $format_callback, 10, 3 );
		} else {
			add_filter( "_wp_post_revision_field_$taxonomy", array( $this, 'taxonomy_format_callback' ), 10, 3 );
		}

	}

	/**
	 * Filter the post revision fields to add the new meta/tax revisions.
	 *
	 * @param  array $fields array key => label.
	 * @return array
	 */
	function post_revision_fields( $fields ) {
		return array_merge( $fields, $this->fields, $this->taxonomies );
	}

	/**
	 * Restore metadata.
	 * This should be hooked in on wp_restore_post_revision
	 *
	 * @param  int $post_id
	 * @param  int $revision_id
	 * @return null
	 */
	function restore_revision_meta( $post_id, $revision_id ) {

		foreach ( array_keys( $this->fields ) as $meta_key ) {

			// Delete all existing meta for this key.
			delete_post_meta( $post_id, $meta_key );

			// Copy meta from revision to parent.
			$values = get_metadata( 'post', $revision_id, $meta_key, false );
			foreach ( $values as $value ) {
				add_post_meta( $post_id, $meta_key, $value );
			}

		}

	}

	/**
	 * Save metadata revision. (hooked in on save_post)
	 * Notes
	 * Uses crazy closure to hook the actual meta data save in after the save post action of the parent has fired.
	 * I wanted to avoid directly saving the $_POST data as plugins may be modifying this before save.
	 *
	 * @param  int $post_id
	 * @param  int $revision_id
	 * @return null
	 */
	function save_revision_meta( $post_id ) {

		$revision_id = $post_id;
		$parent_id   = wp_is_post_revision( $revision_id );

		$closure = function( $post_id ) use ( $revision_id, $parent_id, &$closure  ) {

			if ( $post_id != $parent_id ) {
				return;
			}

			remove_action( 'wp_insert_post', $closure, 100 );

			foreach ( array_keys( $this->fields ) as $meta_key ) {
				$values = get_metadata( 'post', $parent_id, $meta_key );
				delete_metadata( 'post', $revision_id, $meta_key );
				foreach ( $values as $value ) {
					add_metadata( 'post', $revision_id, $meta_key, $value );
				}
			}

		};

		add_action( 'wp_insert_post', $closure, 100 );

	}

	/**
	 * Restore taxonomies.
	 * This should be hooked in on wp_restore_post_revision
	 *
	 * @param  int $post_id
	 * @param  int $revision_id
	 * @return null
	 */
	function restore_revision_taxonomies( $post_id, $revision_id ) {

		foreach ( array_keys( $this->taxonomies ) as $taxonomy ) {

			$terms = wp_get_object_terms( $revision_id, $taxonomy );

			if ( empty( $terms ) ) {
				wp_set_object_terms( $post_id, null, $taxonomy );
			} else {
				$terms = array_map( 'intval', wp_list_pluck( $terms, 'term_id' ) );
				wp_set_object_terms( $post_id, $terms, $taxonomy );
			}

		}

	}

	/**
	 * Save taxonomy revision.
	 * This should be hooked in on save_post.
	 * Note - uses a slightly crazy closure to hook the actual meta data save in
	 * after all the save post actions of the parent have fired.
	 *
	 * @param  int $post_id
	 * @param  int $revision_id
	 * @return null
	 */
	function save_revision_taxonomies( $post_id ) {

		$revision_id = $post_id;
		$parent_id   = wp_is_post_revision( $revision_id );

		$closure = function( $post_id ) use ( $revision_id, $parent_id, &$closure  ) {

			if ( $post_id != $parent_id ) {
				return;
			}

			remove_action( 'wp_insert_post', $closure, 100 );

			foreach ( array_keys( $this->taxonomies ) as $taxonomy ) {
				$terms = wp_get_object_terms( $parent_id, $taxonomy );

				if ( ! empty( $terms ) ) {
					$terms = array_map( 'intval', wp_list_pluck( $terms, 'term_id' ) );
					wp_set_object_terms( $revision_id, $terms, $taxonomy );
				}
			}

		};

		add_action( 'wp_insert_post', $closure, 100 );

	}

	function taxonomy_format_callback( $value, $field, $parent ) {

		$terms = wp_get_object_terms( $parent->ID, $field );

		if ( ! empty( $terms ) ) {
			return implode( "\r", wp_list_pluck( $terms, 'name' ) );
		}

	}

}

add_action( 'plugins_loaded', function() {
	HM_Post_Meta_Revisions::get_instance();
} );

/**
 * Register revisions for a meta key.
 *
 * @param  string $meta_key        meta key
 * @param  string $label           label used in revisions UI
 * @param  mixed  $format_callback callback to format data for use in revisions UI.
 * @return null
 */
function hmpmr_register_revisions_for_meta_key( $meta_key, $label, $format_callback = null ) {
	HM_Post_Meta_Revisions::get_instance()->register_revisions_for_meta_key( $meta_key, $label, $format_callback );
}

/**
 * Register revisions for a taxonomy.
 *
 * @param  string $meta_key        meta key
 * @param  string $label           label used in revisions UI
 * @param  mixed  $format_callback callback to format data for use in revisions UI.
 * @return null
 */
function hmpmr_register_revisions_for_taxonomy( $taxonomy, $format_callback = null ) {
	HM_Post_Meta_Revisions::get_instance()->register_revisions_for_taxonomy( $taxonomy, $format_callback );
}