Ticket #18179: meta-box.3.php

<?php
/*
Plugin Name: Custom Metaboxes for Core
*/

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;

        /**
         * A multi-dimensional array of registered meta fields, and their settings.
         */
        public $meta_fields;


        /**
         * 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_action( 'save_post', array( $this, '_save' ), 10, 99 ); // Effectively infinite args.

                // 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_meta_box' ) );
                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;
        }

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

        /**
         * 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_meta_box' ) );
                remove_action( 'admin_enqueue_scripts', array( $this, '_enqueue_scripts' ) );
        }
        
        /**
         * Register a post meta field.
         * 
         * For use in a subclass.
         */
        protected function register_meta_field( $meta_key, $args = array() ) {

                $defaults = array( 
                        'type' => 'text',
                        'render_callback' => array( $this, 'render_field' ),
                        'sanitize_callback' => array( $this, 'sanitize' ),
                        'auth_callback' => array( $this, 'authorize' ),
                        'title_label' => $meta_key,
                        'data' => array(), // not yet used. to preload form fields that expect data (radios, selects, etc.)
                );

                $args = wp_parse_args( $args, $defaults );

                extract( $args );

                // Register meta with WordPress. Sets up sanitization and authorization callbacks.
                register_meta( 'post', $meta_key, $sanitize_callback, $auth_callback );

                // Store meta field details in an array for later.
                $this->meta_fields[] = array( 
                        'type' => $type, 
                        'meta_key' => $meta_key, 
                        'render_callback' => $render_callback,
                        'title_label' => $title_label, 
                        'data' => array(),
                );
        }

        /**
         * Render the meta box.
         */
        public function render_meta_box() {
                foreach ( $this->meta_fields as $meta_field ) {
                        call_user_func( $meta_field['render_callback'], $meta_field );
                }
        }

        /**
         * Render callback for generic meta fields.
         */
        protected function render_field( $meta_field ) {
                global $post;
                
                extract( $meta_field );
                $meta_value = get_post_meta( $post->ID, $meta_key, true );
                echo "<h4>$title_label</h4>";
                switch ( $type ) {
                        case 'text':
                                echo '<input type="text" id="' . $meta_key . '" name="meta-field-' . $meta_key . '" value="' . esc_attr( $meta_value ) .'">';
                        break;
                        case 'wp_editor':
                                wp_editor( $meta_value, 'meta-field-' . $meta_key );
                        break;
                }
        }

        /**
         * Enqueue meta box scripts. Override in a subclass.
         */
        protected function enqueue_scripts() {
                $unique_meta_types = array_unique( wp_list_pluck( $this->meta_fields, 'type' ) );
                foreach ( $unique_meta_types as $meta_type ) {
                        switch ( $meta_type ) {
                                // Specific script enqueues for the displayed meta fields.
                        }
                }
        }

        /**
         * Sanitization callback for generic meta fields.
         */
        public function sanitize( $meta_value, $meta_key ) {
                foreach ( $this->meta_fields as $meta_field ) {
                        if ( $meta_field['meta_key'] == $meta_key ) {
                                switch ( $meta_field['type'] ) {
                                        case 'text' :
                                                $meta_value = sanitize_text_field( $meta_value );
                                        break;
                                        case 'wp_editor' :
                                                $meta_value = wp_kses_post( $meta_value );
                                        break;
                                }
                        }
                }
                return $meta_value;
        }

        /**
         * Default authorization callback. 
         */
        public function authorize( $allowed, $meta_key, $post_ID, $user_id, $cap, $caps ) {
                return true;
        }

        /**
         * Save the meta fields' data.
         */
        public function save() {
                global $post;
                foreach ( $this->meta_fields as $meta_field ) {
                        // Capabilities check. 
                        if ( current_user_can( 'edit_post_meta', $post->ID, $meta_field['meta_key'] ) ) {
                                // Check if the $_REQUEST array has the specific key set.

