Doing Magento-like-Controllers in WordPress

class-abstract-controller.php

<?php

// make the url "/register/index" and "/register" available
class Register_Controller extends Abstract_Controller {
	public function index_action() {
		wp_die( 'You can register here' );
	}

}

new Register_Controller();

// make the url "/magic/index" and "/magic" available
class Magic_Controller extends Abstract_Controller {
	public function index_action() {
		wp_die( 'Das ist ja wonderbra!' );
	}
}

new Magic_Controller();

// !!! Do not forget to `flush_rewrite_rules()` !!!

// magic upcoming ...

abstract class Abstract_Controller {
	public function __construct() {
		$this->add_action( 'init', 10, 0 );
		$this->add_action( 'parse_request', 0 );

		$this->add_filter( 'rewrite_rules_array' );
	}

	public function init() {
		add_rewrite_tag( '%rmp_controller%', '([^&]+)' );
		add_rewrite_tag( '%rmp_action%', '([^&]+)' );
	}

	public function parse_request() {
		/** @var WP $wp */
		global $wp;

		// is it some kind of my controller?
		if ( ! isset( $wp->query_vars['rmp_controller'] ) ) {
			return;
		}

		// is it this controller?
		if ( get_class( $this ) != $wp->query_vars['rmp_controller'] ) {
			return;
		}

		if ( ! isset( $wp->query_vars['rmp_action'] ) ) {
			return;
		}

		$action = 'index_action';
		if ( $wp->query_vars['rmp_action'] ) {
			$action = $wp->query_vars['rmp_action'] . '_action';
		}

		// is there an action?
		if ( ! method_exists( $this, $action ) ) {
			$action = 'not_found_action';
		}

		$this->$action();
	}

	public function not_found_action() {
		global $wp_query;

		$wp_query->set_404();
		status_header( 404 );
		get_template_part( 404 );
		exit();
	}

	public function index_action() {
		wp_die( 'Yuck! Some developer forgot about this magic place.' );
	}

	public function get_regexp() {
		$prefix = str_replace( '\\', '/', get_class( $this ) );
		$prefix = trim( $prefix, '/' );
		$prefix = preg_replace( '@(.*)_Controller$@', '$1', $prefix );
		$prefix = strtolower( $prefix );

		return $prefix . '/?([^/]*)/?';
	}

	public function rewrite_rules_array( $rules ) {
		return array_merge(
			array(
				$this->get_regexp() =>
					sprintf(
						'index.php?rmp_controller=%s&rmp_action=$matches[1]',
						rawurldecode( get_class( $this ) )
					)
			),
			$rules
		);
	}

	protected function add_action( $tag, $priority = 10, $accepted_args = 1 ) {
		add_action( $tag, array( $this, $tag ), $priority, $accepted_args );
	}

	protected function add_filter( $tag, $priority = 10, $accepted_args = 1 ) {
		add_filter( $tag, array( $this, $tag ), $priority, $accepted_args );
	}
}