class Plugin

class Plugin implements PluginInterface, EventSubscriberInterface, Capable {

  /**
   * The Composer service.
   *
   * @var \Composer\Composer
   */
  protected $composer;

  /**
   * Composer's I/O service.
   *
   * @var \Composer\IO\IOInterface
   */
  protected $io;

  /**
   * The Composer Scaffold handler.
   *
   * @var \Drupal\Composer\Plugin\Scaffold\Handler
   */
  protected $handler;

  /**
   * Record whether the 'require' command was called.
   *
   * @param bool
   */
  protected $requireWasCalled;

  /**
   * {@inheritdoc}
   */
  public function activate(Composer $composer, IOInterface $io) {
    $this->composer = $composer;
    $this->io = $io;
    $this->requireWasCalled = FALSE;
  }

  /**
   * {@inheritdoc}
   */
  public function deactivate(Composer $composer, IOInterface $io) {
  }

  /**
   * {@inheritdoc}
   */
  public function uninstall(Composer $composer, IOInterface $io) {
  }

  /**
   * {@inheritdoc}
   */
  public function getCapabilities() {
    return [
      CommandProvider::class => ScaffoldCommandProvider::class,
    ];
  }

  /**
   * {@inheritdoc}
   */
  public static function getSubscribedEvents() {

    // Important note: We only instantiate our handler on "post" events.
    return [
      ScriptEvents::POST_UPDATE_CMD => 'postCmd',
      ScriptEvents::POST_INSTALL_CMD => 'postCmd',
      PackageEvents::POST_PACKAGE_INSTALL => 'postPackage',
      PluginEvents::COMMAND => 'onCommand',
    ];
  }

  /**
   * Post command event callback.
   *
   * @param \Composer\Script\Event $event
   *   The Composer event.
   */
  public function postCmd(Event $event) {
    $this
      ->handler()
      ->scaffold();
  }

  /**
   * Post package event behavior.
   *
   * @param \Composer\Installer\PackageEvent $event
   *   Composer package event sent on install/update/remove.
   */
  public function postPackage(PackageEvent $event) {
    $this
      ->handler()
      ->onPostPackageEvent($event);
  }

  /**
   * Pre command event callback.
   *
   * @param \Composer\Plugin\CommandEvent $event
   *   The Composer command event.
   */
  public function onCommand(CommandEvent $event) {
    if ($event
      ->getCommandName() == 'require') {
      if ($this->handler) {
        throw new \Error('Core Scaffold Plugin handler instantiated too early. See https://www.drupal.org/project/drupal/issues/3104922');
      }
      $this->requireWasCalled = TRUE;
    }
  }

  /**
   * Instantiates the handler object upon demand.
   *
   * It is dangerous to update a Composer plugin if it loads any classes prior
   * to the `composer update` operation, and later tries to use them in a
   * post-update hook.
   */
  protected function handler() {
    if (!$this->handler) {
      $this->handler = new Handler($this->composer, $this->io);

      // On instantiation of our handler, notify it if the 'require' command
      // was executed.
      if ($this->requireWasCalled) {
        $this->handler
          ->requireWasCalled();
      }
    }
    return $this->handler;
  }

}