sensei-lesson-info-block.php

<?php
/**
 * Plugin Name: Sensei Lesson Info Block
 * Description: Add Lesson Info Gutenberg Block to Sensei Lessons.
 * Version: 0.0.1
 * Author: Automattic
 */

class Sensei_Lesson_Info_Block {
	private static $_instance = null;

	public static function get_instance() {
		self::$_instance = new Sensei_Lesson_Info_Block();
	}

	private function __construct() {
		add_action( 'rest_api_init', array( $this, 'rest_api_init' ) );
		add_action( 'enqueue_block_editor_assets', array( $this, 'enqueue_block_js' ) );
	}

	public function rest_api_init() {
		register_rest_field( 'lesson', 'meta', array(
			'get_callback' => function( $lesson_arr ) {
				$meta_keys = array( '_lesson_length', '_lesson_complexity' );
				$response  = array();

				foreach ( $meta_keys as $key ) {
					$response[ $key ] = get_post_meta( $lesson_arr['id'], $key, true );
				}

				return $response;
			},
			'update_callback' => function( $meta, $lesson ) {
				$meta_keys = array( '_lesson_length', '_lesson_complexity' );

				foreach ( $meta_keys as $key ) {
					if ( isset( $meta[ $key ] ) ) {
						update_post_meta( $lesson->ID, $key, $meta[ $key ] );
					}
				}
			}
		) );
	}

	public function enqueue_block_js() {
		// Only enqueue on CPT Page.
		global $post;

		if ( 'lesson' === $post->post_type ) {
			wp_enqueue_script(
				'sensei_lesson_info_block',
				plugins_url( 'script.js', __FILE__ ),
				array( 'wp-blocks', 'wp-element' ),
				'0.0.1',
				false
			);
		}
	}
}
Sensei_Lesson_Info_Block::get_instance();