IN ('" . implode( "','", $post_type_names ) . "')
					GROUP BY post_type
					ORDER BY date DESC
				";

				foreach ( $wpdb->get_results( $sql ) as $obj ) {
					$post_type_dates[ $obj->post_type ] = $obj->date;
				}
			}
		}

		$dates = array_intersect_key( $post_type_dates, array_flip( $post_types ) );

		if ( count( $dates ) > 0 ) {
			if ( $return_all ) {
				return $dates;
			}

			return max( $dates );
		}

		return false;
	}

	/**
	 * Get the modification date for the last modified post in the post type.
	 *
	 * @param array $post_types Post types to get the last modification date for.
	 *
	 * @return string
	 */
	public function get_last_modified( $post_types ) {
		return YoastSEO()->helpers->date->format( self::get_last_modified_gmt( $post_types ) );
	}

	/**
	 * Notify search engines of the updated sitemap.
	 *
	 * @param string|null $url Optional URL to make the ping for.
	 */
	public static function ping_search_engines( $url = null ) {

		/**
		 * Filter: 'wpseo_allow_xml_sitemap_ping' - Check if pinging is not allowed (allowed by default)
		 *
		 * @api boolean $allow_ping The boolean that is set to true by default.
		 */
		if ( apply_filters( 'wpseo_allow_xml_sitemap_ping', true ) === false ) {
			return;
		}

		if ( get_option( 'blog_public' ) === '0' ) { // Don't ping if blog is not public.
			return;
		}

		if ( empty( $url ) ) {
			$url = rawurlencode( WPSEO_Sitemaps_Router::get_base_url( 'sitemap_index.xml' ) );
		}

		// Ping Google and Bing.
		wp_remote_get( 'https://www.google.com/ping?sitemap=' . $url, [ 'blocking' => false ] );
		wp_remote_get( 'https://www.bing.com/ping?sitemap=' . $url, [ 'blocking' => false ] );
	}

	/**
	 * Get the maximum number of entries per XML sitemap.
	 *
	 * @return int The maximum number of entries.
	 */
	protected function get_entries_per_page() {
		/**
		 * Filter the maximum number of entries per XML sitemap.
		 *
		 * After changing the output of the filter, make sure that you disable and enable the
		 * sitemaps to make sure the value is picked up for the sitemap cache.
		 *
		 * @param int $entries The maximum number of entries per XML sitemap.
		 */
		$entries = (int) apply_filters( 'wpseo_sitemap_entries_per_page', 1000 );

		return $entries;
	}

	/**
	 * Get post statuses for post_type or the root sitemap.
	 *
	 * @param string $type Provide a type for a post_type sitemap, SITEMAP_INDEX_TYPE for the root sitemap.
	 *
	 * @since 10.2
	 *
	 * @return array List of post statuses.
	 */
	public static function get_post_statuses( $type = self::SITEMAP_INDEX_TYPE ) {
		/**
		 * Filter post status list for sitemap query for the post type.
		 *
		 * @param array  $post_statuses Post status list, defaults to array( 'publish' ).
		 * @param string $type          Post type or SITEMAP_INDEX_TYPE.
		 */
		$post_statuses = apply_filters( 'wpseo_sitemap_post_statuses', [ 'publish' ], $type );

		if ( ! is_array( $post_statuses ) || empty( $post_statuses ) ) {
			$post_statuses = [ 'publish' ];
		}

		if ( ( $type === self::SITEMAP_INDEX_TYPE || $type === 'attachment' )
			&& ! in_array( 'inherit', $post_statuses, true )
		) {
			$post_statuses[] = 'inherit';
		}

		return $post_statuses;
	}

	/**
	 * Sends all the required HTTP Headers.
	 */
	private function send_headers() {
		if ( headers_sent() ) {
			return;
		}

		$headers = [
			$this->http_protocol . ' 200 OK' => 200,
			// Prevent the search engines from indexing the XML Sitemap.
			'X-Robots-Tag: noindex, follow'  => '',
			'Content-Type: text/xml; charset=' . esc_attr( $this->renderer->get_output_charset() ) => '',
		];

		/**
		 * Filter the HTTP headers we send before an XML sitemap.
		 *
		 * @param array  $headers The HTTP headers we're going to send out.
		 */
		$headers = apply_filters( 'wpseo_sitemap_http_headers', $headers );

		foreach ( $headers as $header => $status ) {
			if ( is_numeric( $status ) ) {
				header( $header, true, $status );
				continue;
			}
			header( $header, true );
		}
	}
}