plugin.php

<?php

add_action( 'plugins_loaded', 'WPAPIYoast_init' );

/**
 * Plugin Name: Yoast to REST API
 * Description: Adds Yoast fields to page and post metadata to WP REST API responses
 * Author: CodeDrips
 * Author URI: https://github.com/CodeDrips
 * Version: 1.4.2
 * Plugin URI: https://github.com/CodeDrips/yoast-to-rest-api
 */
class Yoast_To_REST_API {

  protected $keys = array(
    'yoast_wpseo_focuskw',
    'yoast_wpseo_title',
    'yoast_wpseo_metadesc',
    'yoast_wpseo_linkdex',
    'yoast_wpseo_metakeywords',
    'yoast_wpseo_meta-robots-noindex',
    'yoast_wpseo_meta-robots-nofollow',
    'yoast_wpseo_meta-robots-adv',
    'yoast_wpseo_canonical',
    'yoast_wpseo_redirect',
    'yoast_wpseo_opengraph-title',
    'yoast_wpseo_opengraph-description',
    'yoast_wpseo_opengraph-image',
    'yoast_wpseo_twitter-title',
    'yoast_wpseo_twitter-description',
    'yoast_wpseo_twitter-image'
  );

  function __construct() {
    add_action( 'rest_api_init', array( $this, 'add_yoast_data' ) );
  }

  function add_yoast_data() {
    // Posts
    register_rest_field( 'post',
      'yoast_meta',
      array(
        'get_callback'    => array( $this, 'wp_api_encode_yoast' ),
        'update_callback' => array( $this, 'wp_api_update_yoast' ),
        'schema'          => null,
      )
    );

    // Pages
    register_rest_field( 'page',
      'yoast_meta',
      array(
        'get_callback'    => array( $this, 'wp_api_encode_yoast' ),
        'update_callback' => array( $this, 'wp_api_update_yoast' ),
        'schema'          => null,
      )
    );

    // Category
    register_rest_field( 'category',
      'yoast_meta',
      array(
        'get_callback'    => array( $this, 'wp_api_encode_yoast_category' ),
        'update_callback' => null,
        'schema'          => null,
      )
    );

    // Tag
    register_rest_field( 'tag',
      'yoast_meta',
      array(
        'get_callback'    => array( $this, 'wp_api_encode_yoast_tag' ),
        'update_callback' => null,
        'schema'          => null,
      )
    );

    // Public custom post types
    $types = get_post_types( array(
      'public'   => true,
      '_builtin' => false
    ) );

    foreach ( $types as $key => $type ) {
      register_rest_field( $type,
        'yoast_meta',
        array(
          'get_callback'    => array( $this, 'wp_api_encode_yoast' ),
          'update_callback' => array( $this, 'wp_api_update_yoast' ),
          'schema'          => null,
        )
      );
    }
  }

  /**
   * Updates post meta with values from post/put request.
   *
   * @param array $value
   * @param object $data
   * @param string $field_name
   *
   * @return array
   */
  function wp_api_update_yoast( $value, $data, $field_name ) {

    foreach ( $value as $k => $v ) {

      if ( in_array( $k, $this->keys ) ) {
        ! empty( $k ) ? update_post_meta( $data->ID, '_' . $k, $v ) : null;
      }
    }

    return $this->wp_api_encode_yoast( $data->ID, null, null );
  }

  function wp_api_encode_yoast( $p, $field_name, $request ) {

    $yoast_meta = array(
      'yoast_wpseo_title'     => $this->get_post_title($p['id']),
      'yoast_wpseo_metadesc'  => $this->get_post_description($p['id']),
      'yoast_wpseo_canonical' => '',
      'yoast_wpseo_focuskw' => get_post_meta( $p['id'], '_yoast_wpseo_focuskw', true ),
    );

    return (array) $yoast_meta;
  }

  private function get_post_description( $post_id ): string {
    $yoast_post_description = get_post_meta( $post_id, '_yoast_wpseo_metadesc', true );
    if ( empty( $yoast_post_description ) ) {
      $wpseo_titles           = get_option( 'wpseo_titles', [] );
      $yoast_post_description = isset( $wpseo_titles[ 'metadesc-' . $post->post_type ] ) ? $wpseo_titles[ 'metadesc-' . $post->post_type ] : '';
    }

    return wpseo_replace_vars( $yoast_post_description, $post );
  }

  private function get_post_title( $post_id ): string {
    $yoast_title = get_post_meta( $post_id, '_yoast_wpseo_title', true );
    if ( empty( $yoast_title ) ) {
      $wpseo_titles = get_option( 'wpseo_titles', [] );
      $yoast_title  = isset( $wpseo_titles[ 'title-' . $post->post_type ] ) ? $wpseo_titles[ 'title-' . $post->post_type ] : get_the_title();
    }

    return wpseo_replace_vars( $yoast_title, $post );
  }

  private function wp_api_encode_taxonomy() {
    $wpseo_frontend = WPSEO_Frontend_To_REST_API::get_instance();
    $wpseo_frontend->reset();

    $yoast_meta = array(
      'yoast_wpseo_title'    => $wpseo_frontend->get_taxonomy_title(),
      'yoast_wpseo_metadesc' => $wpseo_frontend->metadesc( false ),
    );

    return (array) $yoast_meta;
  }

  function wp_api_encode_yoast_category( $category ) {
    query_posts( array(
      'cat' => $category['id'],
    ) );

    the_post();

    $res = $this->wp_api_encode_taxonomy();

    wp_reset_query();

    return $res;
  }

  function wp_api_encode_yoast_tag( $tag ) {
    query_posts( array(
      'tag_id' => $tag['id'],
    ) );

    the_post();

    $res = $this->wp_api_encode_taxonomy();

    wp_reset_query();

    return $res;
  }
}

function WPAPIYoast_init() {
  if ( class_exists( 'WPSEO_Frontend' ) ) {
    include __DIR__ . '/classes/class-wpseo-frontend-to-rest-api.php';

    $yoast_To_REST_API = new Yoast_To_REST_API();
  } else {
    add_action( 'admin_notices', 'wpseo_not_loaded' );
  }
}

function wpseo_not_loaded() {
  printf(
    '<div class="error"><p>%s</p></div>',
    __( '<b>Yoast to REST API</b> plugin not working because <b>Yoast SEO</b> plugin is not active.' )
  );
}