A routing system for WordPress

routing-wp.php

<?php
/*
 * Plugin Name: Routing WP
 * Author: Giuseppe Mazzapica
 * Description: A routing system for WordPress
 */
namespace RoutingWP;

function get_current_url() {
    $current_url = trim( esc_url_raw( add_query_arg( [] ) ), '/' );
    $home_path = trim( parse_url( home_url(), PHP_URL_PATH ), '/' );
    if ( $home_path && strpos( $current_url, $home_path ) === 0 ) {
        $current_url = trim( substr( $current_url, strlen( $home_path ) ), '/' );
    }
    return $current_url;
}

function add_frontend_route( $pattern, callable $callback ) {
    add_filter( 'routing_add_routes', function( $routes ) use( $pattern, $callback ) {
        $routes[ $pattern ] = $callback;
        return $routes;
    } );
}

$allowed = ! is_admin() || ( defined( 'DOING_AJAX' ) && DOING_AJAX );

$allowed and add_action( 'do_parse_request', function( $do_parse, $wp ) {
    $routes = [];
    $current_url = get_current_url();
    $routes = apply_filters( 'routing_add_routes', $routes, $current_url );
    if ( empty( $routes ) || ! is_array( $routes )  ) {
        return $do_parse;
    }
    $urlParts = explode( '?', $current_url, 2 );
    $urlPath = trim( $urlParts[0], '/' );
    $urlVars = [];
    if ( isset( $urlParts[1] ) ) {
        parse_str( $urlParts[1], $urlVars );
    }
    $query_vars = null;
    foreach( $routes as $pattern => $callback ) {
        if ( preg_match( '~' . trim( $pattern, '/' ) . '~', $urlPath, $matches ) ) {
            $routeVars = $callback( $matches );
            if ( is_array( $routeVars ) ) {
                $query_vars = array_merge( $routeVars, $urlVars );
                break;
            }
        }
    }
    if ( is_array( $query_vars ) ) {
        $wp->query_vars = $query_vars;
        do_action( 'routing_matched_vars', $query_vars );
        return false;
    }
    return $do_parse;
}, 30, 2 );

$allowed and add_action( 'routing_matched_vars', function() {
    remove_action( 'template_redirect', 'redirect_canonical' );
}, 30 );

unset( $allowed );