public function track_download( $user_id = null, $user_ip_address = null ) {
		global $wpdb;

		// Must have a permission_id to track download log.
		if ( ! ( $this->get_id() > 0 ) ) {
			throw new Exception( __( 'Invalid permission ID.', 'woocommerce' ) );
		}

		// Increment download count, and decrement downloads remaining.
		// Use SQL to avoid possible issues with downloads in quick succession.
		// If downloads_remaining is blank, leave it blank (unlimited).
		// Also, ensure downloads_remaining doesn't drop below zero.
		$query = $wpdb->prepare(
			"
UPDATE {$wpdb->prefix}woocommerce_downloadable_product_permissions
SET download_count = download_count + 1,
downloads_remaining = IF( downloads_remaining = '', '', GREATEST( 0, downloads_remaining - 1 ) )
WHERE permission_id = %d",
			$this->get_id()
		);
		$wpdb->query( $query ); // WPCS: unprepared SQL ok.

		// Re-read this download from the data store to pull updated counts.
		$this->data_store->read( $this );

		// Track download in download log.
		$download_log = new WC_Customer_Download_Log();
		$download_log->set_timestamp( current_time( 'timestamp', true ) );
		$download_log->set_permission_id( $this->get_id() );

		if ( ! is_null( $user_id ) ) {
			$download_log->set_user_id( $user_id );
		}

		if ( ! is_null( $user_ip_address ) ) {
			$download_log->set_user_ip_address( $user_ip_address );
		}

		$download_log->save();
	}