wp-multi-city/includes/class-link-filter.php

<?php
declare(strict_types=1);

namespace WPMultiCity;

final class LinkFilter
{
    public static function register(): void
    {
        \add_filter('home_url',       [self::class, 'filter_home_url'],       9999, 4);
        \add_filter('post_link',      [self::class, 'filter_post_link'],      10,   3);
        \add_filter('acf/load_value', [self::class, 'filter_acf_load_value'], 9999, 3);
    }

    public static function filter_home_url(string $url, string $path = '', $orig_scheme = null, $blog_id = null): string
    {
        return self::add_town_prefix($url);
    }

    public static function filter_post_link(string $permalink, $post = null, bool $leavename = false): string
    {
        return self::add_town_prefix($permalink);
    }

    public static function filter_acf_load_value($value, $post_id = null, $field = null)
    {
        if (!is_string($value)) {
            return $value;
        }
        return self::add_town_prefix($value);
    }

    public static function add_town_prefix(string $url): string
    {
        // Implementation in Task 4.
        return $url;
    }
}