RouterGroup.php

<?php
class Router
{
  protected $middleware       = [];
  protected $groupStack       = [];
  protected $routes           = [];
  protected $namespaceDefault = 'App\\Controllers\\';

  public function get($uri, $callback)
  {

    if ($this->hasGroupStack()) {

      foreach ($this->getGroupStack() as $key => $value) {

        $namespace = $this->namespaceDefault . $value['namespace'] . '\\';
        $middlewares = ($value['middleware']) ?? [];
      }
    }

    $this->routes['GET'][] = [
      'uri'       => $uri,
      'middlewares' => $middlewares ?? [],
      'callback'  => (!is_callable($callback)) ? ($namespace ?? $this->namespaceDefault) . $callback : $callback,
    ];

    return $this;
  }

  public function getRoutes()
  {
    return $this->routes;
  }

  public function group(array $attributes, Closure $callback)
  {
    $this->updateGroupStack($attributes);

    $this->loadRoutes($callback);

    array_pop($this->groupStack);
  }

  public function getGroupStack()
  {
    return $this->groupStack;
  }

  public function hasGroupStack()
  {
    return !empty($this->groupStack);
  }

  protected function updateGroupStack(array $attributes)
  {
    if ($this->hasGroupStack()) {
      $attributes = $this->mergeWithLastGroup($attributes);
    }

    $this->groupStack[] = $attributes;
  }

  public function mergeWithLastGroup($new)
  {
    return $this->merge($new, end($this->groupStack));
  }

  protected function loadRoutes($callback)
  {
    if ($callback instanceof Closure) {
      $callback($this);
    }
  }

  public function merge($new, $old)
  {
    return $new = array_merge($new, [
      'namespace' => $this->formatNamespace($new, $old),
      'middleware' => $this->formatMiddleware($new, $old),
    ]);
  }

  protected function formatNamespace($new, $old)
  {
    if (isset($new['namespace'])) {
      return isset($old['namespace']) && strpos($new['namespace'], '\\') !== 0
        ? trim($old['namespace'], '\\') . '\\' . trim($new['namespace'], '\\')
        : trim($new['namespace'], '\\');
    }

    return $old['namespace'] ?? null;
  }

  protected function formatMiddleware($new, $old)
  {
    if (isset($new['middleware'])) {
      return isset($old['middleware'])
        ? array_merge($old['middleware'], $new['middleware'])
        : $new['middleware'];
    }

    return $old['middleware'] ?? null;
  }
}

class Route
{
  protected static $router;

  private function __construct()
  {
    /* prevents class instance */
  }

  protected static function getRouter()
  {
    if (empty(self::$router)) {
      self::$router = new Router;
    }
    return self::$router;
  }

  public static function group(array $attributes, Closure $callback)
  {
    return self::getRouter()->group($attributes, $callback);
  }

  public static function get($pattern, $callback)
  {
    return self::getRouter()->get($pattern, $callback);
  }

  public static function getRoutes()
  {
    return self::getRouter()->getRoutes();
  }
}


Route::group(['namespace' => 'Admin', 'middleware' => ['auth']], function () {

  Route::get('/admin', 'PainelController@index');

  Route::group(['namespace' => 'Client', 'middleware' => ['role', 'csrf']], function () {
    Route::get('/admin/client', 'ClientController@index');
  });
});

Route::get('/', 'HomeController@index');
Route::get('/teste', function () {
  //todo
});

Route::group(['namespace' => 'Site', 'middleware' => ['csrf']], function () {
  Route::get('/contato', 'ContatoController@index');
});

echo '<pre>';
print_r(Route::getRoutes());