A class for creating a WordPress rewrite rule to serve a stylesheet from a persistent top-level url

WufooEndpoint.php

<?php

namespace IdeasOnPurpose;

/**
 * This class created a nice little persistent endpoint for an
 * externally referenced stylesheet. This was necessary because
 * our themes are versioned with each release living in a different-
 * named directory. All assets are also generated by Webpack and
 * have hashed filenames.
 *
 * Two filter-functions are included for removing the trailing slash
 * from requests so the content is served at /wufoo.css and not
 * /wufoo.css/
 *
 * This was substantially pared back because WP Engine intercepts
 * all requests for *.css files, so the rewrite rule never got to
 * WordPress.
 */
class WufooEndpoint
{
    public function __construct()
    {
        if ($this->manifest()) {
            add_action('init', [$this, 'register']);
            add_filter('query_vars', [$this, 'var']);
            add_filter('template_redirect', [$this, 'slashRedirect']);
            add_filter('redirect_canonical', [$this, 'noSlash']);
            add_filter('template_include', [$this, 'styles']);
        }
    }

    /**
     * Checks that there's a wufoo stylesheet in the dependency manifest
     * and return that value if found.
     */
    public function manifest()
    {
        $manifest_file = get_template_directory() . '/dist/dependency-manifest.json';
        $manifest = json_decode(file_get_contents($manifest_file), true);

        $this->stylesheet = false;
        // TODO: This will be problematic if there's more than one CSS file.
        foreach ($manifest['wufoo']['files'] as $file) {
            if (pathinfo($file, PATHINFO_EXTENSION) === 'css') {
                $this->stylesheet = $file;
            }
        }
        return $this->stylesheet;
    }

    /**
     * Register the rewrite rule
     */
    public function register()
    {
        add_rewrite_rule('wufoo\.css/?$', 'index.php?wufoo_styles=true', 'top');
    }

    /**
     * Register the wufoo_styles query_var
     */
    public function var($vars)
    {
        $vars[] = 'wufoo_styles';
        return $vars;
    }

    /**
     * Redirect requests for /wufoo.css/ to a slash-free url instead
     */
    public function slashRedirect()
    {
        if (preg_match('%wufoo\.css/$%', $_SERVER['REQUEST_URI'])) {
            wp_redirect(home_url('wufoo.css', 'relative'), 301);
            exit();
        }
    }

    /**
     * Don't add a trailing slash to /wufoo.css requests
     * Without this, $this->slashRedirect will cause a redirect loop
     */
    public function noSlash($url)
    {
        return preg_replace('%wufoo\.css/?$%', 'wufoo.css', $url);
    }

    /**
     * Returns a CSS Content-type header and the stylesheet when the wufoo_styles query_var is set
     */
    public function styles($template)
    {
        if (get_query_var('wufoo_styles')) {
            header('Content-type: text/css', true);
            return ABSPATH . $this->stylesheet;
        }
        return $template;
    }
}