                                if ( isset( $_REQUEST['meta-field-' . $meta_field['meta_key']] ) ) {
                                        $meta_value = $_REQUEST['meta-field-' . $meta_field['meta_key']];
                                        update_post_meta( $post->ID, $meta_field['meta_key'], $meta_value );
                                }
                        }
                }
        }

        /**
         * Determine whether the meta box will be saved. Override in a subclass if necessary.
         *
         * Return true to save, false to cancel.
         * @param int    The post ID.
         * @param $post  The post object.
         */
        protected 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 ) )
                        die;

                return true;
        }

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

        /**
         * Internal function. Registers the meta box.
         */
        public final function _register_meta_box() {
                $id = "{$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() { // todo should this be public? can subclasses access public parent class functions?
                wp_nonce_field( "{$this->unique_id}_nonce", "_wpnonce_{$this->unique_id}", false );
                
                $this->render_meta_box();
        }

        /**
         * 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();
                // Check if we're autosaving/capabilities check.
                if ( call_user_func_array( array( $this, 'maybe_save' ), $args ) ) {
                        // Save the meta fields' data.
                        call_user_func_array( array( $this, 'save' ), $args );
                }
        }
}



/**
 * Meta Box Registry
 *
 * Implemented as singleton
 *
 */
class WP_Meta_Box_Registry {

        /**
         * WP_Meta_Box_Registry singleton implementation
         *
         * @var WP_Meta_Box_Registry
         */
        private static $instance;

        private $instances = array();

        /**
         * WP_Meta_Box_Registry singleton implementation
         *
         * @return WP_Meta_Box_Registry
         */
        public static function instance() {
                if (null === self::$instance)
                        self::$instance = new self();
                return self::$instance;
        }

        /**
         * Search registry for meta box instances
         *
         * @return array result
         */
        public function search($class_or_object, $screen = false, $slug = false) {
                $instances = array();

                foreach($this->instances as $instance) {

                        if ( ! $instance instanceof $class_or_object )
                                continue;

                        if ( $screen !== false && $instance->screen !== $screen )
                                continue;

                        if ( $slug !== false && $instance->slug !== $slug )
                                continue;

                        $instances[] = $instance;
                }

                return $instances;
        }

        /**
         * 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.
         *
         * @param WP_Meta_Box $instance
         */
        public function add( WP_Meta_Box $instance ) {
                static $counter = 0;

                $hash = spl_object_hash( $instance );

                if ( !empty( $instance->slug ) ) {
                        // If slug is specified, remove existing instance
                        $instances = $this->find( $instance, $instance->screen, $instance->slug );

                        if ($instances) 
                                $this->remove($instances[0]);

                } else {
                        // If no slug is specified, get the numerical index.
                        // alternatively get the number of this instances' class by screen and count plus one.
                        $instance->slug = ++$counter;
                }

                $this->instances[ $hash ] = $instance;
        }

        // in case this is still needed.
        public function get( WP_Meta_Box $instance ) {
                $hash = spl_object_hash( $instance );

                if ( isset( $this->instances[ $hash ] ) )
                        return $instance;

                return false;
        }

        /**
         * Remove instance from registry
         *
         * @param WP_Meta_Box $instance
         */
        public function remove( WP_Meta_Box $instance ) {
                $hash = spl_object_hash( $instance );

                if ( isset( $this->instances[ $hash ] ) )
                        unset( $this->instances[ $hash ] );
        }
}

class WP_Basic_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->register_meta_field(
                        '_basic_meta_box_test_field', 
                        array( 
                                'type' => 'text',
                                'title_label' => 'Some Title here' 
                        )
                );
                $this->register_meta_field(
                        '_basic_meta_box_wp_editor_field', 
                        array( 
                                'type' => 'wp_editor',
                                'title_label' => 'WP Editor!' 
                        )
                );
        }
}

new WP_Basic_Meta_Box( 'post', array( 'title' => 'Basic Meta Box' ) );