Pony.fm/app/models/Commands/CommandBase.php

<?php

	namespace Commands;

	abstract class CommandBase {
		private $_listeners = array();

		public function listen($listener) {
			$this->_listeners[] = $listener;
		}

		protected function notify($message, $progress) {
			foreach ($this->_listeners as $listener) {
				$listener($message, $progress);
			}
		}

		/**
		 * @return bool
		 */
		public function authorize() {
			return true;
		}

		/**
		 * @return CommandResponse
		 */
		public abstract function execute();
	}