system/plugins/simple_private_posts/simple_private_posts.plugin.php

<?php

namespace Habari;

if ( !defined( 'HABARI_PATH' ) ) { die( 'No direct access' ); }

class SimplePrivatePosts extends Plugin
{

  public function action_plugin_activation()
  {
    ACL::create_token('private', 'Permission to read posts marked as "private"', 'Private Posts');

    // Deny the anonymous group access to the private token, if the group hasn't been removed (why would you remove it ??)
    $anon = UserGroup::get('anonymous');
    if ( false != $anon ) {
      $anon->deny('private');
    }
  }

  public function filter_token_description_display( $token )
  {
    $desc = array(
        'private' => _t( 'Permission to read posts marked as "private"' ),
    );
    return isset( $desc[$token] ) ? $desc[$token] : $token;
  }

  public function filter_token_group_display( $group )
  {
    $name = array(
        'Private Posts' => _t( 'Private Posts' ),
    );
    return isset( $name[$group] ) ? $name[$group] : $group;
  }

  public function action_plugin_deactivation( $plugin_file )
  {
    if ( Plugins::id_from_file(__FILE__) == Plugins::id_from_file($plugin_file) ) {
      ACL::destroy_token('private');
    }
  }

  public function action_form_publish($form, $post)
  {
    $private_post = FormControlCheckbox::create('private_post');
    $private_post->set_returned_value(true);
    $form->post_settings->append($private_post->label( _t('Private Post') ));
    if ( $post->has_tokens('private') ) {
      $private_post->set_value(true);
    }
    else {
      $private_post->set_value(false);
    }
  }

  public function action_publish_post($post, $form)
  {
    if ( $form->private_post->value == true ) {
      $post->add_tokens('private');
    }
    else {
      $post->remove_tokens('private');
    }
  }

}
?>