<?php
/**
 * DokuWiki Events
 *
 * @license    GPL 2 (http://www.gnu.org/licenses/gpl.html)
 * @author     Christopher Smith <chris@jalakai.co.uk>
 */

if(!defined('DOKU_INC')) die('meh.');

class Doku_Event {

    // public properties
    var $name = '';                // READONLY  event name, objects must register against this name to see the event
    var $data = null;              // READWRITE data relevant to the event, no standardised format (YET!)
    var $result = null;            // READWRITE the results of the event action, only relevant in "_AFTER" advise
    //    event handlers may modify this if they are preventing the default action
    //    to provide the after event handlers with event results
    var $canPreventDefault = true; // READONLY  if true, event handlers can prevent the events default action

    // private properties, event handlers can effect these through the provided methods
    var $_default = true;     // whether or not to carry out the default action associated with the event
    var $_continue = true;    // whether or not to continue propagating the event to other handlers

    /**
     * event constructor
     */
    function Doku_Event($name, &$data) {

        $this->name = $name;
        $this->data =& $data;

    }

    /**
     * advise functions
     *
     * advise all registered handlers of this event
     *
     * if these methods are used by functions outside of this object, they must
     * properly handle correct processing of any default action and issue an
     * advise_after() signal. e.g.
     *    $evt = new Doku_Event(name, data);
     *    if ($evt->advise_before(canPreventDefault) {
     *      // default action code block
     *    }
     *    $evt->advise_after();
     *    unset($evt);
     *
     * @return  results of processing the event, usually $this->_default
     */
    function advise_before($enablePreventDefault=true) {
        global $EVENT_HANDLER;

        $this->canPreventDefault = $enablePreventDefault;
        $EVENT_HANDLER->process_event($this,'BEFORE');

        return (!$enablePreventDefault || $this->_default);
    }

    function advise_after() {
        global $EVENT_HANDLER;

        $this->_continue = true;
        $EVENT_HANDLER->process_event($this,'AFTER');
    }

    /**
     * trigger
     *
     * - advise all registered (<event>_BEFORE) handlers that this event is about to take place
     * - carry out the default action using $this->data based on $enablePrevent and
     *   $this->_default, all of which may have been modified by the event handlers.
     * - advise all registered (<event>_AFTER) handlers that the event has taken place
     *
     * @return  $event->results
     *          the value set by any <event>_before or <event> handlers if the default action is prevented
     *          or the results of the default action (as modified by <event>_after handlers)
     *          or NULL no action took place and no handler modified the value
     */
    function trigger($action=null, $enablePrevent=true) {

        if (!is_callable($action)) $enablePrevent = false;

        if ($this->advise_before($enablePrevent) && is_callable($action)) {
            if (is_array($action)) {
                list($obj,$method) = $action;
                $this->result = $obj->$method($this->data);
            } else {
                $this->result = $action($this->data);
            }
        }

        $this->advise_after();

        return $this->result;
    }

    /**
     * stopPropagation
     *
     * stop any further processing of the event by event handlers
     * this function does not prevent the default action taking place
     */
    function stopPropagation() { $this->_continue = false;  }

    /**
     * preventDefault
     *
     * prevent the default action taking place
     */
    function preventDefault() { $this->_default = false;  }
}

class Doku_Event_Handler {

    // public properties:  none

    // private properties
    var $_hooks = array();          // array of events and their registered handlers

    /**
     * event_handler
     *
     * constructor, loads all action plugins and calls their register() method giving them
     * an opportunity to register any hooks they require
     */
    function Doku_Event_Handler() {

        // load action plugins
        $plugin = null;
        $pluginlist = plugin_list('action');

        foreach ($pluginlist as $plugin_name) {
            $plugin =& plugin_load('action',$plugin_name);

            if ($plugin !== null) $plugin->register($this);
        }
    }

    /**
     * register_hook
     *
     * register a hook for an event
     *
     * @param  $event   (string)   name used by the event, (incl '_before' or '_after' for triggers)
     * @param  $obj     (obj)      object in whose scope method is to be executed,
     *                             if NULL, method is assumed to be a globally available function
     * @param  $method  (function) event handler function
     * @param  $param   (mixed)    data passed to the event handler
     */
    function register_hook($event, $advise, &$obj, $method, $param=null) {
        $this->_hooks[$event.'_'.$advise][] = array(&$obj, $method, $param);
    }

    function process_event(&$event,$advise='') {

        $evt_name = $event->name . ($advise ? '_'.$advise : '_BEFORE');

        if (!empty($this->_hooks[$evt_name])) {
            $hook = reset($this->_hooks[$evt_name]);
            do {
                //        list($obj, $method, $param) = $hook;
                $obj =& $hook[0];
                $method = $hook[1];
                $param = $hook[2];

                if (is_null($obj)) {
                    $method($event, $param);
                } else {
                    $obj->$method($event, $param);
                }

            } while ($event->_continue && $hook = next($this->_hooks[$evt_name]));
        }
    }
}

/**
 * trigger_event
 *
 * function wrapper to process (create, trigger and destroy) an event
 *
 * @param  $name               (string)   name for the event
 * @param  $data               (mixed)    event data
 * @param  $action             (callback) (optional, default=NULL) default action, a php callback function
 * @param  $canPreventDefault  (bool)     (optional, default=true) can hooks prevent the default action
 *
 * @return (mixed)                        the event results value after all event processing is complete
 *                                         by default this is the return value of the default action however
 *                                         it can be set or modified by event handler hooks
 */
function trigger_event($name, &$data, $action=null, $canPreventDefault=true) {

    $evt = new Doku_Event($name, $data);
    return $evt->trigger($action, $canPreventDefault);
}