<?php
class Make_Sort_By extends WP_REST_Controller {
    private $post_type;
    private $sort_type;
    function __construct($post_type, $sort_type) {
        $this->post_type = $post_type;
        $this->sort_type = $sort_type;
    }
    /**
     * Register the routes for the objects of the controller.
     */
    public function register_custom_route($route) {
        $version = '2';
        $namespace = 'craft/v' . $version;
        register_rest_route( $namespace, '/sort/' . $route, [
            array(
                'methods'  => WP_REST_Server::READABLE,
                'callback' => array( $this, $this->sort_type )
            ),
        ]);
    }
    
    public function by_alpha( $request ) {
        global $wpdb;
        $res = $wpdb->get_results($wpdb->prepare(
            "SELECT DISTINCT wp_posts.*, 
            IFNULL(wp_postmeta.meta_value, SUBSTRING_INDEX(wp_posts.post_title, ' ', -1)) AS sort_name
            FROM wp_posts LEFT JOIN wp_postmeta 
            ON (wp_postmeta.post_id = wp_posts.ID AND wp_postmeta.meta_key='artist-sort-name') 
            WHERE wp_posts.post_type='artist' AND wp_posts.post_status='publish'
            ORDER BY sort_name",
            $this->post_type
        ));
        wp_reset_postdata();
        
        return new WP_REST_Response( $this->prepare_items_for_reponse($res), 200 );
    }

    public function by_material( $request ) {
        global $wpdb;
        // !: Make this a real query
        $res = $wpdb->get_results($wpdb->prepare(
            "SELECT * FROM wp_posts
            WHERE post_type = %s 
            AND post_status='publish'",
            $this->post_type
        ));
        wp_reset_postdata();

        return new WP_REST_Response( $this->prepare_items_for_reponse($res), 200 );
    }

    public function prepare_items_for_reponse( $items ) {
        $collection = array();
        forEach( $items as $key => $item ) $collection[$key] = default_post_format($item);
        return $collection;
    }
}

?>