facetwp index file extension

<?php
/** index a url or file path value as the extension to create a file type facet
 ** facet datasource needs to be a value that contains a url or file path for the file that includes the file extension
 **/

add_filter( 'facetwp_index_row', function( $params, $class ) {
    if ( 'my_facet_name' == $params['facet_name'] ) {
        $raw_value = $params['facet_value'];
        $extension = end( explode ( '.', $raw_value) );
        if ( !$extension )
          $params['facet_value'] = ''; // don't index if this is empty
        $params['facet_value'] = $extension;
        $params['facet_display_value'] = $extension;
    }
    return $params;
}, 10, 2 );