<?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.');

/**
 * The event
 */
class Doku_Event {

    // public properties
    public $name = '';                // READONLY  event name, objects must register against this name to see the event
    public $data = null;              // READWRITE data relevant to the event, no standardised format (YET!)
    public $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
    public $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;

    }

    /**
     * @return string
     */
    function __toString() {
        return $this->name;
    }

    /**
     * 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);
     *
     * @param bool $enablePreventDefault
     * @return bool 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
     *
     * @param null|callable $action
     * @param bool $enablePrevent
     * @return  mixed $event->results
     *          the value set by any <event>_before or <event> handlers if the default action is prevented
     *          or the results of the default action (as modified by <event>_after handlers)
     *          or NULL no action took place and no handler modified the value
     */
    function trigger($action=null, $enablePrevent=true) {

        if (!is_callable($action)) {
            $enablePrevent = false;
            if (!is_null($action)) {
                trigger_error('The default action of '.$this.' is not null but also not callable. Maybe the method is not public?', E_USER_WARNING);
            }
        }

        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;  }
}

/**
 * Controls the registration and execution of all events,
 */
class Doku_Event_Handler {

    // public properties:  none

    // private properties
    protected $_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
        /** @var DokuWiki_Action_Plugin $plugin */
        $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  $advise  string
     * @param  $obj     object   object in whose scope method is to be executed,
     *                             if NULL, method is assumed to be a globally available function
     * @param  $method  string   event handler function
     * @param  $param   mixed    data passed to the event handler
     * @param  $seq     int      sequence number for ordering hook execution (ascending)
     */
    function register_hook($event, $advise, $obj, $method, $param=null, $seq=0) {
        $seq = (int)$seq;
        $doSort = !isset($this->_hooks[$event.'_'.$advise][$seq]);
        $this->_hooks[$event.'_'.$advise][$seq][] = array($obj, $method, $param);

        if ($doSort) {
            ksort($this->_hooks[$event.'_'.$advise]);
        }
    }

    /**
     * process the before/after event
     *
     * @param Doku_Event $event
     * @param string     $advise BEFORE or AFTER
     */
    function process_event($event,$advise='') {

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

        if (!empty($this->_hooks[$evt_name])) {
            foreach ($this->_hooks[$evt_name] as $sequenced_hooks) {
                foreach ($sequenced_hooks as $hook) {
                    list($obj, $method, $param) = $hook;

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

                    if (!$event->_continue) return;
                }
            }
        }
    }
}

/**
 * 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);
}