Ticket #18179: meta-box.php

<?php
/*
Plugin Name: WP_Meta_Box
Plugin URI: http://wordpress.org/
Description: The WP_Meta_Box class in development for 3.3.
Version: 0.1
Author: The WordPress Team
*/

class WP_Meta_Box {
        /**
         * The screen where the meta box will be shown.
         */
        public $screen;

        /**
         * A unique slug to allow multiple meta boxes of the same class
         * to exist on the same screen.
         */
        public $slug;

        /**
         * A unique identifier for the meta box.
         *
         * A string composed from the meta box class, screen, and slug.
         */
        public $unique_id;

        /**
         * Arguments passed to the meta box constructor.
         */
        public $args;

        /**
         * A registry that tracks each meta box instance.
         */
        public static $registry;


        /**
         * Constructor.
         *
         * Any subclasses MUST call parent::_construct( $screen, $args ).
         *
         * @param string $screen - The ID (string) for the screen where the meta box will be shown.
         * @param array  $args - An array of supplied arguments. Optional.
         *
         * $args recognized by default:
         *    title    - The title of the meta box.
         *    context  - The context within the page where the box should show ('normal', 'advanced').
         *    priority - The priority within the context where the boxes should show ('high', 'low').
         *    slug     - A unique string to identify the meta box.
         */
        public function __construct( $screen, $args = array() ) {
                // Set variables
                $this->screen = $screen;
                $this->slug   = empty( $args['slug'] ) ? '' : $args['slug'];

                // Remove slug from args
                unset( $args['slug'] );

                // Set default args
                $defaults = array(
                        'title'         => __( 'Untitled' , 'wordcampbase'),
                        'context'       => 'side',
                        'priority'      => 'default',
                );
                $this->args = wp_parse_args( $args, $defaults );

                // Add the meta box to the registry.
                // Generates a slug if one doesn't already exist.
                WP_Meta_Box::registry()->add( $this );

                // Construct the meta box's unique ID.
                $this->unique_id = get_class( $this ) . "_{$this->screen}_{$this->slug}";

                // Bind hooks
                add_action( 'admin_init',            array( $this, '_register' ) );
                add_action( 'admin_enqueue_scripts', array( $this, '_enqueue_scripts' ) );
        }

        /**
         * Fetches the meta box registry.
         */
        public static function registry() {
                if ( ! isset( WP_Meta_Box::$registry ) )
                        WP_Meta_Box::$registry = new WP_Meta_Box_Registry();
                return WP_Meta_Box::$registry;
        }

        /**
         * Remove the meta box.
         */
        public function remove() {
                // Make sure we've removed any data from the registry.
                WP_Meta_Box::registry()->remove( get_class( $this ), $this->screen, $this->slug );

                // Unbind actions.
                remove_action( 'admin_init',            array( $this, '_register' ) );
                remove_action( 'admin_enqueue_scripts', array( $this, '_enqueue_scripts' ) );
        }

        /**
         * Render the meta box. Implement in a subclass.
         */
        protected function render() {}

        /**
         * Save the meta box. Implement in a subclass.
         */
        protected function save() {}

        /**
         * Fires when the meta box is registered. Override in a subclass.
         */
        protected function register() {}

        /**
         * Enqueue meta box scripts. Override in a subclass.
         */
        protected function enqueue_scripts() {}

        /**
         * Determine whether the meta box will be saved. Override in a subclass.
         *
         * Return true to save, false to cancel.
         */
        protected function maybe_save() {
                return true;
        }

        /**
         * Add an action to trigger save.
         *
         * Due to the different types of meta boxes, save will not be triggered by default.
         */
        public function add_save_action( $name, $priority=10 ) {
                add_action( $name, array( $this, '_save' ), $priority, 99 ); // Effectively infinite args.
        }

        /**
         * Remove a save action.
         */
        public function remove_save_action( $name, $priority=10 ) {
                remove_action( $name, array( $this, '_save' ), $priority, 99 ); // Effectively infinite args.
        }


        /* =====================================================================
         * INTERNAL FUNCTIONS
         * ===================================================================== */

        /**
         * Internal function. Registers the meta box.
         */
        public final function _register() {
                $id = "{$this->unique_id}-meta-box";

                add_meta_box( $id, $this->args['title'], array( $this, '_render' ),
                        $this->screen, $this->args['context'], $this->args['priority'],
                        $this->args );

                $this->register();
        }

        /**
         * Internal function. Ensures scripts are only loaded when necessary.
         */
        public final function _enqueue_scripts() {
                $current_screen = get_current_screen();

                if ( isset( $current_screen ) && $this->screen == $current_screen->id )
                        $this->enqueue_scripts();
        }

        /**
         * Internal function, initiates the rendering process.
         */
        public final function _render( $object, $box ) {
                wp_nonce_field( "{$this->unique_id}_nonce", "_wpnonce_{$this->unique_id}", false );

                $this->render();
        }

        /**
         * Internal function, initiates the saving process.
         */
        public final function _save() {
                // Nonce check (sorry, you don't have a choice about this one).
                check_admin_referer( "{$this->unique_id}_nonce", "_wpnonce_{$this->unique_id}" );

                $args = func_get_args();

                // Only save if maybe_save returns true.
                if ( call_user_func_array( array( $this, 'maybe_save' ), $args ) )
                        call_user_func_array( array( $this, 'save' ), $args );
        }
}



class WP_Meta_Box_Registry {
        public $instances = array();

        /**
         * Adds a meta box instance.
         *
         * If $instance->slug is defined, will use $slug.
         * If a meta box with the same slug exists, it will be overwritten.
         */
        public function add( $instance ) {
                $class = get_class( $instance );

                if ( ! isset( $this->instances[ $class ] ) )
                        $this->instances[ $class ] = array();

                if ( ! isset( $this->instances[ $class ][ $instance->screen ] ) )
                        $this->instances[ $class ][ $instance->screen ] = array();

                $screen_instances = $this->instances[ $class ][ $instance->screen ];

                // If no slug is specified, get the numerical index.
                if ( empty( $instance->slug ) ) {
                        $this->instances[ $class ][ $instance->screen ][] = $instance;

                        // Get the index of the instance. I feel dirty.
                        $instance->slug = array_pop( array_keys( $this->instances[ $class ][ $instance->screen ] ) );

                } else {
                        $this->instances[ $class ][ $instance->screen ][ $instance->slug ] = $instance;
                }
        }

        public function get( $class, $screen = false, $slug = false ) {
                if ( ! isset( $this->instances[ $class ] ) )
                        return array();

                if ( empty( $screen ) )
                        return $this->instances[ $class ];

                if ( ! isset( $this->instances[ $class ][ $screen ] ) )
                        return array();

                $screen_instances = $this->instances[ $class ][ $screen ];

                if ( empty( $slug ) )
                        return $screen_instances;

                if ( isset( $screen_instances[ $slug ] ) )
                        return $screen_instances[ $slug ];
                else
                        return false;
        }

        public function remove( $class, $screen = false, $slug = false ) {
                // Ensure that the instance(s) we want to remove exist.
                $instances = $this->get( $class, $screen, $slug );
                if ( empty( $instances ) )
                        return;

                // Remove the appropriate instance(s) from the registry.
                if ( empty( $screen ) )
                        unset( $this->instances[ $class ] );
                elseif ( empty( $slug ) )
                        unset( $this->instances[ $class ][ $screen ] );
                else
                        unset( $this->instances[ $class ][ $screen ][ $slug ] );

                // Call remove on each instance.
                if ( ! empty( $slug ) )
                        $instances = array( $instances );

                foreach ( $instances as $instance ) {
                        $instance->remove();
                }
        }
}



class WP_CPT_Meta_Box extends WP_Meta_Box {
        function __construct( $screen, $args = array() ) {
                // Call the WP_Meta_Box constructor.
                parent::__construct( $screen, $args );

                // Save the meta box contents when 'save_post' is triggered.
                $this->add_save_action( 'save_post' );
        }

        function maybe_save( $post_id, $post ) {
                // Bail if we're autosaving
                if ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE )
                        return;

                // @TODO Add revision check

                // Cap check
                if ( ! current_user_can( 'edit_post', $post_id ) )
                        return;

                return true;
        }
}