Plugins in PHP

gistfile1.aw

<?php

/*
 * Plugins in PHP
 *
 * First read this:
 *  http://blog.ircmaxell.com/2012/03/handling-plugins-in-php.html
 *
 * The 'mediator' pattern is described as the most ubiquitous so I
 * took that, fleshed it out a little, made it compatible with
 * PHP 5.2 and added some error messages.
 * 
 * This will likely be the basis for the plugin architecture in Rat:
 *  https://github.com/DHS/rat
 *
 * Feedback welcome!
 *
 */

class Event {

  protected $events = array();

  public function attach($eventName, $callback) {

    if ( ! isset($this->events[$eventName])) {
      $this->events[$eventName] = array();
    }

    $this->events[$eventName][] = $callback;

  }

  public function trigger($eventName, $data = null) {

    if (isset($this->events[$eventName])) {

      foreach ($this->events[$eventName] as $callback) {

        if (function_exists($callback)) {
          $callback($data, $eventName);
        } else {
          echo "<p>Function '$callback' not found, called by '$eventName' event.</p>";
        }

      }

    } else {
      echo "<p>No functions bound to '$eventName' event.</p>";
    }

  }

}

$event = new Event;


// Define a basic function
function say_hello($name) {
  echo "<p>Hello $name!</p>";
}

// Define another function
function say_hello_from($name, $eventName) {
  echo "<p>Hello $name from the '$eventName' event.</p>";
}


// Attach a function to first event
$event->attach('first', 'say_hello');

// Attach another function to first event
$event->attach('first', 'say_hello_from');

// Attach a non-existent function to first event
$event->attach('first', 'non_existent_function');

// Attach a function to a second event
$event->attach('second', 'say_hello_from');


// Trigger first event
$event->trigger('first', 'world');

// Output:
//  Hello world!
//  Hello world from the 'first' event.
//  Function 'non_existent_function' not found, called by 'first' event.


// Trigger second event
$event->trigger('second');

// Output:
//  Hello from the 'second' event.


// Trigger third event
$event->trigger('third');

// Output:
//  No functions bound to 'third' event.