EventManager.php

<?php

/**
 * Event manager
 *
 * @since 1.3
 */
class EventManager {

	/*** Properties ***********************************************************/

	/**
	 * Registered events list.
	 *
	 * @var array
	 * @since 1.3
	 */
	protected $events = array();


	/** Methods ***************************************************************/

	/**
	 * Trigger all listeners for a given event
	 *
	 * @return void
	 * @since 1.3
	 */
	public function trigger( $event, $arg = '' ) {

		if ( is_array( $event ) ) {

			foreach( $event as $name ) {
				$this->trigger( $name );
			}

		} elseif ( isset( $this->events[ $event ] ) ) {

			$args = array();

			for ( $i = 1; $i < func_num_args(); $i++ ) {
				$args[] = func_get_arg( $i );
			}

			foreach( $this->events[ $event ] as $listener ) {
				call_user_func_array( $listener, $args );
			}

		}

	}

	/**
	 * Attach a listener to an event
	 *
	 * @return void
	 * @since 1.3
	 */
	public function attach( $event, $listener, $priority = 10 ) {

		if ( ! is_callable( $listener ) ) {
			throw new Exception( 'The event listener is not a valid callback.' );
		}

		if ( is_array( $event ) ) {

			foreach( $event as $name ) {
				$this->attach( $name, $listener, $priority );
			}

		} else {

			if ( ! isset( $this->events[ $event ] ) ) {
				$this->events[ $event ] = new PriorityArray();
			}

			$this->events[ $event ]->offsetSet( $this->build_listener_id( $listener ), $listener, $priority );

		}

	}

	/**
	 * Unsubscribe a listener from an event
	 *
	 * @return void
	 * @since 1.3
	 */
	public function detach( $event, $listener ) {

		if ( ! is_callable( $listener ) ) {
			throw new Exception( 'The event listener is not a valid callback.' );
		}

		if ( is_array( $event ) ) {

			foreach( $event as $name ) {
				$this->detach( $name, $listener );
			}

		} elseif ( isset( $this->events[ $event ] ) ) {

			$this->events[ $event ]->offsetUnset( $this->build_listener_id( $listener ) );

		}

	}

	/**
	 * Build Unique ID for listeners callbacks.
	 *
	 * @access private
	 * @return string
	 * @since 1.3
	 */
	protected function build_listener_id( $listener ) {

		if ( is_string( $listener ) ) {
			return $listener;
		}

		return spl_object_hash( (object) $listener );

	}

	/**
	 * Clear all listeners for a given event
	 *
	 * @return void
	 * @since 1.3
	 */
	public function clear_listeners( $event ) {
		unset( $this->events[ $event ] );
	}

	/**
	 * Gel all registered events.
	 *
	 * @return array
	 * @since 1.3
	 */
	public function get_events() {
		return array_keys( $this->events );
	}

}

PriorityArray: https://gist.github.com/nash-ye/9230544