WP_Customize_Widgets::parse_widget_id( string $widget_id )

	public function parse_widget_id( $widget_id ) {
		$parsed = array(
			'number' => null,
			'id_base' => null,
		);

		if ( preg_match( '/^(.+)-(\d+)$/', $widget_id, $matches ) ) {
			$parsed['id_base'] = $matches[1];
			$parsed['number']  = intval( $matches[2] );
		} else {
			// likely an old single widget
			$parsed['id_base'] = $widget_id;
		}
		return $parsed;
	}