<?php


add_filter('post_link', 'rudr_post_type_permalink', 20, 3);
add_filter('post_type_link', 'rudr_post_type_permalink', 20, 3);

function rudr_post_type_permalink($permalink, $post_id, $leavename) {

	$post_type_name = 'product'; // post type name, you can find it in admin area or in register_post_type() function
	$post_type_slug = 'product'; // the part of your product URLs, not always matches with the post type name
	$tax_name = 'product_cat'; // the product categories taxonomy name

	$post = get_post( $post_id );

	if ( strpos( $permalink, $post_type_slug ) === FALSE || $post->post_type != $post_type_name ) // do not make changes if the post has different type or its URL doesn't contain the given post type slug
		return $permalink;

        $terms = wp_get_object_terms( $post->ID, $tax_name ); // get all terms (product categories) of this post (product)


        if ( !is_wp_error( $terms ) && !empty( $terms ) && is_object( $terms[0] ) ) // rewrite only if this product has categories
        	$permalink = str_replace( $post_type_slug, $terms[0]->slug, $permalink );

	return $permalink;
}


add_filter('request', 'rudr_post_type_request', 1, 1 );

function rudr_post_type_request( $query ){
	global $wpdb;

	$post_type_name = 'product'; // specify your own here
	$tax_name = 'product_cat'; // and here

	$slug = $query['attachment']; // when we change the post type link, WordPress thinks that these are attachment pages

	// get the post with the given type and slug from the database
	$post_id = $wpdb->get_var(
		"
		SELECT ID
		FROM $wpdb->posts
		WHERE post_name = '$slug'
		AND post_type = '$post_type_name'
		"
	);

	$terms = wp_get_object_terms( $post_id, $tax_name ); // our post should have the terms


	if( isset( $slug ) && $post_id && !is_wp_error( $terms ) && !empty( $terms ) ) : // change the query

		unset( $query['attachment'] );
		$query[$post_type_name] = $slug;
		$query['post_type'] = $post_type_name;
		$query['name'] = $slug;

	endif;

	return $query;
}