Get custom field value from the function.php

Question

I need to have the value of a custom field in the functions.php file. This what I already have. I can get the value on a page template, but in this case it is need in the functions.php file because I need that value in the facewp function.

add_filter( 'facetwp_preload_url_vars', function( $url_vars ) {
    $offer_id = get_field('offer_type'); // need this value from the current page

    $term = get_term( $offer_id, 'offer' ); // offer = tax slug
    $slug = $term->slug;
    
    if ( empty( $url_vars['offer_type'] ) ) {
        $url_vars['offer_type'] = [$slug];
    }
    return $url_vars;
} );

How can I achieve this? Now I'm getting an empty variable.

Answer 1

Found a solution:

add_filter( 'facetwp_preload_url_vars', function( $url_vars ) {
        //get the id of the current page
        $url = 'http://' . $_SERVER[ 'HTTP_HOST' ] . $_SERVER[ 'REQUEST_URI' ];
        $current_post_id = url_to_postid( $url );

        //get the offer_type (custom field) from the current page id
        $offer_id = get_field('offer_type', $current_post_id); //returns an id
        
        //get the taxonomy slug from the offer_id
        $term = get_term( $offer_id, $taxonomy );
        $slug = $term->slug;

        //preselect the offer_type facet
        if ( empty( $url_vars['offer_type'] ) ) {
            if($slug) {
                $url_vars['offer_type'] = [$slug];
            }
        }
        return $url_vars;
} );