How to do a PHP hook system?

You can build an events system as simple or complex as you want it.

/**
 * Attach (or remove) multiple callbacks to an event and trigger those callbacks when that event is called.
 *
 * @param string $event name
 * @param mixed $value the optional value to pass to each callback
 * @param mixed $callback the method or function to call - FALSE to remove all callbacks for event
 */
function event($event, $value = NULL, $callback = NULL)
{
    static $events;

    // Adding or removing a callback?
    if($callback !== NULL)
    {
        if($callback)
        {
            $events[$event][] = $callback;
        }
        else
        {
            unset($events[$event]);
        }
    }
    elseif(isset($events[$event])) // Fire a callback
    {
        foreach($events[$event] as $function)
        {
            $value = call_user_func($function, $value);
        }
        return $value;
    }
}

Add an event

event('filter_text', NULL, function($text) { return htmlspecialchars($text); });
// add more as needed
event('filter_text', NULL, function($text) { return nl2br($text); });
// OR like this
//event('filter_text', NULL, 'nl2br');

Then call it like this

$text = event('filter_text', $_POST['text']);

Or remove all callbacks for that event like this

event('filter_text', null, false);

Here's another solution:

Creating a hook

Run this wherever you want to create a hook:

x_do_action('header_scripts');

---

Attach a function to the hook

Then attach a function to the above by doing:

x_add_action('header_scripts','my_function_attach_header_scripts');

function my_function_attach_header_scripts($values) {

   /* add my scripts here */

}

---

Global variable to store all hooks/events

Add this to the top of your main PHP functions file, or equivalent

$x_events = array();
global $x_events;

---

Base functions

function x_do_action($hook, $value = NULL) {
    global $x_events;

    if (isset($x_events[$hook])) {

        foreach($x_events[$hook] as $function) {

            if (function_exists($function)) { call_user_func($function, $value); }

        }
    }

}

function x_add_action($hook, $func, $val = NULL) {
    global $x_events;
    $x_events[$hook][] = $func;

